Background CYP2C19 loss-of-function (LOF) alleles impair clopidogrel effectiveness after percutaneous coronary intervention (PCI). The feasibility, sustainability and clinical impact of using CYP2C19 genotype-guided dual antiplatelet therapy (DAPT) selection in practice remains unclear. Methods and Results A single-center observational study was conducted in 1193 patients who underwent PCI and received DAPT following implementation of an algorithm that recommends CYP2C19 testing in high-risk patients and alternative DAPT (prasugrel or ticagrelor) in LOF allele carriers. The frequency of genotype testing and alternative DAPT selection were the primary implementation endpoints. Risk of major adverse cardiovascular or cerebrovascular (MACCE) and clinically significant bleeding events over 12 months were compared across genotype and DAPT groups by proportional hazards regression. CYP2C19 genotype was obtained in 868 (72.8%) patients. Alternative DAPT was prescribed in 186 (70.7%) LOF allele carriers. CYP2C19 testing (P<0.001) and alternative DAPT use in LOF allele carriers (P=0.001) varied over time. Risk for MACCE was significantly higher in LOF carriers prescribed clopidogrel versus alternative DAPT (adjusted hazard ratio [HR] 4.65, 95% confidence interval [CI] 2.22–10.0, P<0.001), whereas no significant difference was observed in those without a LOF allele (adjusted HR 1.37, 95% CI 0.72–2.85, P=0.347). Bleeding event rates were similar across groups (log-rank P=0.816). Conclusions Implementing CYP2C19 genotype-guided DAPT is feasible and sustainable in a real-world setting, but challenging to maintain at a consistently high level of fidelity. The higher risk of MACCE associated with clopidogrel use in CYP2C19 LOF allele carriers suggests that use of genotype-guided DAPT in practice may improve clinical outcomes.

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These findings suggest that using CYP2C19 genotype to guide P2Y12 inhibitor selection is feasible. Original submitted 27 October 2014; revision submitted 19 December 2014.

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