Concomitant administration of cyclosporin and ketoconazole in renal transplant recipients

18 renal transplant recipients receiving cyclosporin, prednisone, and azathioprine were given ketoconazole, a potent inhibitor of the cytochrome P-450 enzyme system. Within a month ketoconazole-induced blockade of cyclosporin metabolism allowed a significant reduction (451 vs 106 mg/day; 77%) of the mean dose of cyclosporin without altering cyclosporin whole blood trough levels, although maximum blood levels were almost halved. This dose reduction was maintained in patients followed up for up to 13 months. Renal and hepatic function were unchanged after the addition of ketoconazole. This drug interaction has the potential to reduce dramatically expenditure on cyclosporin in transplant recipients.