J. O. Cardoso, E. T. Ogburn, Z. Desta; Indiana University, Indianapolis, IN

BACKGROUND: A previous in vitro study has identified CYP2B6 as a minor route of nevirapine metabolism, but clinical studies suggest that CYP2B6 is a major determinant of nevirapine exposure and effect. The purpose of this study was to re-evaluate the contribution of CYPs in nevirapine metabolism.
METHODS: Nevirapine (1-500 µM) was incubated in duplicate for 60 min at 37°C with HLMs and a NADPH-generating system. Metabolites were assayed by LC-MS/MS.
RESULTS: Kinetic parameters for the formation of nevirapine metabolites in seven HLMs are shown in the Table. In a panel of HLMs, CYP2B6 activity correlated significantly with the formation rates of all 4 nevirapine metabolites (Pearson r=0.8-0.89; p<0.001); CYP3A (r ≥ 0.88; p <0.0001) and CYP2A6 (r≥0.6; p<0.05) with 2- and 12-hydroxynevirapine formation rates. In expressed CYPs, multiple enzymes catalyzed nevirapine metabolism. Inhibition studies implicate CYP2B6 and CYP3A in nevirapine metabolism.
CONCLUSION: Multiple CYPs show activity towards nevirapine metabolism, but CYP2B6 and CYP3A appear dominant. Considering the involvement of CYP2B6 in all metabolic routes and that nevirapine autoinduces its own metabolism via upregulation of this enzyme, CYP2B6 may play a major role at steady-state nevirapine
Table 1. Average of apparent kinetic parameters for formation of nevirapine metabolites
Km (µM)Vmax (pmol/min/mg protein)Vmax/Km (µl/min/mg protein)
2-OH-NVP47.95 (± 24.52)17.32 (± 10.32)0.43 (± 0.33)
12-OH-NVP86.37 (± 65.51)22.46 (± 15.33)0.34 (± 0.24)
3-OH-NVP74.19 (± 61.67)9.73 (± 7.89)0.13 (± 0.06)
8-OH-NVP98.49 (± 31.28)5.31 (± 3.05)0.06 (± 0.04)