What is the recommended dosage of sildenafil (Viagra) for an elderly man with a history of myocardial infarction (MI)?

Sildenafil Dosage for an Elderly Man with History of MI

For an elderly man with a history of myocardial infarction, sildenafil should be started at 25 mg taken approximately 1 hour before sexual activity, no more than once daily, with careful screening to ensure he is not taking nitrates and has no active cardiac instability. 1, 2, 3

Critical Safety Assessment Before Prescribing

Absolute Contraindications to Verify

• The patient must not be taking any form of nitrate therapy (oral, sublingual, transdermal, or intravenous nitroglycerin) as the combination causes profound hypotension, myocardial infarction, and death 1, 4, 5
• Verify no use of long-acting nitrates, isosorbide dinitrate, or isosorbide mononitrate 1, 6
• Confirm systolic blood pressure is ≥100 mmHg at baseline 7

Cardiac Stability Requirements

• The MI should be at least 6 months old, as data on sildenafil use in recent (<6 months) MI are not available 8
• Rule out unstable angina, recent stroke, or life-threatening arrhythmias 8
• Consider exercise stress testing to ensure the patient can achieve ≥5 METs without ischemia, as this indicates low risk during sexual activity 1, 6, 3

Recommended Dosing Strategy

Starting Dose for Elderly Post-MI Patients

• Begin with 25 mg taken approximately 1 hour before sexual activity 1, 2, 3
• Maximum frequency: once daily 2, 9
• Elderly patients (≥65 years) have 84% higher plasma concentrations and 107% higher active metabolite levels compared to younger patients, necessitating lower starting doses 2

Dose Titration

• If 25 mg is well-tolerated but insufficiently effective, may increase to 50 mg 1, 9
• Maximum dose is 100 mg once daily, though this higher dose may not be necessary in elderly patients 2, 9
• The standard FDA-approved dosing for pulmonary arterial hypertension (20 mg three times daily) is different from erectile dysfunction dosing 2

Special Considerations in Elderly Post-MI Patients

Medication Interactions

• Reduce dose to 25 mg if patient is taking CYP3A4 inhibitors (erythromycin, cimetidine, certain statins like simvastatin or atorvastatin) as these increase sildenafil plasma levels by approximately 30% 2, 6, 3
• If taking beta-blockers (which most post-MI patients should be on indefinitely), sildenafil clearance is reduced by approximately 34%, supporting the lower starting dose 5, 2
• Concurrent antihypertensive medications cause modest additional blood pressure reductions (typically <10 mmHg systolic/diastolic) but are not contraindicated 1, 6, 3

Renal Function Adjustment

• If creatinine clearance <30 mL/min, start with 25 mg as sildenafil clearance is reduced by approximately 50%, resulting in doubled AUC and Cmax 2, 6

Cardiovascular Monitoring

• Sildenafil causes transient, modest reductions in blood pressure (typically 8-10 mmHg systolic) 6, 3, 8
• The drug has a half-life of 3-5 hours, with effects lasting approximately 4 hours 2, 9
• Sexual activity itself carries a relative risk of 2.5 for MI in the 2 hours afterward, but this represents only 0.9% of MI cases overall 6

Evidence on Safety in Post-MI Patients

Reassuring Safety Data

• Placebo-controlled trials including men with ischemic heart disease showed no increase in MI or serious cardiovascular events with sildenafil versus placebo 8
• Postmarketing data from 6,527 males showed no increase in cardiovascular events in healthy subjects 6
• The expected death rate from MI in sildenafil users (55-64 years) was 52 cases, but only 15 were actually reported 10
• Sildenafil may have cardioprotective "preconditioning" effects on the myocardium 10

Common Pitfalls to Avoid

• Never assume the patient is not taking nitrates—always ask specifically about sublingual nitroglycerin, nitrate patches, or isosorbide preparations 1, 4
• Do not prescribe if the patient has severe aortic stenosis or hypertrophic obstructive cardiomyopathy 6
• Avoid extrapolating reassuring safety data to patients performing at higher cardiac expenditures or in unfamiliar settings with excessive alcohol 6

Emergency Management if Complications Occur

If Hypotension Develops

• Aggressive fluid resuscitation is first-line treatment 6
• Follow with vasoactive drugs if needed 6
• Intraaortic balloon counterpulsation may be necessary in severe cases 6

If Acute Coronary Syndrome Occurs

• Treat according to standard MI/unstable angina guidelines but absolutely avoid nitrates for at least 24 hours after sildenafil use 1, 4, 6
• Use alternative anti-ischemic therapies such as beta-blockers, morphine, or intravenous NTG alternatives 1