Effect of a second sedative drug injection following initial intramuscular dexmedetomidine in dogs: a randomised, crossover study

To evaluate sedation quality following two consecutive dexmedetomidine doses or a subsequent sedative drug injection following an initial dose of dexmedetomidine. Prospective, blinded, crossover, randomized study. Six healthy, adult laboratory Beagles. Each dog was given seven different drug combinations, delivered intramuscularly. Sedation was assessed using a 21 point sedation scale. An initial dexmedetomidine dose (5 μg kg –1 ) was given at T0, followed by a subsequent injection of dexmedetomidine (2.5 μg kg –1 , group DD), butorphanol (0.2 mg kg –1 , DBt), buprenorphine (0.02 mg kg –1 , DBp), tramadol (2 mg kg –1 , DTr), ketamine (2 mg kg –1 , DK), midazolam (0.1 mg kg –1 , DM) or saline (0.5 ml, DS–Control) at T1 (when two sedation scores were equal or a score decreased). Following evaluations, atipamezole was given intramuscularly at T2 (defined as for T1). Sedation scores were analyzed with a quantile regression model. The second drug was injected 34.2 ± 1.6 minutes (mean ± standard deviation) after the initial dose of dexmedetomidine. Median (range) sedation score in the DD group was not significantly higher at T2 compared to T1 [10 (7 – 15), 9.5 (7 – 12) respectively; p = 0.054]. At T2, median sedation score in the DBt, DBp and DTr groups was significantly higher compared to the DS group (all p < 0.035). Sedation score in the DM group was significantly lower at T2 compared to all groups except DS and DK (all p < 0.05 ) . The addition of ketamine resulted in seizure–like activity in three dogs. A second injection of dexmedetomidine or midazolam approximately 34 minutes after an initial low dexmedetomidine dose does not increase sedation and is not recommended. By contrast, addition of butorphanol, buprenorphine or tramadol at the same time point increased sedation.