CYP3A pharmacogenetics and tacrolimus disposition in adult heart transplant recipients

Background: Cytochrome P450 (CYP) 3A polymorphisms are associated with variable CYP3A metabolizing enzyme activity and tacrolimus pharmacokinetics. We sought to determine the singular and combined impact of CYP3A4*22 and CYP3A5*3 variants on tacrolimus drug disposition in adult heart transplant recipients. Methods: The retrospective study included 76 patients greater than one year post-heart transplant and receiving tacrolimus. Patients were genotyped for CYP3A4*22 and CYP3A5*3, and combined genotypes were classified as follows: extensive metabolizers (EM, CYP3A4*1/*1+CYP3A5*1 carriers), intermediate metabolizers (IM, CYP3A4 *1/*1+CYP3A5*3/*3, or CYP3A4*22 carriers+CYP3A5*1 carriers), and poor metabolizers (PM, CYP3A4*22 carriers+CYP3A5*3/*3). The primary outcome was tacrolimus dose-adjusted trough concentration (C0/D, ng/mL per mg/d). Results: In singular analysis, tacrolimus C0/D did not differ significantly between CYP3A4*22 genotype groups. However, tacrolimus C0/D was 1.8-fold lower (P<.001) in CYP3A5 expressers vs non-expressers. When combined CYP3A genotypes were evaluated, tacrolimus C0/D was 1.8-fold lower in EMs vs IMs (P<.001) and EMs vs PMs (P=.001). Tacrolimus C0/D did not differ significantly between CYP3A IMs vs PMs. Conclusion: Combined CYP3A genotype was associated with tacrolimus drug disposition in adult heart transplant recipients, but the effect was largely driven by CYP3A5*3. These data suggest that CYP3A4*22 and combined CYP3A genotypes are unlikely to provide additional information beyond CYP3A5 genotype.