Moderate
Amlodipine × ritonavir
Calcium channel blockers (dihydropyridines)×HIV protease inhibitor / pharmacokinetic booster
Mechanism
Ritonavir is the most potent CYP3A4 inhibitor available – the main amlodipine metabolic route. Amlodipine plasma levels rise 2- to 3-fold, with hypotension and peripheral oedema.
Symptoms
Lower blood pressure, postural dizziness, marked lower-leg oedema. Older patients: fall risk.
Management
Halve amlodipine when combined (starting 2.5 mg/day) and monitor blood pressure 1–2 weeks after. Alternative antihypertensive on ritonavir: ACE-I or ARB (no CYP3A4 dependence).
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.