An Intravenous Ketamine Test as a Predictive Response Tool in Opioid-Exposed Patients with Persistent Pain

Chronic pain patients who are treated with opioid therapy represent a significant challenge to medical professionals. When. pain recurs in the face of a, previously effective opioid regimen, treatment options include (lose escalation., opioid rotation, drug holidays, and the addition Of adjuvants. Some experts advocate the use of N-methyl-D-aspartate receptor (NMDA-R) antagonists to combat tolerance. Recently the use of an, intravenous (i.v.) ketamine infusion to Predict the response to a dextromethorphan (DX) treatment trial has been described. In this study, 56 opioid-exposed patients with recurrent pain were treated with a low-dose (0.1 mg/kg) i.v. ketamine test followed by a DX treatment course. Using previously designated cutoff values for a positive response to ketamine (67% or more pain relief) and DX (50% or more pain relief), the sensitivity, specificity, positive predictive value, and negative Predictive value for an i.v. ketamine infusion to predict subsequent response to DX treatment were 72%, 68%, 52%, and 85%, respectively. The observed agreement between. an.,algesic responses was 78%, indicating a highly significant correlation (r = 0.54, P = 0.0001). Subgroup classification in the response to either ketamine or DX classification revealed no significant differences treatment, based on pain classification (i.e., nociceptive, neuropathic, or mixed) or placebo response. In contrast, a weaker correlation between ketamine and DX response was found in subjects requiring high-dose rather than low-dose opioid therapy. A significant correlation also was noted between. the development of side effects for the two NMDA-R antagonists. Based on These results, we conclude that an i.v. ketamine test may be a valuable toot in predicting subsequent response to DX treatment in opioid-exposed patients. with Persistent pain, J Pain Symptom Manage 2009;37:698-708. (C) 2009 U.S. Cancer Pain Relief Committee. Published by Elsevier Inc. All rights reserved.