Sildenafil Dosing
For erectile dysfunction, start with sildenafil 50 mg taken 1 hour before sexual activity, then adjust to 25 mg if side effects occur or increase to 100 mg if inadequate response; for pulmonary arterial hypertension, use 20 mg three times daily (4-6 hours apart), with possible titration up to 80 mg three times daily if clinical response is insufficient.
Erectile Dysfunction Dosing
Starting Dose and Titration
- Initial dose: 50 mg taken approximately 1 hour before anticipated sexual activity 1
- Dose adjustment:
- Maximum dose: 100 mg once daily 2
- Sexual stimulation is necessary for efficacy 1
Dose-Response Evidence
The evidence shows improvement in erectile function is dose-related for sildenafil (50 mg superior to 25 mg, though 100 mg versus 50 mg showed less clear benefit) 2. Starting at 100 mg has been studied and shows improved treatment satisfaction and reduced anxiety about intercourse attempts compared to 50 mg, without increased adverse events 3.
Special Populations
- Elderly patients or hepatic/renal impairment: Consider starting at 25 mg 4
- Patients on CYP3A4 inhibitors (ritonavir, ketoconazole, erythromycin): Use lower doses 4
Common Pitfall
Before declaring treatment failure, ensure adequate trial: proper timing (1 hour before activity), sexual stimulation, multiple attempts, and titration to maximum dosing 5. Many apparent "non-responders" succeed after re-education and dose optimization 5.
Pulmonary Arterial Hypertension Dosing
FDA-Approved Dosing
- Standard dose: 20 mg three times daily (TID), administered 4-6 hours apart 6
- This is the FDA-approved and recommended dose 7, 8
Dose Titration for Inadequate Response
Although 20 mg TID is FDA-approved, clinical trials demonstrate dose-response effects in hemodynamics, and titration is now permitted:
- For patients failing to achieve adequate clinical response on 20 mg TID, increase in 20 mg increments to maximum 80 mg TID 7
- Recent FDA action (2024) based on the SITAR trial 9 now allows titration up to 80 mg TID if needed
- The SITAR trial demonstrated that 80 mg TID was noninferior to 5 mg TID for mortality (HR 0.51,99.7% CI 0.22-1.21) and superior for time to clinical worsening (HR 0.44) and 6-minute walk distance (18.9 m improvement) 9
Pediatric Dosing (PAH)
- Age <1 year: 0.5-1 mg/kg three times daily orally
- Weight <20 kg: 10 mg three times daily orally
- Weight >20 kg: 20 mg three times daily orally 10
- Critical warning: Avoid higher dosing in children due to increased mortality risk noted in STARTS-2 study 10
WHO Functional Class Considerations
- FC II and FC III patients: Start with 20 mg TID; no preferential agent over other oral therapies 7
- FC III with rapid progression: Consider parenteral prostanoid therapy instead 7
Important Safety Considerations
Absolute contraindication: Concurrent nitrate use in any form (including "poppers") due to severe hypotension risk 1, 6
Drug interactions:
- Riociguat + sildenafil: Risk of systemic hypotension; avoid concurrent use 7
- Male PAH patients on riociguat should not use PDE5 inhibitors for erectile dysfunction 7
Monitoring: Periodic follow-up for efficacy, side effects, and cardiovascular status changes 5
Adverse Effects
Common side effects include headache, flushing, dyspepsia, nasal congestion, visual disturbances (color-tinge, increased light sensitivity), and diarrhea 1, 6. These are generally mild to moderate and dose-related. Retinal hemorrhage occurred in 1.4% at 20 mg TID versus 0% placebo, though patients had concurrent anticoagulation 6. Long-term ocular safety data up to 80 mg TID shows no detrimental effects on visual acuity, color vision, or visual fields 11.