Description
Methadon is a synthetic, long-acting opioid with pharmacologic actions qualitatively similar to morphine and is active by oral and parenteral routes of administration. It is primarily a μ-receptor agonist and may mimic endogenous opioids, enkephalins, and endorphins and affect the release of other neurotransmitters acetylcholine, norepinephrine, substance P, and dopamine.
This accounts for its analgesic and antitussive properties, respiratory depression, sedation, decrease in bowel motility, increase in biliary tone, hormone regulation and increase of prolactin and growth hormone release, miotic pupils, nausea, and hypotension. Patients develop tolerance and physical dependence following repeated use.
