OpenAnesthesia and the APSF: Achieving Safe and Quality Anesthesia Care with Education Innovation

Methadone is a long-acting opioid that has a typical elimination half-life between 15 to 60 hours with a mean of around 22 hours. Metabolism rates vary greatly between individuals, up to a factor of 100, ranging from as few as 4 hours to as many as 130 hours. This variability is apparently due to the variable expression of CYP3A4, CYP2B6, and CYP2D6, the effects of enzyme induction and inhibition by other drugs, as well as environmental factors. Methadone is a racemic mixture of the L- and D- isomers. The opioid activity of racemic methadone results almost entirely the result of L-methadone whereas D-methadone acts as an NMDA antagonist. The likely involvement of NMDA systems in the mechanism of opioid tolerance and hyperalgesia suggests that the NMDA receptor antagonists may be useful for the treatment of postoperative pain. Methadone is unique in that it is an opioid that can attenuate (or even prevent) opioid tolerance.