Effects of Firocoxib, Flunixin Meglumine, and Phenylbutazone on Platelet Function and Thromboxane Synthesis in Healthy Horses.

Objective: Determine the effects of nonsteroidal anti-inflammatory drugs (NSAID) on platelet function and thromboxane synthesis immediately after drug administration and following 5 days of NSAID administration in healthy horses.

Study Design: Randomized cross-over study.

Animals: Healthy adult horses (n=9; 6 geldings and 3 mares).

Methods: Horses received either flunixin meglumine (1.1 mg/kg IV every 12 hours), phenylbutazone (2.2 mg/kg IV every 12 hours), or firocoxib (loading dose of 0.27 mg/kg IV on day 1, then 0.09 mg/kg IV every 24 hours for 4 days) for a total of 5 days. Blood samples were collected prior to drug administration (day 0), 1 hour after initial NSAID administration (day 1), and then 1 hour post-NSAID administration on day 5. Platelet function was assessed using turbidimetric aggregometry and a platelet function analyzer. Serum thromboxane B concentrations were determined by commercial ELISA kit. A minimum 14 day washout period occurred between trials.

Results: At 1 hour and 5 days postadministration of firocoxib, flunixin meglumine, or phenylbutazone, there was no significant effect on platelet aggregation or function using turbidimetric aggregometry or a platelet function analyzer. There was, however, a significant decrease in thromboxane synthesis at 1 hour and 5 days postadministration of flunixin meglumine and phenylbutazone that was not seen with firocoxib.

Conclusion: Preoperative administration of flunixin meglumine, phenylbutazone, or firocoxib should not inhibit platelet function based on our model. The clinical implications of decreased thromboxane B synthesis following flunixin meglumine and phenylbutazone administration are undetermined.