Foscavir

Non-Nucleoside DNA Polymerase Inhibitor Antivirals

Injectable Administration

Foscarnet is administered by slow intravenous infusion. Do not administer by rapid IV infusion or by direct IV injection.
Monitor renal function and adjust doses accordingly.
Adequate hydration is recommended both prior to and during treatment to minimize renal toxicity. It is recommended that 750 to 1,000 mL of 0.9% Sodium Chloride Injection or 5% Dextrose Injection be given prior to the first infusion to establish diuresis. With subsequent infusions, 750 to 1,000 mL of hydration should be given with 90 to 120 mg/kg/dose of foscarnet and 500 mL with 40 to 60 mg/kg/dose of foscarnet. Equivalent oral rehydration may be considered for certain patients. After the first dose, administer the hydration fluid concurrently with each drug infusion.
Visually inspect parenteral products for particulate matter and discoloration prior to administration whenever solution and container permit.

Intravenous Administration

Dilution
No dilution is necessary if administered via a central vein.
For peripheral vein infusion, dilute the commercially available solution with 5% Dextrose Injection or 0.9% Sodium Chloride Injection to a concentration of 12 mg/mL or less prior to administration to minimize the risk of local irritation. Dilute under aseptic conditions.
Administer within 24 hours of first entry into a sealed bottle.
 
Intravenous Infusion
Administer by slow IV infusion using a controlled infusion device. Infuse all doses over at least 1 hour at a rate not exceeding 1 mg/kg/minute (i.e., 60 mg/kg/dose over 1 hour or 120 mg/kg/dose over 2 hours).

Other Injectable Administration

Intravitreal injection†
NOTE: Foscarnet is not approved by the FDA for administration via intravitreal injection.
In clinical studies, intravitreal injection was prepared and administered as follows:
Remove required dose from the commercially available vial (i.e., 24 mg/mL solution).
Pass the solution through a 0.22 micron filter prior to injection.
Clean conjunctiva with topical 5% povidone iodine solution.
Apply topical 4% cocaine HCl as an anesthetic.
Slowly injection into the lower temporal quadrant using a tuberculin syringe and 30 gauge needle.
Remove needle and apply a cotton-tippled applicator to the injection point to avoid reflux.

Severe

nephrotoxicity / Delayed / 12.0-33.0
seizures / Delayed / 7.0-10.0
renal failure (unspecified) / Delayed / 1.0-5.0
pancreatitis / Delayed / 1.0-5.0
thrombosis / Delayed / 1.0-5.0
bronchospasm / Rapid / 1.0-5.0
pneumothorax / Early / 1.0-5.0
AV block / Early / 1.0-5.0
diabetes insipidus / Delayed / 0-1.0
pancytopenia / Delayed / 0-1.0
SIADH / Delayed / 0-1.0
toxic epidermal necrolysis / Delayed / 0-1.0
Stevens-Johnson syndrome / Delayed / 0-1.0
erythema multiforme / Delayed / 0-1.0
cardiac arrest / Early / 0-1.0
coma / Early / 0-1.0
rhabdomyolysis / Delayed / 0-1.0
renal tubular acidosis (RTA) / Delayed / Incidence not known
renal tubular necrosis / Delayed / Incidence not known
nephrotic syndrome / Delayed / Incidence not known
glomerulonephritis / Delayed / Incidence not known
Fanconi syndrome / Delayed / Incidence not known
GI bleeding / Delayed / Incidence not known
esophageal ulceration / Delayed / Incidence not known
angioedema / Rapid / Incidence not known
anaphylactic shock / Rapid / Incidence not known
anaphylactoid reactions / Rapid / Incidence not known
torsade de pointes / Rapid / Incidence not known

Moderate

hypokalemia / Delayed / 16.0-48.0
anemia / Delayed / 8.0-33.0
hypocalcemia / Delayed / 15.0-30.0
neutropenia / Delayed / 16.0-28.0
hypophosphatemia / Delayed / 8.0-26.0
hyperphosphatemia / Delayed / 6.0-6.0
ataxia / Delayed / 1.0-5.0
hallucinations / Early / 1.0-5.0
amnesia / Delayed / 1.0-5.0
meningitis / Delayed / 1.0-5.0
aphasia / Delayed / 1.0-5.0
constipation / Delayed / 1.0-5.0
melena / Delayed / 1.0-5.0
dysphagia / Delayed / 1.0-5.0
stomatitis / Delayed / 1.0-5.0
thrombocytopenia / Delayed / 1.0-5.0
lymphadenopathy / Delayed / 1.0-5.0
hyponatremia / Delayed / 1.0-5.0
hemoptysis / Delayed / 1.0-5.0
erythema / Early / 1.0-5.0
skin ulcer / Delayed / 1.0-5.0
hypotension / Rapid / 1.0-5.0
sinus tachycardia / Rapid / 1.0-5.0
ST-T wave changes / Rapid / 1.0-5.0
hypertension / Early / 1.0-5.0
chest pain (unspecified) / Early / 1.0-5.0
edema / Delayed / 1.0-5.0
candidiasis / Delayed / 1.0-5.0
conjunctivitis / Delayed / 1.0-5.0
elevated hepatic enzymes / Delayed / 1.0-5.0
hematuria / Delayed / 0-1.0
dehydration / Delayed / 0-1.0
bullous rash / Early / 0-1.0
QT prolongation / Rapid / 0-1.0
myopathy / Delayed / 0-1.0
confusion / Early / 5.0
peripheral neuropathy / Delayed / 5.0
depression / Delayed / 5.0
leukopenia / Delayed / 5.0
hypomagnesemia / Delayed / 15.0
dyspnea / Early / 5.0
proteinuria / Delayed / Incidence not known

Mild

fever / Early / 65.0-65.0
nausea / Early / 47.0-47.0
diarrhea / Early / 30.0-30.0
headache / Early / 26.0-26.0
vomiting / Early / 26.0-26.0
infection / Delayed / 0-26.0
nocturia / Early / 1.0-5.0
tremor / Early / 1.0-5.0
agitation / Early / 1.0-5.0
muscle cramps / Delayed / 1.0-5.0
insomnia / Early / 1.0-5.0
drowsiness / Early / 1.0-5.0
dyspepsia / Early / 1.0-5.0
xerostomia / Early / 1.0-5.0
dysgeusia / Early / 1.0-5.0
flatulence / Early / 1.0-5.0
weight loss / Delayed / 1.0-5.0
rhinitis / Early / 1.0-5.0
pharyngitis / Delayed / 1.0-5.0
sinusitis / Delayed / 1.0-5.0
skin discoloration / Delayed / 1.0-5.0
pruritus / Rapid / 1.0-5.0
seborrhea / Delayed / 1.0-5.0
maculopapular rash / Early / 1.0-5.0
flushing / Rapid / 1.0-5.0
influenza / Delayed / 1.0-5.0
ocular pain / Early / 1.0-5.0
injection site reaction / Rapid / 1.0-5.0
myalgia / Early / 1.0-5.0
arthralgia / Delayed / 1.0-5.0
back pain / Delayed / 1.0-5.0
vesicular rash / Delayed / 0-1.0
weakness / Early / 0-1.0
dizziness / Early / 5.0
hypoesthesia / Delayed / 5.0
paresthesias / Delayed / 5.0
anxiety / Delayed / 5.0
anorexia / Delayed / 5.0
abdominal pain / Early / 5.0
cough / Delayed / 5.0
diaphoresis / Early / 5.0
rash / Early / 5.0
malaise / Early / 5.0
asthenia / Delayed / 5.0
fatigue / Early / 5.0
urticaria / Rapid / Incidence not known

Dehydration, nephrotoxicity, renal failure, renal impairment, sodium restriction

Nephrotoxicity is the major toxicity associated with foscarnet therapy; the majority of drug recipients will experience a decline in renal function during therapy. In most cases foscarnet-induced renal toxicity is identified during the second week of induction therapy, but may occur at anytime during treatment. The foscarnet dose MUST be individualized based on the patient's renal function. Health care providers are advised to monitor renal function (based on creatinine clearance, CrCl) at baseline, 2 to 3 times per week during induction, and once weekly during maintenance therapy. Safety and efficacy data are limited for patients with renal impairment as assessed by baseline serum creatinine (SCr) concentrations over 2.8 mg/dL or measured 24-hour CrCl less than 50 mL/minute; use in patients with severe renal impairment or renal failure is not recommended. Discontinue treatment in patients whose CrCl drops below 0.4 mL/minute/kg during treatment. The renal adverse effects are usually, but not always, reversible upon discontinuation or dose adjustment. Dehydration increases the risk for renal toxicity; therefore, maintaining adequate hydration is very important during foscarnet therapy. Prior to the initial foscarnet infusion, establish diuresis by administering 750 mL to 1,000 mL of 0.9% Sodium Chloride Injection or 5% Dextrose Injection. With subsequent infusions, hydration fluids may be given concurrently with foscarnet; the recommended dose for the hydration fluids is 750 mL to 1,000 mL for foscarnet doses of 90 to 120 mg/kg, and 500 mL for foscarnet doses of 40 to 60 mg/kg. In certain patients, oral rehydration with similar regimens may be considered. When selecting hydration fluids, health care providers are advised to consider the sodium content of foscarnet (240 micromole/mL; 5.5 mg/mL), as administration of large quantities of sodium may not be tolerated by certain patients (e.g., those on sodium restriction using a controlled sodium diet).

Cardiac disease, electrolyte imbalance, hypocalcemia, neurological disease, seizure disorder, seizures

Seizures, including cases of status epilepticus, have been reported with foscarnet therapy, and are associated with foscarnet-induced alterations in plasma minerals and electrolytes. Patients must be carefully monitored for electrolyte imbalances and potential sequelae. Supplementation may be required to normalize mineral and electrolyte balance. Electrolyte imbalance has occurred during therapy with foscarnet. Foscarnet may decrease ionized serum calcium without altering total serum calcium concentrations. This effect on ionized calcium is likely due to foscarnets ability to chelate divalent metal ions, and is dose/rate related; thus, slowing the infusion may decrease or prevent symptoms associated with hypocalcemia. Health care providers are advised to monitor and correct altered calcium and/or other electrolyte imbalances prior to initiating therapy. Instruct patients to immediately report symptoms associated with low ionized calcium (perioral tingling, extremity numbness, paresthesias) that develop during therapy. Particular caution is recommended for patients in which changes in electrolyte balance may increase the risk of developing neurologic and cardiac dysfunction, such as those individuals who are receiving other drugs that influence serum electrolytes, patients with baseline renal impairment, or those with preexisting cardiac disease, seizure disorder or other neurological disease. Ensure policies and procedures for managing abnormalities such as tetany, seizures, and cardiac disturbances are in place prior to administering foscarnet.

Foscavir

Rx

Intravenous antiviral agent that does not require phosphorylation for activation
Used for CMV, HSV, and herpes zoster infections in immunocompromised persons
Renal impairment is major toxicity; monitoring of renal function and adequate hydration during administration is necessary

For the treatment of acyclovir-resistant mucocutaneous herpes simplex virus infection (e.g., herpes labialis, herpes febrilis, herpes genitalis) in immunocompromised patients. Intravenous dosage Adults

40 mg/kg/dose IV every 8 to 12 hours for 2 to 3 weeks or until lesions are healed. Doses up to 80 mg/kg/dose IV every 8 hours have also been suggested for genital infections in persons living with HIV.

Adolescents†

40 mg/kg/dose IV every 8 to 12 hours for 2 to 3 weeks or until lesions are healed. Doses up to 80 mg/kg/dose IV every 8 hours have also been suggested for genital infections in persons living with HIV.

Topical dosage†

NOTE: Topical formulations of foscarnet are not commercially available and must be extemporaneously compounded using the intravenous formulation.

Adults

Apply 1% topical foscarnet 5-times daily for at least 21 to 28 days as an alternative.

Adolescents

Apply 1% topical foscarnet 5-times daily for at least 21 to 28 days as an alternative.

For cytomegalovirus (CMV) disease prophylaxis, including cytomegalovirus (CMV) retinitis prophylaxis, in patients at risk for CMV disease. For secondary cytomegalovirus (CMV) retinitis prophylaxis (chronic maintenance therapy) in adult and adolescent patients with HIV after treatment of the acute CMV retinitis infection.
NOTE: For patients who experience progression of CMV retinitis while receiving maintenance therapy, re-induction treatment with the same drug used for maintenance followed by reinstitution of maintenance therapy is recommended.
NOTE: The CDC does not recommend primary prophylaxis in patients with HIV, as end-organ disease is best prevented by using antiretroviral therapy to maintain CD4 counts greater than 100 cells/mm3. Intravenous dosage Adults and Adolescents†

90 to 120 mg/kg IV once daily is recommended as an alternative maintenance therapy after treatment of the acute infection. Treatment duration depends on the immune status of the patient. For HIV-infected patients who have had a sustained immune response to highly active antiretroviral therapy (i.e., CD4 counts greater than 100 cells/mm3 for 3 to 6 months), have been on CMV treatment for at least 3 to 6 months, and have no active lesions, secondary CMV retinitis prophylaxis may be discontinued after consultation with an ophthalmologist. Maintenance therapy should be restarted if subsequent CD4 counts drop to less than 100 cells/mm3, as relapse occurs most frequently in those patients whose counts decrease to less than 50 cells/mm3 after stopping treatment. However, because relapses may occur at any CD4 count, all patients who have had maintenance CMV therapy discontinued should continue to undergo regular ophthalmologic monitoring (every 3 months) for early detection of CMV relapse (as well as for immune reconstitution uveitis).

For secondary cytomegalovirus (CMV) disease prophylaxis (chronic maintenance therapy) in children† with HIV and prior retinitis, neurologic disease, or gastrointestinal disease with relapse†. Intravenous dosage Children†

The HIV guidelines recommend 90 to 120 mg/kg/dose IV once daily. In children aged 1 to 6 years, secondary prophylaxis may be discontinued after at least 6 months of antiretroviral therapy, consultation with an ophthalmologist, and a CD4 percentage at least 15% or a CD4 count greater than 500 cells/mm3 is maintained for at least 3 consecutive months. In children older than 6 years old, secondary prophylaxis may be discontinued after at least 6 months of antiretroviral therapy, consultation with an ophthalmologist, and a CD4 count greater than 100 cells/mm3 is maintained for at least 3 consecutive months. Routine follow-up (every 3 to 6 months) with an ophthalmologist is recommended.

For the treatment of viral encephalitis†. For the treatment of cytomegalovirus (CMV) encephalitis† and for the treatment of cytomegalovirus (CMV) neurological disease† (including encephalitis) in patients with HIV. Intravenous dosage Adults and Adolescents

90 mg/kg/dose IV every 12 hours or 60 mg/kg/dose IV every 8 hours plus ganciclovir to stabilize the disease and maximize response. The optimal duration of therapy has not been established. Routine maintenance therapy is not recommended unless there is concurrent retinitis, there have already been recurrent infections, or severe disease was present initially. Response to treatment with either ganciclovir or foscarnet alone has not led to improved survival; however, the combination followed by maintenance therapy has led to improvement or stabilization in 74% of patients with HIV.

For encephalitis† caused by human herpesvirus 6 (HHV-6)† in immunocompromised patients. Intravenous dosage Adults

60 mg/kg/dose IV every 8 hours or 90 mg/kg/dose IV every 12 hours alone or in combination with ganciclovir 5 mg/kg/dose IV every 12 hours is suggested as reasonable by the IDSA due to lack of other therapeutic options.

For the treatment of cytomegalovirus (CMV) infection, including cytomegalovirus (CMV) retinitis, cytomegalovirus (CMV)-associated gastrointestinal disease†, or cytomegalovirus (CMV) pneumonitis†.
NOTE: For CNS infections, see encephalitis.
For the treatment of cytomegalovirus (CMV) retinitis in persons with HIV. Intravenous dosage Adults and Adolescents†

90 mg/kg/dose IV every 12 hours or 60 mg/kg/dose IV every 8 hours (depending on clinical response) for 14 to 21 days as an initial therapy. For immediate sight-threatening lesions (i.e., within 1,500 microns of the fovea), give in combination with intravitreal injections of ganciclovir (2 mg/injection) or foscarnet (2.4 mg/injection). Induction therapy should be followed-up with chronic maintenance therapy (secondary prophylaxis). The HIV guidelines suggest foscarnet as second-line induction therapy.

Infants† and Children†

As an alternative to ganciclovir (first choice), foscarnet 60 mg/kg/dose IV every 8 hours (or 90 mg/kg/dose IV every 12 hours) for 2 to 3 weeks as induction therapy, then 90 to 120 mg/kg/dose IV once daily as chronic suppression. In HIV-infected patients, the HIV guidelines suggest that a combination of ganciclovir and foscarnet may be used in patients with sight-threatening disease.

Intravitreal injection dosage† Adults and Adolescents

For patients with immediate sight-threatening lesions (i.e., within 1,500 microns of the fovea), give 2.4 mg intravitreal injections once weekly until lesion inactivity is achieved. Intravitreal injections are given to achieve rapid high intraocular drug concentrations and should be administered in combination with systemic induction therapy.

For the treatment of cytomegalovirus (CMV)-associated gastrointestinal disease† (e.g., esophagitis†, colitis†) in HIV-infected patients. Intravenous dosage Adults and Adolescents

90 mg/kg/dose IV every 12 hours or 60 mg/kg/dose IV every 8 hours for 21 to 42 days or until resolution of signs and symptoms is recommended by the HIV guidelines for patients with treatment limiting toxicities to ganciclovir or ganciclovir resistance. Maintenance therapy is usually not necessary, but should be considered after relapse.

For the treatment of well-documented, histologically confirmed cytomegalovirus (CMV) pneumonitis† in HIV patients. Intravenous dosage Adults and Adolescents

Although experience is limited, 90 mg/kg/dose IV every 12 hours or 60 mg/kg/dose IV every 8 hours is reasonable; however, the optimal duration has not been established.

For the treatment of acyclovir-resistant herpes zoster (shingles) infection† in persons living with HIV. Intravenous dosage Adults

90 mg/kg/dose IV every 12 hours. In 1 study, treatment with 100 mg/kg/dose IV twice daily for a mean of 17.8 days resulted in complete healing of acyclovir-resistant herpes zoster in 10 out of 13 patients (77%).

Adolescents

90 mg/kg/dose IV every 12 hours. In 1 study, treatment with 100 mg/kg/dose IV twice daily for a mean of 17.8 days resulted in complete healing of acyclovir-resistant herpes zoster in 10 out of 13 patients (77%).

Infants and Children

40 to 60 mg/kg/dose IV every 8 hours for 7 to 10 days or until no new lesions have appeared for at least 48 hours.

For the treatment of human herpesvirus 6 (HHV-6) infection† in persons living with HIV.
NOTE: For CNS infections, see encephalitis.
Intravenous dosage Adults

90 mg/kg/dose IV every 12 hours or 60 mg/kg/dose IV every 8 hours.

Adolescents

90 mg/kg/dose IV every 12 hours or 60 mg/kg/dose IV every 8 hours.

For the treatment of progressive outer retinal necrosis (PORN)† due to varicella-zoster virus in persons living with HIV. Intravitreal dosage Adults

1.2 mg/0.05 mL intravitreal injection twice weekly, with or without ganciclovir intravitreal injection, in combination with systemic therapy (i.e., ganciclovir or acyclovir). The optimal duration has not been defined; duration should be determined clinically in consultation with an ophthalmologist.

Adolescents

1.2 mg/0.05 mL intravitreal injection twice weekly, with or without ganciclovir intravitreal injection, in combination with systemic therapy (i.e., ganciclovir or acyclovir). The optimal duration has not been defined; duration should be determined clinically in consultation with an ophthalmologist.

Infants and Children

1.2 mg/0.05 mL intravitreal injection twice weekly, with or without ganciclovir intravitreal injection, in combination with systemic therapy (acyclovir or ganciclovir plus IV foscarnet). The optimal duration has not been defined; duration should be determined clinically in consultation with an ophthalmologist.

Intravenous dosage Infants and Children

90 mg/kg/dose IV every 12 hours plus IV acyclovir or ganciclovir plus ganciclovir intravitreal injection and/or foscarnet intravitreal injection is recommended by guidelines. The duration of therapy is not well defined and should be based on clinical, virologic, and immunologic responses in consultation with an ophthalmologist.

†Indicates off-label use

Hepatic Impairment

Specific guidelines for dosage adjustments in hepatic impairment are not available; it appears that no dosage adjustments are needed.

Renal Impairment

Dosage for induction and maintenance therapy should be modified based on creatinine clearance (mL/minute/kg).
 
For HSV induction dosage of 40 mg/kg/dose IV every 12 hours
CrCl more than 1.4 mL/minute/kg: No dosage adjustment necessary.
CrCl 1.1 to 1.4 mL/minute/kg: Decrease dose to 30 mg/kg/dose IV every 12 hours.
CrCl 0.81 to 1 mL/minute/kg: Decrease dose to 20 mg/kg/dose IV every 12 hours.
CrCl 0.61 to 0.8 mL/minute/kg: Decrease dose to 35 mg/kg/dose IV every 24 hours.
CrCl 0.51 to 0.6 mL/minute/kg: Decrease dose to 25 mg/kg/dose IV every 24 hours.
CrCl 0.4 to 0.5 mL/minute/kg: Decrease dose to 20 mg/kg/dose IV every 24 hours.
CrCl less than 0.4 mL/minute/kg: Not recommended.
 
For HSV induction dosage of 40 mg/kg/dose IV every 8 hours
CrCl more than 1.4 mL/minute/kg: No dosage adjustment required.
CrCl 1.1 to 1.4 mL/minute/kg: Decrease dose to 30 mg/kg/dose IV every 8 hours.
CrCl 0.81 to 1 mL/minute/kg: Decrease dose to 35 mg/kg/dose IV every 12 hours.
CrCl 0.61 to 0.8 mL/minute/kg: Decrease dose to 25 mg/kg/dose IV every 12 hours.
CrCl 0.51 to 0.6 mL/minute/kg: Decrease dose to 40 mg/kg/dose IV every 24 hours.
CrCl 0.4 to 0.5 mL/minute/kg: Decrease dose to 35 mg/kg/dose IV every 24 hours.
CrCl less than 0.4 mL/minute/kg: Not recommended.
 
For CMV induction dosage of 60 mg/kg/dose IV every 8 hours
CrCl more than 1.4 mL/minute/kg: No dosage adjustment required.
CrCl 1.1 to 1.4 mL/minute/kg: Decrease dose to 45 mg/kg/dose IV every 8 hours.
CrCl 0.81 to 1 mL/minute/kg: Decrease dose to 50 mg/kg/dose IV every 12 hours.
CrCl 0.61 to 0.8 mL/minute/kg: Decrease dose to 40 mg/kg/dose IV every 12 hours.
CrCl 0.51 to 0.6 mL/minute/kg: Decrease dose to 60 mg/kg/dose IV every 24 hours.
CrCl 0.4 to 0.5 mL/minute/kg: Decrease dose to 50 mg/kg/dose IV every 24 hours.
CrCl less than 0.4 mL/minute/kg: Not recommended.
 
For CMV induction dosage of 90 mg/kg/dose IV every 12 hours
CrCl more than 1.4 mL/minute/kg: No dosage adjustment required.
CrCl 1.1 to 1.4 mL/minute/kg: Decrease dose to 70 mg/kg/dose IV every 12 hours.
CrCl 0.81 to 1 mL/minute/kg: Decrease dose to 50 mg/kg/dose IV every 12 hours.
CrCl 0.61 to 0.8 mL/minute/kg: Decrease dose to 80 mg/kg/dose IV every 24 hours.
CrCl 0.51 to 0.6 mL/minute/kg: Decrease dose to 60 mg/kg/dose IV every 24 hours.
CrCl 0.4 to 0.5 mL/minute/kg: Decrease dose to 50 mg/kg/dose IV every 24 hours.
CrCl less than 0.4 mL/minute/kg: Not recommended.
 
For maintenance dosage of 90 mg/kg/day
CrCl more than 1.4 mL/minute/kg: No dosage adjustment required.
CrCl 1.1 to 1.4 mL/minute/kg: Decrease dose to 70 mg/kg/dose IV every 24 hours.
CrCl 0.81 to 1 mL/minute/kg: Decrease dose to 50 mg/kg/dose IV every 24 hours.
CrCl 0.61 to 0.8 mL/minute/kg: Decrease dose to 80 mg/kg/dose IV every 48 hours.
CrCl 0.51 to 0.6 mL/minute/kg: Decrease dose to 60 mg/kg/dose IV every 48 hours.
CrCl 0.4 to 0.5 mL/minute/kg: Decrease dose to 50 mg/kg/dose IV every 48 hours.
CrCl less than 0.4 mL/minute/kg: Not recommended.
 
For maintenance dosage of 120 mg/kg/day
CrCl more than 1.4 mL/minute/kg: No dosage adjustment required.
CrCl 1.1 to 1.4 mL/minute/kg: Decrease dose to 90 mg/kg/dose IV every 24 hours.
CrCl 0.81 to 1 mL/minute/kg: Decrease dose to 65 mg/kg/dose IV every 24 hours.
CrCl 0.61 to 0.8 mL/minute/kg: Decrease dose to 105 mg/kg/dose IV every 48 hours.
CrCl 0.51 to 0.6 mL/minute/kg: Decrease dose to 80 mg/kg/dose IV every 48 hours.
CrCl 0.4 to 0.5 mL/minute/kg: Decrease dose to 65 mg/kg/dose IV every 48 hours.
CrCl less than 0.4 mL/minute/kg: Not recommended.
 
Intermittent hemodialysis
Use is not recommended as dosage guidelines have not been established.

Abacavir; Lamivudine, 3TC; Zidovudine, ZDV: (Minor) Concurrent use of foscarnet and zidovudine, ZDV may be associated with a higher incidence of anemia; clinicians should follow normal recommendations for blood count monitoring and other parameters.
Acetaminophen; Aspirin, ASA; Caffeine: (Minor) Due to the inhibition of renal prostaglandins by salicylates, concurrent use of salicylates and other nephrotoxic agents, such as foscarnet, may lead to additive nephrotoxicity.
Acetaminophen; Aspirin: (Minor) Due to the inhibition of renal prostaglandins by salicylates, concurrent use of salicylates and other nephrotoxic agents, such as foscarnet, may lead to additive nephrotoxicity.
Acetaminophen; Aspirin; Diphenhydramine: (Minor) Due to the inhibition of renal prostaglandins by salicylates, concurrent use of salicylates and other nephrotoxic agents, such as foscarnet, may lead to additive nephrotoxicity.
Acyclovir: (Major) The risk of renal toxicity may be increased if foscarnet is used in conjunction with other nephrotoxic agents, such as acyclovir. Avoid concurrent use, unless the potential benefits outweigh the risks to the patient.
Adagrasib: (Major) Concomitant use of adagrasib and foscarnet increases the risk of QT/QTc prolongation and torsade de pointes (TdP). Avoid concomitant use if possible, especially in patients with additional risk factors for TdP. Consider taking steps to minimize the risk for QT/QTc interval prolongation and TdP, such as electrolyte monitoring and repletion and ECG monitoring, if concomitant use is necessary.
Aldesleukin, IL-2: (Moderate) Aldesleukin may cause nephrotoxicity. Concurrent administration of drugs possessing nephrotoxic effects with Aldesleukin, such as foscarnet, may increase the risk of kidney dysfunction. In addition, reduced kidney function secondary to Aldesleukin treatment may delay elimination of concomitant medications and increase the risk of adverse events from those drugs.
Alfuzosin: (Major) When possible, avoid concurrent use of foscarnet with other drugs known to prolong the QT interval, such as alfuzosin. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes (TdP). Based on electrophysiology studies performed by the manufacturer, alfuzosin may prolong the QT interval in a dose-dependent manner. If these drugs are administered together, obtain an electrocardiogram and electrolyte concentrations before and periodically during treatment.
Amikacin: (Major) The risk of renal toxicity may be increased if foscarnet is used in conjunction with other nephrotoxic agents such as aminoglycosides.
Aminoglycosides: (Major) The risk of renal toxicity may be increased if foscarnet is used in conjunction with other nephrotoxic agents such as aminoglycosides.
Aminosalicylate sodium, Aminosalicylic acid: (Minor) Due to the inhibition of renal prostaglandins by salicylates, concurrent use of salicylates and other nephrotoxic agents, such as foscarnet, may lead to additive nephrotoxicity.
Amiodarone: (Major) When possible, avoid concurrent use of foscarnet with other drugs known to prolong the QT interval, such as amiodarone. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes (TdP). Amiodarone, a Class III antiarrhythmic agent, is associated with a well-established risk of QT prolongation and TdP. Although the frequency of TdP is less with amiodarone than with other Class III agents, amiodarone is still associated with a risk of TdP. Due to the extremely long half-life of amiodarone, a drug interaction is possible for days to weeks after discontinuation of amiodarone. If these drugs are administered together, obtain an electrocardiogram and electrolyte concentrations before and periodically during treatment.
Amisulpride: (Major) Avoid coadministration of amisulpride and foscarnet due to the potential for additive QT prolongation and torsade de pointes (TdP). Amisulpride causes dose- and concentration- dependent QT prolongation. Both QT prolongation and TdP have been reported during postmarketing use of foscarnet.
Amoxicillin; Clarithromycin; Omeprazole: (Major) When possible, avoid concurrent use of foscarnet with other drugs known to prolong the QT interval, such as clarithromycin. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes (TdP). Clarithromycin is also associated with an established risk for QT prolongation and TdP. If these drugs are administered together, obtain an electrocardiogram and electrolyte concentrations before and periodically during treatment.
Amphotericin B lipid complex (ABLC): (Major) The risk of renal toxicity may be increased if foscarnet is used in conjunction with other nephrotoxic agents such as amphotericin B. Avoid concurrent use, unless the potential benefits outweigh the risks to the patient.
Amphotericin B liposomal (LAmB): (Major) The risk of renal toxicity may be increased if foscarnet is used in conjunction with other nephrotoxic agents such as amphotericin B. Avoid concurrent use, unless the potential benefits outweigh the risks to the patient.
Amphotericin B: (Major) The risk of renal toxicity may be increased if foscarnet is used in conjunction with other nephrotoxic agents such as amphotericin B. Avoid concurrent use, unless the potential benefits outweigh the risks to the patient.
Anagrelide: (Major) When possible, avoid concurrent use of foscarnet with other drugs known to prolong the QT interval, such as anagrelide. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes TdP. Torsade de pointes (TdP) and ventricular tachycardia have also been reported with anagrelide. In addition, dose-related increases in mean QTc and heart rate were observed in healthy subjects. If these drugs are administered together, obtain an electrocardiogram and electrolyte concentrations before and periodically during treatment.
Apomorphine: (Major) When possible, avoid concurrent use of foscarnet with other drugs known to prolong the QT interval, such as apomorphine. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes (TdP). Dose-related QTc prolongation is associated with therapeutic apomorphine exposure. If these drugs are administered together, obtain an electrocardiogram and electrolyte concentrations before and periodically during treatment.
Aprotinin: (Moderate) The manufacturer recommends using aprotinin cautiously in patients that are receiving drugs that can affect renal function, such as foscarnet, as the risk of renal impairment may be increased.
Aripiprazole: (Major) Concomitant use of aripiprazole and foscarnet increases the risk of QT/QTc prolongation and torsade de pointes (TdP). Avoid concomitant use if possible, especially in patients with additional risk factors for TdP. Consider taking steps to minimize the risk for QT/QTc interval prolongation and TdP, such as electrolyte monitoring and repletion and ECG monitoring, if concomitant use is necessary.
Arsenic Trioxide: (Major) When possible, avoid concurrent use of foscarnet with other drugs known to prolong the QT interval, such as arsenic trioxide. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes. Torsade de pointes, QT interval prolongation, and complete atrioventricular block have been reported with arsenic trioxide use. If these drugs are administered together, obtain an electrocardiogram and electrolyte concentrations before and periodically during treatment.
Artemether; Lumefantrine: (Major) When possible, avoid concurrent use of foscarnet with other drugs known to prolong the QT interval, such as artemether. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes (TdP). Artemether; lumefantrine is also associated with prolongation of the QT interval. If these drugs are administered together, obtain an electrocardiogram and electrolyte concentrations before and periodically during treatment. (Major) When possible, avoid concurrent use of foscarnet with other drugs known to prolong the QT interval, such as lumefantrine. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes (TdP). Artemether; lumefantrine is also associated with prolongation of the QT interval. If these drugs are administered together, obtain an electrocardiogram and electrolyte concentrations before and periodically during treatment.
Asenapine: (Major) When possible, avoid concurrent use of foscarnet with other drugs known to prolong the QT interval, such as asenapine. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes (TdP). Asenapine has also been associated with QT prolongation. If these drugs are administered together, obtain an electrocardiogram and electrolyte concentrations before and periodically during treatment.
Aspirin, ASA: (Minor) Due to the inhibition of renal prostaglandins by salicylates, concurrent use of salicylates and other nephrotoxic agents, such as foscarnet, may lead to additive nephrotoxicity.
Aspirin, ASA; Butalbital; Caffeine: (Minor) Due to the inhibition of renal prostaglandins by salicylates, concurrent use of salicylates and other nephrotoxic agents, such as foscarnet, may lead to additive nephrotoxicity.
Aspirin, ASA; Caffeine: (Minor) Due to the inhibition of renal prostaglandins by salicylates, concurrent use of salicylates and other nephrotoxic agents, such as foscarnet, may lead to additive nephrotoxicity.
Aspirin, ASA; Caffeine; Orphenadrine: (Minor) Due to the inhibition of renal prostaglandins by salicylates, concurrent use of salicylates and other nephrotoxic agents, such as foscarnet, may lead to additive nephrotoxicity.
Aspirin, ASA; Carisoprodol: (Minor) Due to the inhibition of renal prostaglandins by salicylates, concurrent use of salicylates and other nephrotoxic agents, such as foscarnet, may lead to additive nephrotoxicity.
Aspirin, ASA; Carisoprodol; Codeine: (Minor) Due to the inhibition of renal prostaglandins by salicylates, concurrent use of salicylates and other nephrotoxic agents, such as foscarnet, may lead to additive nephrotoxicity.
Aspirin, ASA; Citric Acid; Sodium Bicarbonate: (Minor) Due to the inhibition of renal prostaglandins by salicylates, concurrent use of salicylates and other nephrotoxic agents, such as foscarnet, may lead to additive nephrotoxicity.
Aspirin, ASA; Dipyridamole: (Minor) Due to the inhibition of renal prostaglandins by salicylates, concurrent use of salicylates and other nephrotoxic agents, such as foscarnet, may lead to additive nephrotoxicity.
Aspirin, ASA; Omeprazole: (Minor) Due to the inhibition of renal prostaglandins by salicylates, concurrent use of salicylates and other nephrotoxic agents, such as foscarnet, may lead to additive nephrotoxicity.
Aspirin, ASA; Oxycodone: (Minor) Due to the inhibition of renal prostaglandins by salicylates, concurrent use of salicylates and other nephrotoxic agents, such as foscarnet, may lead to additive nephrotoxicity.
Atomoxetine: (Major) Concomitant use of atomoxetine and foscarnet increases the risk of QT/QTc prolongation and torsade de pointes (TdP). Avoid concomitant use if possible, especially in patients with additional risk factors for TdP. Consider taking steps to minimize the risk for QT/QTc interval prolongation and TdP, such as electrolyte monitoring and repletion and ECG monitoring, if concomitant use is necessary.
Azithromycin: (Major) Concomitant use of azithromycin and foscarnet increases the risk of QT/QTc prolongation and torsade de pointes (TdP). Avoid concomitant use if possible, especially in patients with additional risk factors for TdP. Consider taking steps to minimize the risk for QT/QTc interval prolongation and TdP, such as electrolyte monitoring and repletion and ECG monitoring, if concomitant use is necessary.
Bacitracin: (Minor) Additive nephrotoxicity may occur with concurrent use of systemic bacitracin and other nephrotoxic agents. When possible, avoid concomitant administration of systemic bacitracin and other nephrotoxic drugs such as foscarnet. Use of topically administrated preparations containing bacitracin, especially when applied to large surface areas, may have additive nephrotoxic potential with foscarnet.
Bedaquiline: (Major) When possible, avoid concurrent use of foscarnet with other drugs known to prolong the QT interval, such as bedaquiline. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes (TdP). Bedaquiline has also been reported to prolong the QT interval. If these drugs are administered together, obtain an electrocardiogram and electrolyte concentrations before and periodically during treatment.
Benzoic Acid; Hyoscyamine; Methenamine; Methylene Blue; Phenyl Salicylate: (Minor) Due to the inhibition of renal prostaglandins by salicylates, concurrent use of salicylates and other nephrotoxic agents, such as foscarnet, may lead to additive nephrotoxicity.
Bictegravir; Emtricitabine; Tenofovir Alafenamide: (Moderate) Monitor for changes in renal function if tenofovir alafenamide is administered in combination with a nephrotoxic agent, such as foscarnet. Tenofovir is primarily excreted via the kidneys by a combination of glomerular filtration and active tubular secretion. Coadministration of tenofovir alafenamide with a drug that reduces renal function or competes for active tubular secretion may increase concentrations of tenofovir and other renally eliminated drugs; thus, increasing the risk of developing renal-related adverse reactions. (Moderate) Monitor for changes in serum creatinine and adverse reactions, such as lactic acidosis or hepatotoxicity if emtricitabine is administered in combination with nephrotoxic agents, such as foscarnet. Consider the potential for drug interaction prior to and during concurrent use of these medications. Both emtricitabine and foscarnet are excreted via the kidneys by a combination of glomerular filtration and active tubular secretion. While no drug interactions due to competition for renal excretion have been observed, coadministration of these medications may increase concentrations of both drugs.
Bismuth Subcitrate Potassium; Metronidazole; Tetracycline: (Major) Concomitant use of metronidazole and foscarnet increases the risk of QT/QTc prolongation and torsade de pointes (TdP). Avoid concomitant use if possible, especially in patients with additional risk factors for TdP. Consider taking steps to minimize the risk for QT/QTc interval prolongation and TdP, such as electrolyte monitoring and repletion and ECG monitoring, if concomitant use is necessary.
Bismuth Subsalicylate: (Minor) Due to the inhibition of renal prostaglandins by salicylates, concurrent use of salicylates and other nephrotoxic agents, such as foscarnet, may lead to additive nephrotoxicity.
Bismuth Subsalicylate; Metronidazole; Tetracycline: (Major) Concomitant use of metronidazole and foscarnet increases the risk of QT/QTc prolongation and torsade de pointes (TdP). Avoid concomitant use if possible, especially in patients with additional risk factors for TdP. Consider taking steps to minimize the risk for QT/QTc interval prolongation and TdP, such as electrolyte monitoring and repletion and ECG monitoring, if concomitant use is necessary. (Minor) Due to the inhibition of renal prostaglandins by salicylates, concurrent use of salicylates and other nephrotoxic agents, such as foscarnet, may lead to additive nephrotoxicity.
Bleomycin: (Minor) Previous treatment with nephrotoxic agents, like foscarnet, may result in decreased bleomycin clearance if renal function has been impaired. Monitor for signs/symptoms of bleomycin toxicity in patients with concomittant or prior foscarnet therapy.
Bumetanide: (Moderate) Avoid concurrent use of loop diuretics with foscarnet. Coadministration may impair the renal tubular secretion of foscarnet, thereby increasing the possibility for toxicity. When use of a diuretic is indicated in patients being treated with foscarnet, consider a thiazide diuretic.
Buprenorphine: (Major) Concomitant use of buprenorphine and foscarnet increases the risk of QT/QTc prolongation and torsade de pointes (TdP). Avoid concomitant use if possible, especially in patients with additional risk factors for TdP. Consider taking steps to minimize the risk for QT/QTc interval prolongation and TdP, such as electrolyte monitoring and repletion and ECG monitoring, if concomitant use is necessary.
Buprenorphine; Naloxone: (Major) Concomitant use of buprenorphine and foscarnet increases the risk of QT/QTc prolongation and torsade de pointes (TdP). Avoid concomitant use if possible, especially in patients with additional risk factors for TdP. Consider taking steps to minimize the risk for QT/QTc interval prolongation and TdP, such as electrolyte monitoring and repletion and ECG monitoring, if concomitant use is necessary.
Butalbital; Aspirin; Caffeine; Codeine: (Minor) Due to the inhibition of renal prostaglandins by salicylates, concurrent use of salicylates and other nephrotoxic agents, such as foscarnet, may lead to additive nephrotoxicity.
Cabotegravir; Rilpivirine: (Major) When possible, avoid concurrent use of foscarnet with other drugs known to prolong the QT interval, such as rilpivirine. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes (TdP). Supratherapeutic doses of rilpivirine (75 to 300 mg/day) have caused QT prolongation. If these drugs are administered together, obtain an electrocardiogram and electrolyte concentrations before and periodically during treatment.
Capreomycin: (Major) Because capreomycin is eliminated by the kidney, coadministration with other potentially nephrotoxic drugs, including foscarnet, may increase serum concentrations of either drug. Theoretically, the chronic coadministration of these drugs may increase the risk of developing nephrotoxicity, even in patients who have normal renal function. Monitor patients for changes in renal function if these drugs are coadministered.
Ceritinib: (Major) Avoid coadministration of foscarnet with ceritinib due to the risk of QT prolongation. Ceritinib causes concentration-dependent prolongation of the QT interval. If coadministration cannot be avoided, conduct periodic monitoring with electrocardiograms (ECGs) and electrolytes. Both QT prolongation and torsade de pointes (TdP) have been reported during postmarketing use of foscarnet.
Chloroquine: (Major) Avoid coadministration of chloroquine with foscarnet due to the increased risk of QT prolongation. If use together is necessary, obtain an ECG at baseline to assess initial QT interval and determine frequency of subsequent ECG monitoring, avoid any non-essential QT prolonging drugs, and correct electrolyte imbalances. Chloroquine is associated with an increased risk of QT prolongation and torsade de pointes (TdP); the risk of QT prolongation is increased with higher chloroquine doses. Both QT prolongation and TdP have been reported during postmarketing use of foscarnet.
Chlorpromazine: (Major) When possible, avoid concurrent use of foscarnet with other drugs known to prolong the QT interval, such as chlorpromazine. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes (TdP). Chlorpromazine, a phenothiazine, is also associated with an established risk of QT prolongation and TdP. If these drugs are administered together, obtain an electrocardiogram and electrolyte concentrations before and periodically during treatment.
Choline Salicylate; Magnesium Salicylate: (Minor) Due to the inhibition of renal prostaglandins by salicylates, concurrent use of salicylates and other nephrotoxic agents, such as foscarnet, may lead to additive nephrotoxicity.
Cidofovir: (Contraindicated) The administration of cidofovir with another potentially nephrotoxic agent, such as foscarnet, is contraindicated. Foscarnet should be discontinued at least 7 days prior to beginning cidofovir.
Ciprofloxacin: (Major) When possible, avoid concurrent use of foscarnet with other drugs known to prolong the QT interval, such as ciprofloxacin. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes (TdP). Rare cases of QT prolongation and TdP have also been reported with ciprofloxacin during postmarketing surveillance. If these drugs are administered together, obtain an electrocardiogram and electrolyte concentrations before and periodically during treatment. In addition, use of ciprofloxacin with foscarnet may increase the risk of seizures. Since foscarnet is not metabolized by the liver and since renal dysfunction was not present, it is unlikely that drug accumulation is responsible for seizures. An additive effect is proposed since seizures have been associated with ciprofloxacin and foscarnet independently.
Cisapride: (Contraindicated) QT prolongation and ventricular arrhythmias, including torsade de pointes (TdP) and death, have been reported with cisapride. Because of the potential for TdP, use of foscarnet with cisapride is contraindicated.
Cisplatin: (Moderate) Closely monitor renal function if concomitant use with cisplatin and foscarnet is necessary. Both drugs can cause nephrotoxicity, which may be exacerbated with the use of additional nephrotoxins.
Citalopram: (Major) Concomitant use of citalopram and foscarnet increases the risk of QT/QTc prolongation and torsade de pointes (TdP). Avoid concomitant use if possible, especially in patients with additional risk factors for TdP. Consider taking steps to minimize the risk for QT/QTc interval prolongation and TdP, such as electrolyte monitoring and repletion and ECG monitoring, if concomitant use is necessary.
Clarithromycin: (Major) When possible, avoid concurrent use of foscarnet with other drugs known to prolong the QT interval, such as clarithromycin. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes (TdP). Clarithromycin is also associated with an established risk for QT prolongation and TdP. If these drugs are administered together, obtain an electrocardiogram and electrolyte concentrations before and periodically during treatment.
Clindamycin: (Major) Avoid concomitant use of foscarnet and clindamycin; coadministration may result in additive nephrotoxicity. Monitor for renal toxicity if concomitant use is required.
Clofarabine: (Major) Avoid the concomitant use of clofarabine and foscarnet; coadministration may result in additive nephrotoxicity.
Clofazimine: (Major) Concomitant use of clofazimine and foscarnet increases the risk of QT/QTc prolongation and torsade de pointes (TdP). Avoid concomitant use if possible, especially in patients with additional risk factors for TdP. Consider taking steps to minimize the risk for QT/QTc interval prolongation and TdP, such as electrolyte monitoring and repletion and ECG monitoring, if concomitant use is necessary.
Clozapine: (Major) When possible, avoid concurrent use of foscarnet with other drugs known to prolong the QT interval, such as clozapine. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes (TdP). Treatment with clozapine has been associated with QT prolongation, TdP, cardiac arrest, and sudden death. If these drugs are administered together, obtain an electrocardiogram and electrolyte concentrations before and periodically during treatment.
Codeine; Phenylephrine; Promethazine: (Major) Concomitant use of promethazine and foscarnet increases the risk of QT/QTc prolongation and torsade de pointes (TdP). Avoid concomitant use if possible, especially in patients with additional risk factors for TdP. Consider taking steps to minimize the risk for QT/QTc interval prolongation and TdP, such as electrolyte monitoring and repletion and ECG monitoring, if concomitant use is necessary.
Codeine; Promethazine: (Major) Concomitant use of promethazine and foscarnet increases the risk of QT/QTc prolongation and torsade de pointes (TdP). Avoid concomitant use if possible, especially in patients with additional risk factors for TdP. Consider taking steps to minimize the risk for QT/QTc interval prolongation and TdP, such as electrolyte monitoring and repletion and ECG monitoring, if concomitant use is necessary.
Colistimethate, Colistin, Polymyxin E: (Major) Theoretically, chronic coadministration may increase the risk of developing nephrotoxicity, even in patients who have normal renal function. Monitor patients for changes in renal function during concurrent use. Since colistimethate sodium is eliminated by the kidney, coadministration with other potentially nephrotoxic drugs, including foscarnet, may increase serum concentrations of either drug.
Colistin: (Major) Theoretically, chronic coadministration may increase the risk of developing nephrotoxicity, even in patients who have normal renal function. Monitor patients for changes in renal function during concurrent use. Since colistimethate sodium is eliminated by the kidney, coadministration with other potentially nephrotoxic drugs, including foscarnet, may increase serum concentrations of either drug.
Crizotinib: (Major) Avoid coadministration of crizotinib with foscarnet due to the risk of QT prolongation. Crizotinib has been associated with concentration-dependent QT prolongation. Both QT prolongation and torsade de pointes (TdP) have been reported during postmarketing use of foscarnet.
Cyclosporine: (Major) The risk of renal toxicity may be increased if foscarnet is used in conjunction with other nephrotoxic agents such as cyclosporine. Monitor renal function and fluid status carefully during cyclosporine usage.
Darunavir; Cobicistat; Emtricitabine; Tenofovir alafenamide: (Moderate) Monitor for changes in renal function if tenofovir alafenamide is administered in combination with a nephrotoxic agent, such as foscarnet. Tenofovir is primarily excreted via the kidneys by a combination of glomerular filtration and active tubular secretion. Coadministration of tenofovir alafenamide with a drug that reduces renal function or competes for active tubular secretion may increase concentrations of tenofovir and other renally eliminated drugs; thus, increasing the risk of developing renal-related adverse reactions. (Moderate) Monitor for changes in serum creatinine and adverse reactions, such as lactic acidosis or hepatotoxicity if emtricitabine is administered in combination with nephrotoxic agents, such as foscarnet. Consider the potential for drug interaction prior to and during concurrent use of these medications. Both emtricitabine and foscarnet are excreted via the kidneys by a combination of glomerular filtration and active tubular secretion. While no drug interactions due to competition for renal excretion have been observed, coadministration of these medications may increase concentrations of both drugs.
Dasatinib: (Major) When possible, avoid concurrent use of foscarnet with other drugs known to prolong the QT interval, such as dasatinib. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes (TdP). In vitro studies have shown that dasatinib has the potential to prolong the QT interval. If these drugs are administered together, obtain an electrocardiogram and electrolyte concentrations before and periodically during treatment.
Degarelix: (Major) Avoid use of foscarnet with degarelix due to the potential for Both QT prolongation and torsade de pointes (TdP) as these have been reported during postmarketing use of foscarnet. Androgen deprivation therapy (i.e., degarelix) may also prolong the QT/QTc interval.
Desflurane: (Major) When possible, avoid concurrent use of foscarnet with other drugs known to prolong the QT interval, such as halogenated anesthetics. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes (TdP). Halogenated anesthetics can also prolong the QT interval. If these drugs are administered together, obtain an electrocardiogram and electrolyte concentrations before and periodically during treatment.
Deutetrabenazine: (Major) Avoid coadministration of foscarnet with deutetrabenazine due to the potential for QT prolongation. Both QT prolongation and torsade de pointes (TdP) have been reported during postmarketing use of foscarnet. Deutetrabenazine may prolong the QT interval, but the degree of QT prolongation is not clinically significant when deutetrabenazine is administered within the recommended dosage range.
Dexmedetomidine: (Major) Concomitant use of dexmedetomidine and foscarnet increases the risk of QT/QTc prolongation and torsade de pointes (TdP). Avoid concomitant use if possible, especially in patients with additional risk factors for TdP. Consider taking steps to minimize the risk for QT/QTc interval prolongation and TdP, such as electrolyte monitoring and repletion and ECG monitoring, if concomitant use is necessary.
Dextromethorphan; Quinidine: (Major) When possible, avoid concurrent use of foscarnet with other drugs known to prolong the QT interval, such as quinidine. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes (TdP). Quinidine administration is also associated with QT prolongation and TdP. If these drugs are administered together, obtain an electrocardiogram and electrolyte concentrations before and periodically during treatment.
Disopyramide: (Major) When possible, avoid concurrent use of foscarnet with other drugs known to prolong the QT interval, such as disopyramide. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes (TdP). Disopyramide administration is also associated with QT prolongation and TdP. If these drugs are administered together, obtain an electrocardiogram and electrolyte concentrations before and periodically during treatment.
Dofetilide: (Major) Coadministration of dofetilide and foscarnet is not recommended as concurrent use may increase the risk of QT prolongation. Dofetilide, a Class III antiarrhythmic agent, is associated with a well-established risk of QT prolongation and torsade de pointes (TdP). Both QT prolongation and TdP have been reported during postmarketing use of foscarnet.
Dolasetron: (Major) When possible, avoid concurrent use of foscarnet with other drugs known to prolong the QT interval, such as dolasetron. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes (TdP). Dolasetron has been associated with a dose-dependent prolongation in the QT, PR, and QRS intervals on an electrocardiogram. If these drugs are administered together, obtain an electrocardiogram and electrolyte concentrations before and periodically during treatment.
Dolutegravir; Rilpivirine: (Major) When possible, avoid concurrent use of foscarnet with other drugs known to prolong the QT interval, such as rilpivirine. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes (TdP). Supratherapeutic doses of rilpivirine (75 to 300 mg/day) have caused QT prolongation. If these drugs are administered together, obtain an electrocardiogram and electrolyte concentrations before and periodically during treatment.
Donepezil: (Major) When possible, avoid concurrent use of foscarnet with other drugs known to prolong the QT interval, such as donepezil. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes (TdP). Case reports indicate that QT prolongation and TdP can also occur during donepezil therapy. Donepezil is considered a drug with a known risk of TdP. If these drugs are administered together, obtain an electrocardiogram and electrolyte concentrations before and periodically during treatment.
Donepezil; Memantine: (Major) When possible, avoid concurrent use of foscarnet with other drugs known to prolong the QT interval, such as donepezil. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes (TdP). Case reports indicate that QT prolongation and TdP can also occur during donepezil therapy. Donepezil is considered a drug with a known risk of TdP. If these drugs are administered together, obtain an electrocardiogram and electrolyte concentrations before and periodically during treatment.
Doravirine; Lamivudine; Tenofovir disoproxil fumarate: (Moderate) Monitor for changes in serum creatinine and phosphorus if tenofovir is administered in combination with nephrotoxic agents, such as foscarnet. Tenofovir is primarily excreted via the kidneys by a combination of glomerular filtration and active tubular secretion. While no drug interactions due to competition for renal excretion have been observed, coadministration of tenofovir with drugs that are eliminated by active tubular secretion may increase concentrations of tenofovir, and/or the co-administered drug. Drugs that decrease renal function may increase concentrations of tenofovir. Renal impairment, which may include hypophosphatemia, has been reported with the use of tenofovir; a majority of the cases occurred in patients who had underlying systemic or renal disease or who are concurrently taking nephrotoxic agents. Tenofovir containing products should be avoided with concurrent or recent use of a nephrotoxic agent; patients receiving concomitant nephrotoxic agents should be carefully monitored for changes in serum creatinine and phosphorus.
Dronedarone: (Contraindicated) Dronedarone administration is associated with a dose-related increase in the QTc interval. The increase in QTc is approximately 10 milliseconds at doses of 400 mg twice daily (the FDA-approved dose) and up to 25 milliseconds at doses of 1600 mg twice daily. Although there are no studies examining the effects of dronedarone in patients receiving other QT prolonging drugs, coadministration of such drugs may result in additive QT prolongation. Because of the potential for TdP, use of foscarnet with dronedarone is contraindicated.
Droperidol: (Major) When possible, avoid concurrent use of foscarnet with other drugs known to prolong the QT interval, such as droperidol. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes (TdP). Droperidol administration is associated with an established risk for QT prolongation and TdP. In December 2001, the FDA issued a black box warning regarding the use of droperidol and its association with QT prolongation and potential for cardiac arrhythmias based on postmarketing surveillance data. According to the revised 2001 labeling for droperidol, any drug known to have potential to prolong the QT interval should not be coadministered with droperidol. If these drugs are administered together, obtain an electrocardiogram and electrolyte concentrations before and periodically during treatment.
Efavirenz: (Major) When possible, avoid concurrent use of foscarnet with other drugs known to prolong the QT interval, such as efavirenz. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes (TdP). QTc prolongation has also been observed with the use of efavirenz. If these drugs are administered together, obtain an electrocardiogram and electrolyte concentrations before and periodically during treatment.
Efavirenz; Emtricitabine; Tenofovir Disoproxil Fumarate: (Major) When possible, avoid concurrent use of foscarnet with other drugs known to prolong the QT interval, such as efavirenz. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes (TdP). QTc prolongation has also been observed with the use of efavirenz. If these drugs are administered together, obtain an electrocardiogram and electrolyte concentrations before and periodically during treatment. (Moderate) Monitor for changes in serum creatinine and adverse reactions, such as lactic acidosis or hepatotoxicity if emtricitabine is administered in combination with nephrotoxic agents, such as foscarnet. Consider the potential for drug interaction prior to and during concurrent use of these medications. Both emtricitabine and foscarnet are excreted via the kidneys by a combination of glomerular filtration and active tubular secretion. While no drug interactions due to competition for renal excretion have been observed, coadministration of these medications may increase concentrations of both drugs. (Moderate) Monitor for changes in serum creatinine and phosphorus if tenofovir is administered in combination with nephrotoxic agents, such as foscarnet. Tenofovir is primarily excreted via the kidneys by a combination of glomerular filtration and active tubular secretion. While no drug interactions due to competition for renal excretion have been observed, coadministration of tenofovir with drugs that are eliminated by active tubular secretion may increase concentrations of tenofovir, and/or the co-administered drug. Drugs that decrease renal function may increase concentrations of tenofovir. Renal impairment, which may include hypophosphatemia, has been reported with the use of tenofovir; a majority of the cases occurred in patients who had underlying systemic or renal disease or who are concurrently taking nephrotoxic agents. Tenofovir containing products should be avoided with concurrent or recent use of a nephrotoxic agent; patients receiving concomitant nephrotoxic agents should be carefully monitored for changes in serum creatinine and phosphorus.
Efavirenz; Lamivudine; Tenofovir Disoproxil Fumarate: (Major) When possible, avoid concurrent use of foscarnet with other drugs known to prolong the QT interval, such as efavirenz. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes (TdP). QTc prolongation has also been observed with the use of efavirenz. If these drugs are administered together, obtain an electrocardiogram and electrolyte concentrations before and periodically during treatment. (Moderate) Monitor for changes in serum creatinine and phosphorus if tenofovir is administered in combination with nephrotoxic agents, such as foscarnet. Tenofovir is primarily excreted via the kidneys by a combination of glomerular filtration and active tubular secretion. While no drug interactions due to competition for renal excretion have been observed, coadministration of tenofovir with drugs that are eliminated by active tubular secretion may increase concentrations of tenofovir, and/or the co-administered drug. Drugs that decrease renal function may increase concentrations of tenofovir. Renal impairment, which may include hypophosphatemia, has been reported with the use of tenofovir; a majority of the cases occurred in patients who had underlying systemic or renal disease or who are concurrently taking nephrotoxic agents. Tenofovir containing products should be avoided with concurrent or recent use of a nephrotoxic agent; patients receiving concomitant nephrotoxic agents should be carefully monitored for changes in serum creatinine and phosphorus.
Eliglustat: (Major) When possible, avoid concurrent use of foscarnet with other drugs known to prolong the QT interval, such as eliglustat. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes (TdP). Eliglustat is predicted to cause PR, QRS, and/or QT prolongation at significantly elevated plasma concentrations. If these drugs are administered together, obtain an electrocardiogram and electrolyte concentrations before and periodically during treatment.
Elvitegravir; Cobicistat; Emtricitabine; Tenofovir Alafenamide: (Moderate) Monitor for changes in renal function if tenofovir alafenamide is administered in combination with a nephrotoxic agent, such as foscarnet. Tenofovir is primarily excreted via the kidneys by a combination of glomerular filtration and active tubular secretion. Coadministration of tenofovir alafenamide with a drug that reduces renal function or competes for active tubular secretion may increase concentrations of tenofovir and other renally eliminated drugs; thus, increasing the risk of developing renal-related adverse reactions. (Moderate) Monitor for changes in serum creatinine and adverse reactions, such as lactic acidosis or hepatotoxicity if emtricitabine is administered in combination with nephrotoxic agents, such as foscarnet. Consider the potential for drug interaction prior to and during concurrent use of these medications. Both emtricitabine and foscarnet are excreted via the kidneys by a combination of glomerular filtration and active tubular secretion. While no drug interactions due to competition for renal excretion have been observed, coadministration of these medications may increase concentrations of both drugs.
Elvitegravir; Cobicistat; Emtricitabine; Tenofovir Disoproxil Fumarate: (Moderate) Monitor for changes in serum creatinine and adverse reactions, such as lactic acidosis or hepatotoxicity if emtricitabine is administered in combination with nephrotoxic agents, such as foscarnet. Consider the potential for drug interaction prior to and during concurrent use of these medications. Both emtricitabine and foscarnet are excreted via the kidneys by a combination of glomerular filtration and active tubular secretion. While no drug interactions due to competition for renal excretion have been observed, coadministration of these medications may increase concentrations of both drugs. (Moderate) Monitor for changes in serum creatinine and phosphorus if tenofovir is administered in combination with nephrotoxic agents, such as foscarnet. Tenofovir is primarily excreted via the kidneys by a combination of glomerular filtration and active tubular secretion. While no drug interactions due to competition for renal excretion have been observed, coadministration of tenofovir with drugs that are eliminated by active tubular secretion may increase concentrations of tenofovir, and/or the co-administered drug. Drugs that decrease renal function may increase concentrations of tenofovir. Renal impairment, which may include hypophosphatemia, has been reported with the use of tenofovir; a majority of the cases occurred in patients who had underlying systemic or renal disease or who are concurrently taking nephrotoxic agents. Tenofovir containing products should be avoided with concurrent or recent use of a nephrotoxic agent; patients receiving concomitant nephrotoxic agents should be carefully monitored for changes in serum creatinine and phosphorus.
Emtricitabine: (Moderate) Monitor for changes in serum creatinine and adverse reactions, such as lactic acidosis or hepatotoxicity if emtricitabine is administered in combination with nephrotoxic agents, such as foscarnet. Consider the potential for drug interaction prior to and during concurrent use of these medications. Both emtricitabine and foscarnet are excreted via the kidneys by a combination of glomerular filtration and active tubular secretion. While no drug interactions due to competition for renal excretion have been observed, coadministration of these medications may increase concentrations of both drugs.
Emtricitabine; Rilpivirine; Tenofovir alafenamide: (Major) When possible, avoid concurrent use of foscarnet with other drugs known to prolong the QT interval, such as rilpivirine. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes (TdP). Supratherapeutic doses of rilpivirine (75 to 300 mg/day) have caused QT prolongation. If these drugs are administered together, obtain an electrocardiogram and electrolyte concentrations before and periodically during treatment. (Moderate) Monitor for changes in renal function if tenofovir alafenamide is administered in combination with a nephrotoxic agent, such as foscarnet. Tenofovir is primarily excreted via the kidneys by a combination of glomerular filtration and active tubular secretion. Coadministration of tenofovir alafenamide with a drug that reduces renal function or competes for active tubular secretion may increase concentrations of tenofovir and other renally eliminated drugs; thus, increasing the risk of developing renal-related adverse reactions. (Moderate) Monitor for changes in serum creatinine and adverse reactions, such as lactic acidosis or hepatotoxicity if emtricitabine is administered in combination with nephrotoxic agents, such as foscarnet. Consider the potential for drug interaction prior to and during concurrent use of these medications. Both emtricitabine and foscarnet are excreted via the kidneys by a combination of glomerular filtration and active tubular secretion. While no drug interactions due to competition for renal excretion have been observed, coadministration of these medications may increase concentrations of both drugs.
Emtricitabine; Rilpivirine; Tenofovir Disoproxil Fumarate: (Major) When possible, avoid concurrent use of foscarnet with other drugs known to prolong the QT interval, such as rilpivirine. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes (TdP). Supratherapeutic doses of rilpivirine (75 to 300 mg/day) have caused QT prolongation. If these drugs are administered together, obtain an electrocardiogram and electrolyte concentrations before and periodically during treatment. (Moderate) Monitor for changes in serum creatinine and adverse reactions, such as lactic acidosis or hepatotoxicity if emtricitabine is administered in combination with nephrotoxic agents, such as foscarnet. Consider the potential for drug interaction prior to and during concurrent use of these medications. Both emtricitabine and foscarnet are excreted via the kidneys by a combination of glomerular filtration and active tubular secretion. While no drug interactions due to competition for renal excretion have been observed, coadministration of these medications may increase concentrations of both drugs. (Moderate) Monitor for changes in serum creatinine and phosphorus if tenofovir is administered in combination with nephrotoxic agents, such as foscarnet. Tenofovir is primarily excreted via the kidneys by a combination of glomerular filtration and active tubular secretion. While no drug interactions due to competition for renal excretion have been observed, coadministration of tenofovir with drugs that are eliminated by active tubular secretion may increase concentrations of tenofovir, and/or the co-administered drug. Drugs that decrease renal function may increase concentrations of tenofovir. Renal impairment, which may include hypophosphatemia, has been reported with the use of tenofovir; a majority of the cases occurred in patients who had underlying systemic or renal disease or who are concurrently taking nephrotoxic agents. Tenofovir containing products should be avoided with concurrent or recent use of a nephrotoxic agent; patients receiving concomitant nephrotoxic agents should be carefully monitored for changes in serum creatinine and phosphorus.
Emtricitabine; Tenofovir alafenamide: (Moderate) Monitor for changes in renal function if tenofovir alafenamide is administered in combination with a nephrotoxic agent, such as foscarnet. Tenofovir is primarily excreted via the kidneys by a combination of glomerular filtration and active tubular secretion. Coadministration of tenofovir alafenamide with a drug that reduces renal function or competes for active tubular secretion may increase concentrations of tenofovir and other renally eliminated drugs; thus, increasing the risk of developing renal-related adverse reactions. (Moderate) Monitor for changes in serum creatinine and adverse reactions, such as lactic acidosis or hepatotoxicity if emtricitabine is administered in combination with nephrotoxic agents, such as foscarnet. Consider the potential for drug interaction prior to and during concurrent use of these medications. Both emtricitabine and foscarnet are excreted via the kidneys by a combination of glomerular filtration and active tubular secretion. While no drug interactions due to competition for renal excretion have been observed, coadministration of these medications may increase concentrations of both drugs.
Emtricitabine; Tenofovir Disoproxil Fumarate: (Moderate) Monitor for changes in serum creatinine and adverse reactions, such as lactic acidosis or hepatotoxicity if emtricitabine is administered in combination with nephrotoxic agents, such as foscarnet. Consider the potential for drug interaction prior to and during concurrent use of these medications. Both emtricitabine and foscarnet are excreted via the kidneys by a combination of glomerular filtration and active tubular secretion. While no drug interactions due to competition for renal excretion have been observed, coadministration of these medications may increase concentrations of both drugs. (Moderate) Monitor for changes in serum creatinine and phosphorus if tenofovir is administered in combination with nephrotoxic agents, such as foscarnet. Tenofovir is primarily excreted via the kidneys by a combination of glomerular filtration and active tubular secretion. While no drug interactions due to competition for renal excretion have been observed, coadministration of tenofovir with drugs that are eliminated by active tubular secretion may increase concentrations of tenofovir, and/or the co-administered drug. Drugs that decrease renal function may increase concentrations of tenofovir. Renal impairment, which may include hypophosphatemia, has been reported with the use of tenofovir; a majority of the cases occurred in patients who had underlying systemic or renal disease or who are concurrently taking nephrotoxic agents. Tenofovir containing products should be avoided with concurrent or recent use of a nephrotoxic agent; patients receiving concomitant nephrotoxic agents should be carefully monitored for changes in serum creatinine and phosphorus.
Encorafenib: (Major) Avoid coadministration of encorafenib and foscarnet due to QT prolongation. Encorafenib is associated with dose-dependent prolongation of the QT interval. Both QT prolongation and torsade de pointes (TdP) have been reported during postmarketing use of foscarnet.
Entecavir: (Moderate) Entecavir may affect renal function and should be used cautiously in combination with other drugs that may also affect renal function including foscarnet.
Entrectinib: (Major) Avoid coadministration of entrectinib with foscarnet due to the risk of QT prolongation. Entrectinib has been associated with QT prolongation. Both QT prolongation and torsade de pointes (TdP) have been reported during postmarketing use of foscarnet.
Eribulin: (Major) When possible, avoid concurrent use of foscarnet with other drugs known to prolong the QT interval, such as eribulin. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes (TdP). Eribulin has also been associated with QT prolongation. If these drugs are administered together, obtain an electrocardiogram and electrolyte concentrations before and periodically during treatment.
Erythromycin: (Major) Concomitant use of erythromycin and foscarnet increases the risk of QT/QTc prolongation and torsade de pointes (TdP). Avoid concomitant use if possible, especially in patients with additional risk factors for TdP. Consider taking steps to minimize the risk for QT/QTc interval prolongation and TdP, such as electrolyte monitoring and repletion and ECG monitoring, if concomitant use is necessary.
Escitalopram: (Major) Concomitant use of escitalopram and foscarnet increases the risk of QT/QTc prolongation and torsade de pointes (TdP). Avoid concomitant use if possible, especially in patients with additional risk factors for TdP. Consider taking steps to minimize the risk for QT/QTc interval prolongation and TdP, such as electrolyte monitoring and repletion and ECG monitoring, if concomitant use is necessary.
Ethacrynic Acid: (Moderate) Avoid concurrent use of loop diuretics with foscarnet. Coadministration may impair the renal tubular secretion of foscarnet, thereby increasing the possibility for toxicity. When use of a diuretic is indicated in patients being treated with foscarnet, consider a thiazide diuretic.
Fingolimod: (Major) When possible, avoid concurrent use of foscarnet with other drugs known to prolong the QT interval, such as fingolimod. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes (TdP). Fingolimod initiation results in decreased heart rate and may prolong the QT interval. After the first fingolimod dose, overnight monitoring with continuous ECG in a medical facility is advised for patients taking QT prolonging drugs with a known risk of TdP. Fingolimod has not been studied in patients treated with drugs that prolong the QT interval, but drugs that prolong the QT interval have been associated with cases of TdP in patients with bradycardia. If these drugs are administered together, obtain an electrocardiogram and electrolyte concentrations before and periodically during treatment.
Flecainide: (Major) When possible, avoid concurrent use of foscarnet with other drugs known to prolong the QT interval, such as flecainide. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes (TdP). Flecainide is a Class IC antiarrhythmic associated with a possible risk for QT prolongation and TdP; flecainide increases the QT interval, but largely due to prolongation of the QRS interval. Although causality for TdP has not been established for flecainide, patients receiving concurrent drugs which have the potential for QT prolongation may have an increased risk of developing proarrhythmias. If these drugs are administered together, obtain an electrocardiogram and electrolyte concentrations before and periodically during treatment.
Fluconazole: (Major) Concomitant use of foscarnet and fluconazole increases the risk of QT/QTc prolongation and torsade de pointes (TdP). Avoid concomitant use if possible, especially in patients with additional risk factors for TdP. Consider taking steps to minimize the risk for QT/QTc interval prolongation and TdP, such as electrolyte monitoring and repletion and ECG monitoring, if concomitant use is necessary.
Fluoxetine: (Major) Concomitant use of fluoxetine and foscarnet increases the risk of QT/QTc prolongation and torsade de pointes (TdP). Avoid concomitant use if possible, especially in patients with additional risk factors for TdP. Consider taking steps to minimize the risk for QT/QTc interval prolongation and TdP, such as electrolyte monitoring and repletion and ECG monitoring, if concomitant use is necessary.
Fluphenazine: (Minor) When possible, avoid concurrent use of foscarnet with other drugs known to prolong the QT interval, such as fluphenazine. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes (TdP). Fluphenazine is associated with a possible risk for QT prolongation. If these drugs are administered together, obtain an electrocardiogram and electrolyte concentrations before and periodically during treatment.
Fluvoxamine: (Major) There may be an increased risk for QT prolongation and torsade de pointes (TdP) during concurrent use of fluvoxamine and foscarnet. Cases of QT prolongation and TdP have been reported during postmarketing use of fluvoxamine. Both QT prolongation and TdP have been reported during postmarketing use of foscarnet. Because of these reports, avoid the use of foscarnet with other drugs known to prolong the QT interval. If coadministration is necessary, monitor ECG and serum electrolytes.
Fostemsavir: (Major) Avoid use of foscarnet with fostemsavir due to the potential for both QT prolongation and torsade de pointes (TdP) have been reported during postmarketing use of foscarnet. Because of these reports, avoid the use of foscarnet with other drugs known to prolong the QT interval. Supratherapeutic doses of fostemsavir (2,400 mg twice daily, 4 times the recommended daily dose) have been shown to cause QT prolongation. Fostemsavir causes dose-dependent QT prolongation.
Furosemide: (Moderate) Avoid concurrent use of loop diuretics with foscarnet. Coadministration may impair the renal tubular secretion of foscarnet, thereby increasing the possibility for toxicity. When use of a diuretic is indicated in patients being treated with foscarnet, consider a thiazide diuretic.
Gemifloxacin: (Major) When possible, avoid concurrent use of foscarnet with other drugs known to prolong the QT interval, such as gemifloxacin. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes (TdP). Gemifloxacin may prolong the QT interval in some patients. The maximal change in the QTc interval occurs approximately 5 to 10 hours following oral administration of gemifloxacin. The likelihood of QTc prolongation may increase with increasing dose of the drug; therefore, the recommended dose should not be exceeded especially in patients with renal or hepatic impairment where the Cmax and AUC are slightly higher. If these drugs are administered together, obtain an electrocardiogram and electrolyte concentrations before and periodically during treatment.
Gemtuzumab Ozogamicin: (Major) Avoid coadministration of gemtuzumab ozogamicin with foscarnet due to the potential for additive QT interval prolongation and risk of torsade de pointes (TdP). If coadministration is unavoidable, obtain an ECG and serum electrolytes prior to the start of gemtuzumab and as needed during treatment. Although QT interval prolongation has not been reported with gemtuzumab, it has been reported with other drugs that contain calicheamicin. Both QT prolongation andTdP have been reported during postmarketing use of foscarnet.
Gentamicin: (Major) The risk of renal toxicity may be increased if foscarnet is used in conjunction with other nephrotoxic agents such as aminoglycosides.
Gilteritinib: (Major) Avoid concomitant use of foscarnet with gilteritinib due to the potential for additive QT prolongation. Gilteritinib has been associated with QT prolongation. Both QT prolongation and torsade de pointes (TdP) have been reported during postmarketing use of foscarnet.
Glasdegib: (Major) Avoid coadministration of glasdegib with foscarnet due to the potential for additive QT prolongation. Glasdegib therapy may result in QT prolongation and ventricular arrhythmias including ventricular fibrillation and ventricular tachycardia. Both QT prolongation and torsade de pointes (TdP) have been reported during postmarketing use of foscarnet.
Gold: (Moderate) The risk of renal toxicity may be increased if foscarnet is used in conjunction with other nephrotoxic agents, including gold compounds.
Goserelin: (Major) Avoid coadministration of foscarnet with goserelin due to the risk of QT prolongation. Androgen deprivation therapy (i.e., goserelin) may prolong the QT/QTc interval. Both QT prolongation and torsade de pointes (TdP) have been reported during postmarketing use of foscarnet.
Granisetron: (Major) When possible, avoid concurrent use of foscarnet with other drugs known to prolong the QT interval, such as granisetron. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes (TdP). Granisetron has also been associated with QT prolongation. If these drugs are administered together, obtain an electrocardiogram and electrolyte concentrations before and periodically during treatment.
Halogenated Anesthetics: (Major) When possible, avoid concurrent use of foscarnet with other drugs known to prolong the QT interval, such as halogenated anesthetics. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes (TdP). Halogenated anesthetics can also prolong the QT interval. If these drugs are administered together, obtain an electrocardiogram and electrolyte concentrations before and periodically during treatment.
Haloperidol: (Major) When possible, avoid concurrent use of foscarnet with other drugs known to prolong the QT interval, such as haloperidol. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes (TdP). QT prolongation and TdP have also been observed during haloperidol treatment. Excessive doses (particularly in the overdose setting) or IV administration of haloperidol may be associated with a higher risk of QT prolongation. If these drugs are administered together, obtain an electrocardiogram and electrolyte concentrations before and periodically during treatment.
Histrelin: (Major) Avoid coadministration of foscarnet with histrelin due to the risk of QT prolongation. Androgen deprivation therapy (i.e., histrelin) may prolong the QT/QTc interval. Both QT prolongation and torsade de pointes (TdP) have been reported during postmarketing use of foscarnet.
Hyaluronidase, Recombinant; Immune Globulin: (Moderate) Immune Globulin (IG) products have been reported to be associated with renal dysfunction, acute renal failure, osmotic nephrosis, and death. Patients predisposed to acute renal failure include patients receiving known nephrotoxic drugs like foscarnet. Coadminister IG products at the minimum concentration available and the minimum rate of infusion practicable. Also, closely monitor renal function.
Hydroxychloroquine: (Major) Concomitant use of hydroxychlor

oquine and foscarnet increases the risk of QT/QTc prolongation and torsade de pointes (TdP). Avoid concomitant use if possible, especially in patients with additional risk factors for TdP. Consider taking steps to minimize the risk for QT/QTc interval prolongation and TdP, such as electrolyte monitoring and repletion and ECG monitoring, if concomitant use is necessary.
Hydroxyzine: (Major) Concomitant use of hydroxyzine and foscarnet increases the risk of QT/QTc prolongation and torsade de pointes (TdP). Avoid concomitant use if possible, especially in patients with additional risk factors for TdP. Consider taking steps to minimize the risk for QT/QTc interval prolongation and TdP, such as electrolyte monitoring and repletion and ECG monitoring, if concomitant use is necessary.
Hyoscyamine; Methenamine; Methylene Blue; Phenyl Salicylate; Sodium Biphosphate: (Minor) Due to the inhibition of renal prostaglandins by salicylates, concurrent use of salicylates and other nephrotoxic agents, such as foscarnet, may lead to additive nephrotoxicity.
Ibutilide: (Major) When possible, avoid concurrent use of foscarnet with other drugs known to prolong the QT interval, such as ibutilide. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes (TdP). Ibutilide administration can also cause QT prolongation and TdP; proarrhythmic events should be anticipated. If these drugs are administered together, obtain an electrocardiogram and electrolyte concentrations before and periodically during treatment.
Iloperidone: (Major) When possible, avoid concurrent use of foscarnet with other drugs known to prolong the QT interval, such as iloperidone. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes (TdP). Iloperidone has also been associated with QT prolongation. If these drugs are administered together, obtain an electrocardiogram and electrolyte concentrations before and periodically during treatment.
Immune Globulin IV, IVIG, IGIV: (Moderate) Immune Globulin (IG) products have been reported to be associated with renal dysfunction, acute renal failure, osmotic nephrosis, and death. Patients predisposed to acute renal failure include patients receiving known nephrotoxic drugs like foscarnet. Coadminister IG products at the minimum concentration available and the minimum rate of infusion practicable. Also, closely monitor renal function.
Inotersen: (Moderate) Use caution with concomitant use of inotersen and foscarnet due to the risk of glomerulonephritis and nephrotoxicity.
Inotuzumab Ozogamicin: (Major) Avoid coadministration of inotuzumab ozogamicin with foscarnet due to the potential for additive QT interval prolongation and risk of torsade de pointes (TdP). If coadministration is unavoidable, obtain an ECG and serum electrolytes prior to the start of treatment, after treatment initiation, and periodically during treatment. Inotuzumab has been associated with QT interval prolongation. Both QT prolongation and TdP have been reported during postmarketing use of foscarnet.
Isoflurane: (Major) When possible, avoid concurrent use of foscarnet with other drugs known to prolong the QT interval, such as halogenated anesthetics. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes (TdP). Halogenated anesthetics can also prolong the QT interval. If these drugs are administered together, obtain an electrocardiogram and electrolyte concentrations before and periodically during treatment.
Itraconazole: (Major) When possible, avoid concurrent use of foscarnet with other drugs known to prolong the QT interval, such as itraconazole. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes (TdP). Itraconazole has also been associated with prolongation of the QT interval. If these drugs are administered together, obtain an electrocardiogram and electrolyte concentrations before and periodically during treatment.
Ivosidenib: (Major) Avoid coadministration of ivosidenib with foscarnet due to an increased risk of QT prolongation. If concomitant use is unavoidable, monitor ECGs for QTc prolongation and monitor electrolytes; correct any electrolyte abnormalities as clinically appropriate. An interruption of therapy and dose reduction of ivosidenib may be necessary if QT prolongation occurs. Prolongation of the QTc interval and ventricular arrhythmias have been reported in patients treated with ivosidenib. Both QT prolongation and torsade de pointes (TdP) have been reported during postmarketing use of foscarnet.
Ketoconazole: (Contraindicated) Avoid concomitant use of ketoconazole and foscarnet due to an increased risk for torsade de pointes (TdP) and QT/QTc prolongation.
Lamivudine, 3TC; Zidovudine, ZDV: (Minor) Concurrent use of foscarnet and zidovudine, ZDV may be associated with a higher incidence of anemia; clinicians should follow normal recommendations for blood count monitoring and other parameters.
Lamivudine; Tenofovir Disoproxil Fumarate: (Moderate) Monitor for changes in serum creatinine and phosphorus if tenofovir is administered in combination with nephrotoxic agents, such as foscarnet. Tenofovir is primarily excreted via the kidneys by a combination of glomerular filtration and active tubular secretion. While no drug interactions due to competition for renal excretion have been observed, coadministration of tenofovir with drugs that are eliminated by active tubular secretion may increase concentrations of tenofovir, and/or the co-administered drug. Drugs that decrease renal function may increase concentrations of tenofovir. Renal impairment, which may include hypophosphatemia, has been reported with the use of tenofovir; a majority of the cases occurred in patients who had underlying systemic or renal disease or who are concurrently taking nephrotoxic agents. Tenofovir containing products should be avoided with concurrent or recent use of a nephrotoxic agent; patients receiving concomitant nephrotoxic agents should be carefully monitored for changes in serum creatinine and phosphorus.
Lansoprazole; Amoxicillin; Clarithromycin: (Major) When possible, avoid concurrent use of foscarnet with other drugs known to prolong the QT interval, such as clarithromycin. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes (TdP). Clarithromycin is also associated with an established risk for QT prolongation and TdP. If these drugs are administered together, obtain an electrocardiogram and electrolyte concentrations before and periodically during treatment.
Lapatinib: (Major) Avoid coadministration of foscarnet with lapatinib due to the risk of QT prolongation and torsade de pointes (TdP). Both QT prolongation and TdP have been reported during postmarketing use of foscarnet. Lapatinib has also been associated with concentration-dependent QT prolongation; ventricular arrhythmias and TdP have been reported in postmarketing experience with lapatinib.
Lefamulin: (Major) Avoid coadministration of lefamulin with foscarnet as concurrent use may increase the risk of QT prolongation. If coadministration cannot be avoided, monitor ECG during treatment. Lefamulin has a concentration dependent QTc prolongation effect. The pharmacodynamic interaction potential to prolong the QT interval of the electrocardiogram between lefamulin and other drugs that effect cardiac conduction is unknown. Both QT prolongation and torsade de pointes (TdP) have been reported during postmarketing use of foscarnet.
Lenvatinib: (Major) Avoid coadministration of lenvatinib with foscarnet due to the risk of QT prolongation. Prolongation of the QT interval has been reported with lenvatinib therapy. Both QT prolongation and torsade de pointes (TdP) have been reported during postmarketing use of foscarnet.
Leuprolide: (Major) Avoid coadministration of foscarnet with leuprolide due to the risk of QT prolongation. Androgen deprivation therapy (i.e., leuprolide) may prolong the QT/QTc interval. Both QT prolongation and torsade de pointes (TdP) have been reported during postmarketing use of foscarnet.
Leuprolide; Norethindrone: (Major) Avoid coadministration of foscarnet with leuprolide due to the risk of QT prolongation. Androgen deprivation therapy (i.e., leuprolide) may prolong the QT/QTc interval. Both QT prolongation and torsade de pointes (TdP) have been reported during postmarketing use of foscarnet.
Levofloxacin: (Major) When possible, avoid concurrent use of foscarnet with other drugs known to prolong the QT interval, such as levofloxacin. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes (TdP). Quinolones have also been associated with a risk of QT prolongation and TdP. Although extremely rare, TdP has been reported during postmarketing surveillance of levofloxacin. If these drugs are administered together, obtain an electrocardiogram and electrolyte concentrations before and periodically during treatment.
Levoketoconazole: (Contraindicated) Avoid concomitant use of ketoconazole and foscarnet due to an increased risk for torsade de pointes (TdP) and QT/QTc prolongation.
Lithium: (Major) When possible, avoid concurrent use of foscarnet with other drugs known to prolong the QT interval, such as lithium. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes (TdP). Lithium has also been associated with QT prolongation. If these drugs are administered together, obtain an electrocardiogram and electrolyte concentrations before and periodically during treatment. Also, the risk of renal toxicity may be increased if foscarnet is used in conjunction with other nephrotoxic agents such as lithium.
Lofexidine: (Major) Avoid coadministration of lofexidine and foscarnet due to the potential for additive QT prolongation and torsade de pointes (TdP). Monitor ECG if coadministration unavoidable. Lofexidine prolongs the QT interval. In addition, there are postmarketing reports of TdP. Both QT prolongation and TdP have been reported during postmarketing use of foscarnet.
Loop diuretics: (Moderate) Avoid concurrent use of loop diuretics with foscarnet. Coadministration may impair the renal tubular secretion of foscarnet, thereby increasing the possibility for toxicity. When use of a diuretic is indicated in patients being treated with foscarnet, consider a thiazide diuretic.
Loperamide: (Major) When possible, avoid concurrent use of foscarnet with other drugs known to prolong the QT interval, such as loperamide. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes (TdP). At high doses, loperamide has been associated with serious cardiac toxicities, including syncope, ventricular tachycardia, QT prolongation, TdP, and cardiac arrest. If these drugs are administered together, obtain an electrocardiogram and electrolyte concentrations before and periodically during treatment.
Loperamide; Simethicone: (Major) When possible, avoid concurrent use of foscarnet with other drugs known to prolong the QT interval, such as loperamide. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes (TdP). At high doses, loperamide has been associated with serious cardiac toxicities, including syncope, ventricular tachycardia, QT prolongation, TdP, and cardiac arrest. If these drugs are administered together, obtain an electrocardiogram and electrolyte concentrations before and periodically during treatment.
Lopinavir; Ritonavir: (Major) Avoid coadministration of lopinavir with foscarnet due to the potential for additive QT prolongation. If use together is necessary, obtain a baseline ECG to assess initial QT interval and determine frequency of subsequent ECG monitoring, avoid any non-essential QT prolonging drugs, and correct electrolyte imbalances. Lopinavir is associated with QT prolongation. Both QT prolongation and torsade de pointes (TdP) have been reported during postmarketing use of foscarnet. (Moderate) Abnormal renal function has been observed in clinical practice during the use of foscarnet in combination with ritonavir. If these drugs are administered together, monitor kidney function.
Macimorelin: (Major) Avoid concurrent administration of macimorelin with drugs that prolong the QT interval, such as foscarnet. Use of these drugs together may increase the risk of developing torsade de pointes-type ventricular tachycardia. Sufficient washout time of drugs that are known to prolong the QT interval prior to administration of macimorelin is recommended. Treatment with macimorelin has been associated with an increase in the corrected QT (QTc) interval. Both QT prolongation and torsade de pointes (TdP) have been reported during postmarketing use of foscarnet.
Magnesium Salicylate: (Minor) Due to the inhibition of renal prostaglandins by salicylates, concurrent use of salicylates and other nephrotoxic agents, such as foscarnet, may lead to additive nephrotoxicity.
Mannitol: (Major) Avoid use of mannitol and foscarnet, if possible. Concomitant administration of nephrotoxic drugs, such as foscarnet, increases the risk of renal failure after administration of mannitol.
Maprotiline: (Major) When possible, avoid concurrent use of foscarnet with other drugs known to prolong the QT interval, such as maprotiline. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes (TdP). Maprotiline has been reported to prolong the QT interval, particularly in overdose or with higher-dose prescription therapy (elevated serum concentrations). Cases of long QT syndrome and TdP tachycardia have been described with maprotiline use, but rarely occur when the drug is used alone in normal prescribed doses and in the absence of other known risk factors for QT prolongation. Limited data are available regarding the safety of maprotiline in combination with other QT-prolonging drugs. If these drugs are administered together, obtain an electrocardiogram and electrolyte concentrations before and periodically during treatment.
Mefloquine: (Major) When possible, avoid concurrent use of foscarnet with other drugs known to prolong the QT interval, such as mefloquine. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes (TdP). There is evidence that the use of halofantrine after mefloquine causes a significant lengthening of the QTc interval. Mefloquine alone has not been reported to cause QT prolongation. However, due to the lack of clinical data, mefloquine should be used with caution in patients receiving drugs that prolong the QT interval. If these drugs are administered together, obtain an electrocardiogram and electrolyte concentrations before and periodically during treatment.
Methadone: (Major) When possible, avoid concurrent use of foscarnet with other drugs known to prolong the QT interval, such as methadone. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes (TdP). Methadone is also considered to be associated with an increased risk for QT prolongation and TdP, especially at higher doses (more than 200 mg/day but averaging approximately 400 mg/day in adult patients). Most cases involve patients being treated for pain with large, multiple daily doses of methadone, although cases have been reported in patients receiving doses commonly used for maintenance treatment of opioid addiction. If these drugs are administered together, obtain an electrocardiogram and electrolyte concentrations before and periodically during treatment.
Methenamine; Sodium Salicylate: (Minor) Due to the inhibition of renal prostaglandins by salicylates, concurrent use of salicylates and other nephrotoxic agents, such as foscarnet, may lead to additive nephrotoxicity.
Methotrexate: (Major) Avoid concomitant use of methotrexate with foscarnet due to the risk of additive nephrotoxicity as well as an increased risk of severe methotrexate-related adverse reactions. If concomitant use is unavoidable, closely monitor for adverse reactions. Foscarnet and methotrexate are both nephrotoxic drugs; methotrexate is also renally eliminated. Coadministration of methotrexate with foscarnet may result in decreased renal function as well as increased methotrexate plasma concentrations.
Metronidazole: (Major) Concomitant use of metronidazole and foscarnet increases the risk of QT/QTc prolongation and torsade de pointes (TdP). Avoid concomitant use if possible, especially in patients with additional risk factors for TdP. Consider taking steps to minimize the risk for QT/QTc interval prolongation and TdP, such as electrolyte monitoring and repletion and ECG monitoring, if concomitant use is necessary.
Midostaurin: (Major) Avoid the concomitant use of midostaurin and foscarnet; both drugs have been reported to increase the QT interval. Obtain electrocardiograms (ECG) and electrolyte concentrations before and periodically during treatment with foscarnet. In clinical trials, QT prolongation was reported in patients who received midostaurin as single-agent therapy or in combination with cytarabine and daunorubicin. QT prolongation and ventricular arrhythmia, including torsade de pointes, have been reported in postmarketing surveillance of foscarnet.
Mifepristone: (Major) Concomitant use of foscarnet and mifepristone increases the risk of QT/QTc prolongation and torsade de pointes (TdP). Avoid concomitant use if possible, especially in patients with additional risk factors for TdP. Consider taking steps to minimize the risk for QT/QTc interval prolongation and TdP, such as electrolyte monitoring and repletion and ECG monitoring, if concomitant use is necessary.
Mirtazapine: (Major) Concomitant use of foscarnet and mirtazapine increases the risk of QT/QTc prolongation and torsade de pointes (TdP). Avoid concomitant use if possible, especially in patients with additional risk factors for TdP. Consider taking steps to minimize the risk for QT/QTc interval prolongation and TdP, such as electrolyte monitoring and repletion and ECG monitoring, if concomitant use is necessary.
Mobocertinib: (Major) Concomitant use of mobocertinib and foscarnet increases the risk of QT/QTc prolongation and torsade de pointes (TdP). Avoid concomitant use if possible, especially in patients with additional risk factors for TdP. Consider taking steps to minimize the risk for QT/QTc interval prolongation and TdP, such as electrolyte monitoring and repletion and ECG monitoring, if concomitant use is necessary.
Moxifloxacin: (Major) When possible, avoid concurrent use of foscarnet with other drugs known to prolong the QT interval, such as moxifloxacin. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes (TdP). Quinolones have also been associated with a risk of QT prolongation and TdP. Although extremely rare, TdP has been reported during postmarketing surveillance of moxifloxacin. These reports generally involved patients with concurrent medical conditions or concomitant medications that may have been contributory. If these drugs are administered together, obtain an electrocardiogram and electrolyte concentrations before and periodically during treatment.
Nilotinib: (Major) Avoid the concomitant use of nilotinib and foscarnet; significant prolongation of the QT interval may occur. Sudden death and QT prolongation have been reported in patients who received nilotinib therapy. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes.
Nirmatrelvir; Ritonavir: (Moderate) Abnormal renal function has been observed in clinical practice during the use of foscarnet in combination with ritonavir. If these drugs are administered together, monitor kidney function.
Nonsteroidal antiinflammatory drugs: (Minor) The risk of renal toxicity may be increased if foscarnet is used in conjuction with other nephrotoxic agents, such as nonsteroidal antiinflammatory drugs (NSAIDs). Monitor renal function carefully during concurrent therapy.
Ofloxacin: (Major) Concomitant use of ofloxacin and foscarnet increases the risk of QT/QTc prolongation and torsade de pointes (TdP). Avoid concomitant use if possible, especially in patients with additional risk factors for TdP. Consider taking steps to minimize the risk for QT/QTc interval prolongation and TdP, such as electrolyte monitoring and repletion and ECG monitoring, if concomitant use is necessary.
Olanzapine: (Major) When possible, avoid concurrent use of foscarnet with other drugs known to prolong the QT interval, such as olanzapine. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes (TdP). Limited data, including some case reports, suggest that olanzapine may be associated with a significant prolongation of the QTc interval. If these drugs are administered together, obtain an electrocardiogram and electrolyte concentrations before and periodically during treatment.
Olanzapine; Fluoxetine: (Major) Concomitant use of fluoxetine and foscarnet increases the risk of QT/QTc prolongation and torsade de pointes (TdP). Avoid concomitant use if possible, especially in patients with additional risk factors for TdP. Consider taking steps to minimize the risk for QT/QTc interval prolongation and TdP, such as electrolyte monitoring and repletion and ECG monitoring, if concomitant use is necessary. (Major) When possible, avoid concurrent use of foscarnet with other drugs known to prolong the QT interval, such as olanzapine. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes (TdP). Limited data, including some case reports, suggest that olanzapine may be associated with a significant prolongation of the QTc interval. If these drugs are administered together, obtain an electrocardiogram and electrolyte concentrations before and periodically during treatment.
Olanzapine; Samidorphan: (Major) When possible, avoid concurrent use of foscarnet with other drugs known to prolong the QT interval, such as olanzapine. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes (TdP). Limited data, including some case reports, suggest that olanzapine may be associated with a significant prolongation of the QTc interval. If these drugs are administered together, obtain an electrocardiogram and electrolyte concentrations before and periodically during treatment.
Ondansetron: (Major) Concomitant use of ondansetron and foscarnet increases the risk of QT/QTc prolongation and torsade de pointes (TdP). Avoid concomitant use if possible, especially in patients with additional risk factors for TdP. Consider taking steps to minimize the risk for QT/QTc interval prolongation and TdP, such as electrolyte monitoring and repletion and ECG monitoring, if concomitant use is necessary. Do not exceed 16 mg of IV ondansetron in a single dose; the degree of QT prolongation associated with ondansetron significantly increases above this dose.
Osilodrostat: (Major) Avoid coadministration of osilodrostat and foscarnet due to the potential for additive QT prolongation. Both QT prolongation and torsade de pointes have been reported during postmarketing use of foscarnet. Osilodrostat is associated with dose-dependent QT prolongation.
Osimertinib: (Major) Avoid the use of foscarnet with other drugs known to prolong the QT interval such as osimertinib. If concomitant use is necessary, periodically monitor ECGs and electrolytes; an interruption of osimertinib therapy and dose reduction may be necessary if QT prolongation occurs. Both QT prolongation and torsade de pointes (TdP) have been reported during postmarketing use of foscarnet; concentration-dependent QTc prolongation has also occurred during clinical trials of osimertinib.
Oxaliplatin: (Major) Avoid use of foscarnet with oxaliplatin due to the potential for QT prolongation; oxaliplatin-related adverse reactions may also increase. Both QT prolongation and torsade de pointes (TdP) have been reported during postmarketing use of foscarnet. QT prolongation and ventricular arrhythmias including fatal TdP have also been reported with oxaliplatin use in postmarketing experience. Additionally, foscarnet is known to be potentially nephrotoxic; because platinum-containing drugs like oxaliplatin are eliminated primarily through the kidney, oxaliplatin clearance may be decreased by coadministration with nephrotoxic agents.
Ozanimod: (Major) In general, do not initiate ozanimod in patients taking foscarnet due to the risk of additive bradycardia, QT prolongation, and torsade de pointes (TdP). If treatment initiation is considered, seek advice from a cardiologist. Ozanimod initiation may result in a transient decrease in heart rate and atrioventricular conduction delays. Ozanimod has not been studied in patients taking concurrent QT prolonging drugs; however, QT prolonging drugs have been associated with TdP in patients with bradycardia. Both QT prolongation and TdP have been reported during postmarketing use of foscarnet.
Pacritinib: (Major) Concomitant use of pacritinib and foscarnet increases the risk of QT/QTc prolongation and torsade de pointes (TdP). Avoid concomitant use if possible, especially in patients with additional risk factors for TdP. Consider taking steps to minimize the risk for QT/QTc interval prolongation and TdP, such as electrolyte monitoring and repletion and ECG monitoring, if concomitant use is necessary.
Paliperidone: (Major) When possible, avoid concurrent use of foscarnet with other drugs known to prolong the QT interval, such as paliperidone. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes (TdP). Paliperidone has also been associated with QT prolongation; TdP and ventricular fibrillation have been reported in the setting of overdose. If these drugs are administered together, obtain an electrocardiogram and electrolyte concentrations before and periodically during treatment.
Panobinostat: (Major) When possible, avoid concurrent use of foscarnet with other drugs known to prolong the QT interval, such as panobinostat. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes (TdP). QT prolongation has been reported with panobinostat therapy in patients with multiple myeloma in a clinical trial. Obtain an electrocardiogram and electrolyte concentrations at baseline and periodically during treatment. Hold panobinostat if the QTcF increases to 480 milliseconds or more during therapy; permanently discontinue if QT prolongation does not resolve.
Paromomycin: (Major) The risk of renal toxicity may be increased if foscarnet is used in conjunction with other nephrotoxic agents such as aminoglycosides.
Pasireotide: (Major) When possible, avoid concurrent use of foscarnet with other drugs known to prolong the QT interval, such as pasireotide. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes (TdP). Pasireotide may also prolong the QT interval. If these drugs are administered together, obtain an electrocardiogram and electrolyte concentrations before and periodically during treatment.
Pazopanib: (Major) When possible, avoid concurrent use of foscarnet with other drugs known to prolong the QT interval, such as pazopanib. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes (TdP). Pazopanib has also been reported to prolong the QT interval. If these drugs are administered together, obtain an electrocardiogram and electrolyte concentrations before and periodically during treatment.
Penicillamine: (Moderate) The risk of renal toxicity may be increased if foscarnet is used in conjunction with other nephrotoxic agents such as penicillamine.
Pentamidine: (Major) When possible, avoid concurrent use of foscarnet with other drugs known to prolong the QT interval, such as pentamidine. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes (TdP). Systemic pentamidine has also been associated with QT prolongation. If these drugs are administered together, obtain an electrocardiogram and electrolyte concentrations before and periodically during treatment. Also, concomitant use of foscarnet and IV pentamidine can cause significant hypocalcemia, hypomagnesemia, and nephrotoxicity. Both agents are associated with a risk for nephrotoxicity. One fatality has been reported from severe hypocalcemia following this combination. Electrolyte imbalances can precipitate seizures or cardiac dysfunction during therapy with foscarnet.
Perphenazine: (Minor) When possible, avoid concurrent use of foscarnet with other drugs known to prolong the QT interval, such as perphenazine. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes (TdP). Perphenazine is also associated with a possible risk for QT prolongation. If these drugs are administered together, obtain an electrocardiogram and electrolyte concentrations before and periodically during treatment.
Perphenazine; Amitriptyline: (Minor) When possible, avoid concurrent use of foscarnet with other drugs known to prolong the QT interval, such as perphenazine. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes (TdP). Perphenazine is also associated with a possible risk for QT prolongation. If these drugs are administered together, obtain an electrocardiogram and electrolyte concentrations before and periodically during treatment.
Pimavanserin: (Major) When possible, avoid concurrent use of foscarnet with other drugs known to prolong the QT interval, such as pimavanserin. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes (TdP). Pimavanserin may also cause QT prolongation. If these drugs are administered together, obtain an electrocardiogram and electrolyte concentrations before and periodically during treatment.
Pimozide: (Contraindicated) Pimozide is associated with a well-established risk of QT prolongation and torsade de pointes (TdP). Because of the potential for TdP, use of foscarnet with pimozide is contraindicated.
Pitolisant: (Major) Avoid coadministration of pitolisant with foscarnet as concurrent use may increase the risk of QT prolongation. Pitolisant prolongs the QT interval. Both QT prolongation and torsade de pointes (TdP) have been reported during postmarketing use of foscarnet.
Plazomicin: (Major) The risk of renal toxicity may be increased if foscarnet is used in conjunction with other nephrotoxic agents such as aminoglycosides.
Polymyxin B: (Major) Systemic polymyxin B should not be used concurrently or sequentially with other drugs that have the potential for nephrotoxicity or neurotoxicity such as foscarnet. Topical products containing polymyxin B, especially when they are applied over a large body surface area, should be used cautiously with any of the above drugs.
Ponesimod: (Major) In general, do not initiate ponesimod in patients taking foscarnet due to the risk of additive bradycardia, QT prolongation, and torsade de pointes (TdP). If treatment initiation is considered, seek advice from a cardiologist. Ponesimod initiation may result in a transient decrease in heart rate and atrioventricular conduction delays. Ponesimod has not been studied in patients taking concurrent QT prolonging drugs; however, QT prolonging drugs have been associated with TdP in patients with bradycardia. Both QT prolongation and TdP have been reported during postmarketing use of foscarnet.
Posaconazole: (Major) When possible, avoid concurrent use of foscarnet with other drugs known to prolong the QT interval, such as posaconazole. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes (TdP). Posaconazole has also been associated with prolongation of the QT interval as well as rare cases of TdP. If these drugs are administered together, obtain an electrocardiogram and electrolyte concentrations before and periodically during treatment.
Primaquine: (Major) When possible, avoid concurrent use of foscarnet with other drugs known to prolong the QT interval, such as primaquine. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes (TdP). Primaquine may also prolong the QT interval. If these drugs are administered together, obtain an electrocardiogram and electrolyte concentrations before and periodically during treatment.
Procainamide: (Major) When possible, avoid concurrent use of foscarnet with other drugs known to prolong the QT interval, such as procainamide. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes (TdP). Procainamide is associated with a well-established risk of QT prolongation and TdP. If these drugs are administered together, obtain an electrocardiogram and electrolyte concentrations before and periodically during treatment.
Prochlorperazine: (Minor) When possible, avoid concurrent use of foscarnet with other drugs known to prolong the QT interval, such as prochlorperazine. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes (TdP). Prochlorperazine is associated with a possible risk for QT prolongation. If these drugs are administered together, obtain an electrocardiogram and electrolyte concentrations before and periodically during treatment.
Promethazine: (Major) Concomitant use of promethazine and foscarnet increases the risk of QT/QTc prolongation and torsade de pointes (TdP). Avoid concomitant use if possible, especially in patients with additional risk factors for TdP. Consider taking steps to minimize the risk for QT/QTc interval prolongation and TdP, such as electrolyte monitoring and repletion and ECG monitoring, if concomitant use is necessary.
Promethazine; Dextromethorphan: (Major) Concomitant use of promethazine and foscarnet increases the risk of QT/QTc prolongation and torsade de pointes (TdP). Avoid concomitant use if possible, especially in patients with additional risk factors for TdP. Consider taking steps to minimize the risk for QT/QTc interval prolongation and TdP, such as electrolyte monitoring and repletion and ECG monitoring, if concomitant use is necessary.
Promethazine; Phenylephrine: (Major) Concomitant use of promethazine and foscarnet increases the risk of QT/QTc prolongation and torsade de pointes (TdP). Avoid concomitant use if possible, especially in patients with additional risk factors for TdP. Consider taking steps to minimize the risk for QT/QTc interval prolongation and TdP, such as electrolyte monitoring and repletion and ECG monitoring, if concomitant use is necessary.
Propafenone: (Major) Concomitant use of propafenone and foscarnet increases the risk of QT/QTc prolongation and torsade de pointes (TdP). Avoid concomitant use if possible, especially in patients with additional risk factors for TdP. Consider taking steps to minimize the risk for QT/QTc interval prolongation and TdP, such as electrolyte monitoring and repletion and ECG monitoring, if concomitant use is necessary.
Quetiapine: (Major) Concomitant use of quetiapine and foscarnet increases the risk of QT/QTc prolongation and torsade de pointes (TdP). Avoid concomitant use if possible, especially in patients with additional risk factors for TdP. Consider taking steps to minimize the risk for QT/QTc interval prolongation and TdP, such as electrolyte monitoring and repletion and ECG monitoring, if concomitant use is necessary.
Quinidine: (Major) When possible, avoid concurrent use of foscarnet with other drugs known to prolong the QT interval, such as quinidine. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes (TdP). Quinidine administration is also associated with QT prolongation and TdP. If these drugs are administered together, obtain an electrocardiogram and electrolyte concentrations before and periodically during treatment.
Quinine: (Major) When possible, avoid concurrent use of foscarnet with other drugs known to prolong the QT interval, such as quinine. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes (TdP). Quinine has also been associated with QT prolongation and rare cases of TdP. If these drugs are administered together, obtain an electrocardiogram and electrolyte concentrations before and periodically during treatment.
Quizartinib: (Major) Concomitant use of quizartinib and foscarnet increases the risk of QT/QTc prolongation and torsade de pointes (TdP). Avoid concomitant use if possible, especially in patients with additional risk factors for TdP. Consider taking steps to minimize the risk for QT/QTc interval prolongation and TdP, such as electrolyte monitoring and repletion and ECG monitoring, if concomitant use is necessary.
Ranolazine: (Major) When possible, avoid concurrent use of foscarnet with other drugs known to prolong the QT interval, such as ranolazine. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes (TdP). Ranolazine is associated with dose- and plasma concentration-related increases in the QTc interval. Although there are no studies examining the effects of ranolazine in patients receiving other QT prolonging drugs, coadministration of such drugs may result in additive QT prolongation. If these drugs are administered together, obtain an electrocardiogram and electrolyte concentrations before and periodically during treatment.
Relugolix: (Major) Avoid use of foscarnet with relugolix due to the potential for QT prolongation. Both QT prolongation and torsade de pointes (TdP) have been reported during postmarketing use of foscarnet. Androgen deprivation therapy (i.e., relugolix) may also prolong the QT/QTc interval.
Relugolix; Estradiol; Norethindrone acetate: (Major) Avoid use of foscarnet with relugolix due to the potential for QT prolongation. Both QT prolongation and torsade de pointes (TdP) have been reported during postmarketing use of foscarnet. Androgen deprivation therapy (i.e., relugolix) may also prolong the QT/QTc interval.
Ribociclib: (Major) Avoid coadministration of ribociclib with foscarnet due to an increased risk for QT prolongation and torsade de pointes (TdP). Ribociclib has been shown to prolong the QT interval in a concentration-dependent manner. Both QT prolongation and TdP have been reported during postmarketing use of foscarnet. Concomitant use may increase the risk for QT prolongation.
Ribociclib; Letrozole: (Major) Avoid coadministration of ribociclib with foscarnet due to an increased risk for QT prolongation and torsade de pointes (TdP). Ribociclib has been shown to prolong the QT interval in a concentration-dependent manner. Both QT prolongation and TdP have been reported during postmarketing use of foscarnet. Concomitant use may increase the risk for QT prolongation.
Rilpivirine: (Major) When possible, avoid concurrent use of foscarnet with other drugs known to prolong the QT interval, such as rilpivirine. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes (TdP). Supratherapeutic doses of rilpivirine (75 to 300 mg/day) have caused QT prolongation. If these drugs are administered together, obtain an electrocardiogram and electrolyte concentrations before and periodically during treatment.
Risperidone: (Major) When possible, avoid concurrent use of foscarnet with other drugs known to prolong the QT interval, such as risperidone. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes (TdP). Risperidone has also been associated with a possible risk for QT prolongation and TdP. Reports of QT prolongation and TdP during risperidone therapy are noted by the manufacturer, primarily in the overdosage setting. If these drugs are administered together, obtain an electrocardiogram and electrolyte concentrations before and periodically during treatment.
Ritonavir: (Moderate) Abnormal renal function has been observed in clinical practice during the use of foscarnet in combination with ritonavir. If these drugs are administered together, monitor kidney function.
Romidepsin: (Major) When possible, avoid concurrent use of foscarnet with other drugs known to prolong the QT interval, such as romidepsin. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes (TdP). Romidepsin has been reported to prolong the QT interval. If these drugs must be coadministered, appropriate cardiovascular monitoring precautions should be considered, such as the monitoring of electrolytes and ECGs at baseline and periodically during treatment.
Salicylates: (Minor) Due to the inhibition of renal prostaglandins by salicylates, concurrent use of salicylates and other nephrotoxic agents, such as foscarnet, may lead to additive nephrotoxicity.
Salsalate: (Minor) Due to the inhibition of renal prostaglandins by salicylates, concurrent use of salicylates and other nephrotoxic agents, such as foscarnet, may lead to additive nephrotoxicity.
Saquinavir: (Major) When possible, avoid concurrent use of foscarnet with other drugs known to prolong the QT interval, such as saquinavir. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes (TdP). Saquinavir boosted with ritonavir increases the QT interval in a dose-dependent fashion, which may increase the risk for serious arrhythmias such as torsade de pointes (TdP). Also, abnormal renal function has been observed in clinical practice during the use of foscarnet in combination with saquinavir. If these drugs are administered together, obtain an electrocardiogram and electrolyte concentrations before and periodically during treatment.
Selpercatinib: (Major) Avoid coadministration of foscarnet with selpercatinib due to the risk of additive QT prolongation. Monitor ECGs more frequently for QT prolongation if coadministration is necessary. Both QT prolongation and torsade de pointes (TdP) have been reported during postmarketing use of foscarnet. Concentration-dependent QT prolongation has been observed with selpercatinib therapy.
Sertraline: (Major) Concomitant use of sertraline and foscarnet increases the risk of QT/QTc prolongation and torsade de pointes (TdP). Avoid concomitant use if possible, especially in patients with additional risk factors for TdP. Consider taking steps to minimize the risk for QT/QTc interval prolongation and TdP, such as electrolyte monitoring and repletion and ECG monitoring, if concomitant use is necessary. The degree of QT prolongation associated with sertraline is not clinically significant when administered within the recommended dosage range; QT prolongation has been described at 2 times the maximum recommended dose.
Sevoflurane: (Major) When possible, avoid concurrent use of foscarnet with other drugs known to prolong the QT interval, such as halogenated anesthetics. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes (TdP). Halogenated anesthetics can also prolong the QT interval. If these drugs are administered together, obtain an electrocardiogram and electrolyte concentrations before and periodically during treatment.
Siponimod: (Major) Avoid coadministration of siponimod and foscarnet due to the potential for additive QT prolongation. Consult a cardiologist regarding appropriate monitoring if siponimod use is required. Siponimod therapy prolonged the QT interval at recommended doses in a clinical study. Both QT prolongation and torsade de pointes have been reported during postmarketing use of foscarnet.
Sodium Stibogluconate: (Major) Concomitant use of sodium stibogluconate and foscarnet increases the risk of QT/QTc prolongation and torsade de pointes (TdP). Avoid concomitant use if possible, especially in patients with additional risk factors for TdP. Consider taking steps to minimize the risk for QT/QTc interval prolongation and TdP, such as electrolyte monitoring and repletion and ECG monitoring, if concomitant use is necessary.
Solifenacin: (Major) When possible, avoid concurrent use of foscarnet with other drugs known to prolong the QT interval, such as solifenacin. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes (TdP). Solifenacin has been associated with dose-dependent prolongation of the QT interval. In addition, TdP has been reported with postmarketing use of solifenacin, although causality was not determined. If these drugs are administered together, obtain an electrocardiogram and electrolyte concentrations before and periodically during treatment.
Sorafenib: (Major) Avoid coadministration of foscarnet with sorafenib due to the risk of QT prolongation. Sorafenib has been associated with QT prolongation. Both QT prolongation and torsade de pointes (TdP) have been reported during postmarketing experience with foscarnet.
Sotalol: (Major) Concomitant use of sotalol and foscarnet increases the risk of QT/QTc prolongation and torsade de pointes (TdP). Avoid concomitant use if possible, especially in patients with additional risk factors for TdP. Consider taking steps to minimize the risk for QT/QTc interval prolongation and TdP, such as electrolyte monitoring and repletion and ECG monitoring, if concomitant use is necessary.
Streptomycin: (Major) The risk of renal toxicity may be increased if foscarnet is used in conjunction with other nephrotoxic agents such as aminoglycosides.
Streptozocin: (Moderate) Because streptozocin is nephrotoxic, concurrent or subsequent administration of other nephrotoxic agents, such as foscarnet, could exacerbate the renal insult.
Sunitinib: (Major) Avoid coadministration of foscarnet with sunitinib due to the risk of QT prolongation. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes (TdP). Sunitinib can cause dose-dependent QT prolongation, which may increase the risk for ventricular arrhythmias, including TdP.
Tacrolimus: (Major) When possible, avoid concurrent use of foscarnet with other drugs known to prolong the QT interval, such as tacrolimus. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes (TdP). Tacrolimus also causes QT prolongation. Also, concurrent use may result in additive nephrotoxicity. If these drugs are administered together, obtain an electrocardiogram and electrolyte concentrations before and periodically during treatment.
Talimogene Laherparepvec: (Major) Consider the risks and benefits of treatment with talimogene laherparepvec before administering acyclovir or other antivirals to prevent or manage herpetic infection. Talimogene laherparepvec is a live, attenuated herpes simplex virus that is sensitive to acyclovir; coadministration with antiviral agents may cause a decrease in efficacy.
Tamoxifen: (Major) Concomitant use of tamoxifen and foscarnet increases the risk of QT/QTc prolongation and torsade de pointes (TdP). Avoid concomitant use if possible, especially in patients with additional risk factors for TdP. Consider taking steps to minimize the risk for QT/QTc interval prolongation and TdP, such as electrolyte monitoring and repletion and ECG monitoring, if concomitant use is necessary.
Telavancin: (Major) When possible, avoid concurrent use of foscarnet with other drugs known to prolong the QT interval, such as telavancin. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes (TdP). Telavancin has also been associated with QT prolongation. If these drugs are administered together, obtain an electrocardiogram and electrolyte concentrations before and periodically during treatment. Also, concurrent or sequential use of telavancin with other potentially nephrotoxic drugs such as foscarnet may lead to additive nephrotoxicity. Closely monitor renal function and adjust telavancin doses based on calculated creatinine clearance.
Tenofovir Alafenamide: (Moderate) Monitor for changes in renal function if tenofovir alafenamide is administered in combination with a nephrotoxic agent, such as foscarnet. Tenofovir is primarily excreted via the kidneys by a combination of glomerular filtration and active tubular secretion. Coadministration of tenofovir alafenamide with a drug that reduces renal function or competes for active tubular secretion may increase concentrations of tenofovir and other renally eliminated drugs; thus, increasing the risk of developing renal-related adverse reactions.
Tenofovir Alafenamide: (Moderate) Monitor for changes in renal function if tenofovir alafenamide is administered in combination with a nephrotoxic agent, such as foscarnet. Tenofovir is primarily excreted via the kidneys by a combination of glomerular filtration and active tubular secretion. Coadministration of tenofovir alafenamide with a drug that reduces renal function or competes for active tubular secretion may increase concentrations of tenofovir and other renally eliminated drugs; thus, increasing the risk of developing renal-related adverse reactions.
Tenofovir Disoproxil Fumarate: (Moderate) Monitor for changes in serum creatinine and phosphorus if tenofovir is administered in combination with nephrotoxic agents, such as foscarnet. Tenofovir is primarily excreted via the kidneys by a combination of glomerular filtration and active tubular secretion. While no drug interactions due to competition for renal excretion have been observed, coadministration of tenofovir with drugs that are eliminated by active tubular secretion may increase concentrations of tenofovir, and/or the co-administered drug. Drugs that decrease renal function may increase concentrations of tenofovir. Renal impairment, which may include hypophosphatemia, has been reported with the use of tenofovir; a majority of the cases occurred in patients who had underlying systemic or renal disease or who are concurrently taking nephrotoxic agents. Tenofovir containing products should be avoided with concurrent or recent use of a nephrotoxic agent; patients receiving concomitant nephrotoxic agents should be carefully monitored for changes in serum creatinine and phosphorus.
Tetrabenazine: (Major) When possible, avoid concurrent use of foscarnet with other drugs known to prolong the QT interval, such as tetrabenazine. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes (TdP). Tetrabenazine causes a small increase in the corrected QT interval (QTc). If these drugs are administered together, obtain an electrocardiogram and electrolyte concentrations before and periodically during treatment.
Thioridazine: (Contraindicated) Thioridazine is associated with a well-established risk of QT prolongation and torsade de pointes (TdP). Thioridazine is considered contraindicated for use along with agents that may prolong the QT interval and increase the risk of TdP. Because of the potential for TdP, use of foscarnet with thioridazine is contraindicated.
Tobramycin: (Major) The risk of renal toxicity may be increased if foscarnet is used in conjunction with other nephrotoxic agents such as aminoglycosides.
Tolterodine: (Major) When possible, avoid concurrent use of foscarnet with other drugs known to prolong the QT interval, such as tolterodine. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes (TdP). Tolterodine has been associated with dose-dependent prolongation of the QT interval, especially in poor CYP2D6 metabolizers. If these drugs are administered together, obtain an electrocardiogram and electrolyte concentrations before and periodically during treatment.
Toremifene: (Major) Avoid coadministration of foscarnet with toremifene due to the risk of additive QT prolongation. Both QT prolongation and torsade de pointes (TdP) have been reported during postmarketing use of foscarnet. Toremifene has also been shown to prolong the QTc interval in a dose- and concentration-related manner.
Torsemide: (Moderate) Avoid concurrent use of loop diuretics with foscarnet. Coadministration may impair the renal tubular secretion of foscarnet, thereby increasing the possibility for toxicity. When use of a diuretic is indicated in patients being treated with foscarnet, consider a thiazide diuretic.
Trazodone: (Major) Concomitant use of trazodone and foscarnet increases the risk of QT/QTc prolongation and torsade de pointes (TdP). Avoid concomitant use if possible, especially in patients with additional risk factors for TdP. Consider taking steps to minimize the risk for QT/QTc interval prolongation and TdP, such as electrolyte monitoring and repletion and ECG monitoring, if concomitant use is necessary.
Triclabendazole: (Major) Concomitant use of triclabendazole and foscarnet increases the risk of QT/QTc prolongation and torsade de pointes (TdP). Avoid concomitant use if possible, especially in patients with additional risk factors for TdP. Consider taking steps to minimize the risk for QT/QTc interval prolongation and TdP, such as electrolyte monitoring and repletion and ECG monitoring, if concomitant use is necessary.
Trifluoperazine: (Minor) When possible, avoid concurrent use of foscarnet with other drugs known to prolong the QT interval, such as trifluoperazine. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes (TdP). Trifluoperazine is associated with a possible risk for QT prolongation. Theoretically, trifluoperazine may increase the risk of QT prolongation if coadministered with other drugs that have a risk of QT prolongation. If these drugs are administered together, obtain an electrocardiogram and electrolyte concentrations before and periodically during treatment.
Triptorelin: (Major) Avoid coadministration of foscarnet with triptorelin due to the risk of QT prolongation. Androgen deprivation therapy (i.e., triptorelin) may prolong the QT/QTc interval. Both QT prolongation and torsade de pointes (TdP) have been reported during postmarketing use of foscarnet.
Valacyclovir: (Major) The risk of renal toxicity may be increased if foscarnet is used in conjunction with other nephrotoxic agents, such as valacyclovir. Avoid concurrent use, unless the potential benefits outweigh the risks to the patient.
Vancomycin: (Major) The risk of renal toxicity may be increased if foscarnet is used in conjunction with other nephrotoxic agents such as parenteral vancomycin. Nephrotoxicity is also possible in patients receiving oral vancomycin for pseudomembranous colitis, should systemic absorption occur through significantly altered GI mucosa. Renal function should be monitored closely and vancomycin doses should be adjusted according to vancomycin serum concentrations.
Vandetanib: (Major) When possible, avoid concurrent use of foscarnet with other drugs known to prolong the QT interval, such as vandetanib. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes (TdP). Vandetanib can prolong the QT interval in a concentration-dependent manner. TdP and sudden death have also been reported in patients receiving vandetanib. If coadministration is necessary, an ECG and electrolyte concentration monitoring are needed, as well as more frequent monitoring of the QT interval. If QTcF is greater than 500 msec, interrupt vandetanib dosing until the QTcF is less than 450 msec; then, vandetanib may be resumed at a reduced dose.
Vardenafil: (Major) Concomitant use of vardenafil and foscarnet increases the risk of QT/QTc prolongation and torsade de pointes (TdP). Avoid concomitant use if possible, especially in patients with additional risk factors for TdP. Consider taking steps to minimize the risk for QT/QTc interval prolongation and TdP, such as electrolyte monitoring and repletion and ECG monitoring, if concomitant use is necessary.
Vasopressin, ADH: (Moderate) Monitor hemodynamics and adjust the dose of vasopressin as needed when used concomitantly with drugs suspected of causing diabetes insipidus, such as foscarnet. Use together may decrease the pressor and antidiuretic effects of vasopressin.
Vemurafenib: (Major) When possible, avoid concurrent use of foscarnet with other drugs known to prolong the QT interval, such as vemurafenib. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes (TdP). Vemurafenib has also been associated with QT prolongation. If these drugs are administered together, obtain an electrocardiogram and electrolyte concentrations before and periodically during treatment.
Venlafaxine: (Major) Concomitant use of venlafaxine and foscarnet increases the risk of QT/QTc prolongation and torsade de pointes (TdP). Avoid concomitant use if possible, especially in patients with additional risk factors for TdP. Consider taking steps to minimize the risk for QT/QTc interval prolongation and TdP, such as electrolyte monitoring and repletion and ECG monitoring, if concomitant use is necessary.
Voclosporin: (Major) Avoid concomitant use of foscarnet and voclosporin due to the risk of additive QT prolongation and nephrotoxicity. Both QT prolongation and torsade de pointes (TdP) have been reported during postmarketing use of foscarnet. Voclosporin has been associated with QT prolongation at supratherapeutic doses.
Vonoprazan; Amoxicillin; Clarithromycin: (Major) When possible, avoid concurrent use of foscarnet with other drugs known to prolong the QT interval, such as clarithromycin. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes (TdP). Clarithromycin is also associated with an established risk for QT prolongation and TdP. If these drugs are administered together, obtain an electrocardiogram and electrolyte concentrations before and periodically during treatment.
Voriconazole: (Major) When possible, avoid concurrent use of foscarnet with other drugs known to prolong the QT interval, such as voriconazole. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes (TdP). Voriconazole has also been associated with QT prolongation and rare cases of TdP. If these drugs are administered together, obtain an electrocardiogram and electrolyte concentrations before and periodically during treatment.
Vorinostat: (Major) When possible, avoid concurrent use of foscarnet with other drugs known to prolong the QT interval, such as vorinostat. Foscarnet has been associated with postmarketing reports of both QT prolongation and torsade de pointes (TdP). Vorinostat therapy is also associated with a risk of QT prolongation. If these drugs are administered together, obtain an electrocardiogram and electrolyte concentrations before and periodically during treatment.
Zidovudine, ZDV: (Minor) Concurrent use of foscarnet and zidovudine, ZDV may be associated with a higher incidence of anemia; clinicians should follow normal recommendations for blood count monitoring and other parameters.
Ziprasidone: (Major) Both QT prolongation and torsade de pointes (TdP) have been reported during postmarketing use of foscarnet. Because of these reports, avoid the use of foscarnet with other drugs known to prolong the QT interval. Clinical trial data indicate that ziprasidone causes QT prolongation; there are postmarketing reports of TdP in patients with multiple confounding factors.

Foscarnet/Foscarnet Sodium/Foscavir Intravenous Inj Sol: 1mL, 24mg

Adults

180 mg/kg/day IV.

Geriatric

180 mg/kg/day IV.

Adolescents

Safety and efficacy have not been established; however, doses up to 180 mg/kg/day IV have been used off-label.

Children

Safety and efficacy have not been established; however, doses up to 180 mg/kg/day IV have been used off-label.

Infants

Safety and efficacy have not been established; however, doses up to 180 mg/kg/day IV have been used off-label.

Neonates

Safety and efficacy have not been established.

Foscarnet selectively inhibits the viral-specific DNA polymerases and reverse transcriptases at the pyrophosphate-binding site. This occurs through prevention of pyrophosphate cleavage from deoxynucleoside triphosphate and elongation of the viral DNA chain. Cellular DNA polymerases are not affected. Unlike acyclovir or ganciclovir, intracellular phosphorylation by thymidine kinase or other kinases is not a prerequisite for foscarnet activity, which makes it effective in vitro against herpes simplex strains that are deficient in thymidine kinase.
 
In vitro, foscarnet inhibits replication of the herpes simplex virus (HSV), varicella-zoster, Epstein-Barr virus, human herpesvirus 6, and cytomegalovirus. Foscarnet also inhibits HIV reverse transcriptase and hepatitis B DNA polymerase. Cytomegalovirus (CMV) isolates show variable sensitivity to foscarnet. Clinically, although statistically significant decreases in blood and urine CMV titers have occurred after treatment with foscarnet, a correlation has not been found between a reduction in positive blood cultures and clinical efficacy of the drug in patients with CMV infection. The virustatic actions of foscarnet are reversible following discontinuation of treatment.
 
Consider the possibility of viral resistance in those patients with poor clinical response or persistent viral excretion during therapy. Although in vivo data on the development of clinical resistance to foscarnet are limited and likely result from multiple resistant pathways, CMV and HSV isolated observed in cell cultures generated resistance through amino acid substitutions in the viral DNA polymerase. Some of these amino acid substitutions may confer cross-resistance with ganciclovir, acyclovir, and/or cidofovir.

Foscarnet is administered by intravenous infusion. The mean apparent volume of distribution of foscarnet at steady-state was estimated to be between 0.41 and 0.74 L/kg. In vitro studies have shown that 14% to 17% of foscarnet is protein bound at plasma drug concentrations of 1 to 1,000 micromolar. Foscarnet accumulates in bone and is distributed into cartilage. Uptake of foscarnet into the bone matrix is likely due to its structural similarity to phosphate. Penetration into the cerebrospinal fluid also has been observed with concentrations that are 30% to 50% of plasma levels (mean CSF: plasma ratio of 0.66 to 0.69). CSF penetration is increased with meningeal inflammation. Foscarnet is not metabolized in the liver. Foscarnet exhibits triphasic kinetics. In patients with normal renal function, the distribution and elimination half-lives are 0.4 to 1.4 and 3.3 to 6.8 hours, respectively. The terminal half-life is approximately 88 hours. Approximately 90% of a dose is eliminated unchanged in the urine through glomerular filtration and tubular secretion. Tubular reabsorption also can occur.
 
Affected cytochrome P450 isoenzymes and drug transporters: none

Intravenous Route

Mean steady-state Cmax was 589 and 623 micromolar after doses of 60 mg/kg and 90 mg/kg every 8 hours, respectively.

Pregnancy

There are no adequate and well-controlled studies of foscarnet use in human pregnancy. In animal studies, exposure to foscarnet was associated with a slight increase in skeletal anomalies. Foscarnet did not adversely affect fertility and general reproductive performance in animal studies; however, these studies used exposures that are inadequate to define the potential for impairment of fertility at human drug exposure levels. Because animal reproduction studies are not always predictive of human response, use foscarnet during pregnancy only if clearly needed.

It is unknown if foscarnet is distributed into breast milk. Animal studies have shown that foscarnet distributes into breast milk at concentrations that are three times greater than maternal plasma concentrations. Because of the potential for serious adverse events in nursing infants, a decision should be made whether to discontinue breast-feeding or discontinue foscarnet, taking into consideration the importance of the drug to the mother. Additionally, foscarnet may be used to treat infections in persons with HIV. Guidelines recommend clinicians provide mothers with evidence-based, patient-centered counseling to support shared decision-making regarding infant feeding. Inform patients that use of replacement feeding (i.e., formula or banked pasteurized donor human milk) eliminates the risk of HIV transmission; thus, replacement feeding is recommended for use when mothers with HIV are not on antiretroviral therapy (ART) or do not have suppressed viral load during pregnancy, as well as at delivery. For patients on ART who have achieved and maintained viral suppression during pregnancy (at minimum throughout the third trimester) and postpartum, the transmission risk from breast-feeding is less than 1%, but not zero. Virologically suppressed mothers who choose to breast-feed should be supported in this decision. If breast-feeding is chosen, counsel the patient about the importance of adherence to therapy and recommend that the infant be exclusively breast-fed for up to 6 months of age, as exclusive breast-feeding has been associated with a lower rate of HIV transmission as compared to mixed feeding (i.e., breast milk and formula). Promptly identify and treat mastitis, thrush, and cracked or bleeding nipples, as these conditions may increase the risk of HIV transmission through breast-feeding.