Evaluation of the Effect of Gabapentin in the Enhances of the Analgesic Response to Morphine in Tail Flick of Male Rats

  GR. Sepehri PhD [1] , M. Shamsi Meymandi MSc [2] , M. Mobasher [3] , R. Mohammadi [4] , A. Mohalati⁴

  Received: 06/06/06 Sent for Revision: 01/11/06 Received Revised Manuscript: 15/03/07 Accepted: 29/04/07

  Background and Objective: Opioids, as drug of choice in acute pain treatment, have many side effects including dependency. Therefore, the combinational therapy of other drugs accompanied with opioids could decrease the side effects, tolerance and opioid dependency. In this study the effect of gabapentin and morphine co-administration was evaluated in acute model of pain.

  Materials and Methods: In this experimental study, the antinociceptive effect of gabapentin (30 or 90mg/kg, s.c.) and morphine (0.5, 1 and 3mg/kg, s.c.) alone or in combination with gabapentin were measured by Tail-flick test every 15 minuxtes up to 105 mins in intact adult male rats. Control rats received normal saline. Area Under Curve (AUC), as antinociceptive index, was calculated for each groups.

  Results: Both gabapentin (90mg/kg) and morphine (1 and 3mg/kg) showed antinociceptive response as compared to controls (p<0.05). But there was not any significant differences between the (AUC) of 0.5mg/kg morphine and 30mg/kg gabapentin as compared to controls, so these doses were considered as subanalgesic doses. The co-administration of subanalgesic doses of morphine (0.5mg/kg) and gabapentin (30mg/kg) increased significantly AUC as compared to morphine alone (p<0.001). The co-administration of gabapentin (30 and 90mg/kg) with analgesic doses of 1mg/kg (p<0.005) and 3mg/kg morphine also increased significantly AUC antinociceptive index as compared to controls (p<0.05).

  Conclusion: Gabapentin enhanced the antinociceptive effects of both analgesic and subanalgesic doses of morphine in a dose dependent manner in acute pain model in male rats.

  Key words: Gabapentin, Morphine, Co-administration, Acute pain, Antinociception

  [1] - Professor, Dept. of Physiology and Pharmacology, Neuroscience Research Center , Physiology Research Center , University of Medical Sciences, Kerman, Iran

  (Corresponding Author) Tel: (0341)3220081 , Fax: ( 0 341) 3221672, Email: gsepehri@yahoo.com

  [2] - Instructor, Dept. of Physiology ad Pharmacology, University of Medical Sciences, Kerman, Iran

  [3] - Researcher, Neuroscience Research Center , Azad University, Kerman , Iran

  [4] - Student, Physiology Research Center, Azad University, Kerman, Iran