Pharmacologic inhibition of platelet function: correlation between in vitro tests of platelet function and clinical outcomes.

Atherothrombosis continues to be a leading cause of death and disability despite advances in pharmacologic and procedural therapies. Antiplatelet agents have been extensively studied and validated to improve outcomes in multiple settings of cardiovascular disease. The emergence of the phenomenon of resistance to antiplatelet therapy resulted in the availability of platelet function tests to assess the effectiveness of these agents. Subsequent evaluations have shown considerable inter-individual variability in platelet inhibition in patients receiving antiplatelet agents. Several small studies showed that patients who were deemed 'resistant' to antiplatelet therapy by platelet function testing had adverse clinical outcomes. It is essential that ongoing investigations help delineate a standard definition of 'resistance' to antiplatelet therapy, which test of platelet function should be the gold standard, and what therapy, once identified, can help overcome resistance to the currently available antiplatelet agents. Data are needed to determine if outcomes can be improved by changes to existing antiplatelet therapy based on the results of platelet function tests. Alternatively, newer antiplatelet agents may prove effective in overcoming resistance; however, these agents also await validation in large-scale clinical trials.