Comparative evaluation of the sedative and physiological effects of medetomidine alone and in combination with pethidine, morphine, tramadol, and methadone in goats

Background: The use of combinations of alpha(2)-adrenergic agonists and opioids has been published as providing superior sedation than either drug alone. Introduction: The present study aims to compare the sedative and physiological effects of intravenous (IV) administration of medetomidine alone and in combination with methadone, morphine, tramadol, and pethidine in goats. Methods: Ten healthy goats aged 12 +/- 3 months and weight of 22 +/- 4 kg were used in an experimental, crossover (Latin square), randomized, and blinded study. The animals were assigned to five IV treatments with a minimum washout period of 8 days between treatments: medetomidine (20 mu g kg(-1)), medetomidine/methadone (0.5 mg kg(-1)), medetomidine/morphine (0.5 mg kg(-1)), medetomidine/tramadol (5 mg kg(-1)), and medetomidine/pethidine (1 mg kg(-1)). Results: Clinical adverse effects such as tremors (facial and generalized), bruxism, nystagmus, mydriasis, and vocalization were presented in all the medetomidine/opioid treatments. Clinical adverse effects were observed at 10-90 minutes in medetomidine/opioid treatments. Animals in all treatments were sedated at 5-90 minutes. Sedation was significantly higher in medetomidine/opioid treatments than in medetomidine at 15-30 minutes after administration (P < 0.05). In all treatments, heart rate and respiratory rate significantly decreased from baseline at 5-105 and 30-60 minutes, respectively. There was no significant difference in heart and respiratory rates between different treatments at any time point. Ruminal motility was decreased in medetomidine and medetomidine/opioid treatments at 10-75 and 10-105 minutes, respectively. Compared with medetomidine, ruminal motility was significantly lower in medetomidine/opioid treatments at 75-105 minutes. Conclusion: The use of combinations of medetomidine/opioids would be considered for superior sedation at 15-30 minutes after administration in goats. No significant differences were detected among opioids in combination with medetomidine in goats.