Effect of the Interrelation between CYP3A5 Genotype, Concentration/Dose Ratio and Intrapatient Variability of Tacrolimus on Kidney Graft Function: Monte Carlo Simulation Approach.

: Tacrolimus (Tac) is characterized by large between- and within-patient (IPV) variability in pharmacokinetics and exposure. : This study aimed to assess and validate the effect of Tac IPV and trough concentration-to-dose ratio (C/D) over 6-12 months on reduced estimated glomerular filtration rate (eGFR) values in the late period after kidney transplantation (Tx), applying Monte Carlo (MC) simulation. : The previously published linear regression was the basis for MC simulation, performed to determine how variations in significant predictors affect the distribution of eGFR from 13 to 36 months post-transplantation. The input C/D values were derived from CYP3A5 genotype subgroups. : Patients characterized by high Tac IPV and low mean C/D over 6-12 months could have been at greater risk of lower eGFR values in a three-year period following Tx compared to the other patient groups. This effect was more pronounced in patients with a lower eGFR at the 6th month and a history of acute rejection. The proven contribution of CYP3A5 expresser genotype to low C/D values may suggest its indirect effect on long-term graft function. : The findings indicate that simultaneous assessment of Tac IPV, C/D, and CYP3A5 genotype may identify patients at risk of deterioration of graft function in the long-term post-transplantation period.