Oral trazodone results in quantifiable sedation but does not result in a xylazine-sparing effect in healthy adult horses.

Objective: To evaluate sedation and IV xylazine requirements to achieve 45% of baseline head height above ground measurements following oral (PO) administration of 2 trazodone dosages.

Methods: 8 healthy, adult mares of various weights and breeds belonging to a university teaching herd were utilized in a blinded, crossover study design. Horses were randomly assigned to 1 of 3 PO treatments: control (no trazodone), trazodone at 3 mg/kg (low dose [LD]), or trazodone at 6 mg/kg (high dose [HD]). Before treatment, cardiac auscultation, EquiSed sedation score, and head height above ground (HHAG; cm) measurements were performed (baseline) followed by feeding of the treatment mixture. After 120 minutes, sedation score and HHAG were recorded. Xylazine was administered IV (0.25 mg/kg bolus followed by 0.1 mg/kg/min) until HHAG reached 45% of baseline or a total dose of 1 mg/kg was reached. Individual data for xylazine dosage, sedation scores, and HHAG were analyzed using mixed linear models with repeated measures.

Results: Sedation scores were significantly improved (LD, P = .045; HD, P = .01) and HHAG was lowered (LD, P = .045; HD, P = .09) by trazodone administration. Xylazine dose requirements were increased by LD trazodone administration (increase of 0.26 ± 0.26 mg/kg; P = .03) and unchanged by HD (increase of 0.13 ± 0.25 mg/kg; P = .38).

Conclusions: Oral trazodone administration increases quantifiable sedation in horses. Xylazine requirements are significantly increased by LD trazodone administration.

Clinical relevance: Oral administration of LD trazodone may increase xylazine requirements. Further clinical studies are required to fully assess the clinical relevance of this finding on other parameters such as cardiovascular physiology.