Anti-nociceptive synergism of morphine and gabapentin in neuropathic pain induced by chronic constriction injury

Abstract

anti-hyperalgesic effects of these drugs, administered either separately or in combination, were determinedusing the von Frey and acetone tests in a rat model of neuropathic pain (Bennett model). Morphine andgabapentin individually induced moderate attenuation of mechanical hyperalgesia, whereas the morphineand gabapentin combination completely decreased hyperalgesia. Morphine showed its maximal effect at30 min post-injection in the acetone test; however, this effect gradually returned to the baseline value.Gabapentin did not produce an anti-allodynic effect, whereas the morphine and gabapentin combinationcompletely decreased allodynia behavior at 30 min post-injection, an effect that persisted until 120 min. Thearea under the curve (AUC) of the anti-allodynic or anti-hyperalgesic effects produced by the combinationswere significantly greater than the theoretical sum of effects produced by each drug alone or similar to thetheoretical sum. The analysis of the effect, expressed as the AUC of the time course, supports the hypothesisthat the combination of these drugs is useful in neuropathic pain therapy.