Sedative and analgesic effects of two subanaesthetic doses of ketamine in combination with methadone and a low dose of dexmedetomidine in healthy dogs.

Objective: To evaluate the sedative, analgesic and recovery characteristics of two subanaesthetic ketamine doses in combination with dexmedetomidine and methadone for intramuscular sedation in healthy Beagles.
Study Design: Randomized, blinded, crossover, experimental study.
Animals: Six healthy adult Beagles.
Methods: Dogs were randomly given three treatments: dexmedetomidine (3 μg kg ^-1 ) and methadone (0.3 mg kg ^-1 ) combined with ketamine at 1 and 2 mg kg ^-1 (K1 and K2, respectively) or saline (K0), intramuscularly. Sedation score, response to tail clamping and rectal temperature were recorded at baseline, 5, 15, 25, 35, and 45 minutes posttreatment. Pulse rate (PR), respiratory rate, oxygen haemoglobin saturation and noninvasive blood pressure were also recorded at baseline and every 5 minutes until 45 minutes posttreatment. Onset and duration of recumbency, response to venous catheterization and recovery quality were also assessed. Sedation and physiological variables were compared between treatments and within treatments compared to baseline (analysis of variance). Nonparametric data were analysed with the Friedman and Cochran's Q tests; p < 0.050.
Results: Increased sedation was found at 15 (K0 and K1), 25 (all treatments) and 35 (K1) minutes compared with baseline. Sedation score, onset (3-12 minutes) and duration of recumbency (29-51 minutes) were similar between treatments. Recovery quality was considered acceptable in all cases. Response to tail clamping was inconsistent within treatments with no differences between them. None of the dogs responded to venous catheterization. There were no differences between treatments in physiological variables, except for PR which was higher in K2 than in K0. Oxygen supplementation was required in five and three dogs administered saline and ketamine, respectively.
Conclusions and Clinical Relevance: The addition of 1 or 2 mg kg ^-1 of ketamine to methadone and dexmedetomidine combination did not enhance sedation or antinociception in healthy dogs. Recovery quality was unaffected.
(Copyright © 2021 Association of Veterinary Anaesthetists and American College of Veterinary Anesthesia and Analgesia. Published by Elsevier Ltd. All rights reserved.)