Case Reports: Case Report
The Food and Drug Administration approved the μ-opioid receptor antagonist XR naltrexone in 2006 for the prevention of relapse in patients with opioid or alcohol dependence. XR naltrexone is a microsphere-based depot formulation that is injected once per month. The case report by Curatolo et al.1 provides the reader with the necessary context to anticipate potential pitfalls when managing anesthetic care of patients receiving XR naltrexone.
After injection of XR naltrexone, plasma concentrations are sustained and effectively block opioid receptors for about 3 weeks, decrease during the fourth week partially blocking the receptors, and are too low thereafter to block a sufficient number of receptors. Translated into a clinical context this suggests that patients receiving XR naltrexone are unlikely to respond to opioids for about 3 weeks after injection, will likely show a muted response during the fourth week, and can respond in an exaggerated fashion thereafter. This exaggerated response may result from receptor upregulation as the result of prolonged receptor blockade.
Curatolo et al.1 discuss additional pitfalls and offer potential solutions to avoid them. Of special importance, they appropriately conclude that because of altered sensitivity to the effects of opioids in patients injected with XR naltrexone more than 3 weeks earlier, the perioperative use of opioids in such patients should only occur under close observation by an experienced team.
Martin S. Angst, MD
Department of Anesthesia
Stanford University School of Medicine
1. Curatolo C, Trinh M. Challenges in the perioperative management of the patient receiving extended-release naltrexone. A & A Case Reports. 2014;3:142–4