LAUSR

OBJECTIVE To compare the efficacy of a medetomidine constant rate infusion (CRI) with a detomidine CRI for standing sedation in horses undergoing high dose rate brachytherapy. STUDY DESIGN Randomized, controlled, crossover, blinded clinical trial. ANIMALS A total of 50 horses with owner consent, excluding stallions. METHODS Each horse was sedated with intravenous acepromazine (0.02 mg kg-1), followed by an α2-adrenoceptor agonist 30 minutes later and then by butorphanol (0.1 mg kg-1) 5 minutes later. A CRI of the same α2-adrenoceptor agonist was started 10 minutes after butorphanol administration and maintained for the treatment duration. Treatments were given 1 week apart. Each horse was sedated with detomidine (bolus dose, 10 μg kg-1; CRI, 6 μg kg-1 hour-1) or medetomidine (bolus dose, 5 μg kg-1; CRI, 3.5 μg kg-1 hour-1). If sedation was inadequate, a quarter of the initial bolus of the α2-adrenoceptor agonist was administered. Heart rate (HR) was measured via electrocardiography, and sedation and behaviour evaluated using a previously published scale. Between treatments, behaviour scores were compared using a Wilcoxon signed-rank test, frequencies of arrhythmias with chi-square tests, and HR with two-tailed paired t tests. A p value <0.05 indicated statistical significance. RESULTS Total treatment time for medetomidine was longer than that for detomidine (p = 0.04), and ear movements during medetomidine sedation were more numerous than those during detomidine sedation (p = 0.03), suggesting there may be a subtle difference in the depth of sedation. No significant differences in HR were found between treatments (p ≥ 0.09). Several horses had arrhythmias, with no difference in their frequency between the two infusions. CONCLUSIONS AND CLINICAL RELEVANCE Medetomidine at this dose rate may produce less sedation than detomidine. Further studies are required to evaluate any clinical advantages to either drug, or whether a different CRI may be more appropriate.