• horse;
  • sedation;
  • antagonism;
  • detomidine;
  • tolazoline;
  • atipamezole


Reasons for performing study: The ability to shorten the duration of sedation would potentially improve safety and utility of detomidine.

Objectives: To determine the effects of tolazoline and atipamezole after detomidine sedation.

Hypothesis: Administration of tolazoline or atipamezole would not affect detomidine sedation.

Methods: In a randomised, placebo-controlled, double-blind, descriptive study, detomidine (0.02 mg/kg bwt i.v.) was administered to 6 mature horses on 4 separate occasions. Twenty-five mins later, each horse received one of 4 treatments: Group 1 saline (0.9% i.v.) as a placebo control; Group 2 atipamezole (0.05 mg/kg bwt i.v.); Group 3 atipamezole (0.1 mg/kg bwt i.v.); and Group 4 tolazoline (4.0 mg/kg bwt i.v.). Sedation, muscle relaxation and ataxia were scored by 3 independent observers at 9 time points. Horses were led through an obstacle course at 7 time points. Course completion time was recorded and the ability of the horse to traverse the course was scored by 3 independent observers. Horses were videotaped before, during and after each trip through the obstacle course.

Results: Atipamezole and tolazoline administration incompletely antagonised the effects of detomidine, but the time course to recovery was shortened.

Conclusions and potential relevance: Single bolus administration of atipamezole or tolazoline produced partial reversal of detomidine sedation and may be useful for minimising detomidine sedation.