Opioid antagonist

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An opioid antagonist is an receptor antagonist that acts on opioid receptors.

Naloxone and naltrexone are commonly used opioid antagonist drugs which are competitive antagonists that bind to the opioid receptors with higher affinity than agonists but do not activate the receptors. This effectively blocks the receptor, preventing the body from responding to opiates and endorphins.

Some opioid antagonists are not pure antagonists but in fact do produce some weak opioid partial agonist effects, and can produce analgesic effects when administered in high doses to opioid-naive individuals. Examples of such compounds include nalorphine and levallorphan. However the analgesic effects from these drugs are limited and tend to be accompanied by dysphoria, most likely due to action at the kappa opioid receptor. As they induce opioid withdrawal effects in people who are taking, or have previously used, opioid full agonists, these drugs are considered to be antagonists for practical purposes.

The weak partial agonist effect can be useful for some purposes, such as long-term maintenance of former opioid addicts using low dose naltrexone, however it can also have disadvantages such as worsening respiratory depression in patients who have overdosed on non-opioid sedatives such as alcohol or barbiturates. Naloxone on the other hand has no partial agonist effects, and is in fact a weak inverse agonist at mu opioid receptors, and so is the preferred antidote drug for treating opioid overdose.

[edit] In Fiction

• In the episode of House (TV series) - Skin Deep (House episode), opioid antagonist drugs were administered in order to completely remove the patient's heroin induced addiction/withdrawal symptoms (during an induced coma in order to relieve the extreme pain of their use), so that an accurate diagnosis of paraneoplastic syndrome caused by cancer was differentiated.

[edit] See also

• Opioid
• Buprenorphine, an opioid with both partial agonist and antagonist actions

[edit] External links

• David S, Lancaster T, Stead LF. Opioid antagonists for smoking cessation (Cochrane Review), The Cochrane Library, Issue 2, 2005. Chichester, UK: John Wiley & Sons, Ltd.
• MeSH Opioid+Antagonists