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

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.

Prospective randomized experimental study.

Fifteen adult grade mares weighing 328-537 kg.

The horses were randomly assigned to one of the three treatment groups (five horses each). The groups were given detomidine (0.06 mg kg^-1): 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 minutes after treatment, was used to evaluate sedation. Yohimbine (0.1 mg kg^-1 IV) was administered after the 90-minute evaluation. Blood samples were collected from the detomidine-alone group before treatment and at 15, 30, 45, 60, 75, and 90 minutes after treatment. Sera were analyzed for detomidine equivalent concentrations by an ELISA. Head droop percentages were compared using a repeated measures analysis of variance.

Significant mean head droop developed in each treatment group by 30 minutes and persisted until reversal with yohimbine. After yohimbine administration, head positions returned to 87-91% of pre-treatment levels. There were no significant differences among the oral treatment groups at any time. Mean serum detomidine equivalents increased slowly until 45-minute post-administration, but never exceeded 30 ng mL^-1.

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 minutes after administration.