2017 ACVIM Forum Research Abstract Program

Based on calculation of in vitro IC50, dogs were separated into 3 different response groups. Eighteen of the 21 dogs (86%) were consistent as aspirin responders with in vitro IC50 values below 250 umol/L (median 66.7 umol/L, range 34.8-151.4). One dog showed a consistently poor response with in vitro IC50 values between 250-500 umol/L for both trials. Two dogs had marked variation in their in vitro IC50 values between the trials and were classified as variable responders. No dogs were found to be aspirin non-responders consistently for both trials. Between trial variation in in vitro IC50 for all dogs and the 18 dogs with IC50 values below 250 umol/L was mean (range) of 51. 9% (3.4-194. 3) and 38.6% (3.4-78.8), respectively. After administration of 4 mg/kg aspirin orally, 8 of 21 dogs did not show > 50% platelet inhibition by 3 hours. In vivo IC50 values for the remaining 13 dogs for samples collected in EDTA and EDTA fluoride were median (range) of 31.7 umol/L (0.1-107.6) and 30.9 umol/L (0.1-92.4), respectively. All three dogs identified as poor or variable responders in vitro had > 50% inhibition of platelet aggregation in vivo. The addition of fluoride to blood samples resulted in a mean percent reduction in SA concentrations of 17.3% and mean percent increase in ASA concentrations of 41.4%.