Stereoselective metabolism of methadone N-demethylation by cytochrome P4502B6 and 2C19.

Methadone is a clinically used opioid agonist that is oxidatively metabolized by cytochrome P450 (CYP) isoforms to a stable metabolite, EDDP. Methadone is a chiral drug administered as the racemic mixture of (R)-(-)- and (S)-(+)-methadone, but (R)-methadone is the active isomer. The cytochrome P450 (CYP) isoform involved in methadone's metabolism is thought to be CYP3A4, but human drug-drug interaction studies are not consistent with this.