[Methadone as an analgesic]

Methadone is a synthetic opioid agonist which has been available for more than 40 years. Although its main use has been in the maintenance therapy of opioid addicts, it has a number of unique characteristics including excellent analgesic effect, a high bioavailability, no known active metabolites, long duration of action during long-term treatment, high potency, and low cost. However, its use is limited by the complexity of the pharmacokinetics, with a risk of drug accumulation with toxic effects. Recent findings suggest that standard equianalgesic tables are unreliable, because methadone is much more potent when used for long-term treatment. Therefore methadone should be titrated carefully and increases in dosage should be performed every third or fourth day.