2016 ACVIM Forum Research Abstract Program

Calculation of an in vitro EC50 allowed dogs to be separated into four different response groups. Sixteen of the 20 dogs (80%) had in vitro EC50 values below 250 umol/L consistent with an appropriate aspirin response with mean AE SD (range) values of 84.5 AE 36.0 (34.8-151.4) umol/L. When these values were evaluated for repeatability a mean difference of 44.9% was found with the highest difference between independent measurements for each dog of 95.1%. One dog showed a consistently poor response with in vitro EC50 values between 250-500 umol/L at both times measured. Two dogs had substantial variation in their in vitro EC50 values between the two time points and were classified as variable responders. One additional dog showed no significant inhibition of platelet aggregation at any time up to an ASA concentration of 3300 umol/L and was classified as a non-responder. In vivo aspirin dosing at 1 mg/kg did not cause measureable inhibition of platelet aggregation in any of the dogs after a single dose at any time point. An in vivo EC50 could not be established based on these findings as 50% inhibition was never achieved at this dose. Plasma ASA and SA concentrations were available for 18 of 20 dogs. The mean AE SD (range) maximum plasma concentrations (Cmax) for ASA were 0.23 AE 0.21 (0 -0.77) umol/L and for SA were 21 AE 5 (14 -34) umol/L. Two dogs did not have ASA concentrations above the detection limit (0.03 umol/L).