cyclosporine and diltiazem

Diltiazem inhibits the hepatic cytochrome P450 3A4 enzyme, which is responsible for the metabolism of cyclosporine. This leads to reduced clearance and increased plasma concentrations of cyclosporine.

Elevated cyclosporine levels can cause nephrotoxicity, neurotoxicity (e.g., tremors, seizures), hypertension, and gingival hyperplasia. The onset may be within days, and the effect persists as long as diltiazem is continued.

Consider avoiding the combination if possible. If co-prescribed, monitor cyclosporine trough levels frequently (e.g., every 1-2 weeks initially) and adjust the cyclosporine dose to maintain therapeutic concentrations. Monitor renal function and blood pressure. Reduce cyclosporine dose by 30-50% when starting diltiazem, and re-monitor after discontinuation of diltiazem.

Well-established interaction. Multiple studies and clinical reports confirm the inhibitory effect of diltiazem on cyclosporine metabolism. Standard references and product monographs recommend caution.