Naltrexone

Naltrexone is indicated in the treatment of alcohol dependence and for the blockade of the effects of exogenously administered opioids. Naltrexone has not been shown to provide any therapeutic benefit except as part of an appropriate plan of management for the addictions.

Naltrexone acts as a competitive antagonist at opioid receptor sites. It blocks the action of opioids and precipitates withdrawal symptoms in opioid-dependent individuals.

Opioid dependence:

• Initially: 25 mg; increase to 50 mg daily if no withdrawal signs occur.
• Maintenance: 350 mg wkly given as 50 mg daily or divided in 3 doses (given on 3 days of the wk) for improved compliance.

Adjunct in alcohol dependence: 50 mg daily.

Administration

May be taken with or without food.

May reduce effects of opiate-containing preparations e.g. those used for cough and cold, diarrhoea and pain. Increased or decreased serum levels with drugs that alter hepatic metabolism. Potentially increased hepatotoxic effects with disulfiram. Increased risk of naltrexone-induced lethargy and somnolence with thioridazine. May increase insulin requirements.

Patients concurrently dependent on opioids; acute hepatitis or hepatic failure; acute opioid withdrawal; patients on therapeutic opioid analgesics.

Abdominal pain, nausea, vomiting; anxiety, insomnia, lethargy, headache, musculoskeletal pain; anorexia, diarrhoea, constipation; increased thirst; chest pain; chills, dizziness; sexual dysfunction; rash, liver function abnormalities and reversible idiopathic thrombocytopenia. Inj-site reactions.

Pregnancy Category C. Either studies in animals have revealed adverse effects on the foetus (teratogenic or embryocidal or other) and there are no controlled studies in women or studies in women and animals are not available. Drugs should be given only if the potential benefit justifies the potential risk to the foetus.

Hepatic or renal impairment. Monitor LFTs regularly. Patients should be opioid-free for at least 7-10 days prior to initiating naltrexone therapy. Strictly warn patients against the use of opioids while on naltrexone. Monitor for inj-site reactions. Pregnancy, lactation. History of bleeding disorders (including thrombocytopenia).

Symptoms: Clonic-tonic convulsions and respiratory failure.
Management: Supportive and symptomatic.

Antidote preparations

Store at 20-25° C.