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Revista Brasileira de Anestesiologia
On-line version ISSN 1806-907X
SOUSA, Angela Maria; FRANCO, Paula Andrea Baptista; ASHMAWI, Hazem Adel and POSSO, Irimar de Paula. Local effect of tramadol on formalin evoked flinching behavior in rats. Rev. Bras. Anestesiol. [online]. 2008, vol.58, n.4, pp. 371-379. ISSN 1806-907X. http://dx.doi.org/10.1590/S0034-70942008000400006.
BACKGROUND AND OBJECTIVES: 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 µL 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 5mg) 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.
Keywords : ANALGESICS [tramadol]; ANIMALS [rats]; PAIN [Experimental]; PAIN [formalin]; PHARMACOLOGY, Pharmacodynamic [action mecanisms].