title: An observational study on the effect of S+-ketamine on chronic pain versus experimental acute pain in Complex Regional Pain Syndrome type 1 patients.
abstract: OBJECTIVE
  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+/-0.3 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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Anesthesiology, Leiden University Medical Center, 2300 RC Leiden, The Netherlands.
authors.forename: Marnix
authors.initials: M
authors.lastname: Sigtermans
authors.forename: Ingeborg
authors.initials: I
authors.lastname: Noppers
authors.forename: Elise
authors.initials: E
authors.lastname: Sarton
authors.forename: Martin
authors.initials: M
authors.lastname: Bauer
authors.forename: René
authors.initials: R
authors.lastname: Mooren
authors.forename: Erik
authors.initials: E
authors.lastname: Olofsen
authors.forename: Albert
authors.initials: A
authors.lastname: Dahan
mesh_terms: D000208:Acute Disease; D000328:Adult; D000700:Analgesics / Q000008:administration & dosage; D000704:Analysis of Variance; D002908:Chronic Disease; D004305:Dose-Response Relationship, Drug; D005260:Female; D006801:Humans; D007649:Ketamine / Q000008:administration & dosage* / Q000493:pharmacokinetics; D008875:Middle Aged; D010146:Pain / Q000188:drug therapy*; D010147:Pain Measurement; D017288:Pain Threshold / Q000187:drug effects; D018579:Patient Selection; D012019:Reflex Sympathetic Dystrophy / Q000188:drug therapy*
chemical_list: D000700:Analgesics; D007649:Ketamine