Clopidogrel and aspirin are commonly prescribed anti-platelet medications indicated for patients
who have experienced, or are at risk for, ischemic cardiovascular events. The Pharmacogenomics
of Anti-Platelet Intervention (PAPI) Study was designed to characterize determinants of clopidogrel
and dual anti-platelet therapy (DAPT) response in a healthy cohort of Old Order Amish from
Lancaster, PA. Following a loading dose, clopidogrel was taken once a day for 7 days. One hour after the last dose of
clopidogrel, 325 mg of aspirin was given. Ex vivo platelet aggregometry was performed at baseline, post-clopidogrel, and
post-DAPT. Platelet aggregation measurements were significantly lower after both interventions for all agonists tested (p
<0.05), although there was large inter-individual variation in the magnitude of anti-platelet response. Female sex and older
age were associated with higher platelet aggregation at all three time-points. Change in aggregation was correlated among
the various agonists at each time point. Heritability (h2) of change in platelet aggregation was significant for most traits at
all time-points (range h2=0.14-0.57). Utilization of a standardized, short-term intervention provided a powerful approach
to investigate sources of variation in platelet aggregation response due to drug therapy. Further, this short-term intervention
approach may provide a useful paradigm for pharmacogenomics studies.
Keywords: Anti-platelet therapies, aspirin, clopidogrel, pharmacogenomics, platelet aggregation, short-term intervention.
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