Tolazoline as an antagonist in free-living lions immobilised with a ketamine-xylazine combination.

A combination of ketamine at 8.0 mg/kg and xylazine at 3.2 mg/kg was found effective in immobilising lions (Panthera leo) for 4 hours. Ataxia and immobilisation were rapidly induced, with stable respiratory rate, heart rate and body temperature recorded. Tolazoline effectively antagonised xylazine via intravenous or intramuscular injection, resulting in a return to mobility within approximately 20 and 60 minutes, respectively. Tolazoline also elevated the respiratory rate. No mortalities occurred during 97 immobilisations of 76 lions.