Why do Pain Physicians Not Routinely Use Mixed Opioids for the Prevention of Neuraxial Opioid-induced Pruritus?

Background: Pruritus is a very disturbing secondary effect that appears after epidural or intrathecal administration of opioid drugs, especially in the management of postoperative pain. It is induced by the activation of mu opioid receptors and it can often be even more unpleasant than the pain being treated. Objective: A wide variety of drugs with different mechanisms of action have been used, aiming at the prevention of pruritus, with varying results. The aim of this comprehensive review letter is to summarize the current evidence of the available pharmacological options to either treat or prevent pruritus induced by spinal opioids. Method: The articles used in the review were found through a search in Medline, PubMed and Cochrane Library up to December 2016, using the keywords “Neuraxial opioids”, “Intrathecal morphine”, “Pruritus”, “Naloxone”, “Nalbuphine” and “Butorphanol”. Results: The most useful drugs act on the mu and kappa opioid receptors. They are either mu opioid antagonists, like intravenous naloxone, or mixed opioids mu antagonists/kappa agonists, such as intravenous nalbuphine and intravenous or epidural butorphanol, the latter being able also for maintaining the analgesia. Conclusion: Both pruritus prevention and treatment remain a challenge in the treatment of patients receiving spinal opioids for postoperative pain. Recent findings suggest that mixed opioids must be added to evidence-based clinical guidelines for the management of pruritus induced by spinal opioids.