Serious post-operative neurological complications of unknown aetiology are reported in tigers after
immobilisation using tiletamine and zolazepam. These complications may arise from the persistent effects
of tiletamine or active metabolites of tiletamine or zolazepam. Concentrations of tiletamine, zolazepam
and some metabolites were measured using high performance liquid chromatography–mass spectrometry
in plasma from captive tigers (n = 8) and leopards (n = 9; an unaffected species, for comparison) during
anaesthesia for routine clinical procedures. The zolazepam:tiletamine (Z:T) ratio was calculated. Peak
concentrations occurred at 9–33 min and ranged from 83.5 to 379.2 ng/mL for tiletamine and 301.1 to
1239.3 ng/mL for zolazepam after correction for dose by weight. There were no significant differences
between tigers and leopards. The Z:T ratio was generally