Relief of Intractable Pruritus With Naloxone

Abstract

Attempts to elucidate the pathophysiology of pruritus have implicated a number of chemicals that have the ability to trigger itching, the most important being histamine.¹Among other itch-inducing agents are the morphine alkaloids, which are of special interest due to their contrary effects on the sensations of pain and itching; they relieve one while exacerbating the other. The activation of itch by morphine is thought to be due to direct histamine release from tissue mast cells.²However, antihistamines seldom completely block the pruritus secondary to morphine administration and they sometimes provide only a little relief. Furthermore, intracisternal or intramedullary injection of morphine in different animals results in a scratch response that suggests another reason for morphine's effects.^3,4 The central itch-provoking effect of morphine is intriguing in light of recent evidence of the existence of central opiate receptors and naturally occurring peptides with opiate activity in the mammalian