Intramuscular injection of alfaxalone in combination with butorphanol for sedation in cats

To assess quality of sedation following intramuscular (IM) injection of two doses of alfaxalone in combination with butorphanol in cats.

Prospective, randomized, 'blinded' clinical study.

A total of 38 cats undergoing diagnostic imaging or noninvasive procedures.

Cats were allocated randomly to be administered butorphanol 0.2 mg kg^-1 combined with alfaxalone 2 mg kg^-1 (group AB2) or 5 mg kg^-1 (group AB5) IM. If sedation was inadequate, alfaxalone 2 mg kg^-1 IM was administered and cats were excluded from further analysis. Temperament [1 (friendly) to 5 (aggressive)], response to injection, sedation score at 2, 6, 8, 15, 20, 30, 40, 50 and 60 minutes, overall sedation quality scored after data collection [1 (excellent) to 4 (inadequate)] and recovery quality were assessed. Heart rate (HR), respiratory rate (f_R) and arterial haemoglobin saturation (SpO₂) were recorded every 5 minutes. Groups were compared using t tests and Mann-Whitney U tests. Sedation was analysed using two-way anova, and additional alfaxalone using Fisher's exact test (p < 0.05).

Groups were similar for sex, age, body mass and response to injection. Temperament score was lower in group AB2 [2 (1-3)] compared to AB5 [3 (1-5)] (p = 0.006). Group AB5 had better sedation at 6, 8, 20 and 30 minutes and overall sedation quality was better in AB5 [1 (1-3)], compared to AB2 [3 (1-4)] (p = 0.0001). Additional alfaxalone was required for 11 cats in AB2 and two in AB5 (p = 0.005). Recovery quality, HR, f_R and SpO₂ were similar. Seven cats required oxygen supplementation. Complete recovery times were shorter in AB2 (81.8 ± 24.3 versus 126.6 ± 33.3 minutes; p = 0.009). Twitching was the most common adverse event.

In combination with butorphanol, IM alfaxalone at 5 mg kg^-1 provided better quality sedation than 2 mg kg^-1. Monitoring of SpO₂ is recommended.