Recently, a series of publications indicated that clopidogrel active metabolite levels and platelet inhibition are lower in patients receiving PPIs. In addition, a recent survey of >16,690 patients in Medco database indicates that use of PPIs is associated with a 51% increase in the risk of death or myocardial infarction in patients receiving clopidogrel. Recent data have also indicated that patients with loss of function (LOF) haplotypes of the CYP2C19 gene have lower levels of the active metabolite after dosing with clopidogrel. These patients have higher rates of death, myocardial infarction, stent thrombosis and other ischemic complications than do patients with the wild type enzyme. Inadequate responses to clopidogrel therapy have been implicated as an important predictor of adverse clinical events. The reported prevalence of non-responsiveness to clopidogrel among patients with cardiovascular disease is between 4% and 34%, depending on the method and definition used to assess this parameter. Approximately 25% of American population carries a LOF mutation of CYP2C19.