Cyclosporine kinetics in renal transplantation

The pharmacokinetics of cyclosporine were evaluated in 41 recipients of a cadaveric renal transplant. Cyclosporine was taken by mouth (mean dose 14 mg/kg) on one study day and was intravenously infused over 2 hours (mean dose 4.7 mg/kg) on the next study day. Cyclosporine was extracted from whole blood and analyzed by HPLC. After intravenous infusion, cyclosporine exhibited multicompartmental behavior. The mean (+/- SD) terminal disposition rate constant was 0.065 +/- 0.036 hours-1 and the harmonic mean t 1/2 was 10.7 hours. The harmonic mean total body clearance of cyclosporine was 5.73 ml/min/kg and the mean apparent volume of distribution was 4.5 +/- 3.6 L/kg. The absorption of oral cyclosporine was slow and incomplete. Peak blood cyclosporine concentrations (means = 1,103 ng/ml) were reached between 1 and 8 hours after oral dosing (means = 4 hours). The mean relative bioavailability was 27.6% +/- 20%. Oral bioavailability was less than 10% in 17% of our subjects. The absorption and clearance of cyclosporine were highly variable. We conclude that the variability in the kinetics of cyclosporine makes trough blood level monitoring essential in the management of patients who receive renal transplants.