Sildenafil Drug Interactions & Contra-indications — 2025 Safety Checklist

Sildenafil: Quick Interaction Grid (2025)

Category	Examples	Action
Absolute CI	Nitrates, Riociguat	Contra-indicated
Strong CYP3A4 inhib.	Ritonavir, Ketoconazole	Start 25 mg; max 25/48 h
α-Blockers	Tamsulosin, Doxazosin	Separate ≥ 4 h
Inducers	Rifampin, Bosentan	Consider 150–200 mg
Additive BP Drop	Amlodipine, Alcohol ↑	Monitor BP

Absolute Contra-indications

• Nitrates (e.g., nitroglycerin, isosorbide): Severe hypotension risk. Never combine.
• Riociguat: Soluble guanylate cyclase stimulator. Profound BP drop./li>
• Recent MI or stroke (<6 months): Cardiac instability. Avoid use. [PubMed]
• Severe hypotension (<90/50 mmHg): Baseline low BP. Contra-indicated.
• Known hypersensitivity: Allergy to sildenafil or excipients.

Major Caution & Dose-Adjust – CYP3A4 Inhibitors

• Ritonavir, indinavir: Potent CYP3A4 inhibitors. Max 25 mg/48h. [PubMed]
• Ketoconazole, itraconazole: Strong inhibitors. Start low, titrate carefully.
• Erythromycin, clarithromycin: Moderate inhibitors. Monitor for side effects.
• Grapefruit juice: May increase sildenafil levels. Limit intake.
• Saquinavir, atazanavir: HIV protease inhibitors. Use lowest dose possible.

Additive Hypotension – α-blockers, Alcohol, Antihypertensives

• α-Blockers (tamsulosin, doxazosin): Separate doses by ≥4 hours to reduce syncope risk.
• Alcohol (excess): Increases vasodilation, may cause dizziness/fainting.
• Amlodipine, other CCBs: Additive BP lowering. Monitor closely.
• ACE inhibitors, ARBs: Cumulative hypotensive effect possible.
• Diuretics: May potentiate BP drop, especially in elderly.

Special Populations

• Severe renal impairment (CrCl <30 ml/min): Start at 25 mg; titrate with caution.
• Severe hepatic impairment: Use lowest dose; monitor for adverse effects.
• Retinitis pigmentosa: Rare hereditary eye disease; avoid use (risk of vision loss).
• Age >65 years: Increased sensitivity; consider lower starting dose.
• Bleeding disorders: Use with caution; theoretical risk of epistaxis/bleeding.