• Marnix Sigtermans, Ingeborg Noppers, Elise Sarton, Martin Bauer, René Mooren, Erik Olofsen, and Albert Dahan.
• Department of Anesthesiology, Leiden University Medical Center, 2300 RC Leiden, The Netherlands.
• Eur J Pain. 2010 Mar 1;14(3):302-7.

AimsThe aim of the study was to explore the analgesic effect of the N-methyl-d-aspartate receptor (NMDAR) antagonist ketamine in acute experimental versus chronic spontaneous pain in Complex Regional Pain Syndrome type 1 (CRPS-1) patients.MethodsTen patients suffering from chronic CRPS-1 and with a Visual Analogue pain Score (VAS) of >5 were recruited. Seven intravenous 5-min low-dose S(+)-ketamine infusions with increasing doses at 20-min intervals were applied. Spontaneous pain ratings and VAS responses to experimental heat stimuli were obtained during infusion and for 3-h following infusion.ResultsCRPS pain: Ketamine produced potent analgesia with a significant VAS reduction from 6.2+/-0.2 to 0.4+/-0.3 cm at the end of infusion. Analgesia persisted beyond the infusion period (VAS=2.8+/-1.0 cm at 5-h), when measured plasma ketamine concentrations were low (<100 ng/ml). Experimental pain: Ketamine had a dose-dependent antinociceptive effect on experimental pain that ended immediately upon the termination of infusion.DiscussionThe data indicate that while ketamine's effect on acute experimental pain is driven by pharmacokinetics, its effect on CRPS pain persisted beyond the infusion period when drug concentrations were below the analgesia threshold for acute pain. This indicates a disease modulatory role for ketamine in CRPS-1 pain, possibly via desensitization of NMDAR in the spinal cord or restoration of inhibitory sensory control in the brain.Copyright 2009 European Federation of International Association for the Study of Pain Chapters. Published by Elsevier Ltd. All rights reserved.

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