How to Dose Viagra (Sildenafil) for Erectile Dysfunction
Start with 50 mg taken approximately 1 hour before sexual activity, then titrate to 100 mg if inadequate response or reduce to 25 mg if side effects occur or in special populations. 1
Standard Dosing Protocol
- Begin with 50 mg as the initial dose, 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 efficacy 1
- Reduce to 25 mg in patients with hepatic impairment, renal impairment, or those taking CYP3A4 inhibitors (ritonavir, saquinavir, ketoconazole, erythromycin, cimetidine) 1, 2
- The American Urological Association strongly recommends dose titration to optimize efficacy 1
Sexual stimulation is mandatory for effectiveness—this is a critical point that accounts for many apparent treatment failures 1
Dose-Response Relationship
- Efficacy is dose-related: 50 mg is superior to 25 mg, though the difference between 100 mg and 50 mg is less pronounced 1
- Studies show 67-86% of men report improved erections with sildenafil compared to 24% with placebo 3
- Starting with 100 mg may reduce anxiety about the next intercourse attempt (56% felt no anxiety with 100 mg vs 39% with 50 mg), though this should be balanced against tolerability 4
Defining an Adequate Trial
Before declaring treatment failure, ensure at least 5 separate attempts at maximum dose (100 mg) 1. Many failures result from:
- Incorrect timing (not waiting ~1 hour before activity) 1
- Taking with large meals, which delays absorption 1
- Lack of sexual stimulation 1
- Inadequate dose titration 1
Absolute Contraindications and Critical Safety
Concurrent nitrate use is an absolute contraindication due to severe, potentially fatal hypotension 1, 5
- Wait at least 24 hours after sildenafil before administering nitrates in emergency situations under close medical supervision 1
- High-risk cardiovascular conditions requiring cardiac stabilization before treatment include: unstable or refractory angina, uncontrolled hypertension, recent MI or stroke (within 2 weeks), high-risk arrhythmias, and severe heart failure (NYHA class II or higher) 1
Special Populations
- Hepatic impairment: Start with 25 mg 1
- Renal impairment: Start with 25 mg 1
- Elderly patients: Consider starting with 25 mg 2
- Diabetes or post-prostatectomy patients: May respond less robustly due to more severe baseline ED; ensure adequate trial before switching agents 1
Common Pitfalls to Avoid
- Not educating patients about the need for sexual stimulation 1
- Failing to titrate the dose upward when 50 mg is inadequate 1
- Declaring failure after insufficient attempts (need at least 5 attempts at maximum dose) 1
- Not asking about all forms of nitrate use before prescribing 1
- Ignoring food-drug interactions (high-fat meals delay absorption) 1
Expected Adverse Effects
Common side effects are transient and mild-to-moderate, including headache, flushing, dyspepsia, nasal congestion, and abnormal vision 2, 3. These do not typically require discontinuation 6.
Long-Term Management
- Efficacy is maintained with long-term use (up to 1 year), with 90% of patients continuing treatment 6
- Treatment must be continued for improvements to be maintained; withdrawal returns erectile function to pre-treatment values 6
- Periodic follow-up should verify cardiovascular stability, review new medications, and assess treatment effectiveness 1