Effect of nalbuphine or ketamine on xylazine requirements in standing sedated horses

Despite the pivotal role of α2 -agonists for standing sedation in horses, these drugs possess several dose-dependent side effects. Therefore, this study aimed to determine the effect of nalbuphine or ketamine on xylazine requirements necessary to provide constantly moderate sedation in horses. Five healthy adult horses were subjected to three randomized treatments at one-week intervals as follows: xylazine (XYL) (xylazine: 0.55 mg/kg, IV; saline: bolus & CRI); xylazine/nalbuphine (XYL/NAL) (xylazine: 0.55 mg/kg, IV; nalbuphine: 0.3 mg/kg, IV & 0.23 mg/kg/hour CRI) and xylazine/ketamine (XYL/KET) (xylazine: 0.55 mg/kg, IV; ketamine: 0.1 mg/kg, IV & 0.5 mg/kg/hour CRI). On all occasions, moderate sedation was maintained for 120 minutes by administering additional xylazine boluses (0.14 mg/kg, IV) whenever lower sedation was demonstrated. All treatments were assessed in terms of the degree of sedation, the time of administering the first additional xylazine bolus, and xylazine requirements (presented as mg/kg/hour) for maintaining moderate sedation for 120 minutes. The degree of ataxia and adverse events were also monitored. Sedation scores were significantly higher than the baseline for all treatments over 120 minutes. A longer time before the first additional xylazine bolus and lower xylazine requirements (lower calculated infusion rates) for maintaining moderate sedation were evident following the XYL/NAL and XYL/KET treatments compared to the XYL treatment. All treatments were associated with an acceptable degree of ataxia and limited behavioral effects. In conclusion, both nalbuphine and ketamine were efficient in reducing xylazine requirements for constant sedation in horses. Further study is required for comprehensive testing of all studied combinations to elucidate the potential advantages of the demonstrated xylazine sparing effect.