Pathophysiology and management of opioid-induced pruritus.

Pruritus occurs frequently following opioid use, particularly after neuraxial administration. Although not life threatening, pruritus is discomforting and may decrease patient satisfaction. Even though the mechanism of opioid-induced pruritus is not yet fully understood, there is increasing evidence of the important role played by micro opioid receptors. Animal experiments pointing to the role of the micro opioid receptor and the efficacy of micro opioid receptor antagonists for opioid adverse effect prophylaxis and treatment have been replicated in several studies. Serotonin and dopamine D(2) receptors, prostaglandins and spinal inhibitory pathways may also be involved in the genesis of pruritus. Several pharmacological agents have been used both for the treatment of established pruritus and in its prevention. Of these, micro opioid receptor antagonists have been most consistent in terms of attenuating opioid-induced pruritus but present problems in dose and administration. Other drugs, including mixed opioid receptor agonist-antagonists, serotonin 5-HT(3) receptor antagonists, propofol, NSAIDs and D(2) receptor antagonists, have also been demonstrated to be useful. This review summarises the current understanding of the mechanisms causing opioid-induced pruritus and the pharmacological therapies available to prevent and/or manage this disorder.