Systemic, but not intrathecal, ketamine produces preemptive analgesia in the rat formalin model.
BACKGROUND
We investigated the antinociceptive effects of pre- or posttreatment of intrathecal or intravenous ketamine on formalin-induced pain behaviors.


METHODS
Rats were divided into 4 groups of 7 rats each and 2 control groups (saline). Rats received ketamine 1 mg/kg intrathecally (i.t.) through a catheter either 15 min before or 5 min after formalin. In the other groups, they received ketamine 1 mg/kg intravenously (i.v.) through a catheter either 1 min before or 5 min after the formalin. Pain related behavior was quantified by counting the incidence of flinching of the injected paw for 60 min. Formalin induced a biphasic fliching (phase 1, 0-5 min; phase 2, 10-60 min after formalin injection) of injected paw. The inter-group (control, pre, and posttreatment groups) comparisons were performed separately for route of administration (i.t. or i.v.) and phase 1 and 2 using one-way ANOVA and Tukey test.


RESULTS
Flinches of phase 1 were not different among the three i.t. groups. The total flinches of phase 2 were reduced by posttreatment with i.t. ketamine (P < 0.05); In contrast, i.v. ketamine was effective only when given as a pretreatment. Flinches of phase 1 and 2 were reduced by pretreatment with i.v. ketamine (P < 0.05).


CONCLUSIONS
Intrathecal ketamine was an analgesic even when administered as a posttreatment, whereas intravenous ketamine produced effective preemption only when given as a pretreatment.
Lee
I O
IO
Department of Anaesthesia, College of Medicine, Korea University Guro Hospital, 80 Guro-dong, Guro-ku, Seoul, South Korea 152-703. iloklee@hotmail.com
Lee
I H
IH
D000698:Analgesia; D000700:Analgesics / Q000008:administration & dosage*; D000818:Animals; D005557:Formaldehyde; D006930:Hyperalgesia / Q000188:drug therapy; D007275:Injections, Intravenous; D007278:Injections, Spinal; D007649:Ketamine / Q000008:administration & dosage*; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley
D000700:Analgesics; D005557:Formaldehyde; D007649:Ketamine