What are the key considerations before prescribing sildenafil (Viagra) for erectile dysfunction?

Key Considerations Before Prescribing Sildenafil

Before prescribing sildenafil, you must explicitly ask about all forms of nitrate use—including tablets, patches, sprays, ointments, and recreational "poppers"—because the combination causes dangerous, potentially fatal hypotension. 1

Critical Safety Screening

Absolute Contraindications

• Nitrate use in any form is an absolute contraindication due to risk of life-threatening hypotension 1
• Known allergy to sildenafil or its components 1

Cardiovascular Risk Assessment

Most erectile dysfunction patients fall into the low-risk category and can safely receive sildenafil, including those with asymptomatic coronary artery disease with <3 risk factors, controlled hypertension, mild stable angina, successful coronary revascularization, uncomplicated past MI, mild valvular disease, and CHF (NYHA class I) 2

Refer to cardiology before prescribing if the patient:

• Cannot perform moderate physical activity 2
• Has indeterminate cardiovascular risk 2
• Has unstable coronary heart disease 3
• Has resting hypotension (BP <90/50), severe left ventricular outflow obstruction, or autonomic dysfunction 1

High-Risk Conditions Requiring Caution

• Anatomical penis deformities (angulation, cavernosal fibrosis, Peyronie's disease) increase priapism risk 1
• Conditions predisposing to priapism (sickle cell anemia, multiple myeloma, leukemia) 1
• Bleeding disorders or active peptic ulceration have unknown safety profiles 1
• Retinitis pigmentosa requires cautious prescribing due to genetic retinal phosphodiesterase disorders 1
• Previous NAION in one eye increases risk of recurrent vision loss 1
• Severe hepatic impairment generally contraindicates PDE5 inhibitor use 2

Medication Interactions

Critical Drug Interactions

• Alpha-blockers: Monitor blood pressure when co-administering 1
• CYP3A4 inhibitors (ritonavir, saquinavir, ketoconazole, erythromycin, cimetidine) require dose reduction to 25 mg 4
• Antihypertensive medications: Monitor for additive hypotensive effects 1

Avoid Duplicate Therapy

• Sildenafil is also marketed as sildenafil citrate 25 mg, 50 mg, and 100 mg for erectile dysfunction—patients should not take multiple PDE5 inhibitors simultaneously 1

Dosing Strategy

Initial Dosing

• Start with 50 mg taken 30-60 minutes before sexual activity, no more than once daily 4, 3
• Reduce to 25 mg for elderly patients, those with hepatic or renal impairment, or those taking CYP3A4 inhibitors 4
• Maximum dose is 100 mg once daily 4

Dose-Response Relationship

• Improvement in erectile function is dose-related for sildenafil (50 mg vs. 25 mg), though less additional benefit occurs when increasing from 50 mg to 100 mg 5, 6

Patient Education Essentials

Mechanism and Expectations

• Sexual stimulation is necessary for sildenafil to work—it has no effect in the absence of sexual arousal 1, 3, 7
• The drug enhances nitric oxide-mediated vasodilation but does not directly cause erections 7
• Peak effect occurs 1.5-2 hours after ingestion, with duration of action potentially exceeding 10 hours 8

Food and Timing

• No significant loss of efficacy occurs when taken with meals, contrary to common belief 8
• Can be taken 30-60 minutes before sexual activity or up to 1 hour before a meal 8

Emergency Instructions

• Seek immediate medical attention for erections lasting >4 hours to prevent permanent penile tissue damage 1
• Seek immediate medical attention for sudden vision loss in one or both eyes, which may indicate NAION 1
• Seek prompt medical attention for sudden hearing loss, which may be accompanied by tinnitus and dizziness 1

Nitrate Emergency Protocol

• If emergency nitrates are required, wait at least 24 hours after sildenafil before administering nitrates under close medical supervision 6

Adequate Trial Definition

Before declaring treatment failure, ensure the patient has completed at least 5 separate attempts at maximum dose 2

Common Reasons for Apparent Failure

• Inadequate sexual stimulation 2, 6
• Improper timing or frequency of dosing 2, 6
• Hormonal abnormalities (particularly testosterone deficiency) 2, 6
• Food or drug interactions 2, 6
• Heavy alcohol use 2, 6
• Relationship issues with partner 2, 6

Special Populations

Testosterone Deficiency

• Men with testosterone deficiency respond less robustly to sildenafil 2
• Combining sildenafil with testosterone therapy may be more effective than sildenafil alone in men with confirmed hypogonadism 2, 9
• Consider checking total testosterone, free testosterone, and SHBG before declaring treatment failure 2

Diabetes and Post-Prostatectomy

• These patients have more severe ED at baseline and may respond less robustly, but sildenafil remains effective 5, 2, 9

Common Adverse Effects

• Headache, flushing, dyspepsia, nasal congestion are the most common side effects 6, 4, 7
• Less common: abnormal vision, dizziness, diarrhea, rash 6, 7
• Serious adverse events occur in <2% of patients, with no significant difference from placebo 6

Follow-Up Protocol

Periodic follow-up should assess:

• Efficacy and side effects 2, 6
• Verification that cardiovascular health hasn't changed 2
• Review of new medications 2
• Changes in health status 2, 6