An observational study on the effect of S(+)-ketamine on chronic pain versus experimental acute pain in Complex Regional Pain Syndrome type 1 patients
Received 15 April 2009; received in revised form 16 May 2009; accepted 23 May 2009. published online 19 June 2009.
Abstract
Aims
The 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.
Methods
Ten 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.
Results
CRPS pain: Ketamine produced potent analgesia with a significant VAS reduction from 6.2±0.2 to 0.4±0.3cm at the end of infusion. Analgesia persisted beyond the infusion period (VAS=2.8±1.0cm at 5-h), when measured plasma ketamine concentrations were low (<100ng/ml). Experimental pain: Ketamine had a dose-dependent antinociceptive effect on experimental pain that ended immediately upon the termination of infusion.
Discussion
The 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.
Department of Anesthesiology, Leiden University Medical Center, 2300 RC Leiden, The Netherlands
Corresponding author. Address: Department of Anesthesiology, Leiden University Medical Center, P.O. Box 9600, 2300 RC Leiden, The Netherlands. Tel.: +31 71 526 2301.
ABSTRACT