Evaluation of Antinociceptive Efficacy of pre versus post-incisional Morphine, Tramadol or Meloxicam in Rats

To evaluate antinociceptive efficacy of pre- versus post-incisional morphine, tramadol and meloxicam using tail-flick test in an incisional model of pain in rats. Design: Prospective, randomized experimental study. Animals: Eighty, adult, male Wistar rats weighing 250–300 g. Procedures- Animals were randomly divided into eight groups to receive pre- or post-incisional (tail skin incision) saline (1 mL/kg, IP), morphine (4 mg/kg, IP), tramadol (12.5 mg/kg, IP), or meloxicam (1 mg/kg, IP). Antinociceptive effect of drugs was assessed using tail-flick latency (TFL) test following exposure to radiant heat. Morphine injection before or after incision prevented hyperalgesia for 120 minutes, while pre- or post-incisional administration of tramadol prevented hyperalgesia for 90 and 120 minutes, respectively. There was no significant difference between pre- or post-incisional administration of morphine or tramadol. Meloxicam, given either before or after skin incision, did not prevent hyperalgesia as compared with saline control group. Conclusion and Clinical Relevance: The timing of treatment had no significant effects on post-operative nociception. Both morphine and tramadol were effective in reducing post-operative hyperalgesia and can be used for the control of early postoperative nociception in rats.