Sedative and physiological effects of intramuscular alfaxalone 4% with butorphanol or dexmedetomidine in dogs – a randomized crossover study

Objective To evaluate the sedative effects of intramuscular (IM) alfaxalone 4% combined with butorphanol or dexmedetomidine in healthy dogs. Study Design Experimental, randomized, blinded, crossover study. Animals A total of six healthy adult dogs of mixed breeds. Methods Alfaxalone 4% (3 mg kg -1 ) was combined with either butorphanol 0.4 mg kg -1 or dexmedetomidine 5 μg kg -1 injected IM, with a minimum three-day washout. Sedation variables (onset, duration, quality including composite scoring, onset, and recovery), cardiorespiratory variables [heart rate (HR), respiratory rate ( f R ), oxygen saturation of haemoglobin (SpO 2 ), mean arterial pressure (MAP)], and response to cephalic venous catheterization [on a 4-point scale (0–3)] were recorded. Data are shown as median & interquartile range or mean ± standard deviation, p < 0.05. Results All dogs achieved sedation with good to excellent recovery [scores: alfaxalone-butorphanol 3.5 (3.25–4), alfaxalone-dexmedetomidine 4 (4–4)]. Duration of sedation was 88.9 ± 63.7 minutes and 95.8 ± 43.7 minutes ( p = 0.831), and quality of sedation was 21 (19–22) and 22 (18–25.5) out of 27 ( p = 0.249). Catheter placement was successful in all dogs with minimal resistance [scores 3 (3–3)]. HRs decreased from baseline in both groups: alfaxalone-butorphanol (110 ± 30 to 63 ± 12 beats minute -1 ; p = 0.003) and alfaxalone-dexmedetomidine (99 ± 16 to 59 ± 15 beats minute -1 ; p = 0.001). f Rs decreased from baseline with alfaxalone-butorphanol (25 ± 3 to 18 ± 5 breaths minute -1 ; p = 0.031). Mild hypoxaemia (SpO 2 90–94%) occurred in both groups: alfaxalone-butorphanol (3/6), alfaxalone-dexmedetomidine (5/6). MAPs were higher following alfaxalone-dexmedetomidine than alfaxalone-butorphanol (MAP 104 ± 13 mmHg; 79 ± 8mmHg respectively) ( p ≤ 0.020). Conclusions and clinical relevance IM alfaxalone 4% at 3 mg kg -1 combined with butorphanol or dexmedetomidine provided sufficient sedation for IV catheterization. Supplemental oxygen is recommended with both protocols.