Gabapentin enhances anti-nociceptive effects of morphine on heat, cold, and mechanical hyperalgesia in a rat model of neuropathic pain

Neuropathic pain is caused by lesions or diseases affecting the somatosensory system and often responds poorly to typical medications. In this study, we evaluated anti-nociceptive effects of morphine, gabapentin and their combination on heat hyperalgesia, cold and mechanical allodynia in chronic constriction injury (CCI) model of neuropathic pain in rats. Morphine (2, 4 and 8 mg/kg) and gabapentin (5, 10 and 20 mg/kg) were administered either alone or in combination (morphine 2 mg/kg and gabapentin 5 mg/kg). Our results showed that morphine and gabapentin alone produce anti-nociceptive effects at higher doses (morphine 4 and 8 mg/kg and gabapentin 10 and 20 mg/kg) whereas their combination resulted in better analgesia at lower doses as compared to other treatment groups (morphine 2 mg/kg or gabapentin 5 mg/kg). These findings suggest that gabapentin potentiates the analgesic effects of morphine in the chronic constriction injury (CCI) model of neuropathic pain and combination of these drugs may be considered as a beneficial treatment for neuropathic pain.