Comparative evaluation of the sedative and physiological effects of dexmedetomidine alone and in combination with methadone, morphine, tramadol or pethidine in miniature donkeys

Summary Background The use of combinations of α2‐adrenergic agonists and opioids has been published as providing superior sedation than either drug alone. Objectives The present study aimed to compare the sedative and physiological effects of intravenous (IV) administration of dexmedetomidine alone and in combination with methadone, morphine, tramadol or pethidine in miniature donkeys. Study design Experimental, crossover Latin square, randomised, blinded study. Methods Twelve clinically healthy miniature donkeys with a mean age of 6 ± 2 (mean ± SD) years, weight of 94 ± 5 kg and height at withers of 0.80 ± 0.06 m were assigned to six IV treatments. They received either 0.9% saline, 5 μg/kg dexmedetomidine, 5 μg/kg dexmedetomidine and 0.2 mg/kg methadone, 5 μg/kg dexmedetomidine and 0.1 mg/kg morphine, 5 μg/kg dexmedetomidine and 2 mg/kg tramadol or 5 μg/kg dexmedetomidine and 1 mg/kg pethidine, with a washout period of 8 days. The degree of sedation was investigated using a numerical ranking scale of 0–3. Heart rate (HR), respiratory rate (RR), rectal temperature (RT) and intestinal motility were performed before and 5, 10, 15, 30, 45, 60, 75, 90 and 120 min after drug administration. Results Animals in dexmedetomidine or dexmedetomidine/opioid treatments were sedated for 5–60 min. Sedation was significantly higher in dexmedetomidine/opioid treatments than in dexmedetomidine at 15–30 min (p