Sedative and cardiopulmonary effects of xylazine alone or in combination with methadone, morphine or tramadol in sheep

To evaluate the cardiopulmonary and sedative effects of xylazine alone or in combination with methadone, morphine or tramadol in sheep. Experimental, prospective, crossover, randomized, blinded study. Six Santa Inês breed sheep (females) aged 12 ± 8 months and weighing 39.5 ± 7.4 kg. Sheep were sedated with each of four treatments in a randomized, crossover design, with a minimum washout period of 7 days between treatments. Treatments were: X [xylazine (0.1 mg kg−1)]; XM [xylazine (0.1 mg kg−1) and methadone (0.5 mg kg−1)]; XMO [xylazine (0.1 mg kg−1) and morphine (0.5 mg kg−1)], and XT [xylazine (0.1 mg kg−1) and tramadol (5 mg kg−1)]. Each drug combination was mixed in the syringe and injected intravenously. Sedation, heart rate (HR), mean arterial blood pressure (MAP), rectal temperature (RT°C), respiratory rate (fR), arterial blood gases and electrolytes were measured before drug administration (T0) and then at 15 minute intervals for 120 minutes (T15–T120). Heart rate significantly decreased in all treatments compared with T0. PaCO2 values in XM and XMO were higher at all time points compared with T0. In treatments X and XM, pH, bicarbonate ( HCO3-) and base excess were increased at all time points compared with T0. PaO2 was significantly decreased at T15–T75 in XM, at all time points in XMO, and at T15 and T30 in XT. Sedation at T15 and T30 in XM and XMO was greater than in the other treatments. The combinations of methadone, morphine or tramadol with xylazine resulted in cardiopulmonary changes similar to those induced by xylazine alone in sheep. The combinations provided better sedation, principally at 15 minutes and 30 minutes following administration.