Effect of CYP3A4 and CYP3A5 Genetic Polymorphisms on the Pharmacokinetics of Sirolimus in Healthy Chinese Volunteers.

Background: Sirolimus is a promising immunosuppressive drug for preventing the rejection of organ transplants. However, inter-individual variability in sirolimus pharmacokinetics causes adverse drug reactions, compromising therapeutic efficacy. Sirolimus is primarily metabolized by cytochrome CYP3A4 and CYP3A5. This study aimed to clarify the effect of CYP3A genetic polymorphisms, including the CYP3A4*1G and CYP3A5*3 polymorphisms, on the pharmacokinetics of sirolimus.

Methods: Thirty-one healthy Chinese volunteers were included in this study. Their genotypes were determined using the Sequenom MassARRAY iPLEX platform, and blood sirolimus concentrations at different time points were analyzed by liquid chromatography-tandem mass spectrometry (LC-MS/MS). The pharmacokinetic parameters were calculated using WinNonlin version 5.2 software.

Results: The allele frequencies of CYP3A4*1G and CYP3A5*3 were 25.8% and 71.0%, respectively. In CYP3A4*1G carriers (n = 13), the area under the curve AUC0-144, AUC0-∞, and Cmax were significantly lower (P < 0.05) than CYP3A4*1/*1 homozygous subjects (n = 18). Briefly, the AUC0-144, AUC0-∞, and Cmax of *1G/*1G carrier were 315.2 ± 91.5, 372.0 ± 108.2, and 10.2 ± 1.6 ng/mL, respectively, and those of *1/*1 G*1/*1 G carrier were 440.8 ± 130.6, 537.4 ± 167.5, and 13.7 ± 4.3, respectively, whereas those of CYP3A4*1/*1 homozygous subjects were 540.2 ± 150.6, 626.6 ± 166.9, and 19.8 ± 7.5 ng/mL, respectively. In CYP3A5-nonexpressing subjects (*3/*3 homozygous carriers, n = 15), the AUC0-144 and Cmax were 549.6 ± 137.9 and 19.9 ± 7.9 ng/mL, respectively, and were significantly higher (P < 0.05) than the values in CYP3A5-expressing subjects (*1/*1homozygous carrier, n = 2; 314.2 ± 129.3 and 10.3 ± 2.2 ng/mL; *1/*3 heterozygous carrier, n = 15; 440.2 ± 146.3 and 14.6 ± 5.1 ng/mL, respectively).

Conclusions: CYP3A4 and CYP3A5 genetic polymorphisms are important factors affecting pharmacokinetic parameters of sirolimus. Our data support the monitoring of blood sirolimus concentrations, especially in CYP3A5*1 and CYP3A4*1 G carriers, to ensure accurate dosing in the clinical setting.