12 CLINICAL PHARMACOLOGY

Amlodipine; Valsartan; Hydrochlorothiazide, HCTZ: (Moderate) Monitor for additive hypotension if amlodipine is administered concurrently with sildenafil, as both agents act independently to reduce blood pressure. Amoxicillin; Clarithromycin; Omeprazole: (Major) Coadministration of clarithromycin is not recommended in patients receiving sildenafil for pulmonary arterial hypertension (PAH). When sildenafil is used for erectile dysfunction, consider a starting dose of 25 mg for patients receiving clarithromycin. Coadministration of other strong CYP3A4 inhibitors increased the sildenafil AUC between 3- and 11-fold. Apalutamide: (Moderate) Monitor for decreased efficacy of sildenafil if coadministration with apalutamide is necessary. Concomitant administration of strong CYP3A inducers is expected to substantially decrease plasma concentrations of sildenafil. Population pharmacokinetic analysis indicates an approximately 3-fold increase in sildenafil clearance with concomitant use of weak CYP3A inducers. Aprepitant, Fosaprepitant: (Moderate) Monitor for an increase in sildenafil-related adverse reactions if coadministered with multi-day regimens of oral aprepitant. A dose reduction of sildenafil may be required when using for erectile dysfunction. Sildenafil is a CYP3A4 substrate and aprepitant, when administered as a 3-day oral regimen (125 mg/80 mg/80 mg), is a moderate CYP3A4 inhibitor. When administered as a single oral or single intravenous dose, the inhibitory effect of aprepitant on CYP3A4 is weak and did not result in a clinically significant increase in the AUC of a sensitive substrate.

5.6 Combination with Other PDE-5 Inhibitors

(Major) Sildenafil is contraindicated for use with darunavir when used for pulmonary arterial hypertension (PAH). Delavirdine: (Major) Coadministration of delavirdine is not recommended in patients receiving sildenafil for pulmonary arterial hypertension (PAH). When sildenafil is used for erectile dysfunction, the dose of sildenafil should not exceed 25 mg in 48 hours. Dexamethasone: (Moderate) Monitor for decreased efficacy of sildenafil if coadministration with dexamethasone is necessary as concurrent use may decrease sildenafil exposure. Dextromethorphan; Diphenhydramine; Phenylephrine: (Minor) The therapeutic effect of phenylephrine injection may be decreased in patients receiving phosphodiesterase inhibitors. Atazanavir: (Major) Sildenafil is contraindicated for use with atazanavir when used for pulmonary arterial hypertension (PAH). If used for erectile dysfunction, the dose of sildenafil should not exceed 25 mg in 48 hours with increased monitoring for adverse reactions during times of coadministration.

Concurrent use is expected to substantially increase the sildenafil plasma concentrations and may 20mg sildenafil result in increased associated adverse events including hypotension, syncope, visual changes, and prolonged erection.

5.4 Hearing Loss

Dextromethorphan; Guaifenesin; Phenylephrine: (Minor) The therapeutic effect of phenylephrine injection may be decreased in patients receiving phosphodiesterase inhibitors. Dextromethorphan; Quinidine: (Moderate) Sildenafil is metabolized principally by the hepatic isoenzymes CYP3A4 and CYP2C9. Atazanavir; Cobicistat: (Major) Sildenafil is contraindicated for use with atazanavir when used for pulmonary arterial hypertension (PAH). (Major) Sildenafil is contraindicated for use with cobicistat when used for pulmonary arterial hypertension (PAH). Atropine; Difenoxin: (Moderate) Diphenoxylate/difenoxin is a synthetic opiate agonist with a chemical structure similar to that of meperidine.

• Sildenafil interacts with nitrates, causing dangerous blood pressure drops.
• Consult a doctor before starting if on other medications.
• Alcohol may reduce the effectiveness and increase side effects.

Prolonged erections have been reported in two patients taking sildenafil with dihydrocodeine. In both cases, patients reported erections subsided immediately after orgasm when taking sildenafil alone. Although more data are needed, use caution when prescribing opiate agonists and sildenafil concomitantly. Barbiturates: (Minor) Sildenafil is metabolized principally by the hepatic CYP3A4 and CYP2C9 isoenzymes. It can be expected that concomitant administration of CYP3A4 enzyme-inducers will decrease plasma levels of sildenafil, however, no interaction studies have been performed. Belzutifan: (Moderate) Monitor for decreased efficacy of sildenafil if coadministration with belzutifan is necessary as concurrent use may decrease sildenafil exposure. Berotralstat: (Moderate) Monitor for an increase in sildenafil-related adverse reactions if coadministration with berotralstat is necessary; consider a starting dose of 25 mg of sildenafil when prescribed for erectile dysfunction. Brigatinib: (Moderate) Monitor for decreased efficacy of sildenafil if coadministration with brigatinib is necessary as concurrent use may decrease sildenafil exposure. Population pharmacokinetic analysis indicates an approximately 3-fold increase in sildenafil clearance with concomitant use of weak CYP3A4 inducers.

Brompheniramine; Dextromethorphan; Phenylephrine: (Minor) The therapeutic effect of phenylephrine injection may be decreased in patients receiving phosphodiesterase inhibitors. Brompheniramine; Phenylephrine: (Minor) The therapeutic effect of phenylephrine injection may be decreased in patients receiving phosphodiesterase inhibitors. Carbamazepine: (Moderate) Monitor for decreased efficacy of sildenafil if coadministration with carbamazepine is necessary as concurrent use may decrease sildenafil exposure. Sildenafil is a sensitive CYP3A substrate and carbamazepine is a strong CYP3A inducer. 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.

• Overdose symptoms may include dizziness, nausea, or prolonged erections.
• Seek emergency help if an erection lasts over 4 hours.
• Avoid excessive dosing to prevent adverse events.

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. Cenobamate: (Moderate) Monitor for decreased efficacy of sildenafil if coadministration with cenobamate is necessary as concurrent use may decrease sildenafil exposure. Ceritinib: (Major) Coadministration with ceritinib is not recommended in patients receiving sildenafil for pulmonary arterial hypertension (PAH). When sildenafil is used for erectile dysfunction, consider a starting dose of sildenafil spray 25 mg for patients receiving ceritinib. Chloramphenicol: (Major) Coadministration of chloramphenicol is not recommended in patients receiving sildenafil for pulmonary arterial hypertension (PAH). When sildenafil is used for erectile dysfunction, consider a starting dose of 25 mg for patients receiving chloramphenicol. Chlorpheniramine; Dextromethorphan; Phenylephrine: (Minor) The therapeutic effect of phenylephrine injection may be decreased in patients receiving phosphodiesterase inhibitors. Chlorpheniramine; Dihydrocodeine; Phenylephrine: (Minor) The therapeutic effect of phenylephrine injection may be decreased in patients receiving phosphodiesterase inhibitors.

Overdose/Missed Dose

Ciprofloxacin: (Moderate) Monitor for an increase in sildenafil-related adverse reactions if coadministration with ciprofloxacin is necessary; consider a starting dose of 25 mg of sildenafil when prescribed for erectile dysfunction. Clarithromycin: (Major) Coadministration of clarithromycin is not recommended in patients receiving sildenafil for pulmonary arterial hypertension (PAH). Cobicistat: (Major) Sildenafil is contraindicated for use with cobicistat when used for pulmonary arterial hypertension (PAH). Codeine; Phenylephrine; Promethazine: (Minor) The therapeutic effect of phenylephrine injection may be decreased in patients receiving phosphodiesterase inhibitors. Conivaptan: (Moderate) Monitor for an increase in sildenafil-related adverse reactions if coadministration with conivaptan is necessary; consider a starting dose of 25 mg of sildenafil when prescribed for erectile dysfunction.

Prior authorization

In a drug interaction study, coadministration with a moderate CYP3A inhibitor increased the peak and overall exposure of sildenafil by 160% and 182%, respectively. Predictions based on a pharmacokinetic model suggest that drug-drug interactions with CYP3A inhibitors will be less for sildenafil injection than those observed after oral sildenafil administration. Crizotinib: (Moderate) Monitor for an increase in sildenafil-related adverse reactions if coadministration with crizotinib is necessary; sildenafil oral jelly 100 mg consider a starting dose of 25 mg of sildenafil when prescribed for erectile dysfunction. Dabrafenib: (Major) The concomitant use of dabrafenib and sildenafil may lead to decreased sildenafil concentrations and loss of efficacy. Use of an alternative agent is recommended.

How Viagra Works

If concomitant use of these agents together is unavoidable, monitor patients for loss of sildenafil efficacy. Concomitant use of dabrafenib with a single dose of another sensitive CYP3A4 substrate decreased the AUC value of the sensitive CYP3A4 substrate by 65%. Danazol: (Moderate) Monitor for an increase in sildenafil-related adverse reactions if coadministration with danazol is necessary; a dose reduction of sildenafil may be necessary when prescribed for erectile dysfunction. Darunavir: (Major) Sildenafil is contraindicated for use with darunavir when used for pulmonary arterial hypertension (PAH). Darunavir; Cobicistat: (Major) Sildenafil is contraindicated for use with cobicistat when used for pulmonary arterial hypertension (PAH). Chlorpheniramine; Phenylephrine: (Minor) The therapeutic effect of phenylephrine injection may be decreased in patients receiving phosphodiesterase inhibitors.

Other Comments

Cimetidine: (Moderate) Monitor for an increase in sildenafil-related adverse reactions if coadministration with cimetidine is necessary.

• Sildenafil is generally safe when used as prescribed.
• Always follow your healthcare provider’s dosage instructions.
• Do not double doses if a dose is missed.

Concomitant use may increase sildenafil plasma concentrations. Cimetidine 800 mg caused a 56% increase in plasma sildenafil concentrations when coadministered with sildenafil 50 mg to healthy volunteers. Ciprofloxacin: (Moderate) Monitor for an increase in sildenafil-related adverse reactions if coadministration with ciprofloxacin is necessary; consider a starting dose of 25 mg of sildenafil when prescribed for erectile dysfunction. Clarithromycin: (Major) Coadministration of clarithromycin is not recommended in patients receiving sildenafil for pulmonary arterial hypertension (PAH). Cobicistat: (Major) Sildenafil is contraindicated for use with cobicistat when used for pulmonary arterial hypertension (PAH). Codeine; Phenylephrine; Promethazine: (Minor) The therapeutic effect of phenylephrine injection may be decreased in patients receiving phosphodiesterase inhibitors. Conivaptan: (Moderate) Monitor for an increase in sildenafil-related adverse reactions if coadministration with conivaptan is necessary; consider a starting dose of 25 mg of sildenafil when prescribed for erectile dysfunction. In a drug interaction study, coadministration with a moderate CYP3A inhibitor increased the peak and overall exposure of sildenafil by 160% and 182%, respectively. Predictions based on a pharmacokinetic model suggest that drug-drug interactions with CYP3A inhibitors will be less for sildenafil injection than those observed after oral sildenafil administration. Crizotinib: (Moderate) Monitor for an increase in sildenafil-related adverse reactions if coadministration with crizotinib is necessary; sildenafil oral jelly 100 mg consider a starting dose of 25 mg of sildenafil when prescribed for erectile dysfunction. Dabrafenib: (Major) The concomitant use of dabrafenib and sildenafil may lead to decreased sildenafil concentrations and loss of efficacy. Use of an alternative agent is recommended.

5.3 Epistaxis

(Major) Sildenafil is contraindicated for use with cobicistat when used for pulmonary arterial hypertension (PAH). Atropine; Difenoxin: (Moderate) Diphenoxylate/difenoxin is a synthetic opiate agonist with a chemical structure similar to that of meperidine. Prolonged erections have been reported in two patients taking sildenafil with dihydrocodeine. In both cases, patients reported erections subsided immediately after orgasm when taking sildenafil alone. Although more data are needed, use caution when prescribing opiate agonists and sildenafil concomitantly.

Important Safety Information

Barbiturates: (Minor) Sildenafil is metabolized principally by the hepatic CYP3A4 and CYP2C9 isoenzymes. It can be expected that concomitant administration of CYP3A4 enzyme-inducers will decrease plasma levels of sildenafil, however, no interaction studies have been performed. Belzutifan: (Moderate) Monitor for decreased efficacy of sildenafil if coadministration with belzutifan is necessary as concurrent use may decrease sildenafil exposure. Berotralstat: (Moderate) Monitor for an increase in sildenafil-related adverse reactions if coadministration with berotralstat is necessary; consider a starting dose of 25 mg of sildenafil when prescribed for erectile dysfunction. Brigatinib: (Moderate) Monitor for decreased efficacy of sildenafil if coadministration with brigatinib is necessary as concurrent use may decrease sildenafil exposure.

Common Adverse Effects

Population pharmacokinetic analysis indicates an approximately 3-fold increase in sildenafil clearance with concomitant use of weak CYP3A4 inducers. Brompheniramine; Dextromethorphan; Phenylephrine: (Minor) The therapeutic effect of phenylephrine injection may be decreased in patients receiving phosphodiesterase inhibitors. Brompheniramine; Phenylephrine: (Minor) The therapeutic effect of phenylephrine injection may be decreased in patients receiving phosphodiesterase inhibitors. Carbamazepine: (Moderate) Monitor for decreased efficacy of sildenafil if coadministration with carbamazepine is necessary as concurrent use may decrease sildenafil exposure. Sildenafil is a sensitive CYP3A substrate and carbamazepine is a strong CYP3A inducer. If concomitant use of these agents together is unavoidable, monitor patients for loss of sildenafil efficacy. Concomitant use of dabrafenib with a single dose of another sensitive CYP3A4 substrate decreased the AUC value of the sensitive CYP3A4 substrate by 65%. Danazol: (Moderate) Monitor for an increase in sildenafil-related adverse reactions if coadministration with danazol is necessary; a dose reduction of sildenafil may be necessary when prescribed for erectile dysfunction. Darunavir: (Major) Sildenafil is contraindicated for use with darunavir when used for pulmonary arterial hypertension (PAH). Darunavir; Cobicistat: (Major) Sildenafil is contraindicated for use with cobicistat when used for pulmonary arterial hypertension (PAH). (Major) Sildenafil is contraindicated for use with darunavir when used for pulmonary arterial hypertension (PAH). Delavirdine: (Major) Coadministration of delavirdine is not recommended in patients receiving sildenafil for pulmonary arterial hypertension (PAH).

12.2 Pharmacodynamics

Amlodipine; Valsartan; Hydrochlorothiazide, HCTZ: (Moderate) Monitor for additive hypotension if amlodipine is administered concurrently with sildenafil, as both agents act independently to reduce blood pressure. Amoxicillin; Clarithromycin; Omeprazole: (Major) Coadministration of clarithromycin is not recommended in patients receiving sildenafil for pulmonary arterial hypertension (PAH). When sildenafil is used for erectile dysfunction, consider a starting dose of 25 mg for patients receiving clarithromycin. Coadministration of other strong CYP3A4 inhibitors increased the sildenafil AUC between 3- and 11-fold. Apalutamide: (Moderate) Monitor for decreased efficacy of sildenafil if coadministration with apalutamide is necessary.

How it works

Concomitant administration of strong CYP3A inducers is expected to substantially decrease plasma concentrations of sildenafil. Population pharmacokinetic analysis indicates an approximately 3-fold increase in sildenafil clearance with concomitant use of weak CYP3A inducers. Aprepitant, Fosaprepitant: (Moderate) Monitor for an increase in sildenafil-related adverse reactions if coadministered with multi-day regimens of oral aprepitant. A dose reduction of sildenafil may be required when using for erectile dysfunction. Sildenafil is a CYP3A4 substrate and aprepitant, when administered as a 3-day oral regimen (125 mg/80 mg/80 mg), is a moderate CYP3A4 inhibitor.

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When administered as a single oral or single intravenous dose, the inhibitory effect of aprepitant on CYP3A4 is weak and did not result in a clinically significant increase in the AUC of a sensitive substrate. Atazanavir: (Major) Sildenafil is contraindicated for use with atazanavir when used for pulmonary arterial hypertension (PAH). If used for erectile dysfunction, the dose of sildenafil should not exceed 25 mg in 48 hours with increased monitoring for adverse reactions during times of coadministration. Concurrent use is expected to substantially increase the sildenafil plasma concentrations and may 20mg sildenafil result in increased associated adverse events including hypotension, syncope, visual changes, and prolonged erection. Atazanavir; Cobicistat: (Major) Sildenafil is contraindicated for use with atazanavir when used for pulmonary arterial hypertension (PAH). When sildenafil is used for erectile dysfunction, the dose of sildenafil should not exceed 25 mg in 48 hours.

5.7 Combination with other PDE5 Inhibitors or Other Erectile Dysfunction Therapies

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. Cenobamate: (Moderate) Monitor for decreased efficacy of sildenafil if coadministration with cenobamate is necessary as concurrent use may decrease sildenafil exposure.

What causes an erection?

Ceritinib: (Major) Coadministration with ceritinib is not recommended in patients receiving sildenafil for pulmonary arterial hypertension (PAH). When sildenafil is used for erectile dysfunction, consider a starting dose of sildenafil spray 25 mg for patients receiving ceritinib. Chloramphenicol: (Major) Coadministration of chloramphenicol is not recommended in patients receiving sildenafil for pulmonary arterial hypertension (PAH). When sildenafil is used for erectile dysfunction, consider a starting dose of 25 mg for patients receiving chloramphenicol. Chlorpheniramine; Dextromethorphan; Phenylephrine: (Minor) The therapeutic effect of phenylephrine injection may be decreased in patients receiving phosphodiesterase inhibitors.

Study 2: Sildenafil citrate with Doxazosin

Chlorpheniramine; Dihydrocodeine; Phenylephrine: (Minor) The therapeutic effect of phenylephrine injection may be decreased in patients receiving phosphodiesterase inhibitors. Chlorpheniramine; Phenylephrine: (Minor) The therapeutic effect of phenylephrine injection may be decreased in patients receiving phosphodiesterase inhibitors. Cimetidine: (Moderate) Monitor for an increase in sildenafil-related adverse reactions if coadministration with cimetidine is necessary. Concomitant use may increase sildenafil plasma concentrations. Cimetidine 800 mg caused a 56% increase in plasma sildenafil concentrations when coadministered with sildenafil 50 mg to healthy volunteers. Dexamethasone: (Moderate) Monitor for decreased efficacy of sildenafil if coadministration with dexamethasone is necessary as concurrent use may decrease sildenafil exposure. Dextromethorphan; Diphenhydramine; Phenylephrine: (Minor) The therapeutic effect of phenylephrine injection may be decreased in patients receiving phosphodiesterase inhibitors. Dextromethorphan; Guaifenesin; Phenylephrine: (Minor) The therapeutic effect of phenylephrine injection may be decreased in patients receiving phosphodiesterase inhibitors. Dextromethorphan; Quinidine: (Moderate) Sildenafil is metabolized principally by the hepatic isoenzymes CYP3A4 and CYP2C9.