Opioids have three receptors in primates: mu (MOR), kappa (KOR) and delta (DOR). Systemic administration of mu agonists produce scratching but kappa agonist or delta agonists do not evoke scratching. Kappa agonists are able to inhibit opioid-induced itch by preventing or reversing it, as well as mu antagonists. As a mu-antagnist, naltrexone is the most commonly used but others could be effective: naoloxone, nalbuphine, nalmefene and butorphanol. The kappa-agonist nalfurafine is approved in Japan for the treatment of itch.
KeywordsOpioid Kappa receptor Mu receptor
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