Diltiazem does not always increase blood cyclosporin concentration.

The pharmacokinetic interaction between the calcium channel blocking drug, diltiazem (DTZ), the antifungal agent itraconazole (ICZ) and the immunosuppressive drug cyclosporin (CsA) was studied in a patient with a single lung transplant. The CsA area under curve estimations demonstrated a significant increase when ICZ was co-prescribed (5836 micrograms l-1 h vs 8159 micrograms l-1 h) but no increase when DTZ was co-prescribed with CsA (5836 micrograms l-1 h vs 5069 micrograms l-1 h). Despite widespread use as a CsA-sparing agent, DTZ does not always increase CsA concentrations.