Analgesic Interaction Between Morphine with Fentanyl In Experimental Murine Pain

Abstract Opioids are among the most effective pain relievers available, however multimodal antinociception between opioids, has not been extensively studied in diverse animal pain models.In this study the pharmacological interaction of morphine with fentanyl was evaluated in different murine pain models by means of isobolographic analysis. In control animals, morphine and fentanyl produced a dose-related antinociceptive action in the murine assays and the rank of potency was: formalin hind paw phase I > formalin phase II > tail flick. Coadministration of morphine with fentanyl, in a fixed relation 1:1 of their ED50, produces a dose response in all tests and the isobologram resulted in synergism. Fentanyl was more effective than morphine which could be explained according the suggestion that opioids could be acting through other targets, with different binding capacity thru the regulation or activation of non-opioid receptors. Co-administration of morphine with fentanyl induces synergism in all murine trials, confirming the antinociceptive capacity of both opioids which would constitute a promisory idea to multimodal treatment of pain.