Evaluation of anaesthetic potency of medetomidine-ketamine combination in rats, guinea-pigs and rabbits.

In many animal species ketamine hydrochloride is combined with xylazine, an alpha 2-adrenoceptor agonist, to achieve anaesthesia. The purpose of this study was to evaluate the anaesthetic efficacy of various dose combinations of another alpha-2-adrenoceptor agonist medetomidine and ketamine in rats, guinea pigs and rabbits. Both sexes of all three species in groups of five were used. In rats, dose combinations medetomidine/ketamine, both in mg/kg, used were 0.25/60, 1.0/60 and 0.5/70; in guinea pigs 0.5/40 and in rabbits 0.5/25 and 0.5/60. In rats and rabbits the righting reflex was lost within 2-3 min. In rats with doses 0.25/60 and 0.5/75 other reflexes disappeared, reappearing after 20-25 min and 60-70 min in males, the respective values being 120-140 min and 150-180 in females. The righting reflex reappeared after 130-135 and 160-190 min in males and 240 and greater than 300 min in females in the order above. In guinea pigs irrespective of route of ketamine administration all reflexes remained. In rabbits, a dose 0.5/25 caused disappearance of ear pinch reflex. We conclude that the medetomidine-ketamine combination can be used in rats and rabbits as an anaesthetic, and in guinea pigs only for immobilization.