Ritonavir, efavirenz, and nelfinavir inhibit CYP2B6 activity in vitro: potential drug interactions with bupropion.

Since antiretroviral drugs are known to inhibit many cytochrome P450 isoforms, the inhibition of CYP2B6 by non-nucleoside reverse transcriptase inhibitors and viral protease inhibitors was studied in vitro in human liver microsomes using bupropion hydroxylation as the CYP2B6 index reaction. Mean IC(50) values (microM) for inhibition of bupropion hydroxylation were: nelfinavir (2.5), ritonavir (2.2), and efavirenz (5.5). The reaction was only weakly inhibited by indinavir, saquinavir, amprenavir, delavirdine, and nevirapine. The inhibition of bupropion hydroxylation in vitro by nelfinavir, ritonavir, and efavirenz indicates inhibitory potency versus CYP2B6 and suggests the potential for clinical drug interactions.