ABSTRACT
Methadone is a synthetic opiate analgesic with multiple actions quantitatively similar to those of morphine. Its most prominent actions involve the CNS and body organs composed of smooth muscle. An injectable dose of 10 mg of methadone is approximately equivalent in analgesic action to 10 mg of morphine. Methadone is well absorbed following oral ingestion. However, when ingested orally, methadone is approximately one-half as potent as when injected, presumably because of its significant first-pass hepatic metabolism. Oral ingestion is associated with a delay in onset of action, a lowering of the peak blood concentration, and an increase in the duration of analgesic action. Methadone is addicting and habituating and has the potential to be highly abused. Prescribe methadone pharmacotherapy cautiously to patients who have histories of problematic patterns of opiate or other abusable psychotropic use. Methadone pharmacotherapy commonly is associated with dizziness, drowsiness, excessive sweating, GI complaints, lightheadedness, nausea, sedation, and vomiting.
