Evaluation of effects of low-dose aspirin administration on urinary thromboxane metabolites in healthy dogs.

OBJECTIVE

To evaluate markers of in vivo platelet function (urinary 11-dehydro-thromboxane B(2) [11-dehydroTXB(2)] and 2,3-dinorTXB(2)) and assess their response to administration of 2 commonly used dosages of aspirin in healthy dogs.

ANIMALS

20 healthy dogs.

PROCEDURES

Urine was collected prior to aspirin administration and on the morning following the last evening administration. Twenty dogs received aspirin (1 mg/kg, PO, q 24 h) for 7 consecutive doses. After a washout period of 5 months, 10 dogs received a single dose of aspirin (10 mg/kg, PO). Concentrations of urinary thromboxane metabolites 11-dehydroTXB(2) and 2,3-dinorTXB(2) were measured via ELISA, and values were normalized to urine creatinine concentration.

RESULTS

Median baseline 11-dehydroTXB(2) concentrations were 0.38 ng/mg of creatinine (range, 0.15 to 1.13 ng/mg). Mean ± SD baseline 2 at a 3-dinorTXB(2) concentrations were 6.75 ± 2.77 ng/mg of creatinine. Administration of aspirin at a dosage of 1 mg/kg, PO, every 24 hours for 7 days did not significantly decrease urinary 11-dehydroTXB(2) concentration, but administration of the single aspirin dose of 10 mg/kg did significantly decrease 11-dehydroTXB(2) concentration by a median of 45.5% (range, 28.2% to 671%). Administration of the 1 mg/kg aspirin dosage significantly decreased urinary 2,3-dinorTXB(2) concentration by a mean ± SD of 33.0 ± 23.7%. Administration of the single aspirin dose of 10 mg/kg also significantly decreased 2,3-dinorTXB(2) concentration by a mean ± SD of 46.7 ± 12.6%.

CONCLUSIONS AND CLINICAL RELEVANCE

Aspirin administration (1 mg/kg/d) may be insufficient for reliable platelet inhibition in healthy dogs.