Variability of response to antiplatelet therapy

The occurrence of ischaemic events despite aspirin therapy has been called ‘aspirin resistance’ but there is little evidence to support that concept. It has not been established that patients with low levels of response to aspirin treatment on platelet function tests are at increased risk for ischaemic events, and there is no evidence that changing therapy based on test results has any benefit. A subset of patients does appear to be resistant to clopidogrel, which apparently increases their risk for adverse cardiovascular outcomes. Increasing the dose of clopidogrel may improve outcomes. Resistance to newer antiplatelet agents such as prasugrel, cangrelor, and AZD6140 has not been described to date. Low response to glycoprotein (GP) IIb/IIIa inhibitors has been associated with increased incidence of myocardial infarction. Whether platelet function testing should be routinely performed in patients receiving these agents has not been fully assessed.