ABSTRACT
Background: Tacrolimus (Tac) is characterized by large between- and within-patient (IPV) variability in pharmacokinetics and exposure. Aim: This study aimed to assess and validate the effect of Tac IPV and trough concentration-to-dose ratio (C0/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. Methods: 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 C0/D values were derived from CYP3A5 genotype subgroups. Results: Patients characterized by high Tac IPV and low mean C0/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 C0/D values may suggest its indirect effect on long-term graft function. Conclusion: The findings indicate that simultaneous assessment of Tac IPV, C0/D, and CYP3A5 genotype may identify patients at risk of deterioration of graft function in the long-term post-transplantation period.
ABSTRACT
BACKGROUND AND OBJECTIVE: Tacrolimus is a cornerstone of the most immunosuppressive protocols after kidney transplantation, but its use is complicated by notable interpatient and intrapatient variability (IPV). The goal of this study was to evaluate whether or not tacrolimus IPV, or average dose-adjusted trough concentration (C0/D), during 6-12 months post-transplantation might have contributed to graft function decline in a 3-year period following kidney transplantation. After primary evaluation of individual effects of tacrolimus IPV and C0/D, the study aimed to estimate the combined effect of tacrolimus IPV and C0/D on composite endpoint (consisting of graft failure, chronic allograft dysfunction, chronic rejection, and doubling of serum creatinine concentration) in the period between 13 and 36 months after kidney transplantation. In addition, the goal was to analyze the impact of genetics on interpatient variability in tacrolimus exposure in the early and late post-transplantation periods. METHODS: The study enrolled 104 Caucasian patients and included 2541 patient examinations up to 36 months after kidney transplantation. All patients were genotyped on CYP3A5 6986A>G and ABCB1 3435C>T gene polymorphism. Patients were divided into groups based on the tacrolimus IPV tertiles and the median value of average C0/D during 6-12 months post-transplantation. RESULTS: The results showed a more pronounced decline in estimated glomerular filtration rate values within the high IPV tertile group (p = 0.018), as well as within the low C0/D group (p = 0.013) in a 3-year period after kidney transplantation. The carriers of CYP3A5*1/*3 genotype had lower C0/D compared to the CYP3A5*3/*3 carriers during the entire study period, while the results for ABCB1 were inconsistent when considering tacrolimus C0/D. Patients with high IPV/low C0/D had significantly reduced graft survival compared to the other tacrolimus IPV/C0/D combination groups (i.e., high IPV/high C0/D, low IPV/low C0/D, low IPV/high C0/D) with the hazard ratio of 3.14 in Cox analysis for reaching the composite endpoint. CONCLUSION: The findings of this study suggest that combined assessment of tacrolimus IPV and tacrolimus C0/D may categorize patients towards risk of graft deterioration in the long-term post-transplantation period.
