Effects of three antagonists on selected pharmacodynamic effects of sublingually administered detomidine in the horse

Authors

  • Heather K Knych,

    Corresponding author
    1. K. L. Maddy Equine Analytical Chemistry Laboratory, School of Veterinary Medicine, University of California, Davis, CA, USA
    2. Department of Veterinary Molecular Biosciences, School of Veterinary Medicine, University of California, Davis, CA, USA
    • Correspondence: Heather K Knych, K.L. Maddy Equine Analytical Chemistry Laboratory, University of California, Davis, School of Veterinary Medicine, West Health Science Drive, Davis, CA 95616, USA. E-mail: hkknych@ucdavis.edu

    Search for more papers by this author
  • Scott D Stanley

    1. K. L. Maddy Equine Analytical Chemistry Laboratory, School of Veterinary Medicine, University of California, Davis, CA, USA
    2. Department of Veterinary Molecular Biosciences, School of Veterinary Medicine, University of California, Davis, CA, USA
    Search for more papers by this author

Abstract

Objective

To describe the effects of alpha2-adrenergic receptor antagonists on the pharmacodynamics of sublingual (SL) detomidine in the horse.

Study design

Randomized crossover design.

Animals

Nine healthy adult horses with an average age of 7.6 ± 6.5 years.

Methods

Four treatment groups were studied: 1) 0.04 mg kg−1 detomidine SL; 2) 0.04 mg kg−1 detomidine SL followed 1 hour later by 0.075 mg kg−1 yohimbine intravenously (IV); 3) 0.04 mg kg−1 detomidine SL followed 1 hour later by 4 mg kg−1 tolazoline IV; and 4) 0.04 mg kg−1 detomidine SL followed 1 hour later by 0.12 mg kg−1 atipamezole IV. Each horse received all treatments with a minimum of 1 week between treatments. Blood samples were obtained and plasma analyzed for yohimbine, atipamezole and tolazoline concentrations by liquid chromatography-mass spectrometry. Behavioral effects, heart rate and rhythm, glucose, packed cell volume (PCV) and plasma proteins were monitored.

Results

Chin-to-ground distance increased following administration of the antagonists, however, this effect was transient, with a return to pre-reversal values as early as 1 hour. Detomidine induced bradycardia and increased incidence of atrioventricular blocks were either transiently or incompletely antagonized by all antagonists. PCV and glucose concentrations increased with tolazoline administration, and atipamezole subjectively increased urination frequency but not volume.

Conclusions and clinical relevance

At the doses administered in this study, the alpha2-adrenergic antagonistic effects of tolazoline, yohimbine and atipamezole on cardiac and behavioral effects elicited by SL administration of detomidine are transient and incomplete.

Ancillary