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 α(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 μg 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.