Characterization of oxycodone in vitro metabolism by human cytochromes P450 and UDP-glucuronosyltransferases

•Kinetic parameters of oxymorphone and noroxycodone production by HLM were determined.•UGTs 2B4 and 2B7 were involved in oxycodone metabolism.•In vitro inhibitory effect of oxycodone were assessed using two CYP and UGT cocktail approaches.

The hepatic metabolism of oxycodone by cytochromes P450 (CYP) and the UDP-glucuronosyltransferases (UGT), the main metabolic enzymes of phase I and phase II, respectively, was assessed in vitro. The N-demethylation by CYP3A4/5 and the O-demethylation by CYP2D6 in human liver microsomes (HLM) followed Michaelis-Menten kinetics, with intrinsic clearances of 1.46 μL/min/mg and 0.35 μL/min/mg, respectively. Although noroxycodone and oxymorphone mainly contribute to the elimination of oxycodone, the simulated total in vivo clearance using in vitro phase I metabolism was underestimated. For the first time, metabolism of oxycodone by UGT was deeply investigated using HLM, recombinant enzymes and selective inhibitors. Oxycodone-glucuronide was mainly produced by UGT2B7 (Km = 762 ± 153 μM, Vmax = 344 ± 20 peak area/min/mg) and to a lesser extent by UGT2B4 (Km = 2454 ± 497 μM, Vmax = 201 ± 19 peak area/min/mg). Finally, the kinetics of the drug-drug interactions were assessed using two CYP and UGT cocktail approaches. Incubations of HLM with phase I and phase II drug probes showed that oxycodone mainly decreased the in vitro activities of CYP2D6, CYP3A4/5, UGT1A3, UGT1A6 and UGT2B subfamily with an important impact on UGT2B7.

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