Mysimba
Mysimba Uses, Dosage, Side Effects, Food Interaction and all others data.
Naltrexone acts as a competitive antagonist at opioid receptor sites. It blocks the action of opioids and precipitates withdrawal symptoms in opioid-dependent individuals.
Naltrexone, a pure opioid antagonist, is a synthetic congener of oxymorphone with no opioid agonist properties. Naltrexone is indicated in the treatment of alcohol dependence and for the blockade of the effects of exogenously administered opioids. 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. In subjects physically dependent on opioids, naltrexone will precipitate withdrawal symptomatology.
| Trade Name | Mysimba |
| Generic | Naltrexone + bupropion hydrochloride |
| Type | Tablet |
| Therapeutic Class | |
| Manufacturer | Orexigen Therapeutics Ireland Limited |
| Available Country | United Kingdom |
| Last Updated: | September 19, 2023 at 7:00 am |
Uses
Naltrexone is used for 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.
Mysimba is also used to associated treatment for these conditions: Alcohol Dependency, BMI >30 kg/m2, Cholestatic pruritus, Opioid Dependence, Severe Pain
How Mysimba works
Naltrexone is a pure opiate antagonist and has little or no agonist activity. The mechanism of action of naltrexone in alcoholism is not understood; however, involvement of the endogenous opioid system is suggested by preclinical data. Naltrexone is thought to act as a competitive antagonist at mc, κ, and δ receptors in the CNS, with the highest affintiy for the μ receptor. Naltrexone competitively binds to such receptors and may block the effects of endogenous opioids. This leads to the antagonization of most of the subjective and objective effects of opiates, including respiratory depression, miosis, euphoria, and drug craving. The major metabolite of naltrexone, 6-β-naltrexol, is also an opiate antagonist and may contribute to the antagonistic activity of the drug.
Dosage
Mysimba dosage
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.
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.
Toxicity
In the mouse, rat and guinea pig, the oral LD50s were 1,100-1,550 mg/kg; 1,450 mg/kg; and 1,490 mg/kg; respectively. High doses of naltrexone (generally >1,000 mg/kg) produce salivation, depression/reduced activity, tremors, and convulsions.
Precaution
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).
Interaction
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.
Volume of Distribution
- 1350 L [intravenous administration]
Elimination Route
Although well absorbed orally, naltrexone is subject to significant first pass metabolism with oral bioavailability estimates ranging from 5 to 40%.
Half Life
4 hours for naltrexone and 13 hours for the active metabolite 6 beta-naltrexol.
Clearance
- ~ 3.5 L/min [after IV administration]
Elimination Route
Both parent drug and metabolites are excreted primarily by the kidney (53% to 79% of the dose), however, urinary excretion of unchanged naltrexone accounts for less than 2% of an oral dose and fecal excretion is a minor elimination pathway. The renal clearance for naltrexone ranges from 30 to 127 mL/min and suggests that renal elimination is primarily by glomerular filtration.
Pregnancy & Breastfeeding use
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.
Contraindication
Patients concurrently dependent on opioids; acute hepatitis or hepatic failure; acute opioid withdrawal; patients on therapeutic opioid analgesics.
Acute Overdose
Symptoms: Clonic-tonic convulsions and respiratory failure.
Management: Supportive and symptomatic.
Storage Condition
Store at 20-25° C.
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