Major
Amiodarone × Sildenafil
Class III antiarrhythmics (Vaughan Williams)×Phosphodiesterase type 5 inhibitors (PDE5)
Mechanism
Dual mechanism: amiodarone blocks CYP3A4 – a partial sildenafil metabolic route – and both drugs prolong QT. Sildenafil plasma levels rise 2- to 4-fold.
Symptoms
Sudden blood pressure drop: dizziness, syncope. QT prolongation on ECG with torsades de pointes risk. Visual disturbances.
Management
On amiodarone, cap sildenafil at 25 mg (instead of 50–100 mg) and limit to one dose every 48 hours. ECG before start and at 2 weeks; maintain potassium and magnesium.
Check the full regimen, not just this pair
Opens the checker with these two drugs prefilled. Add the rest of the regimen and recompute additive risks.