Cyclosporine kinetics in healthy volunteers

The pharmacokinetics of cyclosporine was studied in five healthy male volunteers following intravenous administration. The subjects received 2.1 mg/kg of cyclosporine as a two-hour intravenous infusion. Blood samples were collected over the subsequent 48 hours. Cyclosporine was extracted from whole blood and analyzed by high-performance liquid chromatography (HPLC) and radioimmunoassay (RIA). Following the intravenous infusion of cyclosporine, the drug exhibited multicompartmental behavior. The harmonic mean distribution half-life based on HPLC data was 0.45 hours, and the harmonic mean terminal disposition half-life was 6.2 hours. The clearance of cyclosporine based on HPLC cyclosporine concentrations was 3.9 mL/min/kg, and the volume of distribution at steady state of cyclosporine was 1.23 L/kg. Cyclosporine has a shorter half-life, lower clearance, and smaller Vss in healthy persons as compared to patient populations. The differences observed in the pharmacokinetics of cyclosporine in healthy persons as compared to patient populations may be due to differences in hematocrit, lipoprotein profiles, and/or concurrent drug therapy between the groups. Cyclosporine concentrations determined by RIA were consistently higher than those determined by HPLC, resulting in a significantly higher area under the blood concentration versus time curve and lower clearance rate for cyclosporine. We conclude that: (1) kinetic parameter estimates for cyclosporine are different in healthy individuals as compared with organ-transplant recipients, and (2) the kinetic parameters for cyclosporine are different, depending on the assay technique used.