Tenex

ADHD Agents, Non-stimulant
Centrally Acting Alpha Agonists

bradycardia / Rapid / 2.0-5.0
AV block / Early / 2.0
arrhythmia exacerbation / Early / 2.0
bronchospasm / Rapid / 2.0
myocardial infarction / Delayed / Incidence not known
renal failure (unspecified) / Delayed / Incidence not known
heart failure / Delayed / Incidence not known
stroke / Early / Incidence not known
exfoliative dermatitis / Delayed / Incidence not known

constipation / Delayed / 1.0-15.0
hypotension / Rapid / 5.0-9.0
orthostatic hypotension / Delayed / 5.0-9.0
impotence (erectile dysfunction) / Delayed / 3.0-7.0
urinary incontinence / Early / 2.0-4.0
sinus tachycardia / Rapid / 2.0-3.0
palpitations / Early / 0-3.0
conjunctivitis / Delayed / 0-3.0
iritis / Delayed / 0-3.0
blurred vision / Early / 0-3.0
dysphagia / Delayed / 0-3.0
dyspnea / Early / 0-3.0
paresis / Delayed / 0-3.0
wheezing / Rapid / 2.0
chest pain (unspecified) / Early / Incidence not known
edema / Delayed / Incidence not known
elevated hepatic enzymes / Delayed / Incidence not known
hypertension / Early / Incidence not known
encephalopathy / Delayed / Incidence not known
withdrawal / Early / Incidence not known

xerostomia / Early / 2.0-60.0
abdominal pain / Early / 2.0-14.0
nausea / Early / 2.0-6.0
diarrhea / Early / 2.0-5.0
vomiting / Early / 2.0-5.0
nocturia / Early / 2.0-4.0
rhinitis / Early / 0-3.0
dysgeusia / Early / 0-3.0
tinnitus / Delayed / 0-3.0
dyspepsia / Early / 2.0-3.0
weight gain / Delayed / 2.0-3.0
purpura / Delayed / 0-3.0
pruritus / Rapid / 2.0-3.0
rash / Early / 2.0-3.0
hyperhidrosis / Delayed / 0-3.0
muscle cramps / Delayed / 0-3.0
malaise / Early / 0-3.0
pallor / Early / Incidence not known
syncope / Early / Incidence not known
alopecia / Delayed / Incidence not known
libido decrease / Delayed / Incidence not known
increased urinary frequency / Early / Incidence not known
tremor / Early / Incidence not known
myalgia / Early / Incidence not known
arthralgia / Delayed / Incidence not known

Intuniv, Tenex

Rx

Oral, central acting alpha-2 adrenergic agonist
Used for hypertension in adults; used for attention deficit hyperactivity disorder (ADHD) in pediatric patients 6 years and older and adult patients
Similar to clonidine but is more selective for alpha-2 adrenergic receptors and longer-acting, which allows for once-daily dosing

†Indicates off-label use

Data are lacking in patients with hepatic impairment. Caution is advised in patients with hepatic failure as 50% of dose is metabolized; in the treatment of ADHD, product labeling suggests that it may be necessary to adjust the dose in patients with significantly impaired hepatic function. In patients with mild to moderate hepatic impairment, initiate guanfacine cautiously. Adjust dosage to attain clinical goals.

CrCl 30 mL/minute or higher: No adjustment needed.
CrCl less than 30 mL/minute: In the treatment of hypertension, product labeling recommends the lower end of the dosing range for guanfacine since 50% of the drug is excreted renally. In the treatment of attention deficit hyperactivity disorder (ADHD), product labeling suggests that it may be necessary to adjust the guanfacine dose in patients with significantly impaired renal function.
 
Intermittent hemodialysis
Follow dosage recommendations for patients with CrCl less than 30 mL/minute. Guanfacine is not significantly removed by hemodialysis.

Acebutolol: (Moderate) Guanfacine can have additive effects when administered with other antihypertensive agents, including beta-blockers. These effects can be used to therapeutic advantage, but dosage adjustments may be necessary.
Acetaminophen; Ibuprofen: (Moderate) NSAIDs may decrease the effect of antihypertensive agents through various mechanisms, including renal and peripheral vasoactive pathways.
Acetazolamide: (Moderate) The concomitant administration of diuretics with other antihypertensive agents can result in additive hypotensive effects. This interaction can be therapeutically advantageous, but dosages must be adjusted accordingly.
Adagrasib: (Major) If coadministration of adagrasib with extended-release (ER) guanfacine is necessary, reduce the guanfacine dosage to half of the recommended dose. Specific recommendations for immediate-release (IR) guanfacine are not available. Monitor patients closely for adverse effects including hypotension, drowsiness, lethargy, and bradycardia. If adagrasib is discontinued, the guanfacine ER dosage should be increased back to the recommended dose. Guanfacine is a CYP3A substrate and adagrasib is a strong CYP3A inhibitor; adagrasib may significantly increase guanfacine plasma concentrations.
Aldesleukin, IL-2: (Moderate) Antihypertensive agents may potentiate the hypotension seen with aldesleukin, IL-2.
Alemtuzumab: (Moderate) Alemtuzumab may cause hypotension. Careful monitoring of blood pressure and hypotensive symptoms is recommended especially in patients with ischemic heart disease and in patients on antihypertensive agents.
Alprazolam: (Moderate) Guanfacine has been associated with sedative effects and can potentiate the actions of other CNS depressants including benzodiazepines.
Alprostadil: (Minor) The concomitant use of systemic alprostadil injection and central-acting antihypertensive agents may cause additive hypotension. Caution is advised with this combination. Systemic drug interactions with the urethral suppository (MUSE) or alprostadil intracavernous injection are unlikely in most patients because low or undetectable amounts of the drug are found in the peripheral venous circulation following administration. In those men with significant corpora cavernosa venous leakage, hypotension might be more likely. Use caution with in-clinic dosing for erectile dysfunction (ED) and monitor for the effects on blood pressure. In addition, the presence of medications in the circulation that attenuate erectile function may influence the response to alprostadil. However, in clinical trials with alprostadil intracavernous injection, anti-hypertensive agents had no apparent effect on the safety and efficacy of alprostadil.
Amifostine: (Major) Patients receiving central-acting adrenergic agents should be closely monitored during amifostine infusions due to additive effects. Patients receiving amifostine at doses recommended for chemotherapy should have antihypertensive therapy interrupted 24 hours preceding administration of amifostine. If the antihypertensive cannot be stopped, patients should not receive amifostine.
Amiodarone: (Major) Amiodarone may significantly increase guanfacine plasma concentrations. FDA-approved labeling for extended-release (ER) guanfacine recommends that, if these agents are taken together, the guanfacine dosage should be decreased to half of the recommended dose. Specific recommendations for immediate-release (IR) guanfacine are not available. Monitor patients closely for alpha-adrenergic effects including hypotension, drowsiness, lethargy, and bradycardia. Upon amiodarone discontinuation, the guanfacine ER dosage should be increased back to the recommended dose. Guanfacine is primarily metabolized by CYP3A4, and amiodarone is a moderate CYP3A4 inhibitor.
Amitriptyline: (Major) Tricyclic antidepressants (TCAs) can inhibit the hypotensive effects of guanfacine, causing an increase in blood pressure if given concomitantly. Consider alternatives to TCAs in patients established on guanfacine therapy for hypertension when possible; it is not clear the effect the combination may have when used in patients treated with guanfacine for attention-deficit, but other options to TCAs should be considered. Increased dosages of guanfacine may be required to control blood pressure in patients who are receiving TCAs concurrently. In addition, concurrent TCAs may enhance the potential for serious rebound hypertension following guanfacine discontinuation, regardless of the indication for treatment. If guanfacine therapy is withdrawn, guanfacine should be tapered gradually and the patient should be monitored for potential hypertension.
Amlodipine; Celecoxib: (Moderate) NSAIDs may decrease the effect of antihypertensive agents through various mechanisms, including renal and peripheral vasoactive pathways.
Amobarbital: (Major) Monitor patients for guanfacine efficacy and for excess sedation during amobarbital coadministration. Guanfacine plasma concentrations can be reduced by amobarbital, by induction of CYP3A4 metabolism. Immediate-release guanfacine may require more frequent dosing to achieve or maintain desired hypotensive response; if it is discontinued, carefully taper the dose to prevent rebound hypertension. The extended-release guanfacine dose for attention deficit hyperactivity disorder (ADHD) may need to be doubled, per FDA-approved labeling; any dose change should occur over 1 to 2 weeks (e.g., dose increase when adding, or decrease when discontinuing, an enzyme inducer). Guanfacine is primarily metabolized by CYP3A4. Barbiturates (e.g., phenobarbital, primidone) are strong CYP3A4 inducers. Guanfacine plasma concentrations and elimination half-life were significantly reduced with coadministration of an enzyme inducer (e.g., phenobarbital, primidone, phenytoin, fosphenytoin) in two patients with renal impairment. Additionally, guanfacine has been associated with sedative effects and can potentiate the actions of CNS depressants, including barbiturates.
Amoxapine: (Major) Cyclic antidepressants like amoxapine can inhibit the hypotensive effects of guanfacine, causing an increase in blood pressure if given concomitantly. Increased dosages of guanfacine may be required in patients who are receiving amoxapine concurrently. In addition, concurrent amoxapine use may enhance the potential for rebound hypertension following guanfacine discontinuation. If guanfacine is withdrawn in the presence of amoxapine or other cyclic antidepressants, guanfacine should be tapered gradually and the patient should be monitored for potential hypertension.
Amoxicillin; Clarithromycin; Omeprazole: (Major) Clarithromycin may significantly increase guanfacine plasma concentrations. FDA-approved labeling for extended-release (ER) guanfacine recommends that, if these agents are taken together, the guanfacine dosage should be decreased to half of the recommended dose. Specific recommendations for immediate-release (IR) guanfacine are not available. Monitor patients closely for alpha-adrenergic effects including hypotension, drowsiness, lethargy, and bradycardia. If clarithromycin is discontinued, the guanfacine ER dosage should be increased back to the recommended dose. Guanfacine is primarily metabolized by CYP3A4, and clarithromycin is a strong CYP3A4 inhibitor.
Amphetamines: (Moderate) Sympathomimetic agents, such as amphetamines, may increase blood pressure and reduce the antihypertensive effects of antihypertensive agents, such as guanfacine. Monitor blood pressure and heart rate periodically when prescribed together. Guanfacine may be used adjunctively to psychostimulants such as amphetamines in the treatment of attention deficit hyperactivity disorder (ADHD). Pharmacokinetic studies reveal that guanfacine does not influence lisdexamfetamine pharmacokinetics and lisdexamfetamine does not affect guanfacine pharmacokinetics. No dosage adjustments are required when guanfacine and amphetamines are used together for ADHD. Monitor heart rate, blood pressure and for sedation during ADHD treatment.
Apalutamide: (Major) A dose increase of extended-release (ER) guanfacine should be considered if coadministration with apalutamide is necessary. Consider doubling the recommended dose of guanfacine if therapy is added to a patient already taking apalutamide; increase the dose of guanfacine over 1 to 2 weeks if apalutamide therapy is added to a patient already taking guanfacine. Specific recommendations for immediate-release (IR) guanfacine are not available. Guanfacine is a CYP3A4 substrate and apalutamide is a strong CYP3A4 inducer. Coadministration with another strong CYP3A4 inducer decreased guanfacine exposure by 70%.
Apomorphine: (Moderate) Use of central-acting adrenergic agents and apomorphine together can increase the hypotensive effects of apomorphine. Monitor blood pressure regularly during use of this combination.
Apraclonidine: (Minor) Alpha blockers as a class may reduce heart rate and blood pressure. While no specific drug interactions have been identified with systemic agents and apraclonidine during clinical trials, it is theoretically possible that additive blood pressure reductions could occur when apraclonidine is combined with the use of antihypertensive agents. Patients using cardiovascular drugs concomitantly with apraclonidine should have their pulse and blood pressure monitored periodically.
Aprepitant, Fosaprepitant: (Major) Aprepitant may significantly increase guanfacine plasma concentrations when used as a 3-day oral regimen (125mg/80mg/80mg) for chemotherapy-induced nausea and vomiting (CINV). FDA-approved labeling for extended-release (ER) guanfacine recommends that, if these agents are taken together with this regimen, the guanfacine dosage should be decreased to half of the recommended dose. Specific recommendations for immediate-release (IR) guanfacine are not available. Monitor patients closely for alpha-adrenergic effects including hypotension, drowsiness, lethargy, and bradycardia. Upon aprepitant, fosaprepitant discontinuation, the guanfacine ER dosage should be increased back to the recommended dose. Guanfacine is primarily metabolized by CYP3A4. Aprepitant, when administered as a 3-day oral regimen (125 mg/80 mg/80 mg), is a moderate CYP3A4 inhibitor and weak inducer. Plasma concentrations of another CYP3A4 substrate, midazolam, increased from 1.25-fold to 3.3-fold after administration of a 3 to 5-day oral aprepitant regimen; midazolam concentrations were subsequently decreased by 19% and 4% on days 8 and 15, respectively. However, as a single 125 mg or 40 mg oral dose, the inhibitory effect of aprepitant on CYP3A4 is weak, with the AUC of midazolam increased by 1.5-fold and 1.2-fold, respectively. After administration, IV fosaprepitant (single dose) is rapidly converted to aprepitant and shares some of the same drug interactions but it only weakly inhibits CYP3A4 for a duration of 2 days, increasing the midazolam AUC by approximately 1.8-fold on day 1 with no effect by day 4. Less than a 2-fold increase in the midazolam AUC is not considered clinically important. There is no evidence of CYP3A4 induction with fosaprepitant.
Aripiprazole: (Minor) Due to aripiprazole's antagonism at alpha 1-adrenergic receptors, the drug may enhance the hypotensive effects of alpha-blockers and other antihypertensive agents.
Articaine; Epinephrine: (Moderate) Antihypertensives, including guanfacine, antagonize the vasopressor effects of parenteral epinephrine.
Asenapine: (Moderate) Secondary to alpha-blockade, asenapine can produce vasodilation that may result in additive effects during concurrent use of antihypertensive agents. The potential reduction in blood pressure can precipitate orthostatic hypotension and associated dizziness, tachycardia, and syncope. If concurrent use of asenapine and antihypertensive agents is necessary, patients should be counseled on measures to prevent orthostatic hypotension, such as sitting on the edge of the bed for several minutes prior to standing in the morning and rising slowly from a seated position. Close monitoring of blood pressure is recommended until the full effects of the combination therapy are known.
Aspirin, ASA; Butalbital; Caffeine: (Major) Monitor patients for guanfacine efficacy and for excess sedation during butalbital coadministration. Guanfacine plasma concentrations can be reduced by butalbital, by induction of CYP3A4 metabolism. Immediate-release guanfacine may require more frequent dosing to achieve or maintain desired hypotensive response; if it is discontinued, carefully taper the dose to prevent rebound hypertension. The extended-release guanfacine dose for attention deficit hyperactivity disorder (ADHD) may need to be doubled, per FDA-approved labeling; any dose change should occur over 1 to 2 weeks (e.g., dose increase when adding, or decrease when discontinuing, an enzyme inducer). Guanfacine is primarily metabolized by CYP3A4. Barbiturates (e.g., phenobarbital, primidone) are strong CYP3A4 inducers. Guanfacine plasma concentrations and elimination half-life were significantly reduced with coadministration of an enzyme inducer (e.g., phenobarbital, primidone, phenytoin, fosphenytoin) in two patients with renal impairment. Additionally, guanfacine has been associated with sedative effects and can potentiate the actions of CNS depressants, including barbiturates.
Atazanavir: (Major) Atazanavir may significantly increase guanfacine plasma concentrations. FDA-approved labeling for extended-release (ER) guanfacine recommends that, if these agents are taken together, the guanfacine dosage should be decreased to half of the recommended dose. Specific recommendations for immediate-release (IR) guanfacine are not available. Monitor patients closely for alpha-adrenergic effects including hypotension, drowsiness, lethargy, and bradycardia. If atazanavir is discontinued, the guanfacine ER dosage should be increased back to the recommended dose. Guanfacine is primarily metabolized by CYP3A4, and atazanavir is a strong CYP3A4 inhibitor.
Atazanavir; Cobicistat: (Major) Atazanavir may significantly increase guanfacine plasma concentrations. FDA-approved labeling for extended-release (ER) guanfacine recommends that, if these agents are taken together, the guanfacine dosage should be decreased to half of the recommended dose. Specific recommendations for immediate-release (IR) guanfacine are not available. Monitor patients closely for alpha-adrenergic effects including hypotension, drowsiness, lethargy, and bradycardia. If atazanavir is discontinued, the guanfacine ER dosage should be increased back to the recommended dose. Guanfacine is primarily metabolized by CYP3A4, and atazanavir is a strong CYP3A4 inhibitor. (Major) If coadministration of cobicistat with extended-release (ER) guanfacine is necessary, reduce the guanfacine dosage to half of the recommended dose. Specific recommendations for immediate-release (IR) guanfacine are not available. Monitor patients closely for alpha-adrenergic effects including hypotension, drowsiness, lethargy, and bradycardia. If cobicistat is discontinued, the guanfacine ER dosage should be increased back to the recommended dose. Guanfacine is a CYP3A4 substrate and cobicistat is a strong CYP3A4 inhibitor. Cobicistat may significantly increase guanfacine plasma concentrations.
Atenolol: (Moderate) Guanfacine can have additive effects when administered with other antihypertensive agents, including beta-blockers. These effects can be used to therapeutic advantage, but dosage adjustments may be necessary.
Atenolol; Chlorthalidone: (Moderate) Guanfacine can have additive effects when administered with other antihypertensive agents, including beta-blockers. These effects can be used to therapeutic advantage, but dosage adjustments may be necessary.
Atropine; Difenoxin: (Moderate) Concurrent administration of diphenoxylate/difenoxin with guanfacine can potentiate the CNS-depressant effects of diphenoxylate/difenoxin. Use caution during coadministration.
Baclofen: (Moderate) Baclofen has been associated with hypotension. Concurrent use with baclofen and antihypertensive agents may result in additive hypotension. Dosage adjustments of the antihypertensive medication may be required.
Benzodiazepines: (Moderate) Guanfacine has been associated with sedative effects and can potentiate the actions of other CNS depressants including benzodiazepines.
Berotralstat: (Major) Decrease the dose of extended-release guanfacine by 50% if coadministration with berotralstat is necessary; if berotralstat is discontinued, the dose of extended-release guanfacine may be increased to the recommended level. Monitor patients closely for adverse effects including hypotension, drowsiness, lethargy, and bradycardia. Recommendations for immediate-release guanfacine are not available. Guanfacine is a CYP3A substrate and berotralstat is a moderate CYP3A inhibitor.
Beta-blockers: (Moderate) Guanfacine can have additive effects when administered with other antihypertensive agents, including beta-blockers. These effects can be used to therapeutic advantage, but dosage adjustments may be necessary.
Betaxolol: (Moderate) Guanfacine can have additive effects when administered with other antihypertensive agents, including beta-blockers. These effects can be used to therapeutic advantage, but dosage adjustments may be necessary.
Bexarotene: (Major) Bexarotene may significantly decrease guanfacine plasma concentrations. FDA-approved labeling for extended-release (ER) guanfacine recommends that, if these agents are taken together, doubling the recommended dose of guanfacine should be considered; if bexarotene is added in a patient already receiving guanfacine, this escalation should occur over 1 to 2 weeks. If bexarotene is discontinued, decrease the guanfacine ER dosage back to the recommended dose over 1 to 2 weeks. Specific recommendations for immediate-release (IR) guanfacine are not available. Guanfacine is primarily metabolized by CYP3A4, and bexarotene is a moderate CYP3A4 inducer in vitro.
Bisoprolol: (Moderate) Guanfacine can have additive effects when administered with other antihypertensive agents, including beta-blockers. These effects can be used to therapeutic advantage, but dosage adjustments may be necessary.
Bisoprolol; Hydrochlorothiazide, HCTZ: (Moderate) Guanfacine can have additive effects when administered with other antihypertensive agents, including beta-blockers. These effects can be used to therapeutic advantage, but dosage adjustments may be necessary.
Bortezomib: (Moderate) Patients on antihypertensive agents receiving bortezomib treatment may require close monitoring of their blood pressure and dosage adjustment of their medication. During clinical trials of bortezomib, hypotension was reported in roughly 12 percent of patients.
Bosentan: (Major) Bosentan may significantly decrease guanfacine plasma concentrations. FDA-approved labeling for extended-release (ER) guanfacine recommends that, if these agents are taken together, doubling the recommended dose of guanfacine should be considered; if bosentan is added in a patient already receiving guanfacine, this escalation should occur over 1 to 2 weeks. If bosentan is discontinued, decrease the guanfacine ER dosage back to the recommended dose over 1 to 2 weeks. Although no specific interactions have been documented, bosentan has vasodilatory effects and may contribute additive hypotensive effects when given with a centrally-acting adrenergic agonist such as guanfacine. Specific recommendations for immediate-release (IR) guanfacine are not available. Guanfacine is primarily metabolized by CYP3A4, and bosentan is a moderate CYP3A4 inducer.
Brexpiprazole: (Moderate) Due to brexpiprazole's antagonism at alpha 1-adrenergic receptors, the drug may enhance the hypotensive effects of alpha-blockers and other antihypertensive agents.
Brimonidine; Timolol: (Moderate) Guanfacine can have additive effects when administered with other antihypertensive agents, including beta-blockers. These effects can be used to therapeutic advantage, but dosage adjustments may be necessary.
Bupivacaine; Epinephrine: (Moderate) Antihypertensives, including guanfacine, antagonize the vasopressor effects of parenteral epinephrine.
Bupivacaine; Meloxicam: (Moderate) NSAIDs may decrease the effect of antihypertensive agents through various mechanisms, including renal and peripheral vasoactive pathways.
Bupropion: (Moderate) There is one case report that describes a grand mal seizure that occurred in a child of 10 years of age receiving guanfacine and bupropion concurrently. It is not possible, based on this limited report, to determine if guanfacine was a contributor to the event. Causality has not been established.
Bupropion; Naltrexone: (Moderate) There is one case report that describes a grand mal seizure that occurred in a child of 10 years of age receiving guanfacine and bupropion concurrently. It is not possible, based on this limited report, to determine if guanfacine was a contributor to the event. Causality has not been established.
Butabarbital: (Major) Monitor patients for guanfacine efficacy and for excess sedation during butabarbital coadministration. Guanfacine plasma concentrations can be reduced by butabarbital, by induction of CYP3A4 metabolism. Immediate-release guanfacine may require more frequent dosing to achieve or maintain desired hypotensive response; if it is discontinued, carefully taper the dose to prevent rebound hypertension. The extended-release guanfacine dose for attention deficit hyperactivity disorder (ADHD) may need to be doubled, per FDA-approved labeling; any dose change should occur over 1 to 2 weeks (e.g., dose increase when adding, or decrease when discontinuing, an enzyme inducer). Guanfacine is primarily metabolized by CYP3A4. Barbiturates (e.g., phenobarbital, primidone) are strong CYP3A4 inducers. Guanfacine plasma concentrations and elimination half-life were significantly reduced with coadministration of an enzyme inducer (e.g., phenobarbital, primidone, phenytoin, fosphenytoin) in two patients with renal impairment. Additionally, guanfacine has been associated with sedative effects and can potentiate the actions of CNS depressants, including barbiturates.
Butalbital; Acetaminophen: (Major) Monitor patients for guanfacine efficacy and for excess sedation during butalbital coadministration. Guanfacine plasma concentrations can be reduced by butalbital, by induction of CYP3A4 metabolism. Immediate-release guanfacine may require more frequent dosing to achieve or maintain desired hypotensive response; if it is discontinued, carefully taper the dose to prevent rebound hypertension. The extended-release guanfacine dose for attention deficit hyperactivity disorder (ADHD) may need to be doubled, per FDA-approved labeling; any dose change should occur over 1 to 2 weeks (e.g., dose increase when adding, or decrease when discontinuing, an enzyme inducer). Guanfacine is primarily metabolized by CYP3A4. Barbiturates (e.g., phenobarbital, primidone) are strong CYP3A4 inducers. Guanfacine plasma concentrations and elimination half-life were significantly reduced with coadministration of an enzyme inducer (e.g., phenobarbital, primidone, phenytoin, fosphenytoin) in two patients with renal impairment. Additionally, guanfacine has been associated with sedative effects and can potentiate the actions of CNS depressants, including barbiturates.
Butalbital; Acetaminophen; Caffeine: (Major) Monitor patients for guanfacine efficacy and for excess sedation during butalbital coadministration. Guanfacine plasma concentrations can be reduced by butalbital, by induction of CYP3A4 metabolism. Immediate-release guanfacine may require more frequent dosing to achieve or maintain desired hypotensive response; if it is discontinued, carefully taper the dose to prevent rebound hypertension. The extended-release guanfacine dose for attention deficit hyperactivity disorder (ADHD) may need to be doubled, per FDA-approved labeling; any dose change should occur over 1 to 2 weeks (e.g., dose increase when adding, or decrease when discontinuing, an enzyme inducer). Guanfacine is primarily metabolized by CYP3A4. Barbiturates (e.g., phenobarbital, primidone) are strong CYP3A4 inducers. Guanfacine plasma concentrations and elimination half-life were significantly reduced with coadministration of an enzyme inducer (e.g., phenobarbital, primidone, phenytoin, fosphenytoin) in two patients with renal impairment. Additionally, guanfacine has been associated with sedative effects and can potentiate the actions of CNS depressants, including barbiturates.
Butalbital; Acetaminophen; Caffeine; Codeine: (Major) Monitor patients for guanfacine efficacy and for excess sedation during butalbital coadministration. Guanfacine plasma concentrations can be reduced by butalbital, by induction of CYP3A4 metabolism. Immediate-release guanfacine may require more frequent dosing to achieve or maintain desired hypotensive response; if it is discontinued, carefully taper the dose to prevent rebound hypertension. The extended-release guanfacine dose for attention deficit hyperactivity disorder (ADHD) may need to be doubled, per FDA-approved labeling; any dose change should occur over 1 to 2 weeks (e.g., dose increase when adding, or decrease when discontinuing, an enzyme inducer). Guanfacine is primarily metabolized by CYP3A4. Barbiturates (e.g., phenobarbital, primidone) are strong CYP3A4 inducers. Guanfacine plasma concentrations and elimination half-life were significantly reduced with coadministration of an enzyme inducer (e.g., phenobarbital, primidone, phenytoin, fosphenytoin) in two patients with renal impairment. Additionally, guanfacine has been associated with sedative effects and can potentiate the actions of CNS depressants, including barbiturates.
Butalbital; Aspirin; Caffeine; Codeine: (Major) Monitor patients for guanfacine efficacy and for excess sedation during butalbital coadministration. Guanfacine plasma concentrations can be reduced by butalbital, by induction of CYP3A4 metabolism. Immediate-release guanfacine may require more frequent dosing to achieve or maintain desired hypotensive response; if it is discontinued, carefully taper the dose to prevent rebound hypertension. The extended-release guanfacine dose for attention deficit hyperactivity disorder (ADHD) may need to be doubled, per FDA-approved labeling; any dose change should occur over 1 to 2 weeks (e.g., dose increase when adding, or decrease when discontinuing, an enzyme inducer). Guanfacine is primarily metabolized by CYP3A4. Barbiturates (e.g., phenobarbital, primidone) are strong CYP3A4 inducers. Guanfacine plasma concentrations and elimination half-life were significantly reduced with coadministration of an enzyme inducer (e.g., phenobarbital, primidone, phenytoin, fosphenytoin) in two patients with renal impairment. Additionally, guanfacine has been associated with sedative effects and can potentiate the actions of CNS depressants, including barbiturates.
Cabergoline: (Moderate) Cabergoline should be used cautiously with antihypertensive agents, including guanfacine. Cabergoline has been associated with hypotension. Initial doses of cabergoline higher than 1 mg may produce orthostatic hypotension. It may be advisable to monitor blood pressure.
Cannabidiol: (Moderate) Monitor for excessive sedation and somnolence during coadministration of cannabidiol and central-acting adrenergic agents. CNS depressants can potentiate the effects of cannabidiol.
Carbamazepine: (Major) Carbamazepine can significantly decrease guanfacine plasma concentrations; guanfacine dosage adjustment is recommended. FDA-approved labeling for extended-release (ER) guanfacine recommends that, if these agents are taken together, doubling the recommended dose of guanfacine should be considered. If carbamazepine is added in a patient already receiving guanfacine, this escalation should occur over 1 to 2 weeks. If carbamazepine is discontinued, decrease the guanfacine ER dosage back to the recommended dose over 1 to 2 weeks. Specific recommendations for immediate-release (IR) guanfacine are not available. Guanfacine is primarily metabolized by CYP3A4, and carbamazepine is a strong CYP3A4 inducer.
Carbidopa; Levodopa: (Moderate) Monitor blood pressure during concomitant use of levodopa and central-acting adrenergic agents due to risk for additive hypotension.
Carbidopa; Levodopa; Entacapone: (Moderate) Monitor blood pressure during concomitant use of levodopa and central-acting adrenergic agents due to risk for additive hypotension.
Carbonic anhydrase inhibitors: (Moderate) The concomitant administration of diuretics with other antihypertensive agents can result in additive hypotensive effects. This interaction can be therapeutically advantageous, but dosages must be adjusted accordingly.
Cariprazine: (Moderate) Orthostatic vital signs should be monitored in patients who are at risk for hypotension, such as those receiving cariprazine in combination with antihypertensive agents. Atypical antipsychotics may cause orthostatic hypotension and syncope, most commonly during treatment initiation and dosage increases. Patients should be informed about measures to prevent orthostatic hypotension, such as sitting on the edge of the bed for several minutes prior to standing in the morning, or rising slowly from a seated position. Consider a cariprazine dose reduction if hypotension occurs.
Carteolol: (Moderate) Guanfacine can have additive effects when administered with other antihypertensive agents, including beta-blockers. These effects can be used to therapeutic advantage, but dosage adjustments may be necessary.
Carvedilol: (Moderate) Guanfacine can have additive effects when administered with other antihypertensive agents, including beta-blockers. These effects can be used to therapeutic advantage, but dosage adjustments may be necessary.
Celecoxib: (Moderate) NSAIDs may decrease the effect of antihypertensive agents through various mechanisms, including renal and peripheral vasoactive pathways.
Celecoxib; Tramadol: (Moderate) NSAIDs may decrease the effect of antihypertensive agents through various mechanisms, including renal and peripheral vasoactive pathways.
Cenobamate: (Major) Monitor for excessive sedation and somnolence during coadministration of cenobamate and guanfacine. Concurrent use may result in additive CNS depression. Additionally, a dose increase of extended-release (ER) guanfacine should be considered if coadministration with cenobamate is necessary. Consider doubling the recommended dose of guanfacine if therapy is added to a patient already taking cenobamate; increase the dose of guanfacine over 1 to 2 weeks if cenobamate therapy is added to a patient already taking guanfacine. Specific recommendations for immediate-release (IR) guanfacine are not available. Guanfacine is a CYP3A4 substrate and cenobamate is a moderate CYP3A4 inducer.
Ceritinib: (Major) If coadministration of ceritinib with extended-release (ER) guanfacine is necessary, reduce the guanfacine dosage to half of the recommended dose. Specific recommendations for immediate-release (IR) guanfacine are not available. Monitor patients closely for alpha-adrenergic effects including hypotension, drowsiness, lethargy, and bradycardia. If ceritinib is discontinued, the guanfacine ER dosage should be increased back to the recommended dose. Guanfacine is a CYP3A4 substrate and ceritinib is a strong CYP3A4 inhibitor. Ceritinib may significantly increase guanfacine plasma concentrations.
Cetirizine: (Moderate) Concurrent use of cetirizine/levocetirizine with guanfacine should generally be avoided. Coadministration may increase the risk of CNS depressant-related side effects. If concurrent use is necessary, monitor for excessive sedation and somnolence.
Cetirizine; Pseudoephedrine: (Moderate) Concurrent use of cetirizine/levocetirizine with guanfacine should generally be avoided. Coadministration may increase the risk of CNS depressant-related side effects. If concurrent use is necessary, monitor for excessive sedation and somnolence.
Chloramphenicol: (Major) Chloramphenicol may significantly increase guanfacine plasma concentrations. FDA-approved labeling for extended-release (ER) guanfacine recommends that, if these agents are taken together, the guanfacine dosage should be decreased to half of the recommended dose. Specific recommendations for immediate-release (IR) guanfacine are not available. Monitor patients closely for alpha-adrenergic effects including hypotension, drowsiness, lethargy, and bradycardia. If chloramphenicol is discontinued, the guanfacine ER dosage should be increased back to the recommended dose. Guanfacine is primarily metabolized by CYP3A4, and chloramphenicol is a strong CYP3A4 inhibitor.
Chlordiazepoxide: (Moderate) Guanfacine has been associated with sedative effects and can potentiate the actions of other CNS depressants including benzodiazepines.
Chlordiazepoxide; Amitriptyline: (Major) Tricyclic antidepressants (TCAs) can inhibit the hypotensive effects of guanfacine, causing an increase in blood pressure if given concomitantly. Consider alternatives to TCAs in patients established on guanfacine therapy for hypertension when possible; it is not clear the effect the combination may have when used in patients treated with guanfacine for attention-deficit, but other options to TCAs should be considered. Increased dosages of guanfacine may be required to control blood pressure in patients who are receiving TCAs concurrently. In addition, concurrent TCAs may enhance the potential for serious rebound hypertension following guanfacine discontinuation, regardless of the indication for treatment. If guanfacine therapy is withdrawn, guanfacine should be tapered gradually and the patient should be monitored for potential hypertension. (Moderate) Guanfacine has been associated with sedative effects and can potentiate the actions of other CNS depressants including benzodiazepines.
Chlordiazepoxide; Clidinium: (Moderate) Guanfacine has been associated with sedative effects and can potentiate the actions of other CNS depressants including benzodiazepines.
Chloroprocaine: (Moderate) Local anesthetics may cause additive hypotension in combination with antihypertensive agents.
Chlorpheniramine; Ibuprofen; Pseudoephedrine: (Moderate) NSAIDs may decrease the effect of antihypertensive agents through various mechanisms, including renal and peripheral vasoactive pathways.
Chlorpromazine: (Moderate) Monitor blood pressure and for unusual drowsiness or excessive sedation during concomitant central-acting adrenergic agent and phenothiazine use. Concomitant use increases the risk for additive hypotension and CNS depression.
Ciprofloxacin: (Major) Ciprofloxacin may significantly increase guanfacine plasma concentrations. FDA-approved labeling for extended-release (ER) guanfacine recommends decreasing the guanfacine dosage to half the recommended dose if these agents are taken together. Specific recommendations for immediate-release (IR) guanfacine are not available. Monitor patients closely for alpha-adrenergic effects including hypotension, drowsiness, lethargy, and bradycardia. Upon ciprofloxacin discontinuation, the guanfacine ER dosage should be increased back to the recommended dose. Guanfacine is primarily metabolized by CYP3A4, and ciprofloxacin is a moderate CYP3A4 inhibitor.
Clarithromycin: (Major) Clarithromycin may significantly increase guanfacine plasma concentrations. FDA-approved labeling for extended-release (ER) guanfacine recommends that, if these agents are taken together, the guanfacine dosage should be decreased to half of the recommended dose. Specific recommendations for immediate-release (IR) guanfacine are not available. Monitor patients closely for alpha-adrenergic effects including hypotension, drowsiness, lethargy, and bradycardia. If clarithromycin is discontinued, the guanfacine ER dosage should be increased back to the recommended dose. Guanfacine is primarily metabolized by CYP3A4, and clarithromycin is a strong CYP3A4 inhibitor.
Clomipramine: (Major) Tricyclic antidepressants (TCAs) can inhibit the hypotensive effects of guanfacine, causing an increase in blood pressure if given concomitantly. Consider alternatives to TCAs in patients established on guanfacine therapy for hypertension when possible; it is not clear the effect the combination may have when used in patients treated with guanfacine for attention-deficit, but other options to TCAs should be considered. Increased dosages of guanfacine may be required to control blood pressure in patients who are receiving TCAs concurrently. In addition, concurrent TCAs may enhance the potential for serious rebound hypertension following guanfacine discontinuation, regardless of the indication for treatment. If guanfacine therapy is withdrawn, guanfacine should be tapered gradually and the patient should be monitored for potential hypertension.
Clonazepam: (Moderate) Guanfacine has been associated with sedative effects and can potentiate the actions of other CNS depressants including benzodiazepines.
Clorazepate: (Moderate) Guanfacine has been associated with sedative effects and can potentiate the actions of other CNS depressants including benzodiazepines.
Clozapine: (Moderate) Clozapine used concomitantly with the antihypertensive agents can increase the risk and severity of hypotension by potentiating the effect of the antihypertensive drug.
Cobicistat: (Major) If coadministration of cobicistat with extended-release (ER) guanfacine is necessary, reduce the guanfacine dosage to half of the recommended dose. Specific recommendations for immediate-release (IR) guanfacine are not available. Monitor patients closely for alpha-adrenergic effects including hypotension, drowsiness, lethargy, and bradycardia. If cobicistat is discontinued, the guanfacine ER dosage should be increased back to the recommended dose. Guanfacine is a CYP3A4 substrate and cobicistat is a strong CYP3A4 inhibitor. Cobicistat may significantly increase guanfacine plasma concentrations.
Cocaine: (Major) Use of cocaine with antihypertensive agents may increase the antihypertensive effects of the antihypertensive medications or may potentiate cocaine-induced sympathetic stimulation.
Codeine; Phenylephrine; Promethazine: (Moderate) Monitor blood pressure and for unusual drowsiness or excessive sedation during concomitant central-acting adrenergic agent and phenothiazine use. Concomitant use increases the risk for additive hypotension and CNS depression.
Codeine; Promethazine: (Moderate) Monitor blood pressure and for unusual drowsiness or excessive sedation during concomitant central-acting adrenergic agent and phenothiazine use. Concomitant use increases the risk for additive hypotension and CNS depression.
Co-Enzyme Q10, Ubiquinone: (Moderate) Monitor blood pressure during concomitant co-enzyme Q10 (ubiquinone) and central-acting adrenergic agents use. Concomitant use may result in additive hypotension.
COMT inhibitors: (Moderate) COMT inhibitors should be given cautiously with other agents that cause CNS depression, including guanfacine, due to the possibility of additive sedation or hypotension. COMT inhibitors have also been associated with sudden sleep onset during activities of daily living such as driving, which has resulted in accidents in some cases. Prescribers should re-assess patients for drowsiness or sleepiness regularly throughout treatment, especially since events may occur well after the start of treatment. Patients should be advised to avoid driving or other tasks requiring mental alertness until they know how the combination affects them.
Conivaptan: (Major) Decrease the dose of extended-release guanfacine by 50% if coadministration with conivaptan is necessary; if conivaptan is discontinued, the dose of extended-release guanfacine may be increased to the recommended level. Monitor patients closely for adverse effects including hypotension, drowsiness, lethargy, and bradycardia. Recommendations for immediate-release guanfacine are not available. Guanfacine is a CYP3A substrate and conivaptan is a moderate CYP3A inhibitor.
Crizotinib: (Major) Reduce the extended-release (ER) guanfacine dosage to half of the recommended dose if coadministration with crizotinib is necessary. Specific recommendations for immediate-release (IR) guanfacine are not available. Monitor patients closely for alpha-adrenergic effects including hypotension, drowsiness, lethargy, and bradycardia. If crizotinib is discontinued, the guanfacine ER dosage should be increased back to the recommended dose. Guanfacine is a CYP3A4 substrate and crizotinib is a moderate CYP3A inhibitor. Crizotinib may significantly increase guanfacine plasma concentrations.
Cyclosporine: (Major) Cyclosporine may significantly increase guanfacine plasma concentrations. FDA-approved labeling for extended-release (ER) guanfacine recommends that, if these agents are taken together, the guanfacine dosage should be decreased to half of the recommended dose. Specific recommendations for immediate-release (IR) guanfacine are not available. Monitor patients closely for alpha-adrenergic effects including hypotension, drowsiness, lethargy, and bradycardia. Upon cyclosporine discontinuation, the guanfacine ER dosage should be increased back to the recommended dose. Guanfacine is primarily metabolized by CYP3A4, and cyclosporine is a moderate CYP3A4 inhibitor.
Darunavir: (Major) Darunavir may significantly increase guanfacine plasma concentrations. FDA-approved labeling for extended-release (ER) guanfacine recommends that, if these agents are taken together, the guanfacine dosage should be decreased to half of the recommended dose. Specific recommendations for immediate-release (IR) guanfacine are not available. Monitor patients closely for alpha-adrenergic effects including hypotension, drowsiness, lethargy, and bradycardia. If darunavir is discontinued, the guanfacine ER dosage should be increased back to the recommended dose. Guanfacine is primarily metabolized by CYP3A4. Darunavir is a strong CYP3A4 inhibitor, and when administered with ritonavir, potent inhibition is expected.
Darunavir; Cobicistat: (Major) Darunavir may significantly increase guanfacine plasma concentrations. FDA-approved labeling for extended-release (ER) guanfacine recommends that, if these agents are taken together, the guanfacine dosage should be decreased to half of the recommended dose. Specific recommendations for immediate-release (IR) guanfacine are not available. Monitor patients closely for alpha-adrenergic effects including hypotension, drowsiness, lethargy, and bradycardia. If darunavir is discontinued, the guanfacine ER dosage should be increased back to the recommended dose. Guanfacine is primarily metabolized by CYP3A4. Darunavir is a strong CYP3A4 inhibitor, and when administered with ritonavir, potent inhibition is expected. (Major) If coadministration of cobicistat with extended-release (ER) guanfacine is necessary, reduce the guanfacine dosage to half of the recommended dose. Specific recommendations for immediate-release (IR) guanfacine are not available. Monitor patients closely for alpha-adrenergic effects including hypotension, drowsiness, lethargy, and bradycardia. If cobicistat is discontinued, the guanfacine ER dosage should be increased back to the recommended dose. Guanfacine is a CYP3A4 substrate and cobicistat is a strong CYP3A4 inhibitor. Cobicistat may significantly increase guanfacine plasma concentrations.
Darunavir; Cobicistat; Emtricitabine; Tenofovir alafenamide: (Major) Darunavir may significantly increase guanfacine plasma concentrations. FDA-approved labeling for extended-release (ER) guanfacine recommends that, if these agents are taken together, the guanfacine dosage should be decreased to half of the recommended dose. Specific recommendations for immediate-release (IR) guanfacine are not available. Monitor patients closely for alpha-adrenergic effects including hypotension, drowsiness, lethargy, and bradycardia. If darunavir is discontinued, the guanfacine ER dosage should be increased back to the recommended dose. Guanfacine is primarily metabolized by CYP3A4. Darunavir is a strong CYP3A4 inhibitor, and when administered with ritonavir, potent inhibition is expected. (Major) If coadministration of cobicistat with extended-release (ER) guanfacine is necessary, reduce the guanfacine dosage to half of the recommended dose. Specific recommendations for immediate-release (IR) guanfacine are not available. Monitor patients closely for alpha-adrenergic effects including hypotension, drowsiness, lethargy, and bradycardia. If cobicistat is discontinued, the guanfacine ER dosage should be increased back to the recommended dose. Guanfacine is a CYP3A4 substrate and cobicistat is a strong CYP3A4 inhibitor. Cobicistat may significantly increase guanfacine plasma concentrations.
Deferasirox: (Major) Deferasirox may significantly decrease guanfacine plasma concentrations. FDA-approved labeling for extended-release (ER) guanfacine recommends that, if these agents are taken together, doubling the recommended dose of guanfacine should be considered; if deferasirox is added in a patient already receiving guanfacine, this escalation should occur over 1 to 2 weeks. If deferasirox is discontinued, decrease the guanfacine ER dosage back to the recommended dose over 1 to 2 weeks. Specific recommendations for immediate-release (IR) guanfacine are not available. Guanfacine is primarily metabolized by CYP3A4, and deferasirox is a moderate CYP3A4 inducer.
Delavirdine: (Major) Delavirdine may significantly increase guanfacine plasma concentrations. FDA-approved labeling for extended-release (ER) guanfacine recommends that, if these agents are taken together, the guanfacine dosage should be decreased to half of the recommended dose. Specific recommendations for immediate-release (IR) guanfacine are not available. Monitor patients closely for alpha-adrenergic effects including hypotension, drowsiness, lethargy, and bradycardia. If delavirdine is discontinued, the guanfacine ER dosage should be increased back to the recommended dose. Guanfacine is primarily metabolized by CYP3A4, and delavirdine is a strong CYP3A4 inhibitor.
Desipramine: (Major) Tricyclic antidepressants (TCAs) can inhibit the hypotensive effects of guanfacine, causing an increase in blood pressure if given concomitantly. Consider alternatives to TCAs in patients established on guanfacine therapy for hypertension when possible; it is not clear the effect the combination may have when used in patients treated with guanfacine for attention-deficit, but other options to TCAs should be considered. Increased dosages of guanfacine may be required to control blood pressure in patients who are receiving TCAs concurrently. In addition, concurrent TCAs may enhance the potential for serious rebound hypertension following guanfacine discontinuation, regardless of the indication for treatment. If guanfacine therapy is withdrawn, guanfacine should be tapered gradually and the patient should be monitored for potential hypertension.
Dextromethorphan; Bupropion: (Moderate) There is one case report that describes a grand mal seizure that occurred in a child of 10 years of age receiving guanfacine and bupropion concurrently. It is not possible, based on this limited report, to determine if guanfacine was a contributor to the event. Causality has not been established.
Dextromethorphan; Quinidine: (Moderate) Quinidine can decrease blood pressure and should be used cautiously in patients receiving antihypertensive agents due to the potential for additive hypotension.
Diazepam: (Moderate) Guanfacine has been associated with sedative effects and can potentiate the actions of other CNS depressants including benzodiazepines.
Diazoxide: (Moderate) Additive hypotensive effects can occur with the concomitant administration of diazoxide with other antihypertensive agents. This interaction can be therapeutically advantageous, but dosages must be adjusted accordingly. The manufacturer advises that IV diazoxide should not be administered to patients within 6 hours of receiving other antihypertensive agents. Diazoxide can enhance the hyperglycemic, hyperuricemic and antihypertensive effects of thiazide diuretics.
Diclofenac: (Moderate) NSAIDs may decrease the effect of antihypertensive agents through various mechanisms, including renal and peripheral vasoactive pathways.
Diclofenac; Misoprostol: (Moderate) NSAIDs may decrease the effect of antihypertensive agents through various mechanisms, including renal and peripheral vasoactive pathways.
Difelikefalin: (Moderate) Monitor for dizziness, somnolence, mental status changes, and gait disturbances if concomitant use of difelikefalin with CNS depressants is necessary. Concomitant use may increase the risk for these adverse reactions.
Diflunisal: (Moderate) NSAIDs may decrease the effect of antihypertensive agents through various mechanisms, including renal and peripheral vasoactive pathways.
Diltiazem: (Major) Diltiazem may significantly increase guanfacine plasma concentrations. FDA-approved labeling for extended-release (ER) guanfacine recommends that, if these agents are taken together, the guanfacine dosage should be decreased to half of the recommended dose. Specific recommendations for immediate-release (IR) guanfacine are not available. Monitor patients closely for alpha-adrenergic effects including hypotension, drowsiness, lethargy, and bradycardia. Upon diltiazem discontinuation, the guanfacine ER dosage should be increased back to the recommended dose. Guanfacine is primarily metabolized by CYP3A4, and diltiazem is a moderate CYP3A4 inhibitor.
Diphenhydramine; Ibuprofen: (Moderate) NSAIDs may decrease the effect of antihypertensive agents through various mechanisms, including renal and peripheral vasoactive pathways.
Diphenhydramine; Naproxen: (Moderate) NSAIDs may decrease the effect of antihypertensive agents through various mechanisms, including renal and peripheral vasoactive pathways.
Diphenoxylate; Atropine: (Moderate) Concurrent administration of diphenoxylate/difenoxin with guanfacine can potentiate the CNS-depressant effects of diphenoxylate/difenoxin. Use caution during coadministration.
Dorzolamide; Timolol: (Moderate) Guanfacine can have additive effects when administered with other antihypertensive agents, including beta-blockers. These effects can be used to therapeutic advantage, but dosage adjustments may be necessary.
Doxepin: (Major) Tricyclic antidepressants (TCAs) can inhibit the hypotensive effects of guanfacine, causing an increase in blood pressure if given concomitantly. Consider alternatives to TCAs in patients established on guanfacine therapy for hypertension when possible; it is not clear the effect the combination may have when used in patients treated with guanfacine for attention-deficit, but other options to TCAs should be considered. Increased dosages of guanfacine may be required to control blood pressure in patients who are receiving TCAs concurrently. In addition, concurrent TCAs may enhance the potential for serious rebound hypertension following guanfacine discontinuation, regardless of the indication for treatment. If guanfacine therapy is withdrawn, guanfacine should be tapered gradually and the patient should be monitored for potential hypertension.
Dronedarone: (Major) Dronedarone may significantly increase guanfacine plasma concentrations. FDA-approved labeling for extended-release (ER) guanfacine recommends that, if these agents are taken together, the guanfacine dosage should be decreased to half of the recommended dose. Specific recommendations for immediate-release (IR) guanfacine are not available. Monitor patients closely for alpha-adrenergic effects including hypotension, drowsiness, lethargy, and bradycardia. Upon dronedarone discontinuation, the guanfacine ER dosage should be increased back to the recommended dose. Guanfacine is primarily metabolized by CYP3A4, and dronedarone is a moderate CYP3A4 inhibitor.
Duloxetine: (Moderate) Monitor blood pressure during concomitant duloxetine and central-acting adrenergic agent use. Concomitant use increases the risk for hypotension, including orthostatic hypotension and syncope. Consider reducing the duloxetine dose or discontinuing duloxetine if symptomatic orthostatic hypotension, falls, or syncope occur during treatment.
Duvelisib: (Major) Decrease the dose of extended-release guanfacine by 50% if coadministration with duvelisib is necessary; if duvelisib is discontinued, the dose of extended-release guanfacine may be increased to the recommended level. Monitor patients closely for alpha-adrenergic effects including hypotension, drowsiness, lethargy, and bradycardia. Recommendations for immediate-release guanfacine are not available. Guanfacine is a CYP3A substrate and duvelisib is a moderate CYP3A inhibitor.
Efavirenz: (Major) Efavirenz may significantly decrease guanfacine plasma concentrations. FDA-approved labeling for extended-release (ER) guanfacine recommends that, if these agents are taken together, doubling the recommended dose of guanfacine should be considered; if efavirenz is added in a patient already receiving guanfacine, this escalation should occur over 1 to 2 weeks. If efavirenz is discontinued, decrease the guanfacine ER dosage back to the recommended dose over 1 to 2 weeks. Specific recommendations for immediate-release (IR) guanfacine are not available. Guanfacine is primarily metabolized by CYP3A4, and efavirenz is a moderate CYP3A4 inducer.
Efavirenz; Emtricitabine; Tenofovir Disoproxil Fumarate: (Major) Efavirenz may significantly decrease guanfacine plasma concentrations. FDA-approved labeling for extended-release (ER) guanfacine recommends that, if these agents are taken together, doubling the recommended dose of guanfacine should be considered; if efavirenz is added in a patient already receiving guanfacine, this escalation should occur over 1 to 2 weeks. If efavirenz is discontinued, decrease the guanfacine ER dosage back to the recommended dose over 1 to 2 weeks. Specific recommendations for immediate-release (IR) guanfacine are not available. Guanfacine is primarily metabolized by CYP3A4, and efavirenz is a moderate CYP3A4 inducer.
Efavirenz; Lamivudine; Tenofovir Disoproxil Fumarate: (Major) Efavirenz may significantly decrease guanfacine plasma concentrations. FDA-approved labeling for extended-release (ER) guanfacine recommends that, if these agents are taken together, doubling the recommended dose of guanfacine should be considered; if efavirenz is added in a patient already receiving guanfacine, this escalation should occur over 1 to 2 weeks. If efavirenz is discontinued, decrease the guanfacine ER dosage back to the recommended dose over 1 to 2 weeks. Specific recommendations for immediate-release (IR) guanfacine are not available. Guanfacine is primarily metabolized by CYP3A4, and efavirenz is a moderate CYP3A4 inducer.
Elagolix: (Major) Elagolix may significantly decrease guanfacine plasma concentrations. FDA-approved labeling for extended-release (ER) guanfacine recommends that, if these agents are taken together, doubling the recommended dose of guanfacine should be considered; if elagolix is added in a patient already receiving guanfacine, this escalation should occur over 1 to 2 weeks. If elagolix is discontinued, decrease the guanfacine ER dosage back to the recommended dose over 1 to 2 weeks. Specific recommendations for immediate-release (IR) guanfacine are not available. Guanfacine is primarily metabolized by CYP3A4, and elagolix is a weak to moderate CYP3A4 inducer.
Elagolix; Estradiol; Norethindrone acetate: (Major) Elagolix may significantly decrease guanfacine plasma concentrations. FDA-approved labeling for extended-release (ER) guanfacine recommends that, if these agents are taken together, doubling the recommended dose of guanfacine should be considered; if elagolix is added in a patient already receiving guanfacine, this escalation should occur over 1 to 2 weeks. If elagolix is discontinued, decrease the guanfacine ER dosage back to the recommended dose over 1 to 2 weeks. Specific recommendations for immediate-release (IR) guanfacine are not available. Guanfacine is primarily metabolized by CYP3A4, and elagolix is a weak to moderate CYP3A4 inducer.
Elvitegravir; Cobicistat; Emtricitabine; Tenofovir Alafenamide: (Major) If coadministration of cobicistat with extended-release (ER) guanfacine is necessary, reduce the guanfacine dosage to half of the recommended dose. Specific recommendations for immediate-release (IR) guanfacine are not available. Monitor patients closely for alpha-adrenergic effects including hypotension, drowsiness, lethargy, and bradycardia. If cobicistat is discontinued, the guanfacine ER dosage should be increased back to the recommended dose. Guanfacine is a CYP3A4 substrate and cobicistat is a strong CYP3A4 inhibitor. Cobicistat may significantly increase guanfacine plasma concentrations.
Elvitegravir; Cobicistat; Emtricitabine; Tenofovir Disoproxil Fumarate: (Major) If coadministration of cobicistat with extended-release (ER) guanfacine is necessary, reduce the guanfacine dosage to half of the recommended dose. Specific recommendations for immediate-release (IR) guanfacine are not available. Monitor patients closely for alpha-adrenergic effects including hypotension, drowsiness, lethargy, and bradycardia. If cobicistat is discontinued, the guanfacine ER dosage should be increased back to the recommended dose. Guanfacine is a CYP3A4 substrate and cobicistat is a strong CYP3A4 inhibitor. Cobicistat may significantly increase guanfacine plasma concentrations.
Enzalutamide: (Major) A dose increase of extended-release (ER) guanfacine should be considered if coadministration with enzalutamide is necessary. Consider doubling the recommended dose of guanfacine if therapy is added to a patient already taking enzalutamide; increase the dose of guanfacine over 1 to 2 weeks if enzalutamide therapy is added to a patient already taking guanfacine. Specific recommendations for immediate-release (IR) guanfacine are not available. Guanfacine is a CYP3A4 substrate and enzalutamide is a strong CYP3A4 inducer. Coadministration with another strong CYP3A4 inducer decreased guanfacine exposure by 70%.
Epinephrine: (Moderate) Antihypertensives, including guanfacine, antagonize the vasopressor effects of parenteral epinephrine.
Epoprostenol: (Moderate) The concomitant administration of epoprostenol with other antihypertensive agents can result in additive hypotensive effects. This can be therapeutically advantageous, but dosages must be adjusted accordingly.
Erythromycin: (Major) Erythromycin may significantly increase guanfacine plasma concentrations. FDA-approved labeling for extended-release (ER) guanfacine recommends that, if these agents are taken together, the guanfacine dosage should be decreased to half of the recommended dose. Specific recommendations for immediate-release (IR) guanfacine are not available. Monitor patients closely for alpha-adrenergic effects including hypotension, drowsiness, lethargy, and bradycardia. Upon erythromycin discontinuation, the guanfacine ER dosage should be increased back to the recommended dose. Guanfacine is primarily metabolized by CYP3A4, and erythromycin is a moderate CYP3A4 inhibitor.
Esketamine: (Moderate) Closely monitor patients receiving esketamine and guanfacine for sedation and other CNS depressant effects. Instruct patients who receive a dose of esketamine not to drive or engage in other activities requiring alertness until the next day after a restful sleep.
Eslicarbazepine: (Major) Eslicarbazepine may significantly decrease guanfacine plasma concentrations. FDA-approved labeling for extended-release (ER) guanfacine recommends that, if these agents are taken together, doubling the recommended dose of guanfacine should be considered; if eslicarbazepine is added in a patient already receiving guanfacine, this escalation should occur over 1 to 2 weeks. If eslicarbazepine is discontinued, decrease the guanfacine ER dosage back to the recommended dose over 1 to 2 weeks. Specific recommendations for immediate-release (IR) guanfacine are not available. Guanfacine is primarily metabolized by CYP3A4, and eslicarbazepine is a moderate CYP3A4 inducer.
Esmolol: (Moderate) Guanfacine can have additive effects when administered with other antihypertensive agents, including beta-blockers. These effects can be used to therapeutic advantage, but dosage adjustments may be necessary.
Estazolam: (Moderate) Guanfacine has been associated with sedative effects and can potentiate the actions of other CNS depressants including benzodiazepines.
Estradiol: (Minor) Estrogens can induce fluid retention and may increase blood pressure in some patients; patients who are receiving antihypertensive agents concurrently with hormone therapy should be monitored for antihypertensive effectiveness.
Ethanol: (Major) Advise patients to avoid alcohol consumption while taking CNS depressants. Alcohol consumption may result in additive CNS depression.
Etodolac: (Moderate) NSAIDs may decrease the effect of antihypertensive agents through various mechanisms, including renal and peripheral vasoactive pathways.
Etomidate: (Moderate) General anesthetics can potentiate the hypotensive effects of antihypertensive agents. Reduced dosages of antihypertensives may be required during heavy sedation.
Etravirine: (Major) Etravirine may significantly decreas e guanfacine plasma concentrations. FDA-approved labeling for extended-release (ER) guanfacine recommends that, if these agents are taken together, doubling the recommended dose of guanfacine should be considered; if etravirine is added in a patient already receiving guanfacine, this escalation should occur over 1 to 2 weeks. If etravirine is discontinued, decrease the guanfacine ER dosage back to the recommended dose over 1 to 2 weeks. Specific recommendations for immediate-release (IR) guanfacine are not available. Guanfacine is primarily metabolized by CYP3A4, and etravirine is a moderate CYP3A4 inducer.
Fedratinib: (Major) Decrease the dose of extended-release guanfacine by 50% if coadministration with fedratinib is necessary; if fedratinib is discontinued, the dose of extended-release guanfacine may be increased to the recommended level. Monitor patients closely for adverse effects including hypotension, drowsiness, lethargy, and bradycardia. Recommendations for immediate-release guanfacine are not available. Guanfacine is a CYP3A substrate and fedratinib is a moderate CYP3A inhibitor.
Fenfluramine: (Moderate) Monitor for excessive sedation and somnolence during coadministration of fenfluramine and guanfacine. Concurrent use may result in additive CNS depression.
Fenoprofen: (Moderate) NSAIDs may decrease the effect of antihypertensive agents through various mechanisms, including renal and peripheral vasoactive pathways.
Fish Oil, Omega-3 Fatty Acids (Dietary Supplements): (Moderate) Monitor blood pressure during concomitant fish oil and central-acting adrenergic agent use. Concomitant use may result in additive hypotension; high doses of fish oil may produce a blood pressure lowering effect.
Fluconazole: (Major) Fluconazole may significantly increase guanfacine plasma concentrations. FDA-approved labeling for extended-release (ER) guanfacine recommends that, if these agents are taken together, the guanfacine dosage should be decreased to half of the recommended dose. Specific recommendations for immediate-release (IR) guanfacine are not available. Monitor patients closely for alpha-adrenergic effects including hypotension, drowsiness, lethargy, and bradycardia. Upon fluconazole discontinuation, the guanfacine ER dosage should be increased back to the recommended dose. Guanfacine is primarily metabolized by CYP3A4, and fluconazole is a moderate CYP3A4 inhibitor.
Fluphenazine: (Moderate) Monitor blood pressure and for unusual drowsiness or excessive sedation during concomitant central-acting adrenergic agent and phenothiazine use. Concomitant use increases the risk for additive hypotension and CNS depression.
Flurazepam: (Moderate) Guanfacine has been associated with sedative effects and can potentiate the actions of other CNS depressants including benzodiazepines.
Flurbiprofen: (Moderate) NSAIDs may decrease the effect of antihypertensive agents through various mechanisms, including renal and peripheral vasoactive pathways.
Fluvoxamine: (Major) Fluvoxamine may significantly increase plasma concentrations of guanfacine, a primary CYP3A4 substrate. FDA-approved labeling for extended-release (ER) guanfacine recommends that if taken with a moderate CYP3A4 inhibitor, such as fluvoxamine, the guanfacine dosage be decreased to half of the recommended dose. Specific recommendations for immediate-release (IR) guanfacine are not available. Monitor patients closely for alpha-adrenergic effects including hypotension, drowsiness, lethargy, and bradycardia. If fluvoxamine is discontinued, the guanfacine ER dosage should be increased back to the recommended dose.
Food: (Major) Advise patients to avoid cannabis use while taking CNS depressants due to the risk for additive CNS depression and potential for other cognitive adverse reactions.
Fosamprenavir: (Major) Decrease the dose of extended-release guanfacine by 50% if coadministration with fosamprenavir is necessary; if fosamprenavir is discontinued, the dose of extended-release guanfacine may be increased to the recommended level. Monitor patients closely for adverse effects including hypotension, drowsiness, lethargy, and bradycardia. Recommendations for immediate-release guanfacine are not available. Guanfacine is a CYP3A substrate and fosamprenavir is a moderate CYP3A inhibitor.
Fosphenytoin: (Major) Monitor patients for guanfacine efficacy during fosphenytoin coadministration. Guanfacine plasma concentrations can be reduced by fosphenytoin, by induction of CYP3A4 metabolism. Immediate-release guanfacine may require more frequent dosing to achieve or maintain desired hypotensive response; if it is discontinued, carefully taper the dose to prevent rebound hypertension. The extended-release guanfacine dose for attention deficit hyperactivity disorder (ADHD) may need to be doubled, per FDA-approved labeling; any dose change should occur over 1 to 2 weeks (e.g., dose increase when adding, or decrease when discontinuing, an enzyme inducer). Guanfacine is primarily metabolized by CYP3A4. Fosphenytoin is a strong CYP3A4 inducer. Guanfacine plasma concentrations and elimination half-life were significantly reduced with coadministration of an enzyme inducer (e.g., phenobarbital, primidone, phenytoin, fosphenytoin) in two patients with renal impairment.
Gabapentin: (Moderate) Monitor for excessive sedation and somnolence during coadministration of guanfacine and gabapentin. Concurrent use may result in additive CNS depression.
General anesthetics: (Moderate) General anesthetics can potentiate the hypotensive effects of antihypertensive agents. Reduced dosages of antihypertensives may be required during heavy sedation.
Grapefruit juice: (Major) Avoid consumption of grapefruit or grapefruit juice with guanfacine. Grapefruit is a strong CYP3A4 inhibitor, and guanfacine is a CYP3A4 substrate. Consumption may significantly increase exposure to guanfacine and increase the risk of alpha-adrenergic effects (e.g., hypotension, drowsiness, lethargy, bradycardia).
Haloperidol: (Moderate) Disturbances of orthostatic regulation (e.g., orthostatic hypotension, dizziness, fatigue) and additive sedation may occur in patients receiving concomitant clonidine and antipsychotics. Also, based on observations in patients in a state of alcoholic delirium, high intravenous doses of clonidine may increase the arrhythmogenic potential (QT prolongation, ventricular fibrillation) of high intravenous doses of haloperidol. A causal relationship and relevance for clonidine oral tablets have not been established.
Hydralazine; Isosorbide Dinitrate, ISDN: (Moderate) Monitor blood pressure during concomitant central-acting adrenergic agent and nitrate use due to risk for additive hypotension; dosage adjustments may be necessary.
Hydrocodone; Ibuprofen: (Moderate) NSAIDs may decrease the effect of antihypertensive agents through various mechanisms, including renal and peripheral vasoactive pathways.
Ibuprofen: (Moderate) NSAIDs may decrease the effect of antihypertensive agents through various mechanisms, including renal and peripheral vasoactive pathways.
Ibuprofen; Famotidine: (Moderate) NSAIDs may decrease the effect of antihypertensive agents through various mechanisms, including renal and peripheral vasoactive pathways.
Ibuprofen; Oxycodone: (Moderate) NSAIDs may decrease the effect of antihypertensive agents through various mechanisms, including renal and peripheral vasoactive pathways.
Ibuprofen; Pseudoephedrine: (Moderate) NSAIDs may decrease the effect of antihypertensive agents through various mechanisms, including renal and peripheral vasoactive pathways.
Idelalisib: (Major) Idelalisib may significantly increase guanfacine plasma concentrations. Guanfacine is primarily metabolized by CYP3A4, and idelalisib is a strong CYP3A4 inhibitor. FDA-approved labeling for extended-release (ER) guanfacine recommends that, if given with a strong CYP3A4 inhibitor, the guanfacine dosage should be decreased to half of the recommended dose. The labeling for idelalisib warns against coadministration with CYP3A4 substrates. If these agents are given together, reduce the guanfacine dosage as recommended and monitor patients closely for alpha-adrenergic effects including hypotension, drowsiness, lethargy, and bradycardia. If idelalisib is discontinued, the guanfacine ER dosage should be increased back to the recommended dose.
Iloperidone: (Moderate) Secondary to alpha-blockade, iloperidone can produce vasodilation that may result in additive effects during concurrent use with antihypertensive agents. The potential reduction in blood pressure can precipitate orthostatic hypotension and associated dizziness, tachycardia, and syncope. If concurrent use of iloperidone and antihypertensive agents is necessary, patients should be counseled on measures to prevent orthostatic hypotension, such as sitting on the edge of the bed for several minutes prior to standing in the morning and rising slowly from a seated position. Close monitoring of blood pressure is recommended until the full effects of the combination therapy are known.
Iloprost: (Moderate) Further reductions in blood pressure may occur when inhaled iloprost is administered to patients receiving other antihypertensive agents.
Imatinib: (Major) Imatinib may significantly increase guanfacine plasma concentrations. FDA-approved labeling for extended-release (ER) guanfacine recommends that, if these agents are taken together, the guanfacine dosage should be decreased to half of the recommended dose. Specific recommendations for immediate-release (IR) guanfacine are not available. Monitor patients closely for alpha-adrenergic effects including hypotension, drowsiness, lethargy, and bradycardia. Upon imatinib discontinuation, the guanfacine ER dosage should be increased back to the recommended dose. Guanfacine is primarily metabolized by CYP3A4, and imatinib is a moderate CYP3A4 inhibitor.
Imipramine: (Major) Tricyclic antidepressants (TCAs) can inhibit the hypotensive effects of guanfacine, causing an increase in blood pressure if given concomitantly. Consider alternatives to TCAs in patients established on guanfacine therapy for hypertension when possible; it is not clear the effect the combination may have when used in patients treated with guanfacine for attention-deficit, but other options to TCAs should be considered. Increased dosages of guanfacine may be required to control blood pressure in patients who are receiving TCAs concurrently. In addition, concurrent TCAs may enhance the potential for serious rebound hypertension following guanfacine discontinuation, regardless of the indication for treatment. If guanfacine therapy is withdrawn, guanfacine should be tapered gradually and the patient should be monitored for potential hypertension.
Indinavir: (Major) Indinavir may significantly increase guanfacine plasma concentrations. FDA-approved labeling for extended-release (ER) guanfacine recommends that, if these agents are taken together, the guanfacine dosage should be decreased to half of the recommended dose. Specific recommendations for immediate-release (IR) guanfacine are not available. Monitor patients closely for alpha-adrenergic effects including hypotension, drowsiness, lethargy, and bradycardia. If indinavir is discontinued, the guanfacine ER dosage should be increased back to the recommended dose. Guanfacine is primarily metabolized by CYP3A4, and indinavir is a strong CYP3A4 inhibitor.
Indomethacin: (Moderate) NSAIDs may decrease the effect of antihypertensive agents through various mechanisms, including renal and peripheral vasoactive pathways.
Intravenous Lipid Emulsions: (Moderate) Monitor blood pressure during concomitant fish oil and central-acting adrenergic agent use. Concomitant use may result in additive hypotension; high doses of fish oil may produce a blood pressure lowering effect.
Isavuconazonium: (Major) Isavuconazonium may significantly increase guanfacine plasma concentrations. FDA-approved labeling for extended-release (ER) guanfacine recommends that, if these agents are taken together, the guanfacine dosage should be decreased to half of the recommended dose. Specific recommendations for immediate-release (IR) guanfacine are not available. Monitor patients closely for alpha-adrenergic effects including hypotension, drowsiness, lethargy, and bradycardia. Upon isavuconazonium discontinuation, the guanfacine ER dosage should be increased back to the recommended dose. Guanfacine is primarily metabolized by CYP3A4, and isavuconazonium is a moderate CYP3A4 inhibitor.
Isoflurane: (Moderate) General anesthetics can potentiate the hypotensive effects of antihypertensive agents. Reduced dosages of antihypertensives may be required during heavy sedation.
Isoniazid, INH; Pyrazinamide, PZA; Rifampin: (Major) Rifampin may significantly decrease guanfacine plasma concentrations. FDA-approved labeling for extended-release (ER) guanfacine recommends that, if these agents are taken together, doubling the recommended dose of guanfacine should be considered; if rifampin is added in a patient already receiving guanfacine, this escalation should occur over 1 to 2 weeks. Upon rifampin discontinuation, decrease the guanfacine ER dosage back to the recommended dose over 1 to 2 weeks. Specific recommendations for immediate-release (IR) guanfacine are not available. Guanfacine is primarily metabolized by CYP3A4, and rifampin is a strong CYP3A4 inducer.
Isoniazid, INH; Rifampin: (Major) Rifampin may significantly decrease guanfacine plasma concentrations. FDA-approved labeling for extended-release (ER) guanfacine recommends that, if these agents are taken together, doubling the recommended dose of guanfacine should be considered; if rifampin is added in a patient already receiving guanfacine, this escalation should occur over 1 to 2 weeks. Upon rifampin discontinuation, decrease the guanfacine ER dosage back to the recommended dose over 1 to 2 weeks. Specific recommendations for immediate-release (IR) guanfacine are not available. Guanfacine is primarily metabolized by CYP3A4, and rifampin is a strong CYP3A4 inducer.
Isosorbide Dinitrate, ISDN: (Moderate) Monitor blood pressure during concomitant central-acting adrenergic agent and nitrate use due to risk for additive hypotension; dosage adjustments may be necessary.
Isosorbide Mononitrate: (Moderate) Monitor blood pressure during concomitant central-acting adrenergic agent and nitrate use due to risk for additive hypotension; dosage adjustments may be necessary.
Itraconazole: (Major) Itraconazole may significantly increase guanfacine plasma concentrations. FDA-approved labeling for extended-release (ER) guanfacine recommends that, if these agents are taken together, the guanfacine dosage should be decreased to half of the recommended dose. Specific recommendations for immediate-release (IR) guanfacine are not available. Monitor patients closely for alpha-adrenergic effects including hypotension, drowsiness, lethargy, and bradycardia. Upon itraconazole discontinuation, the guanfacine ER dosage should be increased back to the recommended dose. Guanfacine is primarily metabolized by CYP3A4, and itraconazole is a strong CYP3A4 inhibitor.
Ketamine: (Moderate) General anesthetics can potentiate the hypotensive effects of antihypertensive agents. Reduced dosages of antihypertensives may be required during heavy sedation.
Ketoconazole: (Major) If coadministration of ketoconazole with extended-release (ER) guanfacine is necessary, it is recommended to reduce the guanfacine dosage to half of the recommended dose for age and weight. Specific recommendations for immediate-release (IR) guanfacine are not available. Monitor patients closely for adverse effects including hypotension, drowsiness, lethargy, and bradycardia. If ketoconazole is discontinued, the guanfacine ER dosage should be increased back to the recommended dose. Guanfacine is a CYP3A4 substrate and ketoconazole is a strong CYP3A4 inhibitor. Ketoconazole may significantly increase guanfacine plasma concentrations, as indicated in pharmacokinetic drug interaction studies.
Ketoprofen: (Moderate) NSAIDs may decrease the effect of antihypertensive agents through various mechanisms, including renal and peripheral vasoactive pathways.
Ketorolac: (Moderate) NSAIDs may decrease the effect of antihypertensive agents through various mechanisms, including renal and peripheral vasoactive pathways.
Labetalol: (Moderate) Guanfacine can have additive effects when administered with other antihypertensive agents, including beta-blockers. These effects can be used to therapeutic advantage, but dosage adjustments may be necessary.
Lansoprazole; Amoxicillin; Clarithromycin: (Major) Clarithromycin may significantly increase guanfacine plasma concentrations. FDA-approved labeling for extended-release (ER) guanfacine recommends that, if these agents are taken together, the guanfacine dosage should be decreased to half of the recommended dose. Specific recommendations for immediate-release (IR) guanfacine are not available. Monitor patients closely for alpha-adrenergic effects including hypotension, drowsiness, lethargy, and bradycardia. If clarithromycin is discontinued, the guanfacine ER dosage should be increased back to the recommended dose. Guanfacine is primarily metabolized by CYP3A4, and clarithromycin is a strong CYP3A4 inhibitor.
Lasmiditan: (Moderate) Monitor for excessive sedation and somnolence during coadministration of lasmiditan and guanfacine. Concurrent use may result in additive CNS depression.
Lemborexant: (Moderate) Monitor for excessive sedation and somnolence during coadministration of lemborexant and guanfacine. Dosage adjustments of lemborexant and guanfacine may be necessary when administered together because of potentially additive CNS effects. The risk of next-day impairment, including impaired driving, is increased if lemborexant is taken with other CNS depressants.
Lenacapavir: (Major) Decrease the dose of extended-release guanfacine by 50% if coadministration with lenacapavir is necessary; if lenacapavir is discontinued, the dose of extended-release guanfacine may be increased to the recommended level. Monitor patients closely for adverse effects including hypotension, drowsiness, lethargy, and bradycardia. Recommendations for immediate-release guanfacine are not available. Guanfacine is a CYP3A substrate and lenacapavir is a moderate CYP3A inhibitor.
Letermovir: (Major) FDA-approved labeling for extended-release (ER) guanfacine recommends that, if these agents are taken together, the guanfacine dosage should be decreased to half of the recommended dose. The magnitude of this interaction may be increased in patients who are also receiving cyclosporine. Specific recommendations for immediate-release (IR) guanfacine are not available. Monitor patients closely for alpha-adrenergic effects including hypotension, drowsiness, lethargy, and bradycardia. Upon letermovir discontinuation, the guanfacine ER dosage should be increased back to the recommended dose. Guanfacine is primarily metabolized by CYP3A4. Letermovir is a moderate CYP3A4 inhibitor; however, when given with cyclosporine, the combined effect on CYP3A4 substrates may be similar to a strong CYP3A4 inhibitor.
Levobunolol: (Moderate) Guanfacine can have additive effects when administered with other antihypertensive agents, including beta-blockers. These effects can be used to therapeutic advantage, but dosage adjustments may be necessary.
Levocetirizine: (Moderate) Concurrent use of cetirizine/levocetirizine with guanfacine should generally be avoided. Coadministration may increase the risk of CNS depressant-related side effects. If concurrent use is necessary, monitor for excessive sedation and somnolence.
Levodopa: (Moderate) Monitor blood pressure during concomitant use of levodopa and central-acting adrenergic agents due to risk for additive hypotension.
Levoketoconazole: (Major) If coadministration of ketoconazole with extended-release (ER) guanfacine is necessary, it is recommended to reduce the guanfacine dosage to half of the recommended dose for age and weight. Specific recommendations for immediate-release (IR) guanfacine are not available. Monitor patients closely for adverse effects including hypotension, drowsiness, lethargy, and bradycardia. If ketoconazole is discontinued, the guanfacine ER dosage should be increased back to the recommended dose. Guanfacine is a CYP3A4 substrate and ketoconazole is a strong CYP3A4 inhibitor. Ketoconazole may significantly increase guanfacine plasma concentrations, as indicated in pharmacokinetic drug interaction studies.
Lidocaine; Epinephrine: (Moderate) Antihypertensives, including guanfacine, antagonize the vasopressor effects of parenteral epinephrine.
Lofexidine: (Major) Lofexidine is a central alpha-2 adrenergic agonist, and its effects can be additive to other medications in the same class. Monitor for excessive hypotension, bradycardia, and sedation during coadministration. Patients being given lofexidine in an outpatient setting should be capable of and instructed on self-monitoring for hypotension, orthostasis, bradycardia, and associated symptoms. If clinically significant or symptomatic hypotension and/or bradycardia occur, the next dose of lofexidine should be reduced in amount, delayed, or skipped.
Lonafarnib: (Major) If coadministration of lonafarnib with extended-release (ER) guanfacine is necessary, reduce the guanfacine dosage to half of the recommended dose. Specific recommendations for immediate-release (IR) guanfacine are not available. Monitor patients closely for adverse effects including hypotension, drowsiness, lethargy, and bradycardia. If lonafarnib is discontinued, the guanfacine ER dosage should be increased back to the recommended dose. Guanfacine is a CYP3A4 substrate and lonafarnib is a strong CYP3A4 inhibitor; lonafarnib may significantly increase guanfacine plasma concentrations.
Lopinavir; Ritonavir: (Major) Ritonavir may significantly alter guanfacine plasma concentrations. Guanfacine is primarily metabolized by CYP3A4. Ritonavir is a potent CYP3A4 inhibitor; moderate CYP3A4 induction has been reported with concomitant use of voriconazole. The net effect of this potential interaction is unclear, but guanfacine dosage adjustments, most likely a dose decrease, may be required. FDA-approved labeling for extended-release (ER) guanfacine recommends that, if used with a moderate to strong CYP3A4 inhibitor, the guanfacine dosage should be decreased to half of the recommended dose and the patient should be closely monitored for alpha-adrenergic effects (e.g., hypotension, drowsiness, bradycardia). However, if used with a moderate to strong CYP3A4 inducer, labeling recommends to consider doubling the recommended dose of guanfacine ER; if the inducer is added in a patient already receiving guanfacine, this escalation should occur over 1 to 2 weeks. If the inducer or inhibitor is discontinued, guanfacine ER should return to its recommended dose (with downward titration occurring over 1 to 2 weeks). Specific recommendations for immediate-release (IR) guanfacine are not available.
Lorazepam: (Moderate) Guanfacine has been associated with sedative effects and can potentiate the actions of other CNS depressants including benzodiazepines.
Lorlatinib: (Major) A dose increase of extended-release (ER) guanfacine should be considered if coadministration with lorlatinib is necessary. Consider doubling the recommended dose of guanfacine if therapy is added to a patient already taking lorlatinib; increase the dose of guanfacine over 1 to 2 weeks if lorlatinib therapy is added to a patient already taking guanfacine. Specific recommendations for immediate-release (IR) guanfacine are not available. Guanfacine is a CYP3A4 substrate and lorlatinib is a moderate CYP3A4 inducer.
Lumacaftor; Ivacaftor: (Major) Lumacaftor; ivacaftor may significantly decrease guanfacine plasma concentrations. FDA-approved labeling for extended-release (ER) guanfacine recommends that, if these agents are taken together, doubling the recommended dose of guanfacine should be considered; if lumacaftor; ivacaftor is added in a patient already receiving guanfacine, this escalation should occur over 1 to 2 weeks. If lumacaftor; ivacaftor is discontinued, decrease the guanfacine ER dosage back to the recommended dose over 1 to 2 weeks. Specific recommendations for immediate-release (IR) guanfacine are not available. Guanfacine is primarily metabolized by CYP3A4, and lumacaftor is a strong CYP3A4 inducer.
Lumacaftor; Ivacaftor: (Major) Lumacaftor; ivacaftor may significantly decrease guanfacine plasma concentrations. FDA-approved labeling for extended-release (ER) guanfacine recommends that, if these agents are taken together, doubling the recommended dose of guanfacine should be considered; if lumacaftor; ivacaftor is added in a patient already receiving guanfacine, this escalation should occur over 1 to 2 weeks. If lumacaftor; ivacaftor is discontinued, decrease the guanfacine ER dosage back to the recommended dose over 1 to 2 weeks. Specific recommendations for immediate-release (IR) guanfacine are not available. Guanfacine is primarily metabolized by CYP3A4, and lumacaftor is a strong CYP3A4 inducer.
Lumateperone: (Moderate) Monitor for excessive sedation, somnolence, and orthostatic hypotension during coadministration of lumateperone and guanfacine. Concurrent use may result in additive CNS depression or orthostasis.
Lurasidone: (Moderate) Due to the antagonism of lurasidone at alpha-1 adrenergic receptors, the drug may enhance the hypotensive effects of alpha-blockers and other antihypertensive agents. If concurrent use of lurasidone and antihypertensive agents is necessary, patients should be counseled on measures to prevent orthostatic hypotension, such as sitting on the edge of the bed for several minutes prior to standing in the morning and rising slowly from a seated position. Close monitoring of blood pressure is recommended until the full effects of the combination therapy are known.
Maprotiline: (Major) Cyclic antidepressants like maprotiline can inhibit the hypotensive effects of guanfacine, causing an increase in blood pressure if given concomitantly. Increased dosages of guanfacine may be required in patients who are receiving maprotiline concurrently. In addition, concurrent maprotiline use may enhance the potential for rebound hypertension following guanfacine discontinuation. If guanfacine is withdrawn in the presence of maprotiline or other cyclic antidepressants, guanfacine should be tapered gradually and the patient should be monitored for potential hypertension.
Mavacamten: (Major) A dose increase of extended-release (ER) guanfacine should be considered if coadministration with mavacamten is necessary. Consider doubling the recommended dose of guanfacine if therapy is added to a patient already taking mavacamten; increase the dose of guanfacine over 1 to 2 weeks if mavacamten therapy is added to a patient already taking guanfacine. Specific recommendations for immediate-release (IR) guanfacine are not available. Guanfacine is a CYP3A substrate and mavacamten is a moderate CYP3A inducer.
Meclofenamate Sodium: (Moderate) NSAIDs may decrease the effect of antihypertensive agents through various mechanisms, including renal and peripheral vasoactive pathways.
Mefenamic Acid: (Moderate) NSAIDs may decrease the effect of antihypertensive agents through various mechanisms, including renal and peripheral vasoactive pathways.
Meloxicam: (Moderate) NSAIDs may decrease the effect of antihypertensive agents through various mechanisms, including renal and peripheral vasoactive pathways.
Methazolamide: (Moderate) The concomitant administration of diuretics with other antihypertensive agents can result in additive hypotensive effects. This interaction can be therapeutically advantageous, but dosages must be adjusted accordingly.
Methylphenidate Derivatives: (Moderate) Psychostimulants, such as methylphenidate and its derivatives, may increase blood pressure and reduce the antihypertensive effects of antihypertensive agents, such as guanfacine. Monitor blood pressure and heart rate periodically when prescribed together. Guanfacine may be used adjunctively to methylphenidate and its derivatives in the treatment of attention deficit hyperactivity disorder (ADHD). Pharmacokinetic studies reveal that guanfacine does not influence methylphenidate pharmacokinetics and methylphenidate does not affect guanfacine pharmacokinetics. No dosage adjustments are required when used together. Patients should be monitored for heart rate, blood pressure, and for sedation during ADHD treatment.
Metoprolol: (Moderate) Guanfacine can have additive effects when administered with other antihypertensive agents, including beta-blockers. These effects can be used to therapeutic advantage, but dosage adjustments may be necessary.
Metoprolol; Hydrochlorothiazide, HCTZ: (Moderate) Guanfacine can have additive effects when administered with other antihypertensive agents, including beta-blockers. These effects can be used to therapeutic advantage, but dosage adjustments may be necessary.
Midazolam: (Moderate) Guanfacine has been associated with sedative effects and can potentiate the actions of other CNS depressants including benzodiazepines.
Milrinone: (Moderate) Concurrent administration of antihypertensive agents could lead to additive hypotension when administered with milrinone. Titrate milrinone dosage according to hemodynamic response.
Mitotane: (Major) Mitotane may significantly decrease guanfacine plasma concentrations. FDA-approved labeling for extended-release (ER) guanfacine recommends that, if these agents are taken together, doubling the recommended dose of guanfacine should be considered; if mitotane is added in a patient already receiving guanfacine, this escalation should occur over 1 to 2 weeks. If mitotane is discontinued, decrease the guanfacine ER dosage back to the recommended dose over 1 to 2 weeks. Specific recommendations for immediate-release (IR) guanfacine are not available. Guanfacine is primarily metabolized by CYP3A4, and mitotane is a strong CYP3A4 inducer.
Monoamine oxidase inhibitors: (Moderate) Additive hypotensive effects may be seen when monoamine oxidase inhibitors (MAOIs) are combined with antihypertensives. In addition, when beginning treatment with antihypertensives that initially increase the release of catecholamine stores, such as guanfacine, hypertensive crisis may occur. Abrupt cessation of therapy with central alpha-2 adrenergic agonists like guanfacine may be associated with increases (from depressed on-therapy levels) in plasma and urinary catecholamines, symptoms of nervousness and anxiety and, less commonly, increases in blood pressure to levels significantly greater than those prior to therapy, which may affect MAO inhibiting therapy.
Nabilone: (Moderate) Monitor for excessive sedation and somnolence during coadministration of nabilone and guanfacine. Concurrent use may result in additive CNS depression.
Nabumetone: (Moderate) NSAIDs may decrease the effect of antihypertensive agents through various mechanisms, including renal and peripheral vasoactive pathways.
Nadolol: (Moderate) Guanfacine can have additive effects when administered with other antihypertensive agents, including beta-blockers. These effects can be used to therapeutic advantage, but dosage adjustments may be necessary.
Naproxen: (Moderate) NSAIDs may decrease the effect of antihypertensive agents through various mechanisms, including renal and peripheral vasoactive pathways.
Naproxen; Esomeprazole: (Moderate) NSAIDs may decrease the effect of antihypertensive agents through various mechanisms, including renal and peripheral vasoactive pathways.
Naproxen; Pseudoephedrine: (Moderate) NSAIDs may decrease the effect of antihypertensive agents through various mechanisms, including renal and peripheral vasoactive pathways.
Nebivolol: (Moderate) Guanfacine can have additive effects when administered with other antihypertensive agents, including beta-blockers. These effects can be used to therapeutic advantage, but dosage adjustments may be necessary.
Nebivolol; Valsartan: (Moderate) Guanfacine can have additive effects when administered with other antihypertensive agents, including beta-blockers. These effects can be used to therapeutic advantage, but dosage adjustments may be necessary.
Nefazodone: (Major) Nefazodone may significantly increase guanfacine plasma concentrations. FDA-approved labeling for extended-release (ER) guanfacine recommends that, if these agents are taken together, the guanfacine dosage should be decreased to half of the recommended dose. Specific recommendations for immediate-release (IR) guanfacine are not available. Monitor patients closely for alpha-adrenergic effects including hypotension, drowsiness, lethargy, and bradycardia. If nefazodone is discontinued, the guanfacine ER dosage should be increased back to the recommended dose. Guanfacine is primarily metabolized by CYP3A4, and nefazodone is a strong CYP3A4 inhibitor.
Nelfinavir: (Major) Nelfinavir may significantly increase guanfacine plasma concentrations. FDA-approved labeling for extended-release (ER) guanfacine recommends that, if these agents are taken together, the guanfacine dosage should be decreased to half of the recommended dose. Specific recommendations for immediate-release (IR) guanfacine are not available. Monitor patients closely for alpha-adrenergic effects including hypotension, drowsiness, lethargy, and bradycardia. If nelfinavir is discontinued, the guanfacine ER dosage should be increased back to the recommended dose. Guanfacine is primarily metabolized by CYP3A4, and nelfinavir is a strong CYP3A4 inhibitor.
Nesiritide, BNP: (Major) The potential for hypotension may be increased when coadministering nesiritide with antihypertensive agents.
Netupitant, Fosnetupitant; Palonosetron: (Major) Netupitant may significantly increase guanfacine plasma concentrations. FDA-approved labeling for extended-release (ER) guanfacine recommends that, if these agents are taken together, the guanfacine dosage should be decreased to half of the recommended dose. Specific recommendations for immediate-release (IR) guanfacine are not available. Monitor patients closely for alpha-adrenergic effects including hypotension, drowsiness, lethargy, and bradycardia. Upon netupitant; palonosetron discontinuation, the guanfacine ER dosage should be increased back to the recommended dose. Guanfacine is primarily metabolized by CYP3A4, and netupitant is a moderate CYP3A4 inhibitor. The inhibitory effect of netupitant can last for multiple days; monitor patients closely.
Niacin, Niacinamide: (Moderate) Cutaneous vasodilation induced by niacin may become problematic if high-dose niacin is used concomitantly with other antihypertensive agents. This effect is of particular concern in the setting of acute myocardial infarction, unstable angina, or other acute hemodynamic compromise. Clonidine has been shown to inhibit niacin-induced flushing. The interaction is harmless unless niacin augments the hypotensive actions of clonidine.
Niacin; Simvastatin: (Moderate) Cutaneous vasodilation induced by niacin may become problematic if high-dose niacin is used concomitantly with other antihypertensive agents. This effect is of particular concern in the setting of acute myocardial infarction, unstable angina, or other acute hemodynamic compromise. Clonidine has been shown to inhibit niacin-induced flushing. The interaction is harmless unless niacin augments the hypotensive actions of clonidine.
Nilotinib: (Major) Nilotinib may significantly increase guanfacine plasma concentrations. FDA-approved labeling for extended-release (ER) guanfacine recommends that, if these agents are taken together, the guanfacine dosage should be decreased to half of the recommended dose. Specific recommendations for immediate-release (IR) guanfacine are not available. Monitor patients closely for alpha-adrenergic effects including hypotension, drowsiness, lethargy, and bradycardia. Upon nilotinib discontinuation, the guanfacine ER dosage should be increased back to the recommended dose. Guanfacine is primarily metabolized by CYP3A4, and nilotinib is a moderate CYP3A4 inhibitor.
Nirmatrelvir; Ritonavir: (Major) Ritonavir may significantly alter guanfacine plasma concentrations. Guanfacine is primarily metabolized by CYP3A4. Ritonavir is a potent CYP3A4 inhibitor; moderate CYP3A4 induction has been reported with concomitant use of voriconazole. The net effect of this potential interaction is unclear, but guanfacine dosage adjustments, most likely a dose decrease, may be required. FDA-approved labeling for extended-release (ER) guanfacine recommends that, if used with a moderate to strong CYP3A4 inhibitor, the guanfacine dosage should be decreased to half of the recommended dose and the patient should be closely monitored for alpha-adrenergic effects (e.g., hypotension, drowsiness, bradycardia). However, if used with a moderate to strong CYP3A4 inducer, labeling recommends to consider doubling the recommended dose of guanfacine ER; if the inducer is added in a patient already receiving guanfacine, this escalation should occur over 1 to 2 weeks. If the inducer or inhibitor is discontinued, guanfacine ER should return to its recommended dose (with downward titration occurring over 1 to 2 weeks). Specific recommendations for immediate-release (IR) guanfacine are not available.
Nitrates: (Moderate) Monitor blood pressure during concomitant central-acting adrenergic agent and nitrate use due to risk for additive hypotension; dosage adjustments may be necessary.
Nitroglycerin: (Moderate) Monitor blood pressure during concomitant central-acting adrenergic agent and nitrate use due to risk for additive hypotension; dosage adjustments may be necessary.
Nitroprusside: (Moderate) Additive hypotensive effects may occur when nitroprusside is used concomitantly with other antihypertensive agents. Dosages should be adjusted carefully, according to blood pressure.
Nonsteroidal antiinflammatory drugs: (Moderate) NSAIDs may decrease the effect of antihypertensive agents through various mechanisms, including renal and peripheral vasoactive pathways.
Nortriptyline: (Major) Tricyclic antidepressants (TCAs) can inhibit the hypotensive effects of guanfacine, causing an increase in blood pressure if given concomitantly. Consider alternatives to TCAs in patients established on guanfacine therapy for hypertension when possible; it is not clear the effect the combination may have when used in patients treated with guanfacine for attention-deficit, but other options to TCAs should be considered. Increased dosages of guanfacine may be required to control blood pressure in patients who are receiving TCAs concurrently. In addition, concurrent TCAs may enhance the potential for serious rebound hypertension following guanfacine discontinuation, regardless of the indication for treatment. If guanfacine therapy is withdrawn, guanfacine should be tapered gradually and the patient should be monitored for potential hypertension.
Olanzapine: (Moderate) Olanzapine may induce orthostatic hypotension and thus enhance the effects of antihypertensive agents.
Olanzapine; Fluoxetine: (Moderate) Olanzapine may induce orthostatic hypotension and thus enhance the effects of antihypertensive agents.
Olanzapine; Samidorphan: (Moderate) Olanzapine may induce orthostatic hypotension and thus enhance the effects of antihypertensive agents.
Omeprazole; Amoxicillin; Rifabutin: (Major) Rifabutin may significantly decrease guanfacine plasma concentrations. FDA-approved labeling for extended-release (ER) guanfacine recommends that, if these agents are taken together, doubling the recommended dose of guanfacine should be considered; if rifabutin is added in a patient already receiving guanfacine, this escalation should occur over 1 to 2 weeks. If rifabutin is discontinued, decrease the guanfacine ER dosage back to the recommended dose over 1 to 2 weeks. Specific recommendations for immediate-release (IR) guanfacine are not available. Guanfacine is primarily metabolized by CYP3A4, and rifabutin is a moderate CYP3A4 inducer.
Opiate Agonists: (Moderate) Concomitant use of opioid agonists with guanfacine may cause excessive sedation and somnolence. Limit the use of opioid pain medication with guanfacine to only patients for whom alternative treatment options are inadequate. If concurrent use is necessary, use the lowest effective doses and minimum treatment durations needed to achieve the desired clinical effect.
Oxaprozin: (Moderate) NSAIDs may decrease the effect of antihypertensive agents through various mechanisms, including renal and peripheral vasoactive pathways.
Oxazepam: (Moderate) Guanfacine has been associated with sedative effects and can potentiate the actions of other CNS depressants including benzodiazepines.
Oxymetazoline: (Major) The vasoconstricting actions of oxymetazoline, an alpha adrenergic agonist, may reduce the antihypertensive effects produced by guanfacine. If these drugs are used together, closely monitor for changes in blood pressure.
Paliperidone: (Moderate) Paliperidone may cause orthostatic hypotension, thereby enhancing the hypotensive effects of antihypertensive agents. Orthostatic vital signs should be monitored in patients receiving paliperidone and central-acting adrenergic agents who are susceptible to hypotension.
Pentobarbital: (Major) Monitor patients for guanfacine efficacy and for excess sedation during pentobarbital coadministration. Guanfacine plasma concentrations can be reduced by pentobarbital, by induction of CYP3A4 metabolism. Immediate-release guanfacine may require more frequent dosing to achieve or maintain desired hypotensive response; if it is discontinued, carefully taper the dose to prevent rebound hypertension. The extended-release guanfacine dose for attention deficit hyperactivity disorder (ADHD) may need to be doubled, per FDA-approved labeling; any dose change should occur over 1 to 2 weeks (e.g., dose increase when adding, or decrease when discontinuing, an enzyme inducer). Guanfacine is primarily metabolized by CYP3A4. Barbiturates (e.g., phenobarbital, primidone) are strong CYP3A4 inducers. Guanfacine plasma concentrations and elimination half-life were significantly reduced with coadministration of an enzyme inducer (e.g., phenobarbital, primidone, phenytoin, fosphenytoin) in two patients with renal impairment. Additionally, guanfacine has been associated with sedative effects and can potentiate the actions of CNS depressants, including barbiturates.
Pentoxifylline: (Moderate) Pentoxifylline has been used concurrently with antihypertensive drugs (beta blockers, diuretics) without observed problems. Small decreases in blood pressure have been observed in some patients treated with pentoxifylline; periodic systemic blood pressure monitoring is recommended for patients receiving concomitant antihypertensives. If indicated, dosage of the antihypertensive agents should be reduced.
Perphenazine: (Moderate) Monitor blood pressure and for unusual drowsiness or excessive sedation during concomitant central-acting adrenergic agent and phenothiazine use. Concomitant use increases the risk for additive hypotension and CNS depression.
Perphenazine; Amitriptyline: (Major) Tricyclic antidepressants (TCAs) can inhibit the hypotensive effects of guanfacine, causing an increase in blood pressure if given concomitantly. Consider alternatives to TCAs in patients established on guanfacine therapy for hypertension when possible; it is not clear the effect the combination may have when used in patients treated with guanfacine for attention-deficit, but other options to TCAs should be considered. Increased dosages of guanfacine may be required to control blood pressure in patients who are receiving TCAs concurrently. In addition, concurrent TCAs may enhance the potential for serious rebound hypertension following guanfacine discontinuation, regardless of the indication for treatment. If guanfacine therapy is withdrawn, guanfacine should be tapered gradually and the patient should be monitored for potential hypertension. (Moderate) Monitor blood pressure and for unusual drowsiness or excessive sedation during concomitant central-acting adrenergic agent and phenothiazine use. Concomitant use increases the risk for additive hypotension and CNS depression.
Phenobarbital: (Major) Monitor patients for guanfacine efficacy and for excess sedation during phenobarbital coadministration. Guanfacine plasma concentrations can be reduced by phenobarbital, by induction of CYP3A4 metabolism. Immediate-release guanfacine may require more frequent dosing to achieve or maintain desired hypotensive response; if it is discontinued, carefully taper the dose to prevent rebound hypertension. The extended-release guanfacine dose for attention deficit hyperactivity disorder (ADHD) may need to be doubled, per FDA-approved labeling; any dose change should occur over 1 to 2 weeks (e.g., dose increase when adding, or decrease when discontinuing, an enzyme inducer). Guanfacine is primarily metabolized by CYP3A4. Barbiturates (e.g., phenobarbital, primidone) are strong CYP3A4 inducers. Guanfacine plasma concentrations and elimination half-life were significantly reduced with coadministration of an enzyme inducer (e.g., phenobarbital, primidone, phenytoin, fosphenytoin) in two patients with renal impairment. Additionally, guanfacine has been associated with sedative effects and can potentiate the actions of CNS depressants, including barbiturates.
Phenobarbital; Hyoscyamine; Atropine; Scopolamine: (Major) Monitor patients for guanfacine efficacy and for excess sedation during phenobarbital coadministration. Guanfacine plasma concentrations can be reduced by phenobarbital, by induction of CYP3A4 metabolism. Immediate-release guanfacine may require more frequent dosing to achieve or maintain desired hypotensive response; if it is discontinued, carefully taper the dose to prevent rebound hypertension. The extended-release guanfacine dose for attention deficit hyperactivity disorder (ADHD) may need to be doubled, per FDA-approved labeling; any dose change should occur over 1 to 2 weeks (e.g., dose increase when adding, or decrease when discontinuing, an enzyme inducer). Guanfacine is primarily metabolized by CYP3A4. Barbiturates (e.g., phenobarbital, primidone) are strong CYP3A4 inducers. Guanfacine plasma concentrations and elimination half-life were significantly reduced with coadministration of an enzyme inducer (e.g., phenobarbital, primidone, phenytoin, fosphenytoin) in two patients with renal impairment. Additionally, guanfacine has been associated with sedative effects and can potentiate the actions of CNS depressants, including barbiturates.
Phenothiazines: (Moderate) Monitor blood pressure and for unusual drowsiness or excessive sedation during concomitant central-acting adrenergic agent and phenothiazine use. Concomitant use increases the risk for additive hypotension and CNS depression.
Phenytoin: (Major) Monitor patients for guanfacine efficacy during phenytoin coadministration. Guanfacine plasma concentrations can be reduced by phenytoin, by induction of CYP3A4 metabolism. Immediate-release guanfacine may require more frequent dosing to achieve or maintain desired hypotensive response; if it is discontinued, carefully taper the dose to prevent rebound hypertension. The extended-release guanfacine dose for attention deficit hyperactivity disorder (ADHD) may need to be doubled, per FDA-approved labeling; any dose change should occur over 1 to 2 weeks (e.g., dose increase when adding, or decrease when discontinuing, an enzyme inducer). Guanfacine is primarily metabolized by CYP3A4. Phenytoin is a strong CYP3A4 inducer. Guanfacine plasma concentrations and elimination half-life were significantly reduced with coadministration of an enzyme inducer (e.g., phenobarbital, primidone, phenytoin, fosphenytoin) in two patients with renal impairment.
Pindolol: (Moderate) Guanfacine can have additive effects when administered with other antihypertensive agents, including beta-blockers. These effects can be used to therapeutic advantage, but dosage adjustments may be necessary.
Piroxicam: (Moderate) NSAIDs may decrease the effect of antihypertensive agents through various mechanisms, including renal and peripheral vasoactive pathways.
Posaconazole: (Major) Posaconazole may significantly increase guanfacine plasma concentrations. FDA-approved labeling for extended-release (ER) guanfacine recommends that, if these agents are taken together, the guanfacine dosage should be decreased to half of the recommended dose. Specific recommendations for immediate-release (IR) guanfacine are not available. Monitor patients closely for alpha-adrenergic effects including hypotension, drowsiness, lethargy, and bradycardia. Upon posaconazole discontinuation, the guanfacine ER dosage should be increased back to the recommended dose. Guanfacine is primarily metabolized by CYP3A4, and posaconazole is a strong CYP3A4 inhibitor.
Prazosin: (Moderate) Prazosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used.
Pregabalin: (Moderate) Monitor for excessive sedation and somnolence during coadministration of guanfacine and pregabalin. Concurrent use may result in additive CNS depression.
Prilocaine; Epinephrine: (Moderate) Antihypertensives, including guanfacine, antagonize the vasopressor effects of parenteral epinephrine.
Primidone: (Major) Monitor patients for guanfacine efficacy and for excess sedation during primidone coadministration. Guanfacine plasma concentrations can be reduced by primidone, by induction of CYP3A4 metabolism. Immediate-release guanfacine may require more frequent dosing to achieve or maintain desired hypotensive response; if it is discontinued, carefully taper the dose to prevent rebound hypertension. The extended-release guanfacine dose for attention deficit hyperactivity disorder (ADHD) may need to be doubled, per FDA-approved labeling; any dose change should occur over 1 to 2 weeks (e.g., dose increase when adding, or decrease when discontinuing, an enzyme inducer). Guanfacine is primarily metabolized by CYP3A4. Barbiturates (e.g., phenobarbital, primidone) are strong CYP3A4 inducers. Guanfacine plasma concentrations and elimination half-life were significantly reduced with coadministration of an enzyme inducer (e.g., phenobarbital, primidone, phenytoin, fosphenytoin) in two patients with renal impairment. Additionally, guanfacine has been associated with sedative effects and can potentiate the actions of CNS depressants, including barbiturates.
Procainamide: (Moderate) Procainamide can decrease blood pressure and should be used cautiously in patients receiving antihypertensive agents. Intravenous administration of procainamide is more likely to cause hypotensive effects.
Prochlorperazine: (Moderate) Monitor blood pressure and for unusual drowsiness or excessive sedation during concomitant central-acting adrenergic agent and phenothiazine use. Concomitant use increases the risk for additive hypotension and CNS depression.
Promethazine: (Moderate) Monitor blood pressure and for unusual drowsiness or excessive sedation during concomitant central-acting adrenergic agent and phenothiazine use. Concomitant use increases the risk for additive hypotension and CNS depression.
Promethazine; Dextromethorphan: (Moderate) Monitor blood pressure and for unusual drowsiness or excessive sedation during concomitant central-acting adrenergic agent and phenothiazine use. Concomitant use increases the risk for additive hypotension and CNS depression.
Promethazine; Phenylephrine: (Moderate) Monitor blood pressure and for unusual drowsiness or excessive sedation during concomitant central-acting adrenergic agent and phenothiazine use. Concomitant use increases the risk for additive hypotension and CNS depression.
Propofol: (Moderate) General anesthetics can potentiate the hypotensive effects of antihypertensive agents. Reduced dosages of antihypertensives may be required during heavy sedation.
Propranolol: (Moderate) Guanfacine can have additive effects when administered with other antihypertensive agents, including beta-blockers. These effects can be used to therapeutic advantage, but dosage adjustments may be necessary.
Propranolol; Hydrochlorothiazide, HCTZ: (Moderate) Guanfacine can have additive effects when administered with other antihypertensive agents, including beta-blockers. These effects can be used to therapeutic advantage, but dosage adjustments may be necessary.
Protriptyline: (Major) Tricyclic antidepressants (TCAs) can inhibit the hypotensive effects of guanfacine, causing an increase in blood pressure if given concomitantly. Consider alternatives to TCAs in patients established on guanfacine therapy for hypertension when possible; it is not clear the effect the combination may have when used in patients treated with guanfacine for attention-deficit, but other options to TCAs should be considered. Increased dosages of guanfacine may be required to control blood pressure in patients who are receiving TCAs concurrently. In addition, concurrent TCAs may enhance the potential for serious rebound hypertension following guanfacine discontinuation, regardless of the indication for treatment. If guanfacine therapy is withdrawn, guanfacine should be tapered gradually and the patient should be monitored for potential hypertension.
Quazepam: (Moderate) Guanfacine has been associated with sedative effects and can potentiate the actions of other CNS depressants including benzodiazepines.
Quinidine: (Moderate) Quinidine can decrease blood pressure and should be used cautiously in patients receiving antihypertensive agents due to the potential for additive hypotension.
Quinine: (Major) Quinine may significantly alter guanfacine plasma concentrations. Guanfacine is primarily metabolized by CYP3A4. Quinine is a moderate inhibitor of CYP3A4; in vitro data suggests it may also moderately induce CYP3A4. The net effect of this potential interaction is unclear, but guanfacine dosage adjustments, most likely a dose decrease, may be required. FDA-approved labeling for extended-release (ER) guanfacine recommends that, if used with a moderate to strong CYP3A4 inhibitor, the guanfacine dosage should be decreased to half of the recommended dose and the patient should be closely monitored for alpha-adrenergic effects (e.g., hypotension, drowsiness, bradycardia). However, if used with a moderate to strong CYP3A4 inducer, labeling recommends to consider doubling the recommended dose of guanfacine ER; if the inducer is added in a patient already receiving guanfacine, this escalation should occur over 1 to 2 weeks. If the inducer or inhibitor is discontinued, guanfacine ER should return to its recommended dose (with downward titration occurring over 1 to 2 weeks). Specific recommendations for immediate-release (IR) guanfacine are not available.
Rasagiline: (Moderate) Orthostatic hypotension has been reported during administration of rasagiline; caution is advised during concurrent use with antihypertensive agents. Patients receiving rasagiline in combination with an antihypertensive should be instructed to rise slowly from a sitting position, and to report syncope, and changes in heart rate or blood pressure to their health care provider. Rasagiline is a selective MAO-B inhibitor at manufacturer recommended doses; therefore, serious hypertensive reactions with agents affecting catecholamine release (e.g., guanabenz, reserpine, guanethidine) are unlikely.
Remimazolam: (Moderate) Guanfacine has been associated with sedative effects and can potentiate the actions of other CNS depressants including benzodiazepines.
Ribociclib: (Major) If coadministration of ribociclib with extended-release (ER) guanfacine is necessary, reduce the guanfacine dosage to half of the recommended dose. Specific recommendations for immediate-release (IR) guanfacine are not available. Monitor patients closely for alpha-adrenergic effects including hypotension, drowsiness, lethargy, and bradycardia. If ribociclib is discontinued, the guanfacine ER dosage should be increased back to the recommended dose. Guanfacine is a CYP3A4 substrate and ribociclib is a strong CYP3A4 inhibitor. Ribociclib may significantly increase guanfacine plasma concentrations.
Ribociclib; Letrozole: (Major) If coadministration of ribociclib with extended-release (ER) guanfacine is necessary, reduce the guanfacine dosage to half of the recommended dose. Specific recommendations for immediate-release (IR) guanfacine are not available. Monitor patients closely for alpha-adrenergic effects including hypotension, drowsiness, lethargy, and bradycardia. If ribociclib is discontinued, the guanfacine ER dosage should be increased back to the recommended dose. Guanfacine is a CYP3A4 substrate and ribociclib is a strong CYP3A4 inhibitor. Ribociclib may significantly increase guanfacine plasma concentrations.
Rifabutin: (Major) Rifabutin may significantly decrease guanfacine plasma concentrations. FDA-approved labeling for extended-release (ER) guanfacine recommends that, if these agents are taken together, doubling the recommended dose of guanfacine should be considered; if rifabutin is added in a patient already receiving guanfacine, this escalation should occur over 1 to 2 weeks. If rifabutin is discontinued, decrease the guanfacine ER dosage back to the recommended dose over 1 to 2 weeks. Specific recommendations for immediate-release (IR) guanfacine are not available. Guanfacine is primarily metabolized by CYP3A4, and rifabutin is a moderate CYP3A4 inducer.
Rifampin: (Major) Rifampin may significantly decrease guanfacine plasma concentrations. FDA-approved labeling for extended-release (ER) guanfacine recommends that, if these agents are taken together, doubling the recommended dose of guanfacine should be considered; if rifampin is added in a patient already receiving guanfacine, this escalation should occur over 1 to 2 weeks. Upon rifampin discontinuation, decrease the guanfacine ER dosage back to the recommended dose over 1 to 2 weeks. Specific recommendations for immediate-release (IR) guanfacine are not available. Guanfacine is primarily metabolized by CYP3A4, and rifampin is a strong CYP3A4 inducer.
Rifapentine: (Major) A dose increase of extended-release (ER) guanfacine should be considered if coadministration with rifapentine is necessary. Consider doubling the recommended dose of guanfacine if therapy is added to a patient already taking rifapentine; increase the dose of guanfacine over 1 to 2 weeks if rifapentine therapy is added to a patient already taking guanfacine. Specific recommendations for immediate-release (IR) guanfacine are not available. Guanfacine is a CYP3A4 substrate and rifapentine is a strong CYP3A4 inducer. Coadministration with another strong CYP3A4 inducer decreased guanfacine exposure by 70%.
Risperidone: (Moderate) Risperidone may induce orthostatic hypotension and thus enhance the hypotensive effects of antihypertensive agents. Lower initial doses or slower dose titration of risperidone may be necessary in patients receiving antihypertensive agents concomitantly.
Ritlecitinib: (Major) Decrease the dose of extended-release guanfacine by 50% if coadministration with ritlecitinib is necessary; if ritlecitinib is discontinued, the dose of extended-release guanfacine may be increased to the recommended level. Monitor patients closely for adverse effects including hypotension, drowsiness, lethargy, and bradycardia. Recommendations for immediate-release guanfacine are not available. Guanfacine is a CYP3A substrate and ritlecitinib is a moderate CYP3A inhibitor.
Ritonavir: (Major) Ritonavir may significantly alter guanfacine plasma concentrations. Guanfacine is primarily metabolized by CYP3A4. Ritonavir is a potent CYP3A4 inhibitor; moderate CYP3A4 induction has been reported with concomitant use of voriconazole. The net effect of this potential interaction is unclear, but guanfacine dosage adjustments, most likely a dose decrease, may be required. FDA-approved labeling for extended-release (ER) guanfacine recommends that, if used with a moderate to strong CYP3A4 inhibitor, the guanfacine dosage should be decreased to half of the recommended dose and the patient should be closely monitored for alpha-adrenergic effects (e.g., hypotension, drowsiness, bradycardia). However, if used with a moderate to strong CYP3A4 inducer, labeling recommends to consider doubling the recommended dose of guanfacine ER; if the inducer is added in a patient already receiving guanfacine, this escalation should occur over 1 to 2 weeks. If the inducer or inhibitor is discontinued, guanfacine ER should return to its recommended dose (with downward titration occurring over 1 to 2 weeks). Specific recommendations for immediate-release (IR) guanfacine are not available.
Saquinavir: (Major) Saquinavir may significantly increase guanfacine plasma concentrations. FDA-approved labeling for extended-release (ER) guanfacine recommends that, if these agents are taken together, the guanfacine dosage should be decreased to half of the recommended dose. Specific recommendations for immediate-release (IR) guanfacine are not available. Monitor patients closely for alpha-adrenergic effects including hypotension, drowsiness, lethargy, and bradycardia. If saquinavir is discontinued, the guanfacine ER dosage should be increased back to the recommended dose. Guanfacine is primarily metabolized by CYP3A4, and saquinavir is a strong CYP3A4 inhibitor.
Secobarbital: (Major) Monitor patients for guanfacine efficacy and for excess sedation during secobarbital coadministration. Guanfacine plasma concentrations can be reduced by secobarbital, by induction of CYP3A4 metabolism. Immediate-release guanfacine may require more frequent dosing to achieve or maintain desired hypotensive response; if it is discontinued, carefully taper the dose to prevent rebound hypertension. The extended-release guanfacine dose for attention deficit hyperactivity disorder (ADHD) may need to be doubled, per FDA-approved labeling; any dose change should occur over 1 to 2 weeks (e.g., dose increase when adding, or decrease when discontinuing, an enzyme inducer). Guanfacine is primarily metabolized by CYP3A4. Barbiturates (e.g., phenobarbital, primidone) are strong CYP3A4 inducers. Guanfacine plasma concentrations and elimination half-life were significantly reduced with coadministration of an enzyme inducer (e.g., phenobarbital, primidone, phenytoin, fosphenytoin) in two patients with renal impairment. Additionally, guanfacine has been associated with sedative effects and can potentiate the actions of CNS depressants, including barbiturates.
Selegiline: (Moderate) Additive hypotensive effects may be seen when monoamine oxidase inhibitors (MAOIs) such as selegiline are combined with antihypertensives. In addition, when beginning treatment with antihypertensives that initially increase the release of catecholamine stores, such as guanfacine, hypertensive crisis may occur. Because selegiline is a selective MAO-B inhibitor at manufacturer recommended doses, serious reactions with agents affecting catecholamine release are less likely than with non-selective MAOIs. Abrupt cessation of therapy with central alpha-2 adrenergic agonists like guanfacine may be associated with increases (from depressed on-therapy levels) in plasma and urinary catecholamines, symptoms of nervousness and anxiety and, less commonly, increases in blood pressure to levels significantly greater than those prior to therapy, which may affect MAO inhibiting therapy.
Sevoflurane: (Moderate) General anesthetics can potentiate the hypotensive effects of antihypertensive agents. Reduced dosages of antihypertensives may be required during heavy sedation.
Silodosin: (Moderate) During clinical trials with silodosin, the incidence of dizziness and orthostatic hypotension was higher in patients receiving concomitant antihypertensive treatment. Thus, caution is advisable when silodosin is administered with antihypertensive agents.
Sotalol: (Moderate) Guanfacine can have additive effects when administered with other antihypertensive agents, including beta-blockers. These effects can be used to therapeutic advantage, but dosage adjustments may be necessary.
Sotorasib: (Major) A dose increase of extended-release (ER) guanfacine should be considered if coadministration with sotorasib is necessary. Consider doubling the recommended dose of guanfacine if therapy is added to a patient already taking sotorasib; increase the dose of guanfacine over one to two weeks if sotorasib therapy is added to a patient already taking guanfacine. Specific recommendations for immediate-release (IR) guanfacine are not available. Guanfacine is a CYP3A4 substrate and sotorasib is a moderate CYP3A4 inducer.
St. John's Wort, Hypericum perforatum: (Major) St. John's Wort, Hypericum perforatum may significantly decrease guanfacine plasma concentrations. FDA-approved labeling for extended-release (ER) guanfacine recommends that, if these agents are taken together, doubling the recommended dose of guanfacine should be considered; if St John's Wort is added in a patient already receiving guanfacine, this escalation should occur over 1 to 2 weeks. If St. John's Wort is discontinued, decrease the guanfacine ER dosage back to the recommended dose over 1 to 2 weeks. Specific recommendations for immediate-release (IR) guanfacine are not available. Guanfacine is primarily metabolized by CYP3A4, and St. John's Wort is a strong CYP3A4 inducer.
Sulindac: (Moderate) NSAIDs may decrease the effect of antihypertensive agents through various mechanisms, including renal and peripheral vasoactive pathways.
Sumatriptan; Naproxen: (Moderate) NSAIDs may decrease the effect of antihypertensive agents through various mechanisms, including renal and peripheral vasoactive pathways.
Temazepam: (Moderate) Guanfacine has been associated with sedative effects and can potentiate the actions of other CNS depressants including benzodiazepines.
Tetrabenazine: (Moderate) Tetrabenazine may induce orthostatic hypotension and thus enhance the hypotensive effects of antihypertensive agents. Lower initial doses or slower dose titration of tetrabenazine may be necessary in patients receiving antihypertensive agents concomitantly.
Tetracaine: (Moderate) Local anesthetics may cause additive hypotension in combination with antihypertensive agents. Use extreme caution with the concomitant use of tetracaine and antihypertensive agents.
Thioridazine: (Moderate) Monitor blood pressure and for unusual drowsiness or excessive sedation during concomitant central-acting adrenergic agent and phenothiazine use. Concomitant use increases the risk for additive hypotension and CNS depression.
Thiothixene: (Moderate) Thiothixene should be used cautiously in patients receiving antihypertensive agents. Additive hypotensive effects are possible. In addition, thiothixene can antagonize the pharmacologic actions of guanethidine. Both guanethidine and guanadrel should be avoided in patients receiving thiothixene.
Timolol: (Moderate) Guanfacine can have additive effects when administered with other antihypertensive agents, including beta-blockers. These effects can be used to therapeutic advantage, but dosage adjustments may be necessary.
Tipranavir: (Major) Tipranavir may significantly increase guanfacine plasma concentrations. FDA-approved labeling for extended-release (ER) guanfacine recommends that, if these agents are taken together, the guanfacine dosage should be decreased to half of the recommended dose. Specific recommendations for immediate-release (IR) guanfacine are not available. Monitor patients closely for alpha-adrenergic effects including hypotension, drowsiness, lethargy, and bradycardia. If tipranavir is discontinued, the guanfacine ER dosage should be increased back to the recommended dose. Guanfacine is primarily metabolized by CYP3A4, and tipranavir is a strong CYP3A4 inhibitor.
Tizanidine: (Major) The use of tizanidine with other alpha 2-adrenergic agonists (such as central-acting adrenergic agonist antihypertensive agents) should be avoided because hypotensive effects may be cumulative. Tizanidine is an alpha 2-adrenergic agonist that can produce hypotension. Syncope has been reported in the postmarketing setting.
Tolmetin: (Moderate) NSAIDs may decrease the effect of antihypertensive agents through various mechanisms, including renal and peripheral vasoactive pathways.
Trandolapril; Verapamil: (Major) Verapamil may significantly increase guanfacine plasma concentrations. FDA-approved labeling for extended-release (ER) guanfacine recommends that, if these agents are taken together, the guanfacine dosage should be decreased to half of the recommended dose. Specific recommendations for immediate-release (IR) guanfacine are not available. Monitor patients closely for alpha-adrenergic effects including hypotension, drowsiness, lethargy, and bradycardia. Upon verapamil discontinuation, the guanfacine ER dosage should be increased back to the recommended dose. Guanfacine is primarily metabolized by CYP3A4, and verapamil is a moderate CYP3A4 inhibitor.
Trazodone: (Moderate) Guanfacine may potentiate the CNS-depressive effects of other sedating drugs, such as trazodone. Monitor blood pressure to ensure blood pressure remains controlled.
Triazolam: (Moderate) Guanfacine has been associated with sedative effects and can potentiate the actions of other CNS depressants including benzodiazepines.
Tricyclic antidepressants: (Major) Tricyclic antidepressants (TCAs) can inhibit the hypotensive effects of guanfacine, causing an increase in blood pressure if given concomitantly. Consider alternatives to TCAs in patients established on guanfacine therapy for hypertension when possible; it is not clear the effect the combination may have when used in patients treated with guanfacine for attention-deficit, but other options to TCAs should be considered. Increased dosages of guanfacine may be required to control blood pressure in patients who are receiving TCAs concurrently. In addition, concurrent TCAs may enhance the potential for serious rebound hypertension following guanfacine discontinuation, regardless of the indication for treatment. If guanfacine therapy is withdrawn, guanfacine should be tapered gradually and the patient should be monitored for potential hypertension.
Trifluoperazine: (Moderate) Monitor blood pressure and for unusual drowsiness or excessive sedation during concomitant central-acting adrenergic agent and phenothiazine use. Concomitant use increases the risk for additive hypotension and CNS depression.
Trimipramine: (Major) Tricyclic antidepressants (TCAs) can inhibit the hypotensive effects of guanfacine, causing an increase in blood pressure if given concomitantly. Consider alternatives to TCAs in patients established on guanfacine therapy for hypertension when possible; it is not clear the effect the combination may have when used in patients treated with guanfacine for attention-deficit, but other options to TCAs should be considered. Increased dosages of guanfacine may be required to control blood pressure in patients who are receiving TCAs concurrently. In addition, concurrent TCAs may enhance the potential for serious rebound hypertension following guanfacine discontinuation, regardless of the indication for treatment. If guanfacine therapy is withdrawn, guanfacine should be tapered gradually and the patient should be monitored for potential hypertension.
Tucatinib: (Major) If coadministration of tucatinib with extended-release (ER) guanfacine is necessary, reduce the guanfacine dosage to half of the recommended dose. Specific recommendations for immediate-release (IR) guanfacine are not available. Monitor patients closely for adverse effects including hypotension, drowsiness, lethargy, and bradycardia. If tucatinib is discontinued, the guanfacine ER dosage should be increased back to the recommended dose. Guanfacine is a CYP3A4 substrate and tucatinib is a strong CYP3A4 inhibitor. Tucatinib may significantly increase guanfacine plasma concentrations.
Valdecoxib: (Moderate) NSAIDs may decrease the effect of antihypertensive agents through various mechanisms, including renal and peripheral vasoactive pathways.
Verapamil: (Major) Verapamil may significantly increase guanfacine plasma concentrations. FDA-approved labeling for extended-release (ER) guanfacine recommends that, if these agents are taken together, the guanfacine dosage should be decreased to half of the recommended dose. Specific recommendations for immediate-release (IR) guanfacine are not available. Monitor patients closely for alpha-adrenergic effects including hypotension, drowsiness, lethargy, and bradycardia. Upon verapamil discontinuation, the guanfacine ER dosage should be increased back to the recommended dose. Guanfacine is primarily metabolized by CYP3A4, and verapamil is a moderate CYP3A4 inhibitor.
Vonoprazan; Amoxicillin; Clarithromycin: (Major) Clarithromycin may significantly increase guanfacine plasma concentrations. FDA-approved labeling for extended-release (ER) guanfacine recommends that, if these agents are taken together, the guanfacine dosage should be decreased to half of the recommended dose. Specific recommendations for immediate-release (IR) guanfacine are not available. Monitor patients closely for alpha-adrenergic effects including hypotension, drowsiness, lethargy, and bradycardia. If clarithromycin is discontinued, the guanfacine ER dosage should be increased back to the recommended dose. Guanfacine is primarily metabolized by CYP3A4, and clarithromycin is a strong CYP3A4 inhibitor.
Voriconazole: (Major) If coadministration of voriconazole with extended-release (ER) guanfacine is necessary, reduce the guanfacine dosage to half of the recommended dose. Specific recommendations for immediate-release (IR) guanfacine are not available. Monitor patients closely for alpha-adrenergic effects including hypotension, drowsiness, lethargy, and bradycardia. If voriconazole is discontinued, the guanfacine ER dosage should be increased back to the recommended dose. Guanfacine is a CYP3A4 substrate and voriconazole is a strong CYP3A4 inhibitor. Voriconazole may significantly increase guanfacine plasma concentrations.
Voxelotor: (Major) Decrease the dose of extended-release guanfacine by 50% if coadministration with voxelotor is necessary; if voxelotor is discontinued, the dose of extended-release guanfacine may be increased to the recommended level. Monitor patients closely for adverse effects including hypotension, drowsiness, lethargy, and bradycardia. Recommendations for immediate-release guanfacine are not available. Guanfacine is a CYP3A substrate and voxelotor is a moderate CYP3A inhibitor.
Ziprasidone: (Minor) Ziprasidone is a moderate antagonist of alpha-1 receptors and may cause orthostatic hypotension with or without tachycardia, dizziness, or syncope. Additive hypotensive effects are possible if ziprasidone is used concurrently with antihypertensive agents.

Guanfacine/Guanfacine Hydrochloride/Intuniv Oral Tab ER: 1mg, 2mg, 3mg, 4mg
Guanfacine/Guanfacine Hydrochloride/Tenex Oral Tab: 1mg, 2mg

3 to 4 mg/day PO (immediate-release); 7 mg/day PO of extended-release tablets (Intuniv) for ADHD.

3 to 4 mg/day PO (immediate-release). Safety and efficacy for ADHD has not been established.

3 to 4 mg/day PO (immediate-release); 7 mg/day PO of extended-release tablets (Intuniv) for ADHD.

6 to 12 years: 4 mg/day PO of extended-release tablets (Intuniv) for ADHD.
4 to 5 years: Safety and efficacy have not been established; however, doses up to 4 mg/day PO (immediate-release) have been used off-label for the treatment of ADHD.
1 to 4 years: Safety and efficacy have not been established.

Safety and efficacy have not been established.

Safety and efficacy have not been established.

Guanfacine stimulates central alpha-2-adrenergic receptors, thereby inhibiting sympathetic nervous system outflow, reducing peripheral vascular resistance, and lowering blood pressure. Guanfacine is a selective agonist, exhibiting a greater affinity for alpha-2-adrenergic receptors than for alpha-1-adrenergic receptors. During long-term therapy with guanfacine, total peripheral resistance is decreased, heart rate is slightly reduced (about 5 beats/minute), but cardiac output is generally unchanged. Guanfacine initially stimulates growth hormone secretion; however, long-term use has no effect on growth hormone plasma concentrations. Circulating levels of plasma catecholamines are reduced during guanfacine therapy, and the rebound hypertension that can occur following withdrawal is presumably due to sympathetic overactivity (increased catecholamine levels). Guanfacine reduces left ventricular hypertrophy and has neutral effects on glucose tolerance; but sexual dysfunction can be a significant problem.
 
It has been theorized that attention-deficit hyperactivity disorder (ADHD) is the result of dysfunction in fronto-striatal pathways, possibly related to dysregulation of neurotransmitters such as catecholamines. Frontal networks control attention and motor intentional behavior. Animal studies have demonstrated that guanfacine improves prefrontal cortical function through post-synaptic alpha-2-receptor agonist effects in the prefrontal cortex. Animal studies indicate that working memory is improved without significant hypotensive and sedative effects. Guanfacine is thought to produce less potent hypotensive effects than other alpha-2-receptors agonists such as clonidine due to its weaker affinity for imidazoline I-1-receptors in the brainstem. In addition, clonidine exhibits more potent inhibition of noradrenergic neurons in the locus ceruleus, which may explain the significant sedation observed with clonidine compared to guanfacine. Clinically, the use of guanfacine in ADHD has resulted in improvements in attention and hyperactive behavior, as well as a reduction in tic severity in those with a comorbid tic disorder.

Guanfacine is administered orally. Guanfacine is 70% bound to plasma proteins and is widely distributed to tissues. Guanfacine is eliminated by renal and metabolic routes. In vitro studies have shown that guanfacine is primarily metabolized by the CYP3A4 isoenzyme. Approximately 50% is excreted unchanged in the urine; the remainder is metabolized primarily as conjugates of metabolites produced by oxidative metabolism of the aromatic ring.
 
Affected cytochrome P450 (CYP450) isoenzymes and drug transporters: CYP3A4, MATE1, OCT1
Guanfacine is primarily metabolized by CYP3A4 and its plasma concentrations can be significantly affected by moderate to strong CYP3A4 inhibitors and inducers. The manufacturer of the extended-release tablets (i.e., Intuniv) recommends a 50% reduction of the target dose during concurrent use of a moderate or strong CYP3A4 inhibitor and consideration of a titration up to double the target dose over 1 to 2 weeks, based on patient response, during concurrent use of a moderate or strong CYP3A4 inducer.
 
Guanfacine inhibits MATE1 and OCT1; coadministration of guanfacine with OCT1 substrates may potentially increase the exposure of OCT1 substrates. Guanfacine is a substrate of OCT1 and OCT2, but not BCRP, OATP1B1, OATP1B3, OAT1, OAT3, MATE1, or MATE2. In vitro studies indicate that guanfacine did not inhibit the activities of the major cytochrome P450 isoenzymes (CYP1A2, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6 or CYP3A4/5); guanfacine is also not an inducer of CYP3A, CYP1A2 and CYP2B6.

There are no adequate and well-controlled studies of the use of guanfacine during pregnancy. Guanfacine should only be used during pregnancy when it is considered essential to achieve therapeutic goals in the mother. Further, guanfacine is not recommended in the treatment of acute hypertension associated with toxemia of pregnancy. If an antihypertensive drug is needed during pregnancy, other agents are preferred, such as methyldopa, for which there are data regarding safety and efficacy in pregnancy. For ADHD treatment, the risks and benefits of continuing or discontinuing guanfacine during pregnancy requires careful consideration. Animal studies have not indicated a risk for developmental toxicity; no fetal harm was observed in rats and rabbits with administration of guanfacine at 4 and 2.7 times, respectively, the maximum recommended human dose (MRHD). Higher doses (13.5 times the MRHD in both rabbits and rats) were associated with reduced fetal survival and maternal toxicity. Animal studies are not always predictive of human response. There is no information available on the effects of guanfacine on the course of labor and obstetric delivery.

It is not known whether guanfacine is excreted in human milk; however, it is excreted into rat milk. Because many drugs are excreted in human milk, caution should be exercised when guanfacine is administered when a woman is breast-feeding an infant. The antihypertensives methyldopa, nifedipine, and the beta-blockers labetalol and propranolol are considered usually compatible with breast-feeding and may represent alternatives to consider for the treatment of hypertension during lactation. While excretion of captopril or enalapril into breast milk is also low, other agents are preferred for hypertensive lactating women taking higher doses of these drugs. Diuretics are generally not recommended since they can reduce the quality of milk production. For ADHD treatment, the risks and benefits of continuing guanfacine or discontinuing guanfacine to allow breast-feeding requires careful consideration. If used, observe breast-fed infants for sedation and somnolence.