What is the recommended dosing for sildenafil (Viagra) in the treatment of 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 for improved efficacy or reduction to 25 mg for tolerability, taken no more than once daily. 1

Standard Dosing Protocol

• The recommended starting dose is 50 mg, taken approximately 1 hour before anticipated sexual activity, not more than once daily. 1, 2
• Titrate to 100 mg (maximum dose) if 50 mg provides inadequate response, or reduce to 25 mg if side effects are problematic. 1, 2
• Sexual stimulation is mandatory for effectiveness—the medication will not work without it. 1

Dose-Response Relationship

• Improvement in erectile function is dose-related for sildenafil (50 mg superior to 25 mg, though 100 mg vs 50 mg shows less clear differentiation). 3
• Starting at 100 mg significantly reduces anxiety about the next intercourse attempt (56% felt no anxiety) compared to 50 mg (39% felt no anxiety), with improved treatment satisfaction and sexual experience, without increased adverse events. 4
• However, guideline consensus supports initiating at 50 mg with upward titration as the standard approach. 1, 2

Special Population Dosing

Reduce starting dose to 25 mg in the following situations: 1

• Severe hepatic impairment (PDE5 inhibitors generally not recommended in severe hepatic disease) 5, 1
• Renal impairment 1
• Concurrent use of CYP3A4 inhibitors including ritonavir, saquinavir, ketoconazole, erythromycin, or cimetidine 1, 2
• Elderly patients may benefit from lower starting doses 2

Timing and Administration

• Take approximately 1 hour before sexual activity for optimal absorption. 1, 2
• Avoid taking with large meals, which delays absorption and reduces efficacy. 1
• The elimination half-life is 3 to 5 hours. 2
• Maximum dosing frequency is once daily. 1, 2

Efficacy Expectations by Population

• Overall response rates: 56% of men with sildenafil achieved improved erections vs 10% with placebo in diabetic men. 6
• Men with diabetes and post-prostatectomy patients have more severe baseline ED and may respond less robustly to PDE5 inhibitors. 5, 1
• Efficacy is maintained across age groups and is not affected by concurrent antihypertensive or antidepressant medications. 2
• In spinal cord injury (T6-L5), 75% on sildenafil vs 7% on placebo reported improved erections. 7

Critical Safety Contraindications

Absolute contraindication: Concurrent nitrate use (organic nitrates, glyceryl trinitrate, isosorbide dinitrate) due to severe, potentially fatal hypotension risk. 1

• Wait at least 24 hours after sildenafil before administering nitrates in emergency situations under close medical supervision. 3, 1
• High-risk cardiovascular conditions requiring cardiac stabilization before treatment include: 1
  • Unstable or refractory angina
  • Uncontrolled hypertension
  • Recent MI or stroke (within 2 weeks)
  • Severe heart failure (NYHA class II or higher)
  • High-risk arrhythmias

Common Pitfalls

• Many "treatment failures" result from incorrect usage rather than true medication failure—patients must understand that sexual stimulation is required. 1
• An adequate trial consists of at least 5 separate attempts at maximum dose before declaring treatment failure. 5
• Consider switching to a different PDE5 inhibitor if the first one fails after adequate trial. 5

Combination Therapy Considerations

• For men with ED and testosterone deficiency, combining sildenafil with testosterone therapy may be more effective than sildenafil alone. 5
• Testosterone therapy alone is not effective monotherapy for ED. 5