Sedative effects of intramuscular alfaxalone–methadone–midazolam versus ketamine–methadone–midazolam in cats

Objective: To assess depth and quality of sedation and the ability to place an intravenous catheter in cats after intramuscular (IM) injection with alfaxalone–methadone–midazolam (AMM) or ketamine–methadone–midazolam (KMM). Study design: Blinded randomized clinical trial. Animals: A group of 46 healthy Domestic Short Hair cats. Methods: Cats were randomly assigned to be administered IM methadone 0.3 mg kg^–1 and midazolam 0.3 mg kg^–1 with either alfaxalone 2 mg kg^–1 (AMM group, n = 23) or ketamine 3 mg kg^–1 (KMM group, n = 23). Before IM injection, a temperament score was assigned. The reaction to injection was scored. After 15 minutes, the depth of sedation was scored using a simple descriptive scale (SDS) and multidimensional sedation score. Success or failure to place an intravenous catheter at first attempt was recorded; p < 0.05. Results: Cats in the AMM group had a significantly higher median temperament score (p = 0.026). Behavioural reaction to injection with AMM was significantly less compared with KMM (p = 0.016). Median sedation scores were significantly higher in the AMM group than in the KMM group: SDS 4 (0–4) versus 2 (0–4), p = 0.01, respectively; multidimensional sedation score AMM 13 (0–13) versus 3 (0–10), indicating superior sedative effect in the AMM group, p = 0.01. Success rate of catheter placement was significantly higher in the AMM group (18/23) than in the KMM group (10/23), p = 0.033. Conclusions: and clinical relevance Addition of 2 mg kg^–1 alfaxalone to 0.3 mg kg^–1 methadone and 0.3 mg kg^–1 midazolam provided better sedation after IM injection than ketamine 3 mg kg^–1 combined with the same doses of methadone and midazolam. This combination of drugs may be particularly desirable as an alternative to α-₂ adrenoceptor agonist-based protocols for cats requiring IM sedation.