Metadon

Metadon, also spelled methadone in many countries, is a synthetic opioid analgesic with a long duration of action. It was developed in the 1930s and first marketed in the 1940s. It is used medically for two main purposes: pain management and maintenance therapy for opioid use disorder. As a full agonist at the mu-opioid receptor, methadone provides analgesia and reduces withdrawal symptoms and cravings in people dependent on opioids.

Methadone is a highly lipophilic compound with variable oral bioavailability. It is mainly metabolized in the liver by cytochrome P450 enzymes, especially CYP3A4, with notable contributions from CYP2B6 and CYP2D6. Its active metabolite is nor-methadone. The elimination half-life is long and highly variable, commonly cited as roughly 8 to 59 hours, which can lead to accumulation with repeated dosing and complicates dosing schedules.

Administration and safety: Methadone is given orally as tablets or liquid, and can be prepared for intravenous use in clinical settings. In many systems, it must be prescribed and dispensed under supervision due to risks of overdose and interactions with other substances. Common side effects include constipation, nausea, drowsiness, sweating, and respiratory depression. It can prolong the QT interval, particularly at higher doses or when combined with certain medications, raising the risk of serious heart rhythm disturbances. Caution is advised in liver disease, in older adults, and when used with other central nervous system depressants such as benzodiazepines, alcohol, or some antidepressants.

Regulation: Methadone is a controlled substance in many jurisdictions. Access for opioid use disorder is often provided through dedicated treatment programs or clinics; use for chronic pain is regulated and monitored.