Interactions between diltiazem and Atazanavir (atazanavir)
diltiazem and atazanavir (Major Drug-Drug)
ADJUST DOSE: Coadministration with atazanavir may significantly increase the plasma concentrations of diltiazem. The mechanism is atazanavir inhibition of CYP450 3A4, the isoenzyme responsible for the metabolic clearance of diltiazem. In addition, both atazanavir and diltiazem can prolong the PR interval of the electrocardiogram and may have additive effects when used in combination. In a pharmacokinetic study, coadministration of atazanavir (400 mg once a day) and diltiazem (180 mg once a day) resulted in a 2-fold increase in diltiazem plasma concentration, and an additive effect on the PR interval was observed. Excessive prolongation of the PR interval may result in conduction disturbances and atrioventricular block.
MANAGEMENT: When used in combination with atazanavir, a reduction of diltiazem dosage by one-half should be considered and ECG monitoring is recommended. Pharmacologic response to diltiazem should be monitored more closely following addition or withdrawal of atazanavir, and the diltiazem dosage adjusted as necessary.
