Serum concentrations and effects of detomidine delivered orally to horses in three different mediums

E.C. Ramsay
Dennis R. Geiser DVM, University of Tennessee - Knoxville
W. Carter
T. Tobin

Abstract

Objective: To compare the effect of orally delivered detomidine on head posture when administered alone or in combination with two different food items and to determine the serum concentrations of detomidine after oral delivery.

Study Design: Prospective randomized experimental study.

Animals: 15 adult grade mares weighing 328-537 kg.

Methods: The horses were randomly assigned to one of the three treatment groups (5 horses each). The groups were given detomidine (Dormosedan, 0.06 mg/kg): alone; mixed with 3 ml of an apple sauce and gum mixture or mixed with 3 ml molasses. Head droop, measured before treatment and at 15, 30, 45, 60, 75, 90 and 105 min after treatment, was used to evaluate sedation. Yohimbine (0.1 mg/kg IV) was administered after the 90-min evaluation. Blood samples were collected from the detomidine-alone group before treatment and at 15, 30, 45, 60, 75 and 90 min after treatment. Sera were analysed for detomidine equivalent concentrations by an ELISA. Head droop percentages were compared using a repeated measures analysis of variance.

Results: Significant mean head droop developed in each treatment group by 30 min and persisted until reversal with yohimbine. After yohimbine administration, head positions returned to 87-91% of pretreatment levels. There were no significant differences among the oral treatment groups at any time. Mean serum detomidine equivalents increased slowly until 45-min post-administration but never exceeded 30 ng/ml.

Conclusions: Orally administered detomidine results in measurable serum drug concentrations using any of the delivery mediums investigated and can be expected to produce profound head droop in horses approximately 45 min after administration.