What is the recommended dose of sildenafil (phosphodiesterase type 5 inhibitor) for erectile dysfunction?

Sildenafil Dosing for Erectile Dysfunction

Start sildenafil at 50 mg taken approximately 1 hour before sexual activity, with dose adjustment to 100 mg if inadequate response or reduction to 25 mg for tolerability issues or in special populations. 1, 2

Standard Dosing Protocol

• The recommended starting dose is 50 mg, taken approximately 1 hour before sexual activity, not more than once daily 1, 2
• Titrate to 100 mg (maximum dose) if 50 mg provides inadequate efficacy 1, 2
• Reduce to 25 mg in patients with severe hepatic impairment, severe renal impairment, or those taking CYP3A4 inhibitors (ritonavir, saquinavir, ketoconazole, erythromycin, cimetidine) 1, 2
• Sexual stimulation is mandatory for effectiveness—the medication will not work without it 1, 3

Dose-Response Relationship

• Improvement in erectile function is dose-related for sildenafil, with 50 mg superior to 25 mg 1
• In clinical trials, 67-86% of patients on sildenafil reported improved erections compared to 24% on placebo 4
• Starting at 100 mg significantly reduces anxiety about the next intercourse attempt (56% felt no anxiety) compared to 50 mg (39% felt no anxiety), without increasing adverse events 5
• However, the American Urological Association recommends dose titration starting at 50 mg to optimize the balance between efficacy and tolerability 6, 1

Defining an Adequate Trial

• Before declaring treatment failure, ensure at least 5 separate attempts at maximum dose (100 mg) 7
• Many apparent failures result from modifiable factors: 6
  • Taking medication with large meals (delays absorption) 1
  • Inadequate sexual stimulation 6, 1
  • Improper timing of dose 6
  • Heavy alcohol use 6
  • Undiagnosed hormonal abnormalities (check testosterone) 6, 7
• After re-education on proper use and dose titration to maximum, some initial non-responders become successful 6

Critical Safety Contraindications

• Absolute contraindication: concurrent nitrate use (organic nitrates, nitroglycerin, isosorbide)—can cause fatal hypotension 1, 3
• If emergency nitrates are needed, wait at least 24 hours after sildenafil administration, under close medical supervision 6, 1
• High-risk cardiovascular conditions requiring cardiac stabilization before treatment: 1
  • Unstable or refractory angina
  • Uncontrolled hypertension
  • Recent MI or stroke (within 2 weeks)
  • Severe heart failure (NYHA class II or higher)

Special Populations

• Men with diabetes and post-prostatectomy patients have more severe baseline ED and may respond less robustly to PDE5 inhibitors 7, 1
• In spinal cord injury patients (T6-L5), 75% on sildenafil 50 mg reported improved erections versus 7% on placebo 8
• For men with testosterone deficiency and ED, combining sildenafil with testosterone therapy may be more effective than sildenafil alone 7

Common Pitfalls to Avoid

• Patients must understand that sexual stimulation is required—sildenafil enhances the natural erectile response to stimulation but does not create spontaneous erections 1, 3
• Avoid taking with large meals, which significantly delays absorption and onset of action 1
• Do not exceed once-daily dosing 1, 2
• Always screen for nitrate use (including recreational "poppers") before every prescription 1, 3

Adverse Effects

• Common adverse events (transient, mild-to-moderate): headache, flushing, dyspepsia, nasal congestion, abnormal vision 2, 3, 4
• These side effects are generally well-tolerated and do not require discontinuation 2, 4

Ongoing Management

• Periodic follow-up should assess efficacy, side effects, and changes in cardiovascular health or new medications 6
• If sildenafil fails after an adequate trial, consider switching to a different PDE5 inhibitor (tadalafil or vardenafil) before proceeding to more invasive therapies 6