Abstract
ObjectiveTo determine if the combinations of morphine, dexmedetomidine and maropitant enhance the analgesic effect and decrease the dose of individual drugs in rats subjected to noxious thermal stimulation with hot-plate and tail-flick tests. Study designRandomized, blinded, prospective experimental study. AnimalsA total of 96 male Sprague–Dawley rats. MethodsThe rats were randomly assigned to the following groups: 1) morphine (3 mg kg–1; Mor); 2) dexmedetomidine (10 μg kg–1; Dex); 3) maropitant (20 mg kg–1; Maro); 4) morphine (1.5 mg kg–1) + dexmedetomidine (5 μg kg–1; Mor + Dex); 5) dexmedetomidine (5 μg kg–1) + maropitant (10 mg kg–1; Dex + Maro); 6) morphine (1.5 mg kg–1) + maropitant (10 mg kg–1; Mor + Maro); 7) morphine (1 mg kg–1) + dexmedetomidine (3.5 μg kg–1) + maropitant (6.5 mg kg–1; Mor + Dex + Maro); and 8) normal saline (0.5 mL; saline), all injected intravenously. The tail-flick and hot-plate tests were performed before and 5, 15, 30, 45, 60, 90 and 120 minutes after the injection of the drugs. These variables were analysed with the effect–time area under the curve (AUC) analysis and a mixed linear model. ResultsData were analysed in 94 rats. The rank order of the total analgesic effects of the treatment groups shown by AUC analysis was found to be Mor > Maro + Mor > Dex + Mor > Dex > Maro > Dex + Maro + Mor > Dex + Maro > saline for the hot-plate test, and Maro + Mor > Mor > Dex + Mor > Dex + Maro + Mor > Maro > Dex > Dex + Maro > saline for the tail-flick test. The mixed model analysis showed a significant difference between latencies of the group morphine + maropitant versus all other treatment groups in the tail-flick test (p < 0.0001) and morphine versus saline in the hot-plate test (p < 0.05). Conclusions and clinical relevanceMorphine and maropitant appeared to show a supra-additive effect for analgesia in the tail-flick test. Clinical trials should be conducted to establish its use in treating pain.
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