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, _, and _ receptors in the CNS, with the highest affintiy for the _ 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-_-naltrexol, is also an opiate antagonist and may contribute to the antagonistic activity of the drug.
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.
Hepatic. When administered orally, naltrexone undergoes extensive biotransformation and is metabolized to 6 beta-naltrexol (which may contribute to the therapeutic effect) and other minor metabolites.
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.
1. Schmitz JM, Stotts AL, Rhoades HM, Grabowski J: Naltrexone and relapse prevention treatment for cocaine-dependent patients. Addict Behav. 2001 Mar-Apr;26(2):167-80. [PubMed:11316375]
2. Krystal JH, Gueorguieva R, Cramer J, Collins J, Rosenheck R: Naltrexone is associated with reduced drinking by alcohol dependent patients receiving antidepressants for mood and anxiety symptoms: results from VA Cooperative Study No. 425, "Naltrexone in the treatment of alcoholism". Alcohol Clin Exp Res. 2008 Jan;32(1):85-91. Epub 2007 Dec 7. [PubMed:18070245]
3. Ray LA, Chin PF, Miotto K: Naltrexone for the treatment of alcoholism: clinical findings, mechanisms of action, and pharmacogenetics. CNS Neurol Disord Drug Targets. 2010 Mar;9(1):13-22. [PubMed:20201811]
4. Kariv R, Tiomny E, Grenshpon R, Dekel R, Waisman G, Ringel Y, Halpern Z: Low-dose naltreoxone for the treatment of irritable bowel syndrome: a pilot study. Dig Dis Sci. 2006 Dec;51(12):2128-33. Epub 2006 Nov 1. [PubMed:17080248]
On July 27, 2020, LGM Pharma announced its acquisition of the formulation development and drug product contract manufacturing business of Nexgen Pharma, Inc. As a result, you will notice our new logo and visuals throughout the website. We’re working on updates to reflect the exciting, expanded CDMO capabilities and services we now can offer you.