Local effect of tramadol on formalin evoked flinching behavior in rats.
OBJECTIVE
Tramadol hydrochloride is known as a centrally acting analgesic drug, used for the treatment of moderate to severe pain. A local analgesic effect has been demonstrated, but its mechanism of action remains unclear.


METHODS
In this study, we examined the effect of local, systemic and nerve block tramadol on the nociceptive flinching behavior elicited by injection of 50 microL of 1% formalin into the dorsal region of hind paw of rats. Nociceptive flinching behavior was observed for 60 minutes.


RESULTS
Local tramadol in higher concentrations (2.5 and 5 mg) almost eliminated flinching behavior during the entire test. Systemic and neural block tramadol did not affect flinching behavior in phase I and partially decreased it in phase II.


CONCLUSIONS
Tramadol presented a local analgesic effect in formalin nociceptive flinching behavior that is different from its central analgesic effect. This analgesic effect, in this model, seems not to be linked to a local anesthetic like effect.
Laboratório de Investigção Médica, LIM-08 da Faculdade de Medicina da Universidade de São Paulo, FM/USP, São Paulo, SP.
Angela Maria
AM
Sousa
Paula Andrea Baptista
PA
Franco
Hazem Adel
HA
Ashmawi
Irimar de Paula
Ide P
Posso
D000701:Analgesics, Opioid / Q000494:pharmacology / Q000627:therapeutic use*; D000818:Animals; D008297:Male; D010146:Pain / Q000188:drug therapy*; D051381:Rats; D017208:Rats, Wistar; D012018:Reflex / Q000187:drug effects; D014147:Tramadol / Q000494:pharmacology / Q000627:therapeutic use*
D000701:Analgesics, Opioid; D014147:Tramadol