title: Increased response to ketamine following treatment at long intervals: implications for intermittent use.
abstract: BACKGROUND
  Ketamine has been used for many years as a dissociative anesthetic; however, there is evidence of increasing abuse, especially at dance clubs and raves. In addition, there is increasing interest in the use of subanesthetic doses of ketamine for the treatment of pain and depression, as well as for clinical research on schizophrenia. Despite growing use, relatively little is known about the consequences of repeated administration of low doses of ketamine.
  
  
  METHODS
  To determine the changes in response to repeated administration, ketamine (20 mg/kg or 50 mg/kg intraperitoneal [IP]) was administered once weekly to laboratory rats and the locomotor response was assessed following each injection.
  
  
  RESULTS
  Repeated administration of ketamine led to an escalation in the stimulant effects of the drug, characteristic of behavioral sensitization. The development of sensitization was greater when ketamine was repeatedly administered in the presence of distinct environmental cues.
  
  
  CONCLUSIONS
  Intermittent administration of ketamine at weekly intervals leads to the development of locomotor sensitization. These results suggest caution in the repeated use of ketamine for recreational or clinical purposes.
authors.affiliation: Department of Psychology and Office for Biomedical Research and Training, California State University San Marcos, San Marcos, California 92096, USA. keith@csusm.edu
authors.forename: Keith A
authors.initials: KA
authors.lastname: Trujillo
authors.forename: Juan J
authors.initials: JJ
authors.lastname: Zamora
authors.forename: Kathleen P
authors.initials: KP
authors.lastname: Warmoth
mesh_terms: D000700:Analgesics / Q000494:pharmacology*; D000704:Analysis of Variance; D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D004334:Drug Administration Schedule; D007649:Ketamine / Q000494:pharmacology*; D008297:Male; D009043:Motor Activity / Q000187:drug effects*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013997:Time Factors
chemical_list: D000700:Analgesics; D007649:Ketamine