Drug use concomitant with cyclosporine immunosuppressive therapy for 3 years after renal transplantation.

Little is known about outpatient drug use concomitant with cyclosporine immunosuppressive therapy following renal transplantation. In part, this stems from the difficulty in monitoring drugs not covered by Medicare. Using several linked state and federal program data bases, a cohort of dually eligible Medicare/Medicaid California residents aged > or = 18 years with a first cadaver transplant in 1988 was followed for 3 years to examine drug use and medical expenditures: 99, 122, and 90 patients met these inclusion criteria in each study year, respectively. More than one third of the study population received one or more drugs that inhibit metabolism and increase cyclosporine circulating blood levels (class I) in each year posttransplant. The most commonly prescribed were diltiazem, verapamil, metoclopramide, and ketoconazole. Patients receiving class I drugs had a lower mean cyclosporine dose compared with those not receiving such drugs in all three study years, suggesting that overall cost savings were obtained among patients using class I drugs. Less than one tenth of the study population in any given year received a drug that induces metabolism and decreases cyclosporine blood levels (class II), the most common of which was phenytoin. Use of nephrotoxic drugs (eg, trimethoprim-sulfamethoxazole, gentamicin, and tobramycin) that exhibit nephrotoxic synergy when used with cyclosporine was common. Almost half of all posttransplant patients were prescribed a nephrotoxic drug during the study period. Pharmaceuticals (primarily cyclosporine) accounted for 35% to 43% of the approximately $17,000 to $19,500 per patient annual health care expenditures incurred in the first 3 years following kidney transplantation.