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Updated: Jun 23, 2026
A Preterm Rat Model for Pain Studies
Published on: February 9, 2024
Local effect of tramadol on formalin evoked flinching behavior in rats
Angela Maria Sousa1, Paula Andrea Baptista Franco, Hazem Adel Ashmawi
1Laboratório de Investigção Médica, LIM-08 da Faculdade de Medicina da Universidade de São Paulo, FM/USP, São Paulo, SP.
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 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.
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