Indications: severe pain, but less sedating than morphine and acts for longer periods; cough in terminal disease; adjunct in the treatment of opioid dependence. It is an opioid agonist and can be substituted for them to prevent the withdrawal symptoms.

Cautions: in prolonged use, avoid administration more often than twice daily to avoid the risk of accumulation and opioid overdosage, hypertension; hypothyroidism; asthma especially during attack and decreased respiratory reserve; pregnancy and breastfeeding; prostate hypertrophy; hepatic and renal impairment; convulsive disorder.

Note: patients with the following risk factors for QT interval prolongation are carefully monitored while taking methadone: heart or liver disease, electrolyte abnormalities, or concomitant treatment with drugs that can prolong QT interval; patients requiring more than 100 mg daily should also be monitored.

Contra-indications: acute respiratory depression; acute alcoholism; paralytic ileus, acute abdomen; increased intracranial pressure or head injury; phaeochromocytoma.

Side Effects: nausea, vomiting, constipation; drowsiness; respiratory depression and hypotension with high doses; difficulty in urination; dry mouth; hallucinations; mood changes; miosis; facial flushing; dependence; decreased libido.

Dose: analgesia, 2.5-10 mg at intervals of 3-8 hours depending on the pain.

Cough suppression, 1-2 mg every 4-6 hours but reduced to twice daily in prolonged use.

Opioid dependence, 10-20 mg initially increased as necessary by 10 mg daily until symptoms of withdrawal disappear.

Usual maintenance dose, 40-60 mg. Child, not recommended.