Pharmacogenetic determinants for interindividual difference of tacrolimus pharmacokinetics 1 year after renal transplantation

What is known and objective: Tacrolimus, a widely used immunosuppressive agent in organ transplantation, has a narrow therapeutic window. It has been suggested that its interaction with lansoprazole could be dependent on polymorphisms of CYP3A5 and CYP2C19. The objective of this study was to investigate how, 1 year after renal transplantation, CYP3A5 and CYP2C19 polymorphisms, biochemical parameters and coadministration with lansoprazole, influenced tacrolimus pharmacokinetics. Methods: The pharmacokinetics of tacrolimus was studied 1 year after renal transplantation, in 75 recipients who were all receiving continuation treatment with 12‐hourly oral tacrolimus, and 30 mg lansoprazole daily (Group 1; n = 20) or, 10 mg rabeprazole daily or no proton pump inhibitor (Group 2; n = 55). Results: There were no significant differences in the dose‐adjusted area under the plasma concentration–time curve (AUC_0–12) and maximum plasma concentration (C_max) of tacrolimus between CYP2C19 genotype groups, but there were significant differences between CYP3A5 genotypes groups (*1/*1 + *1/*3 vs. *3/*3 = 45·2 ± 20·0 vs. 71·0 ± 34·1 ng·h/mL/mg, P < 0·0001 and 6·3 ± 2·6 vs. 9·3 ± 7·0 ng/mL/mg, P = 0·0017, respectively) and between co‐administration with and without lansoprazole (74·5 ± 34·0 vs. 52·4 ± 27·4 ng·h/mL/mg, P = 0·0054 and 10·9 ± 8·8 vs. 6·7 ± 3·0 ng/mL/mg, P = 0·0024, respectively). In a multiple regression analysis, the dose‐adjusted AUC_0–12 and C_max of tacrolimus were associated with CYP3A5*3/*3 and co‐administration with lansoprazole. What is new and conclusion: CYP2C19 does not seem to contribute to the interaction between tacrolimus and lansoprazole. The long‐term combination of tacrolimus and lansoprazole requires careful monitoring of patients with the CYP3A5*3/*3 genotype.