Comparison of sedation in dogs: methadone or butorphanol in combination with dexmedetomidine intravenously.

OBJECTIVE: Opioids can be combined with alpha-2-adrenoreceptor agonists to sedate dogs for radiography. The study investigated the sedative effects of methadone or butorphanol in combination with dexmedetomidine in dogs undergoing stifle radiography.

STUDY DESIGN: Prospective, blinded, randomized, clinical trial.

ANIMALS: A total of 52 healthy dogs requiring sedation for stifle radiography were enrolled.

METHODS: Dogs were assessed for body condition [body condition score (BCS)], temperament and pain using the short-form composite measure pain scale (CMPS-SF). Dogs were randomized to be administered methadone 0.2 mg kg-1 (group M) or butorphanol 0.2 mg kg-1 (group B) in combination with dexmedetomidine 2 μg kg-1 intravenously (IV). Sedation was assessed using a numerical descriptive score, from 0 (no sedation) to 11 (greatest sedation), before administration and at 5, 10, 15 and 20 minutes by one blinded assessor. Onset signs of sedation, pulse rate and respiratory rates were recorded. Positioning for radiography was attempted at 5 minutes. If positioning was not possible at 10 minutes, dexmedetomidine 2 μg kg-1 was administered IV, with the dog recorded as failed sedation and withdrawn from further analysis. Following normality testing, data were assessed using Student t test, Mann-Whitney test, two-way analysis of variance and Fisher's exact test for failed sedations. Results are reported as mean ± standard deviation. Statistical significance was set at p < 0.05.

RESULTS: Groups were similar for sex, age, weight, BCS, temperament and CMPS-SF. The onset of sedation was faster in group B than in group M (p = 0.048). Sedation scores were higher in group B at 10 minutes compared to group M (p = 0.003). Failed sedation occurred in 12 dogs in group M and two in group B (p = 0.002). Pulse rates were lower in group B at 5 and 10 minutes (p = 0.002).

CONCLUSION AND CLINICAL RELEVANCE: IV butorphanol provides more effective sedation at 10 minutes than methadone, in combination with dexmedetomidine.