What are the dose administration instructions for sildenafil (Viagra) in treating erectile dysfunction?

Sildenafil Dose Administration Instructions for Erectile Dysfunction

Start with 50 mg of sildenafil taken approximately 1 hour before sexual activity, with a maximum frequency of once daily, and titrate to 100 mg if inadequate or reduce to 25 mg if side effects occur. 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
• If the 50 mg dose is inadequate, increase to 100 mg (the maximum recommended dose). 1
• If side effects are problematic at 50 mg, reduce to 25 mg. 1
• Sexual stimulation is mandatory for sildenafil to be effective—the medication will not work without it. 1

Timing and Food Considerations

• The optimal window for efficacy is 1-2 hours after ingestion, though sildenafil may remain effective for more than 10 hours. 3
• Taking sildenafil with food does not significantly reduce efficacy, contrary to common belief, though high-fat meals may delay absorption slightly. 3
• Patients can take sildenafil 1 hour before a meal, during a meal, or 30-60 minutes before sexual activity with similar efficacy outcomes. 3

Special Population Dosing Adjustments

Start with 25 mg (not 50 mg) in the following situations: 1

• Severe hepatic impairment
• Severe renal impairment (creatinine clearance <30 mL/min)
• Concurrent use of strong CYP3A4 inhibitors (ritonavir, saquinavir, ketoconazole, erythromycin, cimetidine)
• Age ≥65 years (consider lower starting dose) 2

Defining an Adequate Trial Before Declaring Failure

• Ensure at least 5 separate attempts at the maximum dose (100 mg) before concluding treatment failure. 1
• Many apparent failures result from correctable factors: inadequate sexual stimulation, improper timing, heavy alcohol use, or taking with excessively large meals. 1
• If sildenafil fails after an adequate trial, consider switching to a different PDE5 inhibitor (tadalafil or vardenafil) rather than abandoning the drug class. 1

Absolute Contraindications and Critical Safety Warnings

• Concurrent nitrate use (nitroglycerin, isosorbide dinitrate, isosorbide mononitrate) is an absolute contraindication due to life-threatening hypotension risk. 1
• Wait at least 24 hours after sildenafil before administering nitrates in emergency situations, and only under close medical supervision. 1, 4
• High-risk cardiovascular conditions requiring cardiac stabilization before treatment include: unstable or refractory angina, uncontrolled hypertension, recent MI or stroke (within 2 weeks), severe heart failure (NYHA class II or higher), and high-risk arrhythmias. 1

Expected Efficacy and Side Effects

• Success rates are 69% for successful sexual intercourse attempts with sildenafil versus 35.5% with placebo. 1
• Improvement in erections occurs in 73-88% of men versus 26-32% with placebo. 1
• Sildenafil maintains efficacy across various etiologies, including diabetes, cardiovascular disease, spinal cord injury, and post-prostatectomy, though men with diabetes and post-prostatectomy may respond less robustly. 1, 5
• The most common side effects are headache, flushing, dyspepsia, nasal congestion, and abnormal vision—all transient and mild-to-moderate. 1, 2

Common Pitfalls to Avoid

• Do not declare treatment failure without ensuring adequate sexual stimulation—this is the most common reason for apparent non-response. 1
• Do not advise patients to avoid food entirely; normal meals do not significantly impair efficacy. 3
• Do not assume the medication "isn't working" if the patient only tried it 1-2 times; require at least 5 attempts at maximum dose. 1
• Always explicitly ask about all forms of nitrate use (including recreational "poppers") before prescribing. 4