Adult: As part of a comprehensive management programme for the prevention of relapse after opioid detoxification: Treatment should not be initiated until patient has passed a naloxone challenge test or is opioid-free (including tramadol) for at least 7-10 days after last opioid use. 380 mg every 4 weeks via deep IM gluteal inj.
Intramuscular Adjunct in alcohol dependence
Adult: As part of a comprehensive management programme in patients who are able to abstain from alcohol in an outpatient setting: Treatment should not be initiated until patient has passed a naloxone challenge test or is opioid-free (including tramadol) for at least 7-10 days after last opioid use. 380 mg every 4 weeks via deep IM gluteal inj.
Oral Adjunct in alcohol dependence
Adult: As part of a comprehensive treatment programme to support abstinence: Treatment should not be initiated until patient has passed a naloxone challenge test or is opioid-free (including tramadol) for at least 7-10 days after last opioid use. 50 mg once daily. Dosage recommendations may vary among countries and between individual products (refer to specific product guidelines).
Oral Opioid dependence
Adult: As an adjunct to the maintenance of the opioid-free state in detoxified, formerly opioid-dependent patients: Treatment should not be initiated until patient has passed a naloxone challenge test or is opioid-free (including tramadol) for at least 7-10 days after last opioid use. Initially, 25 mg; if no opioid withdrawal signs occur, may give 50 mg once daily. Maintenance (in order to improve compliance): 100 mg on Monday and on Wednesday, and 150 mg on Friday. Dosage recommendations may vary among countries and between individual products (refer to specific product guidelines).
What are the brands available for Naltrexone in Malaysia?
Narpan
Hepatic Impairment
Severe: Contraindicated.
Administration
Naltrexone May be taken with or without food.
Reconstitution
IM inj: Allow the drug vial and provided diluent to reach room temperature (approx 45 minutes). Reconstitute the drug vial with 3.4 mL of the provided diluent. Shake the vial vigorously for approx 1 minute to dissolve the drug. Withdraw 4.2 mL of the suspension, then remove any air bubbles and push on the plunger until 4 mL of the suspension remains in the syringe. Needle to be used in the preparation and administration of the solution may vary; refer to specific product guidelines.
Contraindications
Current physiological opioid dependence; acute opioid withdrawal; positive urine screen for opioids or failure to pass naloxone challenge; acute hepatitis or liver failure. Severe hepatic impairment. Concurrent use with opioid analgesics or opioid-containing drugs.
Special Precautions
Patient with thrombocytopenia or any coagulation disorder (IM). Patient undergoing surgery. Renal and mild to moderate hepatic impairment. Pregnancy and lactation.
Adverse Reactions
Significant: Abnormal hepatic function test (particularly in patients with alcohol abuse), hepatitis; decreased opioid tolerance, precipitated opioid withdrawal syndrome; depression, suicide, attempted suicide, suicidal ideation (particularly when used for opioid dependence); inj site reactions (e.g. pain, tenderness, induration, swelling, erythema, bruising, pruritus, abscess, cellulitis, tissue necrosis), eosinophilic pneumonia, urticaria, angioedema, anaphylaxis (IM). Cardiac disorders: Tachycardia, palpitations, chest pain. Ear and labyrinth disorders: Vertigo. Eye disorders: Increased lacrimation. Gastrointestinal disorders: Abdominal pain or cramps, nausea, vomiting, diarrhoea, constipation. General disorders and administration site conditions: Feebleness, asthenia, lack of appetite, thirst, increased energy, chills. Investigations: ECG change. Metabolism and nutrition disorders: Decreased appetite. Musculoskeletal and connective tissue disorders: Arthralgia, myalgia. Nervous system disorders: Headache, restlessness, dizziness, shivering. Psychiatric disorders: Insomnia, affective disorders, despondency, irritability, mood swings, nervousness, anxiety. Renal and urinary disorders: Urine retention. Reproductive system and breast disorders: Delayed ejaculation, erectile dysfunction. Skin and subcutaneous tissue disorders: Rash, hyperhidrosis. Potentially Fatal: Accidental opioid overdose (in patients with opioid dependence).
This drug may cause dizziness, if affected, do not drive or operate machinery.
Monitoring Parameters
Perform urine test to assess the absence of opioids before treatment initiation. Obtain LFTs before and during therapy. Assess for signs and symptoms of opioid withdrawal, inj site reactions (IM), and depression and/or suicidal ideation.
Drug Interactions
May decrease the therapeutic effects of opioid-containing analgesics, antidiarrhoeal or antitussives. Increased risk of prolonged respiratory depression with opioid agonists. May increase the risk of hepatotoxicity with disulfiram. Increased lethargy and somnolence with thioridazine. Increased risk of opioid withdrawal syndrome with methadone and methylnaltrexone. Potentially Fatal: Increased risk of respiratory or circulatory impairment with high-dose opioids.
Lab Interference
May result in cross-reactivity with certain opioid immunoassay methods.
Action
Description: Overview: Naltrexone is a cyclopropyl oxymorphone derivative and pure opioid antagonist. Mechanism of Action: Naltrexone acts as a competitive antagonist at opioid receptor sites, showing the highest affinity for mu receptors, and blocks the access for exogenous opioids. Additionally, naltrexone modifies the hypothalamic-pituitary-adrenal axis to suppress alcohol consumption. Pharmacodynamics: In opioid dependence, the blockade of opiate receptors by naltrexone is a competitive phenomenon which results in the elimination of the euphoric effect of opiates. At usual opiate concentrations, naltrexone's greater affinity for the receptor inhibits the binding of the opiate agonist to the receptor. However, when opiate concentrations are extremely high, the opiate can displace the naltrexone which may result in respiratory depression. In alcohol addiction, naltrexone reduces the risk of a full relapse with uncontrolled binge-drinking after having consumed a limited amount of alcohol. Additionally, naltrexone may affect the primary cravings as it is non-reinforcing on isolated consumption of limited amounts of alcohol.
Naltrexone is not associated with physical or mental dependence. Additionally, it is not an aversive therapy and will not result in a disulfiram-like reaction. Duration: Oral: 24 hours (50 mg); 48 hours (100 mg); 72 hours (150 mg). IM: 4 weeks. Pharmacokinetics: Absorption: Rapidly and almost completely absorbed from the gastrointestinal tract. Bioavailability: 5-40% (oral). Time to peak plasma concentration: Oral: Approx 60 minutes. IM: Biphasic: Approx 2 hours (first peak), approx 2-3 days (second peak). Distribution: Widely distributed throughout the body but with interindividual variation. Crosses the placenta and enters breast milk. Volume of distribution: Approx 1,350 L. Plasma protein binding: 21%. Metabolism: Extensively metabolised in the liver via noncytochrome dehydrogenase to 6β-naltrexol (primary metabolite) and glucuronide conjugates. Undergoes enterohepatic recycling and extensive first-pass effect. Excretion: Mainly via urine (as metabolites and small amounts of unchanged drug). Elimination half-life: Oral: 4 hours; 13 hours (6β-naltrexol). IM: 5-10 days (naltrexone and 6β-naltrexol).
Chemical Structure
Naltrexone Source: National Center for Biotechnology Information. PubChem Compound Summary for CID 5360515, Naltrexone. https://pubchem.ncbi.nlm.nih.gov/compound/Naltrexone. Accessed Dec. 18, 2025.
Storage
Oral: Tab: Store below 30°C. Protect from light.
Intramuscular: Extended-release injectable suspension: Store between 2-8°C. Alternatively, may store below 25°C for up to 7 days. Do not freeze.
N07BB04 - naltrexone ; Belongs to the class of drugs used in the management of alcohol dependence.
References
Brayfield A, Cadart C (eds). Naltrexone. Martindale: The Complete Drug Reference [online]. London. Pharmaceutical Press. https://www.medicinescomplete.com. Accessed 13/10/2025.Joint Formulary Committee. Naltrexone Hydrochloride. British National Formulary [online]. London. BMJ Group and Pharmaceutical Press. https://www.medicinescomplete.com. Accessed 13/10/2025.Max Health Ltd. Naltrexone 50 mg Film-coated Tablets data sheet 01 October 2020. Medsafe. http://www.medsafe.govt.nz. Accessed 13/10/2025.Naltrexone Hydrochloride 50 mg Film-coated Tablets (Accord Healthcare Limited). MHRA. https://products.mhra.gov.uk. Accessed 13/10/2025.Naltrexone Hydrochloride Tablet, Film Coated (Accord Healthcare, Inc.). DailyMed. Source: U.S. National Library of Medicine. https://dailymed.nlm.nih.gov/dailymed. Accessed 13/10/2025.Naltrexone. Gold Standard Drug Database in ClinicalKey [online]. Elsevier Inc. https://www.clinicalkey.com. Accessed 15/12/2025.Naltrexone. UpToDate Lexidrug, AHFS DI (Adult and Pediatric) Online. American Society of Health-System Pharmacists, Inc. Waltham, MA. UpToDate, Inc. https://online.lexi.com. Accessed 13/10/2025.Naltrexone. UpToDate Lexidrug, Lexi-Drugs Multinational Online. Waltham, MA. UpToDate, Inc. https://online.lexi.com. Accessed 13/10/2025.Napran Tablet (Duopharma [M] Sdn Bhd). National Pharmaceutical Regulatory Agency - Ministry of Health Malaysia. https://www.npra.gov.my. Accessed 13/10/2025.Vivitrol (Alkermes, Inc.). DailyMed. Source: U.S. National Library of Medicine. https://dailymed.nlm.nih.gov/dailymed. Accessed 13/10/2025.
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