Tamiflu

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Tamiflu

Classes

Neuraminidase Inhibitor Antivirals

Administration
Oral Administration

May be taken orally with or without food; tolerability may be enhanced if taken with food.
Begin treatment within 48 hours of symptom onset. Begin prophylaxis within 48 hours of exposure.

Oral Solid Formulations

For patients who cannot swallow capsules, the commercially available oral suspension is the preferred formulation. However, if the oral suspension is not available, the capsules may be opened and mixed with sweetened liquids such as regular or sugar-free chocolate syrup, corn syrup, caramel topping, or light brown sugar dissolved in water. If the appropriate strengths of capsules are not available to mix with sweetened liquids and the commercially available oral suspension is not available, then a compounded supply of oral suspension can be prepared by the pharmacist (see below).

Oral Liquid Formulations

Shake well before use.
Administer using a calibrated measuring device.
 
Reconstitution of commercially available 6 mg/mL oral suspension:
Review the reconstitution instructions for the particular product and package size, as the amount of water required for reconstitution varies from manufacturer to manufacturer.
Loosen powder from sides of the bottle. Add the specified amount of water and shake well for 15 seconds. The final oseltamivir concentration is 6 mg/mL.
Remove the child-resistant cap and push bottle adapter into the neck of the bottle.
Close tightly with the child-resistant cap. This will ensure proper sealing of the bottle.
Place an ancillary label on the bottle stating 'Shake Well Before Use', and dispense with the appropriate oral dosing syringe.
Storage after reconstitution: Use within 17 days of reconstitution when stored under refrigeration [2 to 8 degrees C (36 to 46 degrees F); DO NOT freeze] or within 10 days if stored at room temperature [15 to 30 degrees C (59 to 86 degree F)]. Write the expiration date on the label.

Extemporaneous Compounding-Oral

Shake well before use.
Administer using a calibrated measuring device.
 
Extemporaneous 6 mg/mL oral suspension (using capsules):
Compounded suspensions are for use only during emergency situations and should not be used for convenience or when the FDA-approved oral suspension is commercially available.
The recommended vehicles are Cherry Syrup (Humco), Ora-Sweet SF (Paddock Laboratories), or simple syrup; other vehicles have not been studied. The final oseltamivir concentration in the compounded suspension is 6 mg/mL, which is the SAME as the commercially available oral suspension.
The total volume of suspension needed to prepare a full course (5-day treatment course or 10-day course of prophylaxis) is based on the patient's dose (see below). If the oseltamivir dose is between the doses listed, the total volume of the oral suspension should default to the next greater dose listed.
Oseltamivir dose of 15 mg or less: Prepare a 37.5 mL suspension using three (3) 75-mg capsules (225 mg oseltamivir), 2.5 mL of water, and 34.5 mL of recommended vehicle.
Oseltamivir dose of 30 mg: Prepare a 75 mL suspension using six (6) 75-mg capsules (450 mg oseltamivir), 5 mL of water, and 69 mL of recommended vehicle.
Oseltamivir dose of 45 mg: Prepare a 100 mL suspension using eight (8) 75-mg capsules (600 mg oseltamivir), 7 mL of water, and 91 mL of recommended vehicle.
Oseltamivir dose of 60 mg: Prepare a 125 mL suspension using ten (10) 75-mg capsules (750 mg oseltamivir), 8 mL of water, and 115 mL of recommended vehicle.
Oseltamivir dose of 75 mg: Prepare a 150 mL suspension using twelve (12) 75-mg capsules (900 mg oseltamivir), 10 mL of water, and 137 mL of recommended vehicle.
 
Compounding the 6 mg/mL oral suspension:
Add the above specified volume of water to a polyethyleneterephthalate (PET) or glass bottle; a funnel may be used to prevent spillage.
Carefully open each capsule and transfer contents into the PET or glass bottle.
Gently swirl the suspension for at least 2 minutes.
Slowly add the above specified volume of vehicle to the bottle; a funnel may be used to prevent spillage.
Shake well for 30 seconds to completely dissolve the active drug and to ensure homogenous distribution of the dissolved drug in the resulting suspension. It should be noted that oseltamivir phosphate readily dissolves in the recommended vehicles and that the suspension is due to some inert ingredients of the capsules that are insoluble in these vehicles.
Place an ancillary label on the bottle stating 'Shake Well Before Use', and dispense with the appropriate oral dosing syringe.
The compounded oral suspension is stable for 5 days when stored at room temperature 25 degrees C (77 degrees F) or for 5 weeks (35 days) under refrigeration at 2 to 8 degrees C (36 to 46 degrees F). However, if pharmacies are preparing batches of the extemporaneously compounded suspension due to high prescription volume, the compounded suspension must be refrigerated until dispensed, stirred thoroughly before dispensing, and refrigerated by the patient at home.

Adverse Reactions
Severe

GI bleeding / Delayed / Incidence not known
Stevens-Johnson syndrome / Delayed / Incidence not known
erythema multiforme / Delayed / Incidence not known
laryngeal edema / Rapid / Incidence not known
anaphylactoid reactions / Rapid / Incidence not known
angioedema / Rapid / Incidence not known
toxic epidermal necrolysis / Delayed / Incidence not known
anaphylactic shock / Rapid / Incidence not known
seizures / Delayed / Incidence not known
arrhythmia exacerbation / Early / Incidence not known

Moderate

elevated hepatic enzymes / Delayed / Incidence not known
hepatitis / Delayed / Incidence not known
colitis / Delayed / Incidence not known
psychosis / Early / Incidence not known
hallucinations / Early / Incidence not known
confusion / Early / Incidence not known
delirium / Early / Incidence not known
hyperglycemia / Delayed / Incidence not known

Mild

headache / Early / 2.0-17.0
diaper dermatitis / Delayed / 7.0-7.0
rash / Early / Incidence not known
urticaria / Rapid / Incidence not known
emotional lability / Early / Incidence not known
anxiety / Delayed / Incidence not known
agitation / Early / Incidence not known
nightmares / Early / Incidence not known
hypothermia / Delayed / Incidence not known

Common Brand Names

Tamiflu

Dea Class

Rx

Description

Oral neuraminidase inhibitor
Used for treatment and prevention of uncomplicated infections due to seasonal influenza virus A or B
Most effective if initiated early (e.g., within 48 hours of symptom onset or exposure)

Dosage And Indications
For the treatment of acute influenza A virus infection or influenza B virus infection. Oral dosage Adults

75 mg PO twice daily for 5 days.[31109] May consider extended courses for patients who remain severely ill after 5 days of treatment.[62315] [63866]

Children and Adolescents weighing more than 40 kg

75 mg PO twice daily for 5 days.[31109] May consider extended courses for patients who remain severely ill after 5 days of treatment.[62315] [63866]

Children weighing 24 to 40 kg

60 mg PO twice daily for 5 days.[31109] May consider extended courses for patients who remain severely ill after 5 days of treatment.[62315] [63866]

Children weighing 16 to 23 kg

45 mg PO twice daily for 5 days.[31109] May consider extended courses for patients who remain severely ill after 5 days of treatment.[62315] [63866]

Children weighing 15 kg or less

30 mg PO twice daily for 5 days.[31109] May consider extended courses for patients who remain severely ill after 5 days of treatment.[62315] [63866]

Infants 9 to 11 months

3.5 mg/kg/dose PO twice daily for 5 days is recommended by the American Academy of Pediatrics (AAP) based on pharmacokinetic data indicating that a slightly higher dosage is needed in this age group to achieve target drug exposure.[56854] [63520] The FDA-approved dosage is 3 mg/kg/dose PO twice daily for 5 days. May consider extended courses for patients who remain severely ill after 5 days of treatment.[62315] [63866]

Infants 1 to 8 months

3 mg/kg/dose PO twice daily for 5 days.[31109] May consider extended courses for patients who remain severely ill after 5 days of treatment.[62315] [63866]

Term Neonates 14 to 29 days

3 mg/kg/dose PO twice daily for 5 days.[31109] May consider extended courses for patients who remain severely ill after 5 days of treatment.[62315] [63866]

Premature Neonates older than 40 weeks postmenstrual age† and Term Neonates 0 to 13 days†

3 mg/kg/dose PO twice daily for 5 days.[62315] [63520] May consider extended courses for patients who remain severely ill after 5 days of treatment.[62315] [63866]

Premature Neonates 38 to 40 weeks postmenstrual age†

1.5 mg/kg/dose PO twice daily for 5 days.[62315] [63520] May consider extended courses for patients who remain severely ill after 5 days of treatment.[62315] [63866]

Premature Neonates younger than 38 weeks postmenstrual age†

1 mg/kg/dose PO twice daily for 5 days.[62315] [63520] May consider extended courses for patients who remain severely ill after 5 days of treatment.[62315] [63866]

For seasonal influenza prophylaxis. Oral dosage Adults

75 mg PO once daily for at least 10 days after close contact and for up to 6 weeks during a community outbreak. Safety and efficacy have been demonstrated for up to 6 weeks in immunocompetent patients and safety has been demonstrated for up to 12 weeks in immunocompromised patients (efficacy has not been demonstrated).[25978] [31109] The duration of protection lasts for as long as dosing is continued. The CDC recommends a 7-day course after the last known exposure. For those vaccinated during an outbreak, a 2-week course is recommended. For control of outbreaks in long-term care facilities and hospitals, the CDC recommends chemoprophylaxis for a minimum of 2 weeks and up to 1 week after the last known identified case. High-risk patients may require prophylaxis during the entire influenza season.[62315] [63866] Oseltamivir treatment for 42 days has been efficacious in preventing influenza in 92% of those in residential nursing home settings during a flu outbreak; note that 80% of the residents had previously received influenza vaccination.[31109]

Children weighing more than 40 kg and Adolescents

75 mg PO once daily for at least 10 days after close contact and for up to 6 weeks during a community outbreak.[31109] The duration of protection lasts for as long as dosing is continued. The CDC recommends a 7-day course after the last known exposure. For those vaccinated during an outbreak, a 2-week course is recommended. For control of outbreaks in long-term care facilities and hospitals, the CDC recommends chemoprophylaxis for a minimum of 2 weeks and up to 1 week after the last known identified case. High-risk patients may require prophylaxis during the entire influenza season.[62315] [63866]

Children weighing 24 to 40 kg

60 mg PO once daily for 10 days or for up to 6 weeks during a community outbreak.[31109] The duration of protection lasts for as long as dosing is continued. The CDC recommends a 7-day course after the last known exposure. For those vaccinated during an outbreak, a 2-week course is recommended. For control of outbreaks in long-term care facilities and hospitals, the CDC recommends chemoprophylaxis for a minimum of 2 weeks and up to 1 week after the last identified case. High-risk patients may require prophylaxis during the entire influenza season.[62315] [63866]

Children weighing 16 to 23 kg

45 mg PO once daily for 10 days or for up to 6 weeks during a community outbreak.[31109] The duration of protection lasts for as long as dosing is continued. The CDC recommends a 7-day course after the last known exposure. For those vaccinated during an outbreak, a 2-week course is recommended. For control of outbreaks in long-term care facilities and hospitals, the CDC recommends chemoprophylaxis for a minimum of 2 weeks and up to 1 week after the last identified case. High-risk patients may require prophylaxis during the entire influenza season.[62315] [63866]

Children weighing 15 kg or less

30 mg PO once daily for 10 days or for up to 6 weeks during a community outbreak.[31109] The duration of protection lasts for as long as dosing is continued. The CDC recommends a 7-day course after the last known exposure. For those vaccinated during an outbreak, a 2-week course is recommended. For control of outbreaks in long-term care facilities and hospitals, the CDC recommends chemoprophylaxis for a minimum of 2 weeks and up to 1 week after the last identified case. High-risk patients may require prophylaxis during the entire influenza season.[62315] [63866]

Infants 9 to 11 months†

3.5 mg/kg/dose PO once daily is recommended by the American Academy of Pediatrics (AAP) based on pharmacokinetic data indicating that a slightly higher dosage is needed in this age group to achieve target drug exposure. [63520] The duration of therapy is dependent on type of exposure: 7 days after the last known exposure; 2 weeks for those vaccinated during an outbreak; a minimum of 2 weeks and up to 1 week after the last-identified case for control of outbreaks in long-term care facilities and hospitals. High-risk patients may require prophylaxis during the entire influenza season.[62315] [63520] [63866]

Infants 3 to 8 months†

3 mg/kg/dose PO once daily.[62315] [63520] The duration of therapy is dependent on type of exposure: 7 days after the last known exposure; 2 weeks for those vaccinated during an outbreak; a minimum of 2 weeks and up to 1 week after the last identified case for control of outbreaks in long-term care facilities and hospitals. High-risk patients may require prophylaxis during the entire influenza season.[62315] [63520] [63866]

Infants 1 to 2 months†

Because of the lack of data in this age group, chemoprophylaxis is not recommended unless the exposure situation is judged to be critical.[62315] [63520] A variety of oseltamivir dosages have been safely used for influenza prophylaxis in infants in limited studies.[43072] [52863] [52865] [52866] A dosage of 1 mg/kg/dose PO twice daily for 10 days was effective in a small study of 13 neonates (mean gestational age 39 weeks [range, 36 to 41 weeks]) exposed to influenza H1N1; no patients developed influenza.[52865]

Neonates†

Because of the lack of data in this age group, chemoprophylaxis is not recommended unless the exposure situation is judged to be critical.[62315] [63520] A variety of oseltamivir dosages have been safely used for influenza prophylaxis in neonates in limited studies.[43072] [52863] [52865] [52866] A dosage of 1 mg/kg/dose PO twice daily for 10 days was effective in a small study of 13 neonates (mean gestational age 39 weeks [range, 36 to 41 weeks]) exposed to influenza H1N1; no patients developed influenza.[52865]

For the treatment of novel influenza A viruses associated with severe human disease†, including avian influenza A virus infection†. Oral dosage Adults

75 mg PO twice daily for 5 days, with longer courses (e.g., 10 days) considered for severely ill hospitalized patients or immunosuppressed patients. Clinical judgment and virologic testing should guide duration assessment. Oseltamivir is recommended for hospitalized patients as well as outpatients.

Children weighing more than 40 kg and Adolescents

75 mg PO twice daily for 5 days, with longer courses (e.g., 10 days) considered for severely ill hospitalized patients or immunosuppressed patients. Clinical judgment and virologic testing should guide duration assessment. Oseltamivir is recommended for hospitalized patients as well as outpatients.

Children weighing 24 to 40 kg

60 mg PO twice daily for 5 days, with longer courses (e.g., 10 days) considered for severely ill hospitalized patients or immunosuppressed patients. Clinical judgment and virologic testing should guide duration assessment. Oseltamivir is recommended for hospitalized patients as well as outpatients.

Children weighing 16 to 23 kg

45 mg PO twice daily for 5 days, with longer courses (e.g., 10 days) considered for severely ill hospitalized patients or immunosuppressed patients. Clinical judgment and virologic testing should guide duration assessment. Oseltamivir is recommended for hospitalized patients as well as outpatients.

Children weighing 15 kg or less

30 mg PO twice daily for 5 days, with longer courses (e.g., 10 days) considered for severely ill hospitalized patients or immunosuppressed patients. Clinical judgment and virologic testing should guide duration assessment. Oseltamivir is recommended for hospitalized patients as well as outpatients.

Infants 9 to 11 months

3.5 mg/kg/dose PO twice daily for 5 days, with longer courses (e.g., 10 days) considered for severely ill hospitalized patients or immunosuppressed patients. Clinical judgment and virologic testing should guide duration assessment. Oseltamivir is recommended for hospitalized patients as well as outpatients.[56854] [62315] [62336] [63520]

Infants 1 to 8 months

3 mg/kg/dose PO twice daily for 5 days, with longer courses (e.g., 10 days) considered for severely ill hospitalized patients or immunosuppressed patients. Clinical judgment and virologic testing should guide duration assessment. Oseltamivir is recommended for hospitalized patients as well as outpatients.[56854] [62315] [62336] [63520]

Premature Neonates older than 40 weeks postmenstrual age and Term Neonates

3 mg/kg/dose PO twice daily for 5 days, with longer courses (e.g., 10 days) considered for severely ill hospitalized patients or immunosuppressed patients. Clinical judgment and virologic testing should guide duration assessment. Oseltamivir is recommended for hospitalized patients as well as outpatients.[62315] [62336] [63520]

Premature Neonates 38 to 40 weeks postmenstrual age

1.5 mg/kg/dose PO twice daily for 5 days, with longer courses (e.g., 10 days) considered for severely ill hospitalized patients or immunosuppressed patients. Clinical judgment and virologic testing should guide duration assessment. Oseltamivir is recommended for hospitalized patients as well as outpatients.[62315] [62336] [63520]

Premature Neonates younger than 38 weeks postmenstrual age

1 mg/kg/dose PO twice daily for 5 days, with longer courses (e.g., 10 days) considered for severely ill hospitalized patients or immunosuppressed patients. Clinical judgment and virologic testing should guide duration assessment. Oseltamivir is recommended for hospitalized patients as well as outpatients.[62315] [62336] [63520]

For prophylaxis of novel influenza A viruses associated with severe human disease†, including avian influenza prophylaxis†. Oral dosage Adults

75 mg PO twice daily. Initiate therapy as soon as possible after first exposure to the confirmed or probable case. If exposure was time-limited and not ongoing, 5 days of treatment from the last known exposure is recommended. If exposure is likely to be ongoing (i.e., household setting), 10 days of treatment is recommended.

Children weighing 40 kg or more and Adolescents

75 mg PO twice daily. Initiate therapy as soon as possible after first exposure to the confirmed or probable case. If exposure was time-limited and not ongoing, 5 days of treatment from the last known exposure is recommended. If exposure is likely to be ongoing (i.e., household setting), 10 days of treatment is recommended.

Children weighing 24 to 40 kg

60 mg PO twice daily. Initiate therapy as soon as possible after first exposure to the confirmed or probable case. If exposure was time-limited and not ongoing, 5 days of treatment from the last known exposure is recommended. If exposure is likely to be ongoing (i.e., household setting), 10 days of treatment is recommended.

Children weighing 16 to 23 kg

45 mg PO twice daily. Initiate therapy as soon as possible after first exposure to the confirmed or probable case. If exposure was time-limited and not ongoing, 5 days of treatment from the last known exposure is recommended. If exposure is likely to be ongoing (i.e., household setting), 10 days of treatment is recommended.

Children weighing 15 kg or less

30 mg PO twice daily. Initiate therapy as soon as possible after first exposure to the confirmed or probable case. If exposure was time-limited and not ongoing, 5 days of treatment from the last known exposure is recommended. If exposure is likely to be ongoing (i.e., household setting), 10 days of treatment is recommended.

Term Neonates and Infants 14 days and older

3 mg/kg/dose PO twice daily.[62315] The American Academy of Pediatrics (AAP) recommends 3.5 mg/kg/dose PO twice daily for infants 9 to 11 months of age based on pharmacokinetic data indicating that a slightly higher dosage is needed in this age group to achieve target drug exposure.[56854] [63520] Initiate therapy as soon as possible after first exposure to the confirmed or probable case. If exposure was time-limited and not ongoing, 5 days of treatment from the last known exposure is recommended. If exposure is likely to be ongoing (i.e., household setting), 10 days of treatment is recommended.[62337] [62338]

Premature Neonates older than 40 weeks postmenstrual age and Term Neonates 0 to 13 days

3 mg/kg/dose PO twice daily. Initiate therapy as soon as possible after first exposure to the confirmed or probable case. If exposure was time-limited and not ongoing, 5 days of treatment from the last known exposure is recommended. If exposure is likely to be ongoing (i.e., household setting), 10 days of treatment is recommended.

Premature Neonates 38 to 40 weeks postmenstrual age

1.5 mg/kg/dose PO twice daily. Initiate therapy as soon as possible after first exposure to the confirmed or probable case. If exposure was time-limited and not ongoing, 5 days of treatment from the last known exposure is recommended. If exposure is likely to be ongoing (i.e., household setting), 10 days of treatment is recommended.

Premature Neonates younger than 38 weeks postmenstrual age

1 mg/kg/dose PO twice daily. Initiate therapy as soon as possible after first exposure to the confirmed or probable case. If exposure was time-limited and not ongoing, 5 days of treatment from the last known exposure is recommended. If exposure is likely to be ongoing (i.e., household setting), 10 days of treatment is recommended.

†Indicates off-label use

Dosing Considerations
Hepatic Impairment

No dosage adjustments are recommended for patients with mild to moderate hepatic impairment (Child-Pugh score 9 or less). The safety and pharmacokinetics of oseltamivir in patients with severe hepatic impairment have not been established.

Renal Impairment

The following dose adjustments are recommended for adult patients with renal impairment. Dose adjustment recommendations are unavailable for pediatric patients; however, similar dose adjustments should be considered, particularly in pediatric patients receiving the adult dosage.[31109]
 
Influenza treatment
CrCl more than 60 mL/minute: No dosage adjustment necessary.
CrCl 31 to 60 mL/minute: 30 mg PO twice daily for 5 days.
CrCl 11 to 30 mL/minute: 30 mg PO once daily for 5 days.
CrCl 10 mL/minute or less, not undergoing dialysis: Oseltamivir is not recommended.
 
Influenza prophylaxis
CrCl more than 60 mL/minute: No dosage adjustment necessary.
CrCl 31 to 60 mL/minute: 30 mg PO once daily.
CrCl 11 to 30 mL/minute: 30 mg PO every other day.
CrCl 10 mL/minute or less, not undergoing dialysis: Oseltamivir is not recommended.
 
Intermittent hemodialysis (ESRD patients with CrCl 10 mL/minute or less)
For influenza treatment: 30 mg after every hemodialysis cycle; treatment duration not to exceed 5 days. The initial dose may be given immediately, with subsequent doses administered after each dialysis.
For influenza prophylaxis: 30 mg after alternate hemodialysis cycles. The initial dose may be given prior to the start of dialysis.[31109]
 
Continuous ambulatory peritoneal hemodialysis (ESRD patients with CrCl 10 mL/minute or less)
For influenza treatment: A single 30 mg dose given immediately after dialysis exchange.
For influenza prophylaxis: 30 mg once weekly immediately after dialysis exchange.[31109]

Drug Interactions

Dichlorphenamide: (Major) Concomitant use of dichlorphenamide and oseltamivir is not recommended because of an increased risk of oseltamivir-related adverse effects. Monitor closely for signs of drug toxicity if coadministration cannot be avoided. Increased oseltamivir exposure is possible. Dichlorphenamide inhibits OAT1. Oseltamivir is a sensitive OAT1 substrate. Consider if an alternative to oseltamivir would be appropriate for the patient.
Live Attenuated Influenza Vaccine (intranasal): (Major) Do not administer intranasal live attenuated influenza vaccine (LAIV) 2 weeks before or 48 hours after administration of oseltamivir, unless medically indicated. Inactivated influenza vaccines may be used, as appropriate. Because of its antiviral properties, oseltamivir may interfere with the efficacy of live attenuated influenza vaccines. Therefore, live influenza virus vaccines are not recommended during treatment with oseltamivir. Consult currently recommended guidance on the use of antiviral drugs against influenza.
Probenecid: (Minor) Coadministration of oseltamivir and probenecid results in a two-fold increase in exposure to oseltamivir carboxylate due to a decrease in active anionic tubular secretion in the kidney. However, due to the safety margin of oseltamivir carboxylate, no dosage adjustments are required when oseltamivir is given concomitantly with probenecid.
Probenecid; Colchicine: (Minor) Coadministration of oseltamivir and probenecid results in a two-fold increase in exposure to oseltamivir carboxylate due to a decrease in active anionic tubular secretion in the kidney. However, due to the safety margin of oseltamivir carboxylate, no dosage adjustments are required when oseltamivir is given concomitantly with probenecid.

How Supplied

Oseltamivir/Oseltamivir Phosphate/Tamiflu Oral Cap: 30mg, 45mg, 75mg
Oseltamivir/Oseltamivir Phosphate/Tamiflu Oral Pwd F/Recon: 1mL, 6mg

Maximum Dosage
Adults

75 mg PO twice daily.

Geriatric

75 mg PO twice daily.

Adolescents

75 mg PO twice daily.

Children

weight more than 40 kg: 75 mg PO twice daily.
weight 24 to 40 kg: 60 mg PO twice daily.
weight 16 to 23 kg: 45 mg PO twice daily.
weight 15 kg or less: 30 mg PO twice daily.

Infants

9 to 11 months: 3 mg/kg/dose PO twice daily is the FDA-approved dosage; however, 3.5 mg/kg/dose PO twice daily has been used off-label.
1 to 8 months: 3 mg/kg/dose PO twice daily.

Neonates

Term Neonates 14 days and older: 3 mg/kg/dose PO twice daily.
Premature Neonates older than 40 weeks postmenstrual age and Term Neonates 0 to 13 days: Safety and efficacy have not been established; however, 3 mg/kg/dose PO twice daily has been used off-label.
Premature Neonates 38 to 40 weeks postmenstrual age: Safety and efficacy have not been established; however, 1.5 mg/kg/dose PO twice daily has been used off-label.
Premature Neonates younger than 38 weeks postmenstrual age: Safety and efficacy have not been established; however, 1 mg/kg/dose PO twice daily has been used off-label.

Mechanism Of Action

Oseltamivir is an ethyl ester prodrug that requires hydrolysis to the active metabolite, oseltamivir carboxylate. Once in circulation, oseltamivir carboxylate acts extracellularly by selectively binding to an unoccupied area of viral neuraminidase (a surface glycoprotein on influenza A and B that catalyzes the cleavage of the linkage between a terminal sialic acid and adjacent sugar residue), resulting in competitive inhibition of the enzyme. By inhibiting the actions of viral neuraminidase, oseltamivir ultimately prevents the spread of virus in the respiratory tract.
 
Influenza viruses are classified into 3 distinct types, influenza A, influenza B, and influenza C. Influenza A is further divided into subtypes based on their hemagglutinin (H or HA) and neuraminidase (N or NA) activity. At least 16 distinct HAs (H1 to H16) and 9 NAs (N1 to N9) have been described. Influenza infection may be attributed to either influenza A virus or influenza B virus. Influenza A virus subtypes include H1N1 and H3N2. In 2009, a novel influenza A H1N1 virus (previously referred to as swine influenza) was identified; this virus is included in season influenza A viruses. Human cases of influenza illness from the avian H5N1 virus (commonly known as avian flu) have been reported since 1997. Human infections with avian H7N9, H5N2, H5N8, H9N2, H7N7, and H7N3 viruses have also been described.
 
A neuraminidase assay of clinical isolates identified the median IC50 (50% inhibitory concentration) for oseltamivir carboxylate against influenza A/H1N1, influenza A/H3N2, and influenza B to be 2.5 nM (range 0.93 to 4.16 nM), 0.96 nM (range 0.13 to 7.95 nM), and 60 nM (range 20 to 285 nM), respectively. An evaluation of antiviral activity using laboratory and clinical influenza isolates found the concentrations of oseltamivir carboxylate required for inhibition of influenza virus in cell culture to be highly variable depending on the assay method used and virus testing. Specifically, the EC50 and EC90 (50% and 90% effective inhibitory concentration) of these cell cultures ranged from 0.0008 micromolar to more than 35 micromolar and 0.004 micromolar to more than 100 micromolar, respectively. A relationship between antiviral activity in cell culture, inhibitory activity in neuraminidase assay, and inhibition of influenza virus replication in humans has not been established. Influenza treatment emergent resistance to oseltamivir has been reported, with most cases occurring in influenza A/H1N1 viruses. Genetic analysis shows that reduced susceptibility to oseltamivir carboxylate is associated with mutations that result in amino acid changes in the viral neuraminidase or viral hemagglutinin or both. The prevalence of oseltamivir-resistant viruses varies based on season and geographic location. Severely immunosuppressed persons (e.g., hematopoietic stem cell transplant recipients) are at highest risk for developing an oseltamivir-resistant influenza virus infection during or after antiviral therapy. In addition, selection of influenza A viruses resistant to oseltamivir appears to occur at higher frequencies in pediatric populations. During small pediatric studies, the incidence of oseltamivir treatment-associated resistance for influenza A/H1N1 and influenza A/H3N2 were 27% to 37% and 3% to 18%, respectively. The actual risk of resistance to oseltamivir during clinical use cannot be determined from these small pediatric studies. The CDC Influenza Division is available for consultation regarding resistance testing as needed.

Pharmacokinetics

Oseltamivir is administered orally. Following absorption from the gastrointestinal tract, most of the dose (at least 90%) is hydrolyzed by hepatic esterase to the active metabolite, oseltamivir carboxylate. Oseltamivir carboxylate does not undergo any further metabolism and is only minimally bound to human plasma proteins (3%). The elimination half-life of oseltamivir carboxylate is 6 to 10 hours, with more than 99% being eliminated in the urine via glomerular filtration and active tubular secretion. The elimination half-life of the parent drug is 1 to 3 hours.
 
Affected cytochrome P450 isoenzymes: none
Neither oseltamivir nor oseltamivir carboxylate are substrates for, or inhibitors of, cytochrome P450 isoenzymes.

Oral Route

After oral administration, 75% of the dose reaches systemic circulation as oseltamivir carboxylate; less than 5% of the total dose reaches the systemic circulation as oseltamivir. Administration with food has no effect on the maximum plasma concentration (Cmax) or exposure (AUC) values for oseltamivir carboxylate.

Pregnancy And Lactation
Pregnancy

No adequate and well-controlled studies have been conducted regarding the use of oseltamivir during pregnancy; however, a collection of observational studies have evaluated drug exposure in more than 5,000 pregnant women. Although, individually, these studies lacked adequate sample size, pooled data found no increased risk of congenital malformations when compared to the general population. In addition, the gestational period in which exposure occurred appeared to have no effect on pregnancy outcome, as approximately 1,000 women were exposed during the first trimester. In animal studies, slight and marked maternal toxicities and a dose-dependent increase in skeletal abnormalities in offspring were observed. The manufacturer states that oseltamivir should only be used during pregnancy if the potential benefit justifies the potential risk to the fetus. According to the CDC, pregnant women are known to be at higher risk for complications from influenza infection and severe disease among women has been reported in past pandemics; therefore, guidelines state that the benefits of treatment against the influenza virus likely outweigh the theoretical risks of antiviral use. The CDC considers oseltamivir the preferred antiviral for treatment of influenza in pregnant women.[28647] [31109] [62315]

Limited data suggest oseltamivir and oseltamivir carboxylate are excreted in human breast milk. The concentration of oseltamivir and oseltamivir carboxylate in breast milk was found to be lower than the concentrations in plasma following a single 75 mg oral dose. The estimated infant exposure to oseltamivir, assuming a 2.75 kg infant receiving 750 mL of breast milk daily, was 0.76 mcg/kg/day. This dose is much lower than oseltamivir doses used in neonates and infants for treatment of influenza; thus, exposure through breast milk is unlikely to lead to toxicity in the breastfed infant. Postmarketing experience has not reported any information to suggest serious adverse effects of oseltamivir exposure via breast milk in infants. It is not known if oseltamivir affects human milk production. The developmental and health benefits of breast-feeding should be considered along with the mother's clinical need for oseltamivir and any potential adverse effects on the breastfed child from the drug or from the underlying maternal condition.