Activity Variations of CYP2B6 Determine the Metabolic Stratification of Efavirenz

To investigate the effects of hepatic enzyme activity variations and CYP2B6 gene polymorphisms on the in vivo and in vitro metabolism of efavirenz.

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.

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%.

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.