Detection and Pharmacokinetics of Grapiprant Following Oral Administration to Exercised Thoroughbred Horses.

Traditional therapeutic options for the treatment of lameness associated with inflammation in performance horses include administration of cyclooxygenase enzyme inhibiting non-steroidal anti-inflammatory drugs (NSAID). As long-term use of these drugs can adversely impact the health of the horse, anti-inflammatories with a more favorable safety profile are warranted. Grapiprant is a newly approved non-cyclooxygenase inhibiting NSAID that has demonstrated efficacy and safety in other species and which may be a valuable alternative to traditional NSAIDs used in the horse. The objectives of the current study were to describe drug concentrations and the pharmacokinetics of grapiprant in exercised Thoroughbred horses and to develop an analytical method that could be used to regulate its use in performance horses. To that end, grapiprant, at a dose of 2mg/kg was administered orally to 12 exercised Thoroughbred horses. Blood and urine samples were collected prior to and for up to 96hours post drug administration. Drug concentrations were measured using liquid chromatography-tandem mass spectrometry. Grapiprant remained above the LOQ of the assay (0.005ng/mL) in serum for 72hours post administration and urine concentrations were above the LOQ until 96hours. The C-max, T-max and elimination half-life were 31.9 +/- 13.9ng/mL, 1.5 +/- 0.5hours and 5.86 +/- 2.46hours, respectively. The drug was well tolerated in all horses at a dose of 2mg/kg. Results support further study of this compound in horses. Furthermore, development of a highly sensitive analytical method demonstrate that this compound can be adequately regulated in performance horses.