Activity Variations of CYP2B6 Determine the Metabolic Stratification of Efavirenz

Purpose: To investigate the effects of hepatic enzyme activity variations and CYP2B6 gene polymorphisms on the in vivo and in vitro metabolism of efavirenz. Main methods: In vitro enzyme systems using rat and human liver microsomes (RLM/HLM) were established, with in vivo studies conducted on Sprague–Dawley rats. Metabolite detection was performed via LC-MS/MS. Human recombinant CYP2B6 microsomes were prepared using a baculovirus-insect cell system and ultracentrifugation, with efavirenz serving as the substrate to study enzyme kinetics. Results: Isavuconazole exhibited an IC₅₀ of 21.14 ± 0.57 μM in RLM, indicating a mixed competitive and noncompetitive mechanism, and an IC₅₀ of 40.44 ± 4.23 μM in HLM, suggesting an anticompetitive mechanism. In rats, coadministration of efavirenz and isavuconazole significantly increased the AUC, T_max, and C_max of efavirenz. Co-administration of efavirenz and rifampicin significantly elevated the AUC, T_max, and C_max of 8-OH-efavirenz. The activity of CYP2B6.4, 6, and 7 increased significantly compared to CYP2B6.1, with relative clearance ranging from 158.34% to 212.72%. Conversely, the activity of CYP2B6.3, 8, 10, 11, 13–15, 18–21, 23–27, 31–33, and 37 was markedly reduced, ranging from 4.30% to 79.89%. Conclusion: Variations in liver enzyme activity and CYP2B6 genetic polymorphisms can significantly alter the metabolism of efavirenz. It provides laboratory-based data for the precise application of efavirenz and other CYP2B6 substrate drugs.