Efeito analgésico periférico do tramadol em ratos / Local analgesic effect of tramadol in rats

AUTOR(ES)
DATA DE PUBLICAÇÃO

2010

RESUMO

INTRODUCTION: Tramadol is a centrally and peripherally-acting drug, found as a racemic mixture of two enantiomers (+) and (-)-tramadol and effective in the treatment of moderate to severe pain. Tramadol has an -opioid effect ten times less potent than codeine. After first pass metabolism, tramadol is metabolized to various compounds and its major metabolites, (+) and (-)-odesmethyl- tramadol (M1), are therapeutically active as an analgesic and has opioid affinity similar to codeine. Tramadol reduces the peak amplitude of compound action potentials of isolated sciatic nerves and is utilized as adjuvant to lidocaine in brachial plexus blockade in humans. METHODS: Male Wistar rats, 5 to 6 per group were enrolled in the experiments. Two animal models of hyperalgesia were studied: nociceptive flinching behavior induced by formalin and mechanical hyperalgesia after plantar incision. Systemic and intraplantar tramadol were utilized in the two models. Perineural tramadol was injected by the sciatic nerve after localization with nerve stimulator. Opioid receptor antagonist, naloxone, was used in both methods. RESULTS: Dose dependent effect was observed in the flinching behavior test. Five and 2.5 mg intraplantar tramadol completely blocked the first phase formalin test while 1.25 mg abolished the first phase and diminished, but not blocked the second phase. Systemic 5 mg tramadol reduced the second phase of the flinching behavior test without interfering with the first phase. Perineural tramadol was equally effective as intraplantar tramadol at the same dose. In the plantar incision model, 5 mg intraplantar tramadol completely blocked mechanical hyperalgesia with Von Frey monofilaments test; systemic tramadol in the same dose was effective only after 45 minutes of injection. Systemic naloxone antagonized the analgesic effect after 45 minutes of intraplantar tramadol, while intraplantar naloxone was not effective. CONCLUSIONS: Tramadol reduces analgesia in a dose dependent way. Intraplantar tramadol has an early and prolonged analgesic effect not mediated by opioid receptors in the two studied models. Besides, it has an early and important analgesic effect when perineurally administered with a weak motor effect similar to local anesthetics

ASSUNTO(S)

ratos tramadol bloqueio nervoso medições da dor pain tramadol nerve block rats

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