Letter to the Editors-in-Chief

Association of genetic variants in CYP2C19 and adverse clinical outcomes after treatment with clopidogrel: An updated meta-analysis

The P2Y12 inhibitors, clopidogrel, prasugrel, and ticagrelor, are administered in fixed doses without laboratory monitoring. Randomized trials in acute coronary syndrome have shown that prasugrel and ticagrelor are more effective than standard-dose clopidogrel. Nonetheless, standard-dose clopidogrel remains widely used because it causes less bleeding and is less expensive. Patients treated with standard-dose clopidogrel have substantial variability in platelet inhibition, which is partly explained by genetic polymorphisms encoding CYP2C19, the hepatic enzyme involved in biotransformation of clopidogrel to its active metabolite. Some advocate tailoring P2Y12 inhibitor therapy according to the results of routine laboratory testing. Although there is good evidence for analytic, biological, and clinical validity of several phenotypic and genotypic biomarkers, the benefit of a management strategy that incorporates routine biomarker testing over standard of care without such testing remains unproven. Appropriately designed, adequately powered trials are needed but face the challenges of feasibility, cost, and the progressive switch from clopidogrel to prasugrel or ticagrelor.

Background: A large number of clinical studies have documented that a loss‐of‐function variant CYP2C19*2 affects clinical profiles of clopidogrel (efficacy and safety). However, data on the impact of a gain‐of‐function variant CYP2C19*17 on the response to that drug seem to be less consistent. Objectives: To systematically summarize all available clinical data assessing the role of the CYP2C19*17 variant in patients taking clopidogrel. Methods: A literature search was conducted and a meta‐analysis was performed for 11 eligible studies. The endpoints included the major adverse cardiovascular events (MACE, representing non‐fatal myocardial infarction, stroke, revascularization, or death), bleeding events, mortality, stent thrombosis and high platelet reactivity (HPR). Results: Data from six clinical studies demonstrated that carriers of the CYP2C19*17 variant had a marked protection against recurrent cardiovascular events in patients with coronary artery disease compared with non‐carriers, as measured by a 16% decrease in the incidence of MACE (10.0% vs. 11.9%; OR, 0.82; 95% CI, 0.72–0.94; P= 0.005). On the other hand, carriers had an increased risk of developing bleeding as expected (8.0% vs. 6.5%; OR, 1.25; 95% CI, 1.07–1.47; P= 0.006; four studies). Moreover, the presence of the CYP2C19*17 variant might lead to increased response to clopidogrel, as shown by a marked lower prevalence of HPR in carriers than in non‐carriers (37.9% vs. 50.8%; OR, 0.60; 95% CI, 0.45–0.79; P= 0.0003; three studies). Conclusions: Carriers of the CYP2C19*17 variant have greater therapeutic responsiveness to clopidogrel than non‐carriers, but they have an increased risk of developing bleeding as well.