Antiplatelet effects and pharmacodynamics of clopidogrel in cats

Objective-To evaluate antiplatelet effects and pharmacodynamics of clopidogrel in cats. Design-Original study. Animals-5 purpose-bred domestic cats. Procedure-Clopidogrel was administered at dosages of 75 mg, PO, every 24 hours for 10 days; 375 mg, PO, every 24 hours for 10 days; and 18.75 mg, PO, every 24 hours for 7 days. In all cats, treatments were administered in this order, with at least 2 weeks between treatments. Platelet aggregation in response to ADP and collagen and oral mucosal bleeding times (OMBTs) were measured before and 3, 7, and 10 days (75 and 375 mg) or 7 days (18.75 mg) after initiation of drug administration. Serotonin concentration in plasma following stimulation of platelets with ADP or collagen was measured before and on the last day of drug administration. Platelet aggregation, OMBT and serotonin concentration were evaluated at various times after drug administration was discontinued to determine when drug effects were lost. Results-For all 3 dosages, platelet aggregation in response to ADP platelet aggregation in response to collagen, and serotonin concentration were significantly reduced and OMBT was significantly increased at all measurement times during drug administration periods. All values returned to baseline values by 7 days after drug administration was discontinued. No significant differences were identified between doses. None of the cats developed adverse effects associated with drug administration. Conclusions and Clinical Relevance-Results suggest that administration of clopidogrel at dosages ranging from 18.75 to 75 mg, PO, every 24 hours, results in significant antiplatelet effects in cats.