Resistance to antiplatelet drugs

No single pathway mediates all thrombotic events-multiple pathways of platelet activation 

Aspirin is the most economical and effective antiplatelet drug prescribed for the treatment of cardiovascular and cerebrovascular (CV) diseases. Initially, Vane et al. (38) 

Aspirin is rapidly absorbed peak plasma concentrations are achieved within 40 minutes and significant platelet inhibition is observed within an hour. Although the plasma half-life is 20 minutes, irreversible binding and the lack of de-novo protein synthesis in platelets results in COX-1 inhibition for the life span of platelets ( I0 days). The stable metabolite ofTxA2, can be measured in plasma or urine and is a specific indicator of platelet response to aspirin therapy (43,44), 

The extensive analyses of primary and secondary clinical trials have indicated that aspirin treatment is associated with a 20% to 44% reduction in cardiovascular adverse events (26,27), Based on the results of these trials, the US Preventive Services Task Force (USPSTF) recommends that low-dose aspirin (81 mg/day) should be administered in patients whose 5-year risk of a first CV event is 3% and whose 10-year risk is 6%. Whenever rapid and 

The Relevant Pathway to Measure Platelet Aspirin Responsiveness 

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Tantry US, Bliden KR Gurbel PA. Resistance to antiplatelet drugs current status and future research. Expert Opin Pharmacother 2005 6 2027-2045. 

The reported incidence of resistance to these drugs varies greatly, from less than 5% to 75%. In part this tremendous variation in incidence reflects the definition of resistance (recurrent thrombosis while on antiplatelet therapy vs in vitro testing), methods by which drug response is measured, and patient compliance. Several methods for testing aspirin and clopidogrel resistance in vitro are now FDA-approved however, their utility outside of clinical trials remains controversial. 

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