Methadone inhibits CYP2D6 and UGT2B7/2B4<i>in vivo</i>: a study using codeine in methadone‐ and buprenorphine‐maintained subjects

Abstract

Methadone is associated with inhibition of CYP2D6 and UGTs 2B4 and 2B7 reactions in vivo, even though it is not a substrate for these enzymes. Plasma morphine was not altered, owing to the opposing effects of inhibition of both formation and elimination; however, morphine-6-glucuronide (analgesically active) concentrations were substantially reduced. Drug interactions with methadone are likely to include drugs metabolized by various UGTs and CYP2D6.