Clopidogrel Resistance
A large body of data from observational studies indicates that clopidogrel therapy is associated with major pharmacodynamic (PD) limitations including wide response variability and nonresponsiveness (high on-treatment platelet reactivity (HPR) to adenosine diphosphate (ADP)) that have been linked to post-percutaneous coronary intervention (PCI) ischemic event occurrence, including stent thrombosis (ST). Insufficient active metabolite generation is the primary explanations for clopidogrel nonresponsiveness, and it is due to (i) variable or limited intestinal absorption that may be influenced by ABCB1 gene polymorphism and (ii) functional variability in P450 isoenzyme activity that is influenced by drug-drug interactions (DDI) and single nucleotide polymorphisms (SNPs) in genes encoding CYP450 isoenzymes. Treatment with high-dose clopidogrel (600mg loading dose plus 150mg maintenance dose) is not an optimal strategy to overcome clopidogrel HPR and to reduce recurrent ischemic event occurrence, and more potent P2Y12 receptor blockers, such as prasugrel and ticagrelor, are credible alternative strategies to overcome HPR during clopidogrel therapy.