Algorithm for suggested clinical actions based on CYP2C19 genotype in patients with acute coronary syndromes initiating antiplatelet therapy. ACS, acute coronary syndrome; EM, extensive metabolizer; IM, intermediate metabolizer; PCI, percutaneous coronary intervention; PM, poor metabolizer; UM, ultrarapid metabolizer. ¹Other rare CYP2C19 genotypes exist apart from those illustrated (see Supplementary Data online for other genotypes and frequencies). ²Higher-dose clopidogrel has not been adequately studied at the time of this writing but may improve platelet function in a subset of IMs and PMs (Supplementary Table S8 online).³Note that prasugrel is recommended only when its use is not clinically contraindicated.