Naltrexone
Naltrexone is an opioid receptor antagonist used in the management of alcohol dependence and opioid dependence. It is marketed as its hydrochloride salt, naltrexone hydrochloride, under the trade name Revia. __TOC__
Chemical Structure Naltrexone can be described as a substituted oxymorphone – here the tertiary amine methyl-substituent is replaced with methylcyclopropane.
Pharmacology
Naltrexone, and its active metabolite 6-β-naltrexol, are competitive antagonists at μ- and κ-opioid receptors, and to a lesser extent at δ-opioid receptors. This blockade of opioid receptors is the basis behind its action in the management of opioid dependence—it reversibly blocks or attenuates the effects of opioids. Its use in alcohol (ethanol) dependence has been studied and has been shown to be effective. Its mechanism of action in this indication is not fully understood, but as an opioid-receptor antagonist is likely to be due to the modulation of the dopaminergic mesolimbic pathway which ethanol is believed to activate.
Rapid detoxification
Naltrexone is sometimes used for rapid detoxification ("rapid detox") regimens for opioid dependence. The principle of rapid detoxification is to induce opioid-receptor blockade while the patient is in a state of impaired consciousness so as to attenuate the withdrawal symptoms experienced by the patient. Rapid detoxification under general anaesthesia involves an unconscious patient and requires intubation and external ventilation. Rapid detoxification is also possible under sedation. The rapid detoxification procedure is followed by oral naltrexone daily for up to 12 months for opioid dependence management. Rapid detoxification has been criticised by some for its questionable efficacy in long-term opioid dependence management. Rapid detoxification has often been misrepresented as a one-off "cure" for opioid dependence, when it is only intended as the initial step in an overall management regimen. Rapid detoxification is effective for short-term opioid detoxification, but is approximately 10 times more expensive than conventional detoxification procedures.
Safety
There has been some controversy regarding the use of opioid-receptor antagonists, such as naltrexone, in the long-term management of opioid dependence due to the effect of these agents in sensitising the opioid receptors. That is, after therapy, the opioid receptors continue to have increased sensitivity for a period during which the patient is at increased risk of opioid overdose. This effect reinforces the necessity of monitoring of therapy and provision of patient support measures by medical practitioners.
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