Forty-three renal transplant recipients receiving cyclosporine were started on 200 mg/day of oral ketoconazole 10 days to 75 months posttransplant. The cyclosporine dose was reduced by 70% when ketoconazole was started. The mean cyclosporine dose was 5.6 mg/kg/day preketoconazole, and 0.9, 0.8, and 0.7 mg/kg/day at one, two, and three years after addition of ketoconazole (cyclosporine dose reduction 84%, 86%, and 88% at one, two, and three years, respectively). Two patients died after two years of combination therapy, six patients returned to dialysis, and ketoconazole was discontinued in four. Renal function in patients on ketoconazole remained stable (serum creatinine 1.8, 1.7, 1.7, and 1.8 mg/dl preketoconazole and at one, two, and three years, respectively). In a second study, 52 patients were randomized to standard doses of cyclosporine (n=28), or reduced doses of cyclosporine with ketoconazole (n=24); seven of the patients were not started on ketoconazole. In 28 patients on standard-dose cyclosporine, there were two deaths and one graft loss. In 17 patients receiving ketoconazole there were two deaths and no graft losses. Renal function and the frequency of rejection episodes was similar in the two groups. In the ketoconazole group, the cyclosporine dose was <20% of that in the patients on standard doses. In both studies addition of ketoconazole to cyclosporine-treated patients resulted in significant inhibition of cyclosporine metabolism and decrease in dosage in patients followed for up to four years. This drug interaction provides a significant reduction in cost of immunosuppressive therapy in organ transplant recipient.
