Alfaxalone induction dose following administration of medetomidine and butorphanol in the dog.

Objective: To determine in dogs the effects of medetomidine and butorphanol, alone and in combination, on the induction dose of alfaxalone and to describe the induction and intubation conditions.

Study Design: Prospective, randomized, blinded clinical trial.

Animals: Eighty-five client-owned dogs (ASA 1 or 2).

Methods: Subjects were block randomized to treatment group according to temperament. The treatment groups were: medetomidine 4 microg kg(-1) (M), butorphanol 0.1 mg kg(-1) (B), or a combination of both (MB), all administered intramuscularly. After 30 minutes, a sedation score was assigned, and alfaxalone 0.5 mg kg(-1) was administered intravenously over 60 seconds by an observer who was unaware of treatment group. Tracheal intubation conditions were assessed and, if tracheal intubation was not possible after 20 seconds, further boluses of 0.2 mg kg(-1) were given every 20 seconds until intubation was achieved. Induction dose and adverse events (sneezing, twitching, paddling, excitement, apnoea and cyanosis) were recorded; induction quality and intubation conditions were scored and recorded.

Results: The mean dose of alfaxalone required for induction was similar for groups M and B: 1.2 +/- 0.4 mg kg(-1). The mean dose requirement for group MB (0.8 +/- 0.3 mg kg(-1)) was lower than groups M and B (p < 0.0001). Induction dose was not influenced by temperament or level of sedation. Induction and intubation scores did not differ between treatment groups. Adverse events were noted in 16 dogs; there was no association with treatment group, temperament or level of sedation.

Conclusions And Clinical Relevance: Medetomidine and butorphanol administered in combination reduce the anaesthetic induction dose of alfaxalone compared to either agent alone. This difference should be taken into account when using this combination of drugs in a clinical setting.