Effect of hepar‐protecting Wuzhi capsule on pharmacokinetics and dose‐effect character of tacrolimus in healthy volunteers

Wuzhi capsule (WZC), a preparation of Fructus Schisandra sphenanthera extract, has been used widely for the treatment of viral and drug-induced hepatitis in China. This study aimed to determine the pharmacokinetic parameters of tacrolimus (TAC) when co-administered with WZC and the dose-effect of WZC on tacrolimus in healthy volunteers. The effect of an increased dosage of WZC (1, 2, 6, and 8 capsules once daily) on the relative oral exposure of tacrolimus was assessed to explore the dose-response relationship between WZC and tacrolimus using bioanalysis, pharmacokinetic, and genotypical analyses. The influence of CYP3A5 and MDR1 genetic polymorphisms on the WZC dose was elucidated by maintaining the Ctrough of tacrolimus in Chinese healthy volunteers. When co-administered with WZC, the Tmax of tacrolimus was increased significantly while the apparent oral clearance was decreased. The plasma tacrolimus level in volunteers with high CYP3A5 expression was much lower than that in those with mutant CYP3A5. However, polymorphisms of MDR1 exon26 C3435T, exon21 G2677T/A, and exon12 C1236T were not associated with plasma tacrolimus levels. Our findings provide important information on interactions between modern medications and herbal products, thus facilitating a better usage of tacrolimus in patients receiving WZC.