What is the initial dosing recommendation for sildenafil (phosphodiesterase type 5 inhibitor)?

Initial Dosing of Sildenafil

The recommended initial dose of sildenafil for erectile dysfunction is 50 mg taken approximately one hour before sexual activity, with subsequent dose adjustments based on efficacy and tolerability. 1, 2, 3

Dosing Algorithm for Erectile Dysfunction

Initial Dosing

• Standard starting dose: 50 mg taken as needed approximately 1 hour before sexual activity 1, 2
• Maximum frequency: No more than once daily 2
• Lower starting dose (25 mg) recommended for:
  • Elderly patients (>65 years)
  • Patients with hepatic or renal impairment
  • Patients taking CYP3A4 inhibitors (e.g., ritonavir, saquinavir, ketoconazole, erythromycin, cimetidine) 2

Dose Adjustment

• If 50 mg is ineffective, dose may be increased to 100 mg 3
• If 50 mg causes unacceptable side effects, dose may be decreased to 25 mg 2, 4
• Allow at least 5 separate occasions at the maximum dose before declaring treatment ineffective 5

Timing Considerations

• Take sildenafil on an empty stomach for faster onset of action (30-60 minutes) 2
• When taken with food, onset may be delayed 6
• Effects typically last 3-5 hours based on elimination half-life 2

Special Considerations

Cardiovascular Risk Assessment

• Cardiovascular risk should be assessed before initiating sildenafil 5
• Sexual activity is equivalent to walking 1 mile in 20 minutes or climbing 2 flights of stairs in 20 seconds 5
• Patients unable to perform this level of activity without symptoms should be referred to a cardiologist before treatment 5

Absolute Contraindications

• Concurrent use of nitrates (risk of severe hypotension) 1, 2
• Wait at least 24 hours after sildenafil administration before using nitrates 1

Optimizing Treatment Success

• Provide clear instructions on proper use:
  • Take 1 hour before sexual activity
  • Sexual stimulation is required for the medication to work
  • Avoid heavy meals which may delay onset 6, 7
• Dose optimization and customized instructions significantly improve satisfaction rates (from 75% to 86%) 7

Common Side Effects

• Headache, flushing, dyspepsia, nasal congestion, and abnormal vision 2
• Side effects are typically transient and mild to moderate 2

For Pulmonary Arterial Hypertension

Note that for pulmonary arterial hypertension, the dosing regimen is different: 20 mg three times daily, administered 4-6 hours apart 8.