Generic Medicine Info
Indications and Dosage
Opioid dependence
Adult: As hydrochloride: 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
Adult: As hydrochloride: 50 mg daily.
May be taken with or without food.
Patients concurrently dependent on opioids; acute hepatitis or hepatic failure; acute opioid withdrawal; patients on therapeutic opioid analgesics.
Special Precautions
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).
Adverse Reactions
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.
Symptoms: Clonic-tonic convulsions and respiratory failure. Management: Supportive and symptomatic.
Drug Interactions
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.
Lab Interference
May interfere in the detection of urinary opiates using some immunoassay or enzymatic methods.
Description: Naltrexone acts as a competitive antagonist at opioid receptor sites. It blocks the action of opioids and precipitates withdrawal symptoms in opioid-dependent individuals.
Absorption: Well absorbed from the GI tract. Peak plasma concentrations after about 1 hr.
Distribution: 20% bound to plasma proteins.
Metabolism: Extensively metabolised in the lvier. Undergoes considerable 1st-pass metabolism and may undergo enterohepatic recycling.
Excretion: Via urine (as <1% unchanged drug and as metabolites). Elimination half-life: Approx 4 hr.
Store at 2-8°C (36-46°F); do not freeze.
Store at 20-25°C (68-77°F).
MIMS Class
Drugs Used in Substance Dependence
Disclaimer: This information is independently developed by MIMS based on Naltrexone from various references and is provided for your reference only. Therapeutic uses, prescribing information and product availability may vary between countries. Please refer to MIMS Product Monographs for specific and locally approved prescribing information. Although great effort has been made to ensure content accuracy, MIMS shall not be held responsible or liable for any claims or damages arising from the use or misuse of the information contained herein, its contents or omissions, or otherwise. Copyright © 2021 MIMS. All rights reserved. Powered by
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