Major
Ketoconazole × ritonavir
Systemic antimycotics. Imidazole derivatives×HIV protease inhibitor / pharmacokinetic booster
Mechanism
Dual potent CYP3A4 inhibition. Ketoconazole plasma levels may rise 3-fold. Hepatotoxicity and adrenal cortex suppression intensify.
Symptoms
Nausea, rising liver enzymes (ALT, AST). Prolonged use: adrenal insufficiency risk with hypotension, hypoglycaemia, hyponatraemia. Cardiac symptoms from QT prolongation.
Management
Avoid the combination. Alternative antifungals on ritonavir: terbinafine for dermatophytosis or echinocandins for systemic mycoses.
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.