Trazodone is a serotonin receptor antagonist and reuptake inhibitor (SARI) used in humans, dogs, cats, and, more recently, horses. It is our experience that trazodone is widely used by referral hospitals and by primary care clinicians. Platelet stores of serotonin within dense granules are released as activated platelets participate in blood clotting and inflammation. Previous studies in humans and dogs have shown trazodone may cause a decrease in platelet function, potentially increasing the risk for bleeding. If platelet function (but not platelet count) is affected by trazodone administration, routine blood tests such as a complete blood cell count will not be sufficient in assessing risks of peri-operative trazodone administration. Understanding the effects of trazodone on equine platelets is imperative for the safe and effective use of the drug in horses. Although in vitro assays may provide some insight, an in vivo study that also detects the effects of drug metabolites is more clinically relevant.

We hypothesize that administration of trazodone at a clinically relevant dose (7 mg/kg BID) will not affect platelet count but will lead to decreased platelet function.