Platelet aggregometry testing during aspirin or clopidogrel treatment and measurement of clopidogrel metabolite concentrations in dogs with protein‐losing nephropathy

BACKGROUND: Dogs with protein‐losing nephropathy (PLN) are treated with antiplatelet drugs for thromboprophylaxis but no standardized method exists to measure drug response. It is also unknown if clopidogrel metabolite concentrations [CM] differ between healthy and PLN dogs. OBJECTIVES: Assess response to aspirin or clopidogrel in PLN dogs using platelet aggregometry (PA) and compare [CM] between healthy and PLN dogs. ANIMALS: Six healthy and 14 PLN dogs. METHODS: Platelet aggregometry using adenosine diphosphate (ADP), arachidonic acid (AA), and saline was performed in healthy dogs at baseline and 1‐week postclopidogrel administration to identify responders or nonresponders. A decrease of ≥60% for ADP or ≥30% for AA at 1 or 3 hours postpill was used to define a responder. At 1 and 3 hours postclopidogrel, [CM] and PA were measured in healthy and PLN dogs. Platelet aggregometry was performed in PLN dogs at baseline, 1, 6, and 12 weeks after clopidogrel or aspirin administration. RESULTS: In PLN dogs receiving clopidogrel, PA differed from baseline at all time points for ADP but not for AA at any time point. Most dogs responded at 1 or both time points except for 1 dog that showed no response. For PLN dogs receiving aspirin, no differences from baseline were observed at any time point for either ADP or AA. No differences in [CM] were found at either time point between healthy and PLN dogs. CONCLUSIONS AND CLINICAL IMPORTANCE: Platelet aggregometry may represent an objective method to evaluate response to clopidogrel or aspirin treatment and PLN dogs appear to metabolize clopidogrel similarly to healthy dogs.