Clopidogrel response up to six months after acute myocardial infarction.

High on-treatment platelet reactivity (HTPR) despite clopidogrel therapy is associated with adverse cardiac events after acute myocardial infarction (AMI). Most studies to date have assessed clopidogrel response at a single time point before or after percutaneous coronary intervention (PCI). It is unclear, however, whether the HTPR phenotype is stable over time. Therefore, we aimed to examine response to clopidogrel in patients with AMI treated with PCI over a 6-month period. Patients (n = 57) with AMI treated with PCI were assessed for response to clopidogrel at 3 time points: in hospital, 30 days, and 6 months after index hospitalization. Response to clopidogrel was determined by the VerifyNow P2Y12 assay (reported as P2Y12 response units) and multiple electrode aggregometry (MEA; reported as aggregation units). HTPR was defined as ≥235 P2Y12 response units or ≥47 aggregation units. Patients' mean age was 54.5 ± 10.9 years, 91% were men, 19% had diabetes, and 74% were admitted with ST-segment elevation MI. HTPR based on MEA was observed in 22.8% of patients in hospital, 26.3% at 30 days, and 17.5% at 6 months (p = NS). HTPR based on the VerifyNow assay was observed in 38.6% of patients in hospital, 28.1% at 30 days, and 33.3% at 6 months (p = NS). Individual HTPR phenotypic assignment at baseline was stable in 73.7% (based on MEA) and 70.2% (based on VerifyNow) of patients at 6-month follow-up. In conclusion, this is the first study evaluating the stability of clopidogrel response over time after AMI. Rates of HTPR to clopidogrel therapy appear to be relatively stable up to 6 months after AMI.