Sildenafil Dosing for Erectile Dysfunction
The recommended starting dose of sildenafil for erectile dysfunction is 50 mg taken approximately 1 hour before sexual activity, with titration to 100 mg if inadequate response or reduction to 25 mg based on tolerability. 1
Standard Dosing Algorithm
Initial dose: Start with 50 mg taken approximately 1 hour before sexual activity, not more than once daily. 1
Dose titration strategy:
- If 50 mg provides inadequate response after proper trial, increase to 100 mg (maximum dose). 1
- The American Urological Association strongly recommends dose titration to optimize efficacy. 1
- Evidence shows dose-related improvement (50 mg superior to 25 mg), though the incremental benefit from 50 mg to 100 mg is less pronounced. 2, 3
- If 50 mg is insufficient, reduce anxiety about intercourse attempts significantly improves with the 100 mg dose (56% vs 39% feeling no anxiety). 4
Dose reduction to 25 mg required for:
- Severe hepatic impairment 1
- Severe renal impairment 1
- Concurrent CYP3A4 inhibitors (ritonavir, saquinavir, ketoconazole, erythromycin, cimetidine) 1, 5
- Elderly patients may benefit from lower starting doses 5
Critical Administration Requirements
Sexual stimulation is mandatory for sildenafil to be effective—the medication has no effect in its absence. 1, 3, 6
Timing considerations:
- Take approximately 1 hour before sexual activity 1, 5
- Peak plasma concentrations occur within 30-120 minutes after oral dosing 6
- Avoid taking with large meals, which delays absorption 1
Defining Treatment Failure vs. Inadequate Trial
Before declaring treatment failure, ensure:
- At least 5 separate attempts at maximum dose (100 mg) 1
- Proper timing (1 hour before activity) 1
- Adequate sexual stimulation 1, 3
- Avoidance of heavy alcohol use 1
- Not taken with large meals 1
Many apparent "treatment failures" result from incorrect usage rather than true medication failure. 1 After addressing these modifiable factors and re-educating on proper use with dose titration to maximum, many patients respond successfully. 1
Absolute Contraindications and Safety
Concurrent nitrate use is absolutely contraindicated due to severe hypotension risk (organic nitrates, glyceryl trinitrate, isosorbide dinitrate). 1
In emergency situations requiring nitrates:
- Wait at least 24 hours after sildenafil administration before giving nitrates 1, 3
- Administer only under close medical supervision 1
High-risk cardiovascular conditions requiring cardiac stabilization before treatment:
- Unstable or refractory angina 1
- Uncontrolled hypertension 1
- Recent MI or stroke (within 2 weeks) 1
- Severe heart failure (NYHA class II or higher) 1
Expected Efficacy Outcomes
Success rates with sildenafil:
- 69% successful sexual intercourse attempts vs 35.5% with placebo 2
- 73-88% improvement in erections vs 26-32% with placebo 2, 3
- Efficacy maintained across various etiologies including diabetes, cardiovascular disease, depression, spinal cord injury, and post-prostatectomy 2, 7, 8
Special populations with potentially reduced response:
- Men with diabetes and post-prostatectomy patients have more severe baseline ED and may respond less robustly 1
- However, treatment response remains significantly superior to placebo even in these populations (63% vs 24% in diabetes) 8
Common Adverse Effects
Most frequent side effects (transient and mild-to-moderate):
- Headache, flushing, dyspepsia, nasal congestion, abnormal vision 2, 3, 5
- Less common: myalgia, nausea, diarrhea, vomiting, dizziness, chest pain 3
- Serious adverse events occur in <2% of patients, with no significant difference from placebo 3
Ongoing Management
Periodic follow-up should assess:
- Efficacy and side effects 1, 3
- Changes in cardiovascular health 1
- New medications that may interact 1, 3
- Adequate trial parameters before switching therapies 1, 3
If sildenafil fails after an adequate trial (at least 5 attempts at 100 mg with proper use), consider switching to a different PDE5 inhibitor. 1