Lack of inhibitory effect of acetylsalicylic acid and meloxicam on whole blood platelet aggregation in cats.

OBJECTIVE: To determine the effects of acetylsalicylic acid (ASA) and meloxicam on feline platelet aggregation and associated platelet thromboxane production and serotonin release. DESIGN: Prospective interventional study. SETTING: University research facility. ANIMALS: Eight healthy male castrated domestic short hair cats from a research colony. INTERVENTIONS: Oral medications were administered to 8 cats for 14 days in a randomized, placebo-controlled, crossover design. Treatment groups included: aspirin (ASA) (5 mg/kg q 48 h), meloxicam (0.05 mg/kg q 24 h), and placebo (0.5 mL of water q 24 h). Thromboxane assays (TXB(2) ) and whole blood (impedance) aggregometry (WBA) were performed on samples collected before drug administration, and on days 7, 15, and 17, using adenosine diphosphate (ADP; 10 µM) and collagen (5 µg/mL) as agonists for WBA. Serotonin release was assayed on postaggregation plasma. Oral mucosal bleeding time (OMBT) and complete blood cell counts were measured on days 0 and 15. MEASUREMENTS AND MAIN RESULTS: Neither medication affected WBA at any time point. OMBT decreased in the ASA group relative to baseline. No differences were detected in WBA and OMBT baseline between any groups. No difference was detected in serotonin secretion at any time point. TXB(2) was significantly decreased in the ASA group at all times after initiation of treatment but no change was noted in the meloxicam or placebo groups. CONCLUSIONS: At the doses studied, neither meloxicam nor ASA had an inhibitory effect on WBA or OMBT in cats. Thromboxane concentrations were significantly decreased with ASA treatment.