EFFECTS OF GENETIC POLYMORPHISMS OFCYP3A4,CYP3A5ANDMDR1ON CYCLOSPORINE PHARMACOKINETICS AFTER RENAL TRANSPLANTATION

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Abstract
SUMMARY: The calcineurin inhibitor cyclosporine is widely used to prevent allograft rejection after solid organ transplantation. It has a narrow therapeutic index and shows considerable interindividual differences in its pharmacokinetics. Interindividual differences in the activity and expression of the metabolising enzymes cytochrome P450 (CYP) 3A4 and 3A5 and the multidrug efflux pump P‐glycoprotein (P‐gp) contribute considerably to cyclosporine pharmacokinetics. Variability in the activity of CYP3A4, CYP3A5 and P‐gp could be considered to result from genetic polymorphisms encoding their genes. The aim of the present study was to evaluate retrospectively the effects of genetic polymorphisms ofCYP3A4,CYP3A5andMDR1on cyclosporine dose adjusted trough blood concentration during the early period after renal transplantation in Chinese patients. One hundred and six renal transplant recipients in China were genotyped by polymerase chain reaction–restriction fragment length polymorphism forCYP3A4*18A,CYP3A5*3andMDR1 C3435T.Cyclosporine whole blood levels were measured by fluorescence polarization immunoassay. Dose‐adjusted trough blood concentrations (C0) were determined and compared among the different genotype groups. The frequency of theCYP3A4*18A, CYP3A5*3andMDR1 C3435Tvariant alleles were 0.005 (95% confidence interval (CI) 0.048, 0.0049), 0.783 (95% CI 0.781, 0.785) and 0.528 (95% CI 0.526, 0.531), respectively, and these alleles exhibited incomplete linkage disequilibrium. The median cyclosporine dose‐adjusted C0inCYP3A5*1/*1genotype subjects (n = 6) was 14.8 ng/mL per mg per kg (range 11.1–26.8 ng/mL per mg per kg), inCYP3A5*1/*3patients (n = 34) it was 23.7 ng/mL per mg per kg (range 9.0–61.0 ng/mL per mg per kg) and forCYP3A5*3/*3patients (n = 66) it was 26.4 ng/mL per mg per kg (range 9.8–85.8 ng/mL per mg per kg;P = 0.012, Kruskal–Wallis test). Accordingly, cyclosporine dose‐adjusted C0was larger in CYP3A5 non‐expressors than expressors in the first week after renal transplantation. In addition, wild‐type homozygotes (n = 21) forMDR1 C3435Thad a slight but significantly lower dose‐adjusted C0compared with heterozygotes (n = 58): 17.7 (10.3–60.8) versus 26.4 (9.0–67.3) ng/mL per mg per kg, respectively (P = 0.014, Mann–WhitneyU‐test). In conclusion, the present study shows that genetic polymorphisms inCYP3A5may be responsible, in part, for the large interindividual variability of cyclosporine pharmacokinetics during the early phase after renal transplantation in Chinese patients. Patients with theCYP3A5*3variant genotype require a low dose of cyclosporine to reach target levels compared with those with theCYP3A5*1allele.