Opioid antagonists

Opioid antagonists are compounds that have expressed antagonistic activity, and that differ from the mixed agonist-antagonists in that they do not exhibit agonistic activity.

The efficacy and strength of opioid antagonists varies depending on the type of opioid receptors (u-, S-, K-, a-) with which they interact. The mechanism of their action is not fully clear. However, it has been suggested that they antagonize the action of endogenous opioid peptides.

These compounds are also antagonists in relation to agonist-antagonists. They antagonize the action of agonists, mixed agonists-antagonists, and they do not result in dependence or tolerance. They are used upon overdose of opioid analgesics or in the event of patient intolerance to them, and also in treating drug addiction.

Naloxone: Naloxone, (—)-17-(allyl)-4,5-epoxy-3,14-dihydroxymorphinan-6-one (3.1.92), is synthesized by the alkylation of 14-hydroxydihydronormorphinane (3.1.82) by allylbro-mide [55-58].

It is worth mentioning that N-allylic substitution in a number of morphine derivatives, as a rule, leads to antagonistic properties. Naloxone is a few times stronger than nalorphine as an antagonist. It blocks opiate receptors. It eliminates central and peripheral action of opioids, including respiratory depression. Naloxone is used upon overdose of narcotic analgesics.Synonyms for this drug are narkan, talwin, and others.

Naltrexone: Naltrexone, (—)-17-(cyclopropylmethyl)-4,5-epoxy-3,14-dihydroxymorphi-nan-6-one (3.1.93), is an N-cyclopropylmethyl derivative of oxymorphone (3.1.82). One of the methods of synthesis is analogous to the synthesis of naloxone, which consists of using cyclopropylmethylbromide instead of allylbromide [59].

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