Naltrexone information from DrugsUpdate
P - Caution when used during pregnancy
L - Caution when used during lactation
LI - Lab *
Naltrexone is an opioid receptor antagonist used primarily in the management of alcohol dependence and opioid dependence. It is marketed in generic form as its hydrochloride salt, naltrexone hydrochloride, and marketed under the trade names Revia and Depade.
Pharmacodynamics
Naltrexone is a pure opioid antagonist. It markedly attenuates or completely blocks, reversibly, the subjective effects of intravenously administered opioids.
When co-administered with morphine, on a chronic basis, Naltrexone blocks the physical dependence to morphine, heroin and other opioids.
Naltrexone has few, if any, intrinsic actions besides its opioid blocking properties. However, it does produce some pupillary constriction, by an unknown mechanism.
The administration of Naltrexone is not associated with the development of tolerance or dependence. In subjects physically dependent on opioids, Naltrexone will precipitate withdrawal symptomatology.
Clinical studies indicate that 50 mg of Naltrexone hydrochloride will block the pharmacologic effects of 25 mg of intravenously administered heroin for periods as long as 24 hours. Other data suggest that doubling the dose of Naltrexone hydrochloride provides blockade for 48 hours, and tripling the dose of Naltrexone hydrochloride provides blockade for about 72 hours.
Pharmacokinetics
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 hours.
Naltrexone Indications / Naltrexone Uses
Information Not Available
Naltrexone Adverse Reactions / Naltrexone Side Effects
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.
Precautions
When Reversal of Naltrexone Blockade is Required – In an emergency situation in patients receiving fully blocking doses of Naltrexone, a suggested plan of management is regional analgesia, conscious sedation with a benzodiazepine, use of non-opioid analgesics or general anesthesia.
In a situation requiring opioid analgesia, the amount of opioid required may be greater than usual, and the resulting respiratory depression may be deeper and more prolonged.
A rapidly acting opioid analgesic which minimizes the duration of respiratory depression is preferred. The amount of analgesic administered should be titrated to the needs of the patient. Non-receptor mediated actions may occur and should be expected (e.g., facial swelling, itching, generalized erythema, or bronchoconstriction) presumably due to histamine release.
Irrespective of the drug chosen to reverse Naltrexone blockade, the patient should be monitored closely by appropriately trained personnel in a setting equipped and staffed for cardiopulmonary resuscitation.
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).
Other 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.
Other Interactions
Information Not Available
Dosage
Oral
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.
Oral
Adjunct in the management of alcohol dependence
Adult: As hydrochloride: 50 mg daily.
Intramuscular
Adjunct in the management of alcohol dependence
Adult: 380 mg once every 4 weeks.
Food(before/after)
May be taken with or without food
List of Contraindications
Naltrexone and Pregnancy
Caution when used during 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.
Naltrexone and Lactation
Caution when used during lactation
Naltrexone and Children
Information Not Available
Naltrexone and Geriatic
Information Not Available
Naltrexone and Other Contraindications
Patients concurrently dependent on opioids; acute hepatitis or hepatic failure; acute opioid withdrawal; patients on therapeutic opioid analgesics.
Storage
Intramuscular
Store at 2-8°C (36-46°F); do not freeze.
Oral
Store at 20-25°C (68-77°F).
Lab interference
Intramuscular
Store at 2-8°C (36-46°F); do not freeze.
Oral
Store at 20-25°C (68-77°F).
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