Viagra (Sildenafil) Dosing for Erectile Dysfunction
For erectile dysfunction, the recommended starting dose of Viagra is 50 mg taken approximately 1 hour before sexual activity, with dose adjustment to 25 mg or 100 mg based on efficacy and tolerability, taken no more than once daily. 1, 2
Standard Dosing Algorithm
Starting dose:
- 50 mg is the recommended initial dose for most men with erectile dysfunction 1, 2, 3
- Take approximately 1 hour before anticipated sexual activity 2, 3
- Maximum frequency: once daily 2, 3
Dose titration based on response:
- Increase to 100 mg if 50 mg provides inadequate response and is well-tolerated 1, 2, 3
- Decrease to 25 mg if side effects are problematic or in specific populations (see below) 2
- Evidence shows dose-related improvement between 25 mg and 50 mg, but less additional benefit when increasing from 50 mg to 100 mg 1, 4
Special Population Dosing Adjustments
Lower starting dose (25 mg) recommended for:
- Elderly patients (≥65 years) 2
- Hepatic impairment 2
- Renal impairment 2
- Concurrent use of CYP3A4 inhibitors (ritonavir, saquinavir, ketoconazole, erythromycin, cimetidine) 2
Critical Safety Considerations
Absolute contraindications:
- Concurrent nitrate use (oral or any form) is absolutely contraindicated due to risk of potentially fatal hypotension 5
- If emergency nitrates are needed, wait 24 hours after sildenafil administration before giving nitrates under close medical supervision 6
Relative contraindications and cautions:
- Unstable angina pectoris 5
- Use within 6 months of acute myocardial infarction or stroke 5
- Cardiac failure 5
- Uncontrolled hypertension 5
- Impaired cardiac reserve 5
Ensuring Adequate Trial Before Declaring Failure
An adequate trial consists of at least 5 separate attempts at maximum tolerated dose before considering treatment failure 6
Common reasons for apparent treatment failure:
- Lack of sexual stimulation (sexual stimulation is necessary for effectiveness) 6
- Incorrect timing (medication taken with large meal delays absorption) 6
- Inadequate number of attempts 6
- Unaddressed hormonal abnormalities 6
- Heavy alcohol use 6
Expected Efficacy
Success rates with sildenafil:
- Approximately 69% of men report successful sexual intercourse attempts versus 35.5% with placebo 1, 4
- 56% of men with diabetes reported improved erections versus 10% with placebo 3
- Efficacy maintained across various etiologies including diabetes, cardiovascular disease, spinal cord injury, and post-prostatectomy 1, 7
Common Adverse Effects
Most frequent side effects (transient and mild-to-moderate):
- Headache (11% vs 2% placebo) 3
- Flushing 2, 5
- Dyspepsia (9% vs 0% placebo) 3
- Nasal congestion (6% vs 2% placebo) 3
- Abnormal vision 2
These adverse effects are largely due to vasodilatory properties and are generally well-tolerated 5
Important Clinical Pearls
- Cardiovascular risk assessment is essential before prescribing: patients unable to perform moderate physical activity should be referred to cardiology first 6
- Most ED patients fall into low cardiovascular risk category and can safely receive sildenafil, including those with controlled hypertension, mild stable angina, successful coronary revascularization, uncomplicated past MI, and CHF NYHA class I 6
- For men with testosterone deficiency and ED, combining sildenafil with testosterone therapy may be more effective than sildenafil alone 6
- Long-term efficacy and tolerability are maintained in studies up to 1 year 2