Yohimbine antagonizes the anaesthetic effects of ketamine-xylazine in captive Indian wild felids

Abstract

Objective: To determine the effectiveness of yohimbine as an antagonist of ketamine-xylazine anaesthesia in captive Asiatic lions (Panthera leo persica), tigers (Panthera tigris) and leopards (Panthera pardus). Study design: Prospective clinical trial. Animals: Fifty-two healthy adult lions, 55 adult leopards and 16 adult male tigers. Methods: Captive wild felids in Indian zoos were anaesthetized with a combination of ketamine (2.2-2.6 mg kg⁻¹) and xylazine (1.1-1.3 mg kg⁻¹) using a dart propelled from a blowpipe. Time to onset of anaesthesia, lateral recumbency and induction time were measured, and physiological variables (respiration, heart rate and rectal temperature) were recorded once after the onset of complete anaesthesia. Anaesthesia was antagonized at various time periods with an intravenous administration of either 0.1 or 0.15 mg kg⁻¹ yohimbine. Onset of arousal and time to complete anaesthetic recovery were recorded. Results: A total of 123 immobilizations were conducted between 2000 and 2005. Anaesthetic induction was achieved in 15-25 minutes in all animals. Incidents of sudden recovery or life-threatening effects associated with immobilizations were not observed. Yohimbine effectively antagonized anaesthesia in all animals within 10 minutes without any excitatory behaviour compared to control animals. No adverse reactions/side effects to yohimbine were recorded except that a few leopards exhibited seizure-like signs for a short period immediately after yohimbine administration. The duration of anaesthesia had no significant effect on the recovery time in any of the animals. Conclusion and clinical relevance: Yohimbine antagonized the xylazine portion of ketamine-xylazine anaesthesia and thereby hastened recovery from anaesthesia in Asiatic lions, tigers and leopards.