Impact of Donor and Recipient CYP3A5*3 Genotype on Tacrolimus Population Pharmacokinetics in Chinese Adult Liver Transplant Recipients

Background: Tacrolimus (TAC) is widely used after liver transplantation, but the therapeutic window is narrow. Objective: The purpose was to study both donor and recipient CYP3A5*3 genotypes affecting TAC apparent clearance rate (CL/F) and investigate a TAC population pharmacokinetic (PPK) model in Chinese liver transplant recipients for potential starting-dose individualized medication. Methods: A data set of 721 TAC concentrations was obtained from 43 adult liver transplant recipients. The TAC PPK model was analyzed using nonlinear mixed-effects modeling. Potential covariates, including demographic characteristics, physiological and pathological data, concomitant medications, and CYP3A5*3 genotype, were evaluated. The final model was validated using normalized prediction distribution errors and bootstrapping. Results: A 2-compartment model with first-order absorption and elimination was used to describe TAC disposition. Population estimates of TAC, CL/F, apparent central distribution volume (V2/F), rate of absorption (K_a), and apparent peripheral distribution volume (V₃/F) were 18.1 L/h (12%), 72.7 L (34%), 0.163 h⁻¹ (17%), and 412 L (21%), respectively. The model and estimated parameters were found to be stable. Other covariates did not influence TAC CL/F. Both donor and recipient CYP3A5*1 genotypes were significantly correlated with TAC clearance, and CL/F was 1.70-fold higher in both donor and recipient CYP3A5*1 carriers than in noncarriers among Chinese liver transplant recipients. Conclusion and Relevance: A PPK model of TAC was established in Chinese adult liver transplantation recipients for starting-dose individualized medication, which can be expanded to optimize clinical efficacy and minimize toxicity with therapeutic drug monitoring.