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Sildenafil (Erectile Dysfunction) (Monograph)

Brand name: Viagra
Drug class: Calcium-Channel Blocking Agents

Medically reviewed by Drugs.com on Apr 10, 2024. Written by ASHP.

Introduction

Vasodilating agent; a selective phosphodiesterase (PDE) type 5 inhibitor.1 2 4 5 7 8 10 24 27 33 41 56 57 67 91 131

Uses for Sildenafil (Erectile Dysfunction)

Erectile Dysfunction (ED)

Used for the treatment of erectile dysfunction (ED, impotence).1 4 6 7 8 9 10 25 33 34 67 81 102 104 105 107 108 112 118 126 127 128 129 130 131 132 133 134 140 142 143 144 189

Experts recommend a selective PDE type 5 inhibitor as first-line therapy for ED unless contraindicated.189 601 Evidence currently insufficient to support the superiority of one selective PDE type 5 inhibitor over another.189 601 602

Sildenafil (Erectile Dysfunction) Dosage and Administration

Administration

Oral Administration

Administer orally about 1 hour (range: 4 hours to 30 minutes) before sexual activity.1 91 127 132

Administration with a high-fat meal may delay the onset of action.1 117 131 602 603

Sexual stimulation is required for response to therapy.1

Dosage

Available as sildenafil citrate; dosage expressed in terms of sildenafil.1 203

Adults

ED
Oral

Initially, 50 mg as a single dose as needed no more than once daily.1 28 33 81 91 93 94 102 105 118 130 132 161

Depending on effectiveness and tolerance, increase dosage to a maximum of 100 mg once daily or decrease to 25 mg once daily.1 28 33 91 93 94 105 161

Dosage Modifications for Drug Interactions

α-Adrenergic Blocking Agent: Patients should be stable on the α-adrenergic blocking agent before initiating sildenafil; initiate sildenafil at the lowest dose.1

CYP3A4 Inhibitors:Strong CYP3A4 inhibitors (e.g., itraconazole, ketoconazole, cobicistat) or the moderate CYP3A4 inhibitor erythromycin: Initial recommended dose of sildenafil is 25 mg.1 200

Protease Inhibitors (e.g., Ritonavir):Do not exceed a maximum single sildenafil dose of 25 mg in a 48 hour period.1

Special Populations

Hepatic Impairment

Reduce initial dose to 25 mg.1

Renal Impairment

Clcr <30 mL/minute: reduce initial dose to 25 mg.1

Geriatric Patients

Reduce initial dose to 25 mg in men ≥65 years of age.1

Detailed Sildenafil dosage information

Cautions for Sildenafil (Erectile Dysfunction)

Contraindications

Warnings/Precautions

Cardiovascular Effects

Potential for cardiac risk of sexual activity in patients with preexisting cardiovascular disease.1 Generally should not be used in men for whom sexual activity is inadvisable because of their underlying cardiovascular status.1

Use with caution in patients with a recent (within 6 months) MI, stroke, or life-threatening arrhythmia;1 31 101 127 144 154 155 159 in patients with resting hypotension (BP <90/50 mm Hg) or hypertension (BP >170/110 mm Hg);1 31 101 127 144 154 155 159 or in patients with cardiac failure or CAD causing unstable angina.1 31 101 127 144 154 155 159

Consider whether patients with underlying cardiovascular disease (e.g., severe left ventricular outflow obstruction, autonomic dysfunction, resting hypotension [BP <90/50 mm Hg], fluid depletion) could be adversely affected by sildenafil’s vasodilatory activity, especially in combination with sexual activity.1 67 154

Ocular Effects

Nonarteritic anterior ischemic optic neuropathy (NAION) reported rarely in patients receiving PDE type 5 inhibitors for the treatment of ED.1 190 191 192 196 197 Potential increased risk of NAION in the second eye in patients who already have had NAION in one eye.1 196

If sudden vision loss or decreased vision occurs in one or both eyes, discontinue drug and contact a clinician immediately.1

Use with caution in patients with retinitis pigmentosa.1 31 155

Otic Effects

Sudden decrease or loss of hearing, with or without concomitant vestibular manifestations (e.g., tinnitus, vertigo, dizziness) reported with all PDE type 5 inhibitors, including sildenafil.1

Not clear whether such effects are directly related to PDE type 5 inhibitors or to other underlying risk factors for hearing loss, a combination of these factors, or to other factors.1

Discontinue sildenafil and seek medical attention immediately if sudden hearing loss or decreased hearing occurs.1

Priapism

Possible prolonged (>4 hours) erections and priapism (painful erection >6 hours).1 31 139 146 147

May result in penile tissue damage and permanent loss of potency if priapism is not treated immediately.1 31

Use with caution in patients with anatomic deformation of the penis (e.g., angulation, cavernosal fibrosis, Peyronie's disease) and conditions predisposing to priapism (e.g., sickle cell anemia, multiple myeloma, leukemia).1 33 159

Concomitant Administration with α-Adrenergic Blocking Agents

Use with caution in patients receiving α-adrenergic blocking agents; possible potentiation of hypotensive effects due to additive vasodilatory action.1 In some cases, dose adjustments necessary; in other cases, concomitant administration not recommended.1

In patients who exhibit hemodynamic instability while receiving an α-adrenergic blocking agent, use caution.1 Patients should be stable on an α-adrenergic blocking agent prior to initiation of sildenafil, and sildenafil should be administered at the lowest possible dose.1 In patients receiving an optimal dose of sildenafil, initiate the α-adrenergic blocking agent at the lowest dose.1

Concomitant Use with Ritonavir

Concomitant administration of ritonavir substantially increases serum concentrations of sildenafil; decreased BP, syncope, and prolonged erection reported.1

Use caution; reduce sildenafil dosage to decrease risk of adverse reactions.1

Bleeding

Use with caution in patients with bleeding disorders or active peptic ulcers.1 27 33 67 131

Combination with other PDE Type 5 Inhibitors or other ED Therapies

Safety and efficacy not established for use in combination with other PDE type 5 inhibitors or other treatments for ED; such combinations may further lower BP and not recommended.1

Counseling Patients about Sexually Transmitted Diseases

Use of sildenafil provides no protection against sexually transmitted diseases; counsel patients regarding protective measures to guard against such transmission.1 26 68

Specific Populations

Pregnancy

Not indicated for use in females.1 No data in pregnant women to inform any drug-associated risks for adverse developmental outcomes.1

No evidence of teratogenicity, embryotoxicity, or fetotoxicity in animal studies.1

Lactation

Not indicated for use in females.1

Limited data indicate that sildenafil and its active metabolite are present in human milk.1

No data on effects on the breastfed infant or on milk production.1

Females and Males of Reproductive Potential

No evidence of impaired fertility in animal studies.1

No effect on sperm motility of morphology in healthy human adults.1

Pediatric Use

Not indicated for use in pediatric patients.1 Safety and efficacy not established in children.1

Geriatric Use

No overall differences in safety and efficacy between geriatric (≥65 years of age) and younger patients.1

Decreased clearance and increased plasma concentrations may increase incidence of adverse effects in geriatric patients.1

Hepatic Impairment

Child-Pugh class A or B: Decreased clearance.1 31 67 69 Pharmacokinetics in patients with severe hepatic impairment (Child-Pugh class C): Not studied.1 Starting dose of 25 mg should be considered in patients with any degree of hepatic impairment.1

Renal Impairment

Pharmacokinetics not altered in patients with mild or moderate (Clcr30–80 mL/minute) renal impairment.1

Decreased clearance in patients with severe (Clcr<30 mL/minute) renal impairment; consider reducing initial dose to 25 mg.1 67 80

Common Adverse Effects

Common adverse effects (≥2%): headache, flushing, dyspepsia, abnormal vision, nasal congestion, back pain, myalgia, nausea, dizziness, rash.1

Drug Interactions

Metabolized principally by CYP3A4 and to some extent by CYP2C9; weakly inhibits CYP1A2, 2C9, 2C19, 2D6, 2E1, and 3A4.1 26 67 91 250

Drugs Affecting Hepatic Microsomal Enzymes

Inhibitors of CYP3A4 and CYP2C9: Potential pharmacokinetic interaction (increased plasma sildenafil concentrations).1 26 67 91

Inducers of CYP3A4: Potential pharmacokinetic interaction (decreased plasma sildenafil concentrations).1 26 67 91 212

Drugs Metabolized by Hepatic Microsomal Enzymes

Substrates of CYP1A2, 2C9, 2C19, 2D6, 2E1, and 3A4: sildenafil not expected to alter pharmacokinetics of substrate drug.1 26 67

Specific Drugs

Drug

Interaction

Comments

α-Adrenergic blockers

Possible potentiation of systemic vasodilation and symptomatic hypotension1

In patients stable on an α-adrenergic blocker, initiate sildenafil at lowest recommended dosage for treatment of ED; in those currently receiving sildenafil, initiate α-adrenergic blocker at the lowest dosage 1

Use concomitantly with caution1

Alcohol

No additive hypotensive effects reported1

Antacids

Oral bioavailability of sildenafil unaffected by single doses of aluminum and magnesium hydroxide-containing antacid1

Antidepressants (e.g., SSRIs, tricyclic antidepressants)

No effect on sildenafil pharmacokinetics1

No change in efficacy of sildenafil for treatment of ED1

Antifungals, azole (itraconazole, ketoconazole)

Possible increased systemic exposure of sildenafil1 250

Consider lower initial sildenafil dose (25 mg) for treatment of ED1 67

Antihypertensive and hypotensive agents

Potential additive hypotensive effects1 29 67

Amlodipine: Additional reductions in supine BP observed1 29 154

Thiazides and related diuretics, ACE inhibitors, calcium channel-blocking agents: No effect on sildenafil pharmacokinetics1

Loop and potassium-sparing diuretics, nonspecific β-adrenergic blocking agents: Increased AUC of active sildenafil metabolite (N-desmethyl sildenafil),1 but effect not expected to be clinically important1

Antiretroviral agents (HIV protease inhibitors, alone or in combination with ritonavir)

Decreased clearance, increased plasma concentrations of sildenafil, and increased risk of sildenafil-associated adverse effects (e.g., hypotension, visual changes, prolonged erection)1 26 67 139 200 240

Reduce initial sildenafil dose for treatment of ED to 25 mg and do not exceed a single 25-mg dose every 48 hours1 200 240

Antiretroviral agents (nonnucleoside reverse transcriptase inhibitors [NNRTIs])

Etravirine: Decreased plasma sildenafil concentrations200

May administer concomitantly without dosage adjustment, but increase in sildenafil dosage may be needed based on clinical effect200

Aspirin

No increase in bleeding time reported1 65 67

Bosentan

Decreased plasma sildenafil concentrations; increased plasma bosentan concentrations1 241 212

Clinical importance of pharmacokinetic interaction unclear241

Cimetidine

Increased plasma sildenafil concentrations1 67

Consider lower initial sildenafil dose (25 mg) for treatment of ED67

Cobicistat in combination with elvitegravir

Increased plasma sildenafil concentrations expected200

Reduce sildenafil dose to 25 mg and do not exceed a single 25-mg dose every 48 hours200

Heparin

Increased bleeding time reported in animals1

Current evidence does not preclude concomitant heparin67

Inhaled nitrites (e.g., amyl or butyl nitrite)

Possible sudden and marked BP reduction; potentially serious or even fatal26 67

Concomitant use contraindicated1 29 57 67 148 154

Macrolides (azithromycin, erythromycin)

Azithromycin: No pharmacokinetic interaction observed to date138 239

Erythromycin: Increased AUC of sildenafil1 69 239

Azithromycin: No dosage adjustments necessary 239

Erythromycin: Consider lower initial sildenafil dose (25 mg)1 239

Nitrates and nitrites (e.g., nitroglycerin, isosorbide dinitrate)

Potentiation of vasodilatory effects (e.g., decrease in systolic BP of >25 mm Hg) of organic nitrates and nitrites; potentially life-threatening hypotension and/or hemodynamic compromise can result1 28 29 31 33 53 57 61 67 69 91 127 131 148

Concomitant use contraindicated1 29 57 67 148 154

Some clinicians suggest that nitrates and nitrites may be given >24 hours after sildenafil, but the point at which these drugs can be given safely after sildenafil is unclear;1 29 31 67 154 avoid concomitant use unless benefits outweigh risks67

PDE inhibitors

Safety and efficacy of concomitant use not evaluated1

Combination therapy not recommended1

Rifamycins (rifabutin, rifampin)

Possible decreased plasma sildenafil concentrations1 69

Riociguat

Possible additive hypotensive effects1 247

Concomitant use contraindicated1 247

Sodium nitroprusside

Potentiation of vasodilatory effects (e.g., decrease in systolic BP of >25 mm Hg) of organic nitrates and nitrites; potentially life-threatening hypotension and/or hemodynamic compromise can result1 28 29 31 33 53 57 61 67 69 91 127 131 148

Also may potentiate the inhibitory effect of nitric oxide and sodium nitroprusside (a nitric oxide donor) on platelet aggregation1 57 67

Concomitant use contraindicated1 29 57 67 148 154

Some clinicians suggest that nitrates and nitrites may be given >24 hours after sildenafil, but the point at which these drugs can be given safely after sildenafil is unclear;1 29 31 67 154 avoid concomitant use unless benefits outweigh risks67

Tolbutamide

No effect on sildenafil pharmacokinetics1 67

Vitamin K antagonists (e.g., acenocoumarol, phenprocoumon, warfarin)

No substantial effect on INR;1 67

Warfarin: No pharmacokinetic interaction observed1 67
Sildenafil drug interactions (more detail)

Sildenafil (Erectile Dysfunction) Pharmacokinetics

Absorption

Bioavailability

Rapidly absorbed following oral administration;1 4 56 67 91 116 203 mean absolute bioavailability 41% (range, 25–63%).1 4 56 67 91 116 131

Peak plasma concentrations usually attained within 30–120 minutes.1 4 91 127 130

Duration

Erectile responsiveness: Approximately 2 hours.1

Onset

Erectile responsiveness: 14–20 minutes, self-recorded in the home setting.178

Food

Administration with a high-fat meal delays GI absorption;1 131 peak plasma concentrations reduced by about 30% and time to peak plasma concentrations delayed by about 60 minutes.1 131

Distribution

Extent

Appears to be widely distributed in the body.1 4 67 116 131

Distributed to a limited extent in semen,1 67 but such concentrations are unlikely to cause any effects in sexual partners.67

Plasma Protein Binding

Approximately 96%.1 67 91 116 131

Elimination

Metabolism

Undergoes extensive metabolism in GI mucosa during absorption and on first pass through liver.91 116

Metabolized in the liver 116 131 principally by CYP3A4 and to a lesser extent by CYP2C9.1 91 131

N-desmethtyl metabolite accounts for about 20% of pharmacologic activity.1

Elimination Route

Excreted as metabolites in the feces (approximately 80%) and urine (approximately 13%).1 67 116 131

Half-life

Biphasic; terminal elimination half-life about 4 hours.1 4 67 91 116 127 130 131

Special Populations

Clearance in patients ≥65 years of age is reduced compared with that in younger adults.1 31 67 91 131 139

In patients with severe renal impairment (Clcr <30 mL/minute), clearance was reduced resulting in a two-fold increase in AUC and peak plasma concentrations compared with values in healthy adults.1 31 67 91 131 139 Pharmacokinetics not altered in mild to moderate renal impairment.1 31 131

Reduced clearance in patients with hepatic cirrhosis (Child-Pugh class A or B).1 31 131

Stability

Storage

Oral

Tablets

25°C (may be exposed to 15–30°C).1

Actions

Advice to Patients

Additional Information

The American Society of Health-System Pharmacists, Inc. represents that the information provided in the accompanying monograph was formulated with a reasonable standard of care, and in conformity with professional standards in the field. Readers are advised that decisions regarding use of drugs are complex medical decisions requiring the independent, informed decision of an appropriate health care professional, and that the information contained in the monograph is provided for informational purposes only. The manufacturer’s labeling should be consulted for more detailed information. The American Society of Health-System Pharmacists, Inc. does not endorse or recommend the use of any drug. The information contained in the monograph is not a substitute for medical care.

Preparations

Excipients in commercially available drug preparations may have clinically important effects in some individuals; consult specific product labeling for details.

Please refer to the ASHP Drug Shortages Resource Center for information on shortages of one or more of these preparations.

* available from one or more manufacturer, distributor, and/or repackager by generic (nonproprietary) name

Sildenafil Citrate

Routes

Dosage Forms

Strengths

Brand Names

Manufacturer

Oral

Tablets, film-coated

25 mg (of sildenafil)*

Sildenafil Tablets

Viagra

Pfizer

50 mg (of sildenafil)*

Sildenafil Tablets

Viagra

Pfizer

100 mg (of sildenafil)*

Sildenafil Tablets

Viagra

Pfizer

AHFS DI Essentials™. © Copyright 2024, Selected Revisions April 10, 2024. American Society of Health-System Pharmacists, Inc., 4500 East-West Highway, Suite 900, Bethesda, Maryland 20814.

References

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