Preliminary investigation comparing a detomidine continuous rate infusion combined with either morphine or buprenorphine for standing sedation in horses

Objective: To compare sedative and analgesic properties of buprenorphine or morphine for standing procedures combined with a detomidine continuous rate infusion (CRI). 

Study design: Blinded, prospective, randomized clinical pilot study. 

Animals: Ten horses presented for dental or sinus procedures. 

Methods: Horses received 0.02 mg kg^-1 acepromazine intravenously (IV), followed 30 minutes later by detomidine 10 μg kg^-1 IV. Five minutes later, buprenorphine 0.01 mg kg^-1 (n = 6) or morphine 0.1 mg kg^-1 (n = 4) was administered IV. Detomidine was administered by CRI (0.2 μg kg^-1 minute^-1) and adjusted to maintain appropriate sedation. Heart rate, respiratory frequency, gastrointestinal motility and rectal temperature were measured; pain, ataxia and sedation were scored. Sedation, pain scores and ataxia scores were analysed using a mixed linear model. Detomidine dose and procedure success scores were compared using Wilcoxon's rank sum test. Complications between groups were analysed using Fisher's exact test. 

Results: Two horses had incomplete data. Weights and ages were not different between groups (p = 0.15 and p = 0.42, respectively). The dose rate for detomidine was not different between groups (0.33 ± 0.02 μg kg^-1 minute^-1 in the buprenorphine group and 0.33 ± 0.05 μg kg^-1 minute^-1, in the morphine group p = 0.89). Intraoperative visual analogue scale scores were greater after buprenorphine than morphine (mean ± SD, buprenorphine 48 ± 4, morphine 40 ± 5, p = 0.0497). Procedure duration was not different between groups (buprenorphine 142 ± 33, morphine 140 ± 12 minutes). All horses treated with buprenorphine experienced complications compared with none in the morphine group (p = 0.0286). 

Conclusions and clinical relevance: At the doses used, buprenorphine produced greater sedation but more post-operative complications than morphine. However, Type I or Type II errors cannot be excluded and larger studies are required to confirm these findings.