Population pharmacokinetic characteristics of sirolimus in healthy Chinese subjects and renal transplant patients

Aim: To identify the factors affecting the pharmacokinetics (PKs) of sirolimus in healthy Chinese subjects and renal transplant patients. Methods: A population PK model of sirolimus was constructed using dense data from 22 healthy volunteers and sparse data from 105 renal transplant patients. Results: The data were well described by a two-compaitment model with first-order absorption. The estimates of absorption rate constant (Ka), clearance (CL/F), and central volume of distribution (V2/F) were 0.24 h(-1), 8.81 L/h, and 676 L, respectively. The CL/F in renal transplant patients was 45.5% lower than that in healthy subjects. Based on the final model, CL/F decreased significantly with increasing cyclosporine (CsA) daily dose and age. A decrease of 7.3% in CL/F for every 100-mg increase in the CsA daily dose and a decrease of 34.2% in CL/F for every 20-year increase in age was observed. Moreover, V2/F increased significantly with increasing serum creatinine in our study. However, the range of serum creatinine concentration and the interindividual variability for V2/F are large. Conclusion: This is the first study to characterize the population PKs of sirolimus using a two-compartment model in healthy Chinese subjects and renal transplant patients. A decrease of 7.3% in the sirolimus CL/F for every 100-mg increase in the CsA daily dose and a decrease of 34.2% in the sirolimus CL/F for every 20-year increase in age was observed, which allowed us to better optimize sirolimus dosing regimens in Chinese renal transplant patients.