Effects of vatinoxan on gastrointestinal motility, sedation, and antinociception during and after long-lasting detomidine infusion in horses.

Background: Sedation in horses is typically achieved using alpha-2 adrenoceptor agonists, although their use is associated with multiple side effects. A peripheral alpha-2 adrenoceptor antagonist, vatinoxan, can alleviate many of these.

Objectives: To evaluate the effects of vatinoxan infusion on gastrointestinal motility, sedation, and antinociception in horses sedated with detomidine infusion.

Study design: Randomised, blinded cross-over in vivo experiments.

Methods: Eight horses were given two 4-h infusions: detomidine (0.01 mg/kg + 0.015 mg/kg/h IV) (DET) and a combination of detomidine and vatinoxan (0.15 mg/kg + 0.05 mg/kg/h IV) (DET + VAT). Plastic marker balls were administered via nasogastric entubation before the start of the infusion. Borborygmi score was monitored. The expelling of balls and faecal output were repeatedly monitored for 72 h after the infusion. Sedation score (SS) and antinociception were monitored during the infusion.

Results: Borborygmi score remained significantly higher during DET + VAT infusion and the following hour than with DET (p < 0.05) at different time points. Median (range) cumulative weight of faeces was significantly higher with DET + VAT [6.25 kg (3.52-8.65)] than with DET [2.85 kg (1.7-6.6)] (p = 0.007) during the first 8 h after the end of infusion. The markers were expelled significantly faster after DET (mean AUC_12-72 3928 ± 1620) than after DET + VAT (mean AUC_12-72 2460 ± 1199) infusion (p = 0.02). All animals were appropriately sedated. Median SS was significantly lower at 60 min during DET + VAT [7 (5-7)] than during DET [7.5 (7, 8)] (p = 0.04). No other significant differences were detected in SS or antinociception between treatments.

Conclusions: Vatinoxan significantly improved the borborygmi score. Horses treated with DET + VAT passed more faeces in the initial period after infusion, although the expelling of plastic balls was faster with DET. Combining vatinoxan with detomidine infusion may slightly reduce the level of sedation in the initial phase of infusion. Vatinoxan may improve gastrointestinal motility in horses treated with detomidine infusion.