Pharmacokinetics of prednisolone during administration of sirolimus in patients with renal transplants

The pharmacokinetic interaction of multiple oral doses of sirolimus (rapamycin) and prednisone were evaluated in 40 stable patients with renal transplants receiving concomitant multiple doses of cyclosporine. Nine sirolimus dosage levels from 1 mg/m²/day to 13 mg/m²/day were studied and compared with placebo. Plasma concentrations of prednisone, prednisolone, and cortisol were measured by high-performance liquid chromatography and analyzed by noncompartmental methods. Mean pharmacokinetic values of prednisolone found before sirolinus administration were as follows: peak plasma concentration (C(max)) was 187 mg/mL; time to peak plasma concentration (t(max)) was 2.03 hours: rate of reaching peak plasma concentration (C(max)) divided by the area under the concentration-time curve [AUC]) was 0.149 hour^-1; terminal half-life (t( 1/4 )) was 3.60 hours; AUC was 1206 ng · hour/mL; and apparent clearance (Cl/F) was 0.094 L/hour/kg. During the 2 weeks of concomitant administration, prednisolone elimination decreased in relation to sirolimus dosages. These changes were modest, with mean increases of 18% in C(max) and 27% in t( 1/4 ) and mean decreases of 27% in Cl/F for the groups receiving 6 mg/m²/day to 13 mg/m²/day. Most patients initially had plasma cortisol concentrations indicative of adrenal suppression. With sirolimus treatment, the C(max) of cortisol did not decrease further, but the AUC (8:00 AM-8:00 PM) values were significantly lower, independent of sirolimus exposure. The AUC for cyclosporine did not correlate with sirolimus and prednisolone exposure. A 2-week course of sirolimus showed a slight pharmacokinetic interaction between sirolimus and prednisolone/prednisone/cortisol in stable patients with renal transplants.