Impact of CYP2C19 polymorphisms on the antiplatelet effect of clopidogrel in an actual clinical setting in Japan

Effect of cilostazol on optimized standard antiplatelet therapy in a patient with a cytochrome P450 2C19 *2/*2 genotype

A 54-year-old man with acute coronary syndrome underwent primary percutaneous coronary intervention (PCI) to implant a bare metal stent. Three weeks later, a subclinical in-stent thrombus was found at staged PCI despite dual antiplatelet therapy with aspirin and clopidogrel. Platelet function tests revealed high post-treatment platelet reactivity, indicating an inadequate response to clopidogrel. The patient's cytochrome P450 2C19 genotype was *2/*2. Cilostazol at 200 mg/day was initiated in addition. Three months later, platelet inhibition was enhanced, and no thrombus was detectable by coronary angiography. Our experience suggests that triple antiplatelet therapy with cilostazol as well as aspirin and clopidogrel could prevent stent thrombosis with improved clopidogrel responsiveness.

Relation of CYP2C19 loss-of-function polymorphism to the occurrence of stent thrombosis

IMPORTANCE OF THE FIELD

Major adverse cardiovascular events including stent thrombosis associated with residual platelet reactivity on antiplatelet treatment in high risk vascular patients is a hot issue that needs a strong effort to be solved. Dual antiplatelet therapy with clopidogrel and aspirin prevents ischemic events and improves outcomes following acute coronary syndromes and percutaneous coronary intervention. However, adverse cardiovascular events occur in these patients, and several studies have shown that patients who suffer cardiovascular complications have high post-treatment platelet reactivity despite antiplatelet treatment. Clopidogrel requires conversion to active metabolite by CYP isoenzymes. Recently, CYP2C19*2 polymorphism (G681A nucleotide substitution) has been shown to be associated with decreased metabolisation of clopidogrel, poor antiaggregant effect and increased adverse cardiovascular events.

AREAS COVERED IN THIS REVIEW

This review summarises the principal studies contributing to establish the relationship between CYP2C19*2 polymorphism and adverse outcomes in high risk patients on clopidogrel treatment.

TAKE HOME MESSAGE

Prospective studies are urgently needed to determine the clinical impact of a score that takes into account individual characteristics of patients - CYP2C19*2 genotypes, residual platelet reactivity, drug-drug interaction, as well as traditional and procedural risk factors - for the identification of the therapeutic strategy that provides the best benefit for the single subject.

Determinants to optimize response to clopidogrel in acute coronary syndrome

The inhibition of platelet function by antiplatelet therapy determines the improvement of the survival of patients with clinically evident cardiovascular disease. Clopidogrel in combination with aspirin is the recommended standard of care for reducing the occurrence of cardiovascular events in patients with acute coronary syndromes undergoing percutaneous coronary intervention. However, major adverse cardiovascular events including stent thrombosis occur in patients taking clopidogrel and aspirin. A growing body of evidence demonstrates that high post-treatment platelet reactivity on antiplatelet treatment is associated with increased risk of adverse clinical events. Clopidogrel requires conversion to active metabolite by cytochrome P450 isoenzymes. The active metabolite inhibits ADP-stimulated platelet activation by irreversibly binding to P2Y₁₂ receptors. Recently, the loss-of-function CYP2C19*2 allele has been associated with decreased metabolization of clopidogrel, poor antiaggregant effect, and increased cardiovascular events. In high risk vascular patients, the CYP2C19*2 polymorphism is a strong predictor of adverse cardiovascular events and particularly of stent thrombosis. Prospective studies evaluating if an antiplatelet treatment tailored on individual characteristics of patients, CYP2C19*2 genotypes, platelet phenotype, drug–drug interaction, as well as traditional and procedural risk factors, are now urgently needed for the identification of therapeutic strategies providing the best benefit for the single subject.

Implications of Inter-Individual Differences in Clopidogrel Metabolism, with Focus on Pharmacogenetics

Increasing evidence for the role of pharmacogenetics in treatment resistance to the antiplatelet agent clopidogrel has been gained during the last years. Apart from CYP2C19 genetic polymorphisms, nongenetic factors, particularly drug-drug interactions, age and other clinical characteristics influence the interindividual variability in clopidogrel response to varying degrees. The present article reviews the so far accumulated evidence on the role of pharmacogenetic traits influencing CYP-activity as determinants of the antiplatelet response to clopidogrel, and its clinical implications. The genetic variation in CYP2C19 activity seems to influence short- and long-term antithrombotic effects of clopidogrel to a substantial extent. Prediction models for clopidogrel non-responsiveness that include CYP2C19 genotyping together with relevant non-genetic risk factors are needed to be verified for their potential benefit in individualization of antithrombotic therapy.