ABSTRACT
BACKGROUND: Tacrolimus is a widely prescribed immunosuppressant agent for kidney transplantation. However, optimal dosing is challenging due to its narrow therapeutic index, potentially serious adverse effects, and wide inter-individual variability in pharmacokinetics. Cytochrome P450 3A (CPY3A) enzymes metabolize tacrolimus, so allelic variants such as CYP3A4*22 and CYP3A5*3 may contribute to individual differences in pharmacokinetics and therapeutic efficacy of tacrolimus. This study assessed the frequency and influences of CYP3A4*22 and CYP3A5*3 genotypes, alone and combined, on tacrolimus pharmacokinetics and dose requirements in Egyptian kidney transplant patients. METHODS: This is a prospective multicenter observational cohort study. Patients were genotyped for the CYP3A4*22 (rs35599367), and CYP3A5*3 (rs776746). Tacrolimus dose (mg), through blood level (ng/ml), and dose-adjusted trough concentration (C0/D) (ng/ml per mg/kg) were recorded during the first and third months post-transplantation and compared among genotype groups. RESULTS: The CYP3A4*22 allele was rare (3.2% of subjects) while the CYP3A5*3 allele was widespread (90.38%) in this cohort. At the third month post-transplantation, median C0/D was significantly higher among CYP3A4*22 carriers than CYP3A4*1/*1 (146.25 [100-380] versus 85.57 [27-370] ng/ml per mg/kg, p = 0.028). Patients harbouring the one copy of the CYP3A4*22 allele and the CYP3A5*3/*3 genotype (n = 5) were classified as poor tacrolimus metabolizers, the CYP3A5*3/*3 plus CYP3A4*1/*1 genotype as intermediate metabolizers (n = 60), and the CYP3A4*1/*1 plus CYP3A5*1/*1 genotype as normal metabolizers (n = 13). During the first month post-transplantation, C0/D was significantly greater in poor metabolizers (113.07 ng/ml per mg/kg) than intermediate and normal metabolizers (90.380 and 49.09 ng/ml per mg/kg) (p < 0.0005). This rank order was also observed during the third month. Acute rejection rate and renal function at discharge did not differ among genotypes. CONCLUSION: Pharmacogenetics testing for CYP3A4*22 and CYP3A5*3 before renal transplantation may help in the adjustment of tacrolimus starting dose and identify patients at risk of tacrolimus overexposure or underexposure.
