Hydroxychloroquine is Metabolized by Cytochrome P450 2D6, 3A4 and 2C8, and Inhibits Cytochrome P450 2D6, while its Metabolites also Inhibit Cytochrome P450 3A in vitro

This study aimed to explore the cytochrome P450 (CYP) metabolic and inhibitory profile of hydroxychloroquine (HCQ). Hydroxychloro-quine metabolism was studied using human liver microsomes (HLMs) and recombinant CYP enzymes. The inhibitory effects of HCQ and its metabolites on nine CYPs were also determined in HLMs, us-ing an automated substrate cocktail method. Our metabolism data in-dicated that CYP3A4, CYP2D6, and CYP2C8 are the key enzymes involved in HCQ metabolism. All three CYPs formed the primary me-tabolites desethylchloroquine (DCQ) and desethylhydroxychloro-quine (DHCQ) to various degrees. Although the intrinsic clearance (CLint) value of HCQ depletion by recombinant CYP2D6 was > 10-fold higher than that by CYP3A4 (0.87 versus 0.075 mu l/min/pmol), scaling of recombinant CYP CLint to HLM level resulted in almost equal HLM CLint values for CYP2D6 and CYP3A4 (11 and 14 mu l/min/mg, respec-tively). The scaled HLM CLint of CYP2C8 was 5.7 mu l/min/mg. Data from HLM experiments with CYP-selective inhibitors also suggested rela-tively equal roles for CYP2D6 and CYP3A4 in HCQ metabolism, with a smaller contribution by CYP2C8. In CYP inhibition experiments, HCQ, DCQ, DHCQ, and the secondary metabolite didesethylchloroquine were direct CYP2D6 inhibitors, with 50% inhibitory concentration (IC50) val- ues between 18 and 135 mu M. HCQ did not inhibit other CYPs. Further- more, all metabolites were time-dependent CYP3A inhibitors (IC50 shift 2.2-3.4). To conclude, HCQ is metabolized by CYP3A4, CYP2D6, and CYP2C8 in vitro. HCQ and its metabolites are reversible CYP2D6 inhibi- tors, and HCQ metabolites are time-dependent CYP3A inhibitors. These data can be used to improve physiologically-based pharmacokinetic models and update drug-drug interaction risk estimations for HCQ.Peer reviewe