The clinical effectiveness of atipamezole as a medetomidine antagonist in the dog

Vähä‐Vahe, A.T. The clinical effectiveness of atipamezole as a medetomidine antagonist in the dog. J. vet. Pharmacol. Therap. 13, 198–205. The efficacy of atipamezole, a recently introduced α 2 ‐adrenoceptor antagonist, in reversing medetomidine‐induced effects in dogs was investigated in a clinical study. Dogs from eight Finnish small‐animal hospitals were sedated with a 40‐μg/kg dose of the α 2 ‐agonist medetomidine i.m. In the first part of the study (n =319), a randomized, double‐blind design with respect to the dose of atipamezole (0, 80, 160 and 240μg/kg i.m.) was used. In a separate study (n =358), which was an open trial, the selected dose of atipamezole was 200μg/kg i.m. Atipamezole at dose rates of 80–240μg/kg rapidly and effectively reversed medetomidine‐induced deep sedation‐analgesia, recumbency and bradycardia. The median arousal time after atipamezole was 3–5 min, and walking time was 6–10 min compared to >30 min for both effects after placebo. Heart rate also increased in a dose‐related manner after atipamezole administration. The investigators' overall evaluation of the ability of atipamezole to reverse the effects of medetomidine was ‘good’ in 90%, and ‘moderate’ in 9% of cases. Relapse into sedation was reported in three individual cases. Side‐effects were minimal. It is concluded that at doses four‐to sixfold the medetomidine dose, atipamezole is a highly effective and safe agent in reversing medetomidine‐induced sedation‐analgesia, recumbency and bradycardia in dogs in veterinary practice. A. T. Vähä‐Vahe, Farmos Group Ltd., Research Center, PO Box 425, SF‐2010I Turku, Finland.