Comparison of sedation scores and propofol induction doses in dogs after intramuscular administration of dexmedetomidine alone or in combination with methadone, midazolam, or methadone plus midazolam.

The objectives of this study were to determine: (1) the sedative effects of dexmedetomidine in combination with methadone, midazolam, or both, and (2) the propofol dose required to achieve endotracheal intubation in healthy dogs. Seven healthy Beagle dogs were included in a prospective experimental, crossover, randomised and masked design. All dogs received four treatments IM, with at least 1 week between sessions, as follows: dexmedetomidine 5 µg/kg (D) alone, or combined with methadone 0.3 mg/kg (DMe), midazolam 0.3 mg/kg (DMi), or both (DMeMi). The degree of sedation was evaluated using a numerical scale (maximum 15 points). The dose of propofol required for intubation was also calculated for each group. Recovery time and quality were determined. Statistical analysis was performed using parametric (ANOVA) and nonparametric tests (Friedman, Cochran Q), as appropriate. The degree of sedation obtained with DMe and DMeMi (13, [7-14]; 13, [6-14], respectively) was significantly higher than in the control group (2, [1-4]; P = 0.023, P = 0.006, respectively). The required dose of propofol was lower in all groups (DMi, 1.5 ± 0.5 mg/kg, P = 0.002; DMe, 1.2 ± 0.5 mg/kg, P <0.001; DMeMi, 0.9 ± 0.3 mg/kg) than in the control group (2.9 ± 0.9 mg/kg; P <0.001). Recovery quality was not different between groups (P = 0.137). In healthy dogs, the addition of midazolam did not enhance the sedative effects of dexmedetomidine or a dexmedetomidine-methadone combination at the doses studied, and propofol requirements were reduced. The sedative effect of dexmedetomidine was enhanced with methadone, and the required dose of propofol was reduced.