Pharmacodynamic and pharmacokinetic evaluation of clopidogrel and the carboxylic acid metabolite SR 26334 in healthy dogs.

OBJECTIVE: To determine pharmacodynamic and pharmacokinetic properties of clopidogrel and the metabolite SR 26334 in dogs. ANIMALS: 9 mixed-breed dogs. PROCEDURES: 8 dogs received clopidogrel (mean +/- SD 1.13 +/- 0.17 mg/kg, PO, q 24 h) for 3 days; 5 of these dogs subsequently received a lower dose of clopidogrel (0.5 +/- 0.18 mg/kg, PO, q 24 h) for 3 days. Later, 5 dogs received clopidogrel (1.09 +/- 0.12 mg/kg, PO, q 24 h) for 5 days. Blood samples were collected for optical platelet aggregometry, citrated native and platelet mapping thrombelastography (TEG), and measurement of plasma drug concentrations. Impedance aggregometry was performed on samples from 3 dogs in each 3-day treatment group.
RESULTS: ADP-induced platelet aggregation decreased (mean +/- SD 93 +/- 6% and 80 +/- 22% of baseline values, respectively) after 72 hours in dogs in both 3-day treatment groups; duration of effect ranged from > 3 to > 7 days. Platelet mapping TEG and impedance aggregometry yielded similar results. Citrated native TEG was not different among groups. Clopidogrel was not detected in any samples; in dogs given 1.13 +/- 0.17 mg/kg, maximum concentration of SR 26334 (mean +/- SD, 0.206 +/- 0.2 microg/mL) was detected 1 hour after administration. CONCLUSIONS AND CLINICAL RELEVANCE: Clopidogrel inhibited ADP-induced platelet aggregation in healthy dogs and may be a viable antiplatelet agent for use in dogs. Impact for Human Medicine-Pharmacodynamic effects of clopidogrel in dogs were similar to effects reported in humans; clopidogrel may be useful in studies involving dogs used to investigate human disease.