Effects of CYP3A4, CYP3A5, and ABCB1 genetic variants on tacrolimus metabolism during the early period after kidney transplantation

CYP3A5 rs776746 is the main genetic determinant of tacrolimus metabolic rate, with CYP3A4 rs4646437 providing additional stratification and ABCB1 rs1045642 a modest effect.

Tacrolimus shows substantial interindividual pharmacokinetic variability, complicating early dose optimisation after kidney transplantation. In 120 kidney transplant recipients, tacrolimus exposure was assessed using dose-normalised trough concentrations (C0/D) during the first post-transplant month, with patients below 1.05 ng/mL per mg/day classified as fast metabolizers. Fast metabolizers (48.3 %) had lower trough levels, required higher doses and showed reduced C0/D ratios compared with slow metabolizers (0.95 ± 0.12 versus 2.39 ± 0.53 ng/mL per mg/day; p < 0.001). CYP3A5 rs776746 was the primary determinant, each A allele being strongly associated with fast metabolism (adjusted OR 44.11, 95 % CI 11.70-166.36; p < 0.001), while CYP3A4 rs4646437 provided additional stratification and ABCB1 rs1045642 modest effects. Combined CYP3A5 and CYP3A4 risk genotypes identified fast metabolizers in 88.2 % of cases, leading the authors to support genotype-informed tacrolimus dosing.

Synthesis written by Geno'X. For the full original abstract, please refer to the source publication.

An OR of 44 with a confidence interval from 12 to 166 conveys both the strength of the CYP3A5 signal and the narrowness of the cohort: in 120 patients the order of magnitude is established, the calibration of a starting dose is not. The specific contribution is adding CYP3A4 rs4646437, which raises detection of fast metabolizers to 88 %, potentially useful for a binary result before the first dose provided it is replicated outside this population. The endpoint remains strictly pharmacokinetic — no rejection, no nephrotoxicity — so nothing here replaces therapeutic drug monitoring.

Analysis by Dr Thibaut Benquey