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

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Abstract
The efficacy of atipamezole, a recently introduced .alpha.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-.mu.g/kg dose of the .alpha.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 240 .mu.g/kg i.m.) was used. In a separate study (n = 358), which was an open trial, the selected dose of atipamezole was 200 .mu.g/kg i.m. Atipamezole at dose rates of 80-240 .mu.g/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.