The influence of CYP2C19*2 and *17 on on-treatment platelet reactivity and bleeding events in patients undergoing elective coronary stenting.

OBJECTIVES: To investigate the impact of genotypes on the basis of the loss-of-function variant CYP2C19*2 and the gain-of-function variant CYP2C19*17 on on-treatment platelet reactivity and on the occurrence of Thrombolysis in Myocardial Infarction (TIMI) major bleedings in 820 clopidogrel-treated patients who underwent elective coronary stenting. METHODS: On-treatment platelet reactivity was quantified using ADP-induced light transmittance aggregometry (LTA) and the VerifyNow P2Y12 assay. Postdischarge TIMI major bleedings within 1 year after enrollment were recorded. RESULTS: In total, 25 major bleedings (3.0% of the study population) were observed. Patients with the CYP2C19*1/*17 and *17/*17 diplotypes exhibited a lower magnitude of platelet reactivity as compared with patients with the CYP2C19*1/*1 diplotype (for the light transmittance aggregometry-adjusted mean difference: -5.8%, 95% confidence interval: -9.6 to -2.1, P=0.002). Patients with the *1/*17 and *17/*17 genotype had a 2.7-fold increased risk in the occurrence of major bleedings [adjusted hazard ratio: 2.7, 95% confidence interval: 1.1-7.0, P=0.039]. The diplotypes *2/*17, *1/*2, and *2/*2 exhibited higher on-treatment platelet reactivity as compared with the wild type (P<0.0001). However, this was not translated into an altered risk on major bleedings as compared with the wild type [hazard ratio: 1.3 (0.45-4.0), P=0.60]. Results have not been adjusted for multiple testing. CONCLUSION: Patients with the CYP2C19*1/*17 and *17/*17 diplotype have a lower magnitude of on-treatment platelet reactivity and are at a 2.7-fold increased risk of postdischarge TIMI major bleeding events after coronary stenting than patients with the *1/*1 genotype. The diplotypes *2/*17, *1/*2, and *2/*2 are associated with increased on-treatment platelet reactivity; however, this is not translated into a lower risk of bleeding events.

CYP2C19*2 and CYP2C9*3 alleles are associated with stent thrombosis: a case-control study.

AIMS: despite treatment with clopidogrel on top of aspirin, stent thrombosis (ST) still occurs being the most serious complication after percutaneous coronary interventions (PCIs). In this study, we aimed to determine the effect of variations in genes involved in the absorption (ABCB1 C1236T, G2677T/A, C3435T), metabolism (CYP2C19*2 and *3, CYP2C9*2 and *3, CYP3A4*1B and CYP3A5*3), and pharmacodynamics (P2Y1 A1622G) of clopidogrel on the occurrence of ST. METHODS AND RESULTS: the selected genetic variants were assessed in 176 subjects who developed ST while on dual antiplatelet therapy with aspirin and clopidogrel and in 420 control subjects who did not develop adverse cardiovascular events, including ST, within 1 year after stenting. The timing of the definite ST was acute in 66, subacute in 87, and late in 23 cases. The presence of the CYP2C19*2 and CYP2C9*3 variant alleles was significantly associated with ST (OR(adj): 1.7, 95% CI: 1.0-2.6, P = 0.018 and OR(adj): 2.4, 95% CI: 1.0-5.5, P = 0.043, respectively). The influence of CYP2C19*2 (OR(adj): 2.5, 95% CI: 1.1-5.5, P = 0.026) and CYP2C9*3 (OR(adj): 3.3, 95% CI: 1.1-9.9, P = 0.031) was most strongly associated with subacute ST. No significant associations of the other genetic variations and the occurrence of ST were found. CONCLUSION: carriage of the loss-of-function alleles CYP2C19*2 and CYP2C9*3 increases the risk on ST after PCI.

Besides CYP2C19*2, the variant allele CYP2C9*3 is associated with higher on-clopidogrel platelet reactivity in patients on dual antiplatelet therapy undergoing elective coronary stent implantation.

INTRODUCTION: The prodrug, clopidogrel, plays an important role in the prevention of thrombotic events in patients undergoing coronary stenting. However, a substantial number of atherothrombotic events still occur, which can partially be explained by heightened residual platelet reactivity. Several studies report that the genetic variation in CYP2C19 (*2) is associated with an impaired response to clopidogrel. OBJECTIVES: To evaluate the effect of genetic variants affecting clopidogrel's absorption (ABCB1 C1236T, G2677T/A, C3435T), metabolism (CYP2C9*2, *3, CYP2C19*3, CYP3A4*1B, and CYP3A5*3), and pharmacodynamics (P2Y1 A1622G) on top of the influence of CYP2C19*2 on platelet reactivity in patients undergoing elective coronary stenting on dual antiplatelet therapy. METHODS: Platelet function was assessed by light transmittance aggregometry and VerifyNow P2Y12 assay in 428 consecutive patients. Patients were either on chronic clopidogrel maintenance therapy (75 mg/day for > or =5 days before the intervention) or received a 300 mg clopidogrel loading dose (1-5 days before the intervention, followed by 75 mg/day). Linear and logistic regressions were used to assess the associations between genetic variants and platelet reactivity and poor responder status. RESULTS: In both the treatment groups, CYP2C19*2-carriage was associated with higher platelet reactivity (P<0.002) and poor responder status; 75 mg group: adjusted odds ratio (ORadj): 3.8, 95% confidence interval (CI): 2.0-7.2, 300 mg group: ORadj: 4.1, 95% CI: 1.6-10.4. In the 300 mg group, CYP2C9*3-carriage was associated with higher platelet reactivity (P<0.05) and poor responder status (ORadj: 11.1, 95% CI: 1.6-78.8, P=0.016). CONCLUSION: Besides CYP2C19*2, the variant allele CYP2C9*3 plays an important role in the response to clopidogrel in patients on dual antiplatelet therapy undergoing coronary stenting.

Comparison of platelet function tests in predicting clinical outcome in patients undergoing coronary stent implantation.

Context High on-treatment platelet reactivity is associated with atherothrombotic events following coronary stent implantation. Objective To evaluate the capability of multiple platelet function tests to predict clinical outcome. Design, Setting, and Patients Prospective, observational, single-center cohort study of 1069 consecutive patients taking clopidogrel undergoing elective coronary stent implantation between December 2005 and December 2007. On-treatment platelet reactivity was measured in parallel by light transmittance aggregometry, Verify Now P2Y12 and Platelet works assays, and the IMPACT-R and the platelet function analysis system (PFA-100) (with the Dade PFA collagen/adenosine diphosphate (ADP) cartridge and Innovance PFA P2Y). Cutoff values for high on-treatment platelet reactivity were established by receiver operating characteristic curve (ROC) analysis. Main Outcome Measurement The primary end point was defined as a composite of all-cause death, nonfatal acute myocardial infarction, stent thrombosis, and ischemic stroke. The primary safety end point included TIMI (Thrombolysis In Myocardial Infarction) criteria major and minor bleeding. Results Kaplan-Meier analysis demonstrated that at 1-year follow-up, the primary end point occurred more frequently in patients with high on-treatment platelet reactivity when assessed by light transmittance aggregometry (52 [11.7%; 95% confidence interval {CI}, 8.9%-15.0%] vs 36 [6.0%;95%CI, 4.2%-8.2%] P.001; n=1049),Verify Now (54 [13.3%; 95% CI, 10.2%-17.0%] vs 37 [5.7%; 95% CI, 4.1%-7.8%]P.001; n=1052), Platelet works (33 [12.6%; 95% CI, 8.8%-17.2%] vs 21 [6.1%;95% CI, 3.8%-9.2%] P=.005; n=606), and Innovance PFA P2Y (18 [12.2%; 95%CI; 7.4%-18.6%] vs 28 [6.3%; 95% CI, 4.3%-8.9%] P=.02; n=588). ROC-curve analysis demonstrated that light transmittance aggregometry (area under the curve[AUC], 0.63; 95% CI, 0.58-0.68), Verify Now (AUC, 0.62; 95% CI, 0.57-0.67), and Platelet works (AUC, 0.61; 95% CI, 0.53-0.69) had modest ability to discriminate between patients with and without primary end point at 1-year follow-up. The IMPACT-R(n=905) and the Siemens PFA Collagen/ADP (n=812) were unable to discriminate between patients with and without the primary end point at 1-year follow-up (all AUCs included 0.50 in the CI). None of the tests identified patients at risk for bleeding. Conclusions Of the platelet function tests assessed, light transmittance aggregometry,Verify Now, Platelet works, and Innovance PFA P2Y were significantly associated with the primary end point. However, the predictive accuracy of these 4 tests was only modest. None of the tests provided accurate prognostic information to identify patients at higher risk of bleeding following stent implantation. Trial Registration clinical trials.gov Identifier: NCT00352014 [corrected].

The influence of clinical characteristics, laboratory and inflammatory markers on 'high on-treatment platelet reactivity' as measured with different platelet function tests.

High on-clopidogrel platelet reactivity (HCPR) and high on-aspirin platelet reactivity (HAPR) are independently associated with an increased risk of atherothrombotic events. However, despite this positive correlation, the definitions of both HCPR and HAPR vary largely throughout studies and between different platelet function assays. The aim of the present study was to explore clinical and laboratory parameters that are associated with HCPR and HAPR as measured with different platelet function tests. 530 clopidogrel and aspirin pre-treated patients undergoing elective PCI (percutaneous coronary intervention) were enrolled. Platelet function measurements were performed with: optical aggregometry, the VerifyNow device and PFA-100 cartridges (including the novel INNOVANCE P2Y assay). HCPR as measured with Adenosin-Di-Phospate-induced (ADP) aggregation based tests was associated with clinical factors such as older age, female gender and Diabetes mellitus (DM). The VerifyNow P2Y12 assay was significantly influenced by haemoglobin and haematocrit levels. HAPR as measured with aggregation based tests was significantly influenced by the presence of malignancy, BMI (Body-Mass Index), older age and increased levels of hsCRP (high sensitivity c-reactive proteine). The PFA-100 COL/EPI (collagen-epinephrine) and COL/ADP (collagen-ADP) cartridges were significantly influenced by monocyte count, hs-CRP, MPV (mean platelet volume), vWF-antigen (von Willebrand factor) and vWF-activity. HCPR as measured with the novel INNOVANCE P2Y cartridge was associated with clinical determinants such as BMI, female gender, impaired LVEF (left ventricular ejection fraction), renal failure and dosing of clopidogrel. Laboratory markers that were associated with HCPR as measured with INNOVANCE P2Y were platelet count, white blood cells (WBC), hsCRP and fibrinogen. Both HCPR and HAPR are highly dependent on the type of platelet function assay. Each platelet function assay, in turn, is significantly influenced by distinct clinical and laboratory variables.

Determinants of agreement between proposed therapeutic windows of platelet function tests in vulnerable patients.

AIMS: Therapeutic windows for residual platelet reactivity in patients with coronary artery disease on P2Y12 inhibitors were proposed in a consensus document. We aimed to explore the level of agreement between windows for different platelet function tests (PFTs) used to classify patients in low, optimal, and high on-treatment platelet reactivity categories, and to identify variables contributing to the level of agreement. METHODS AND RESULTS: In this explorative clinical study, the VerifyNow P2Y12, Multiplate adenosine diphosphate (ADP), and light transmission aggregometry (LTA) 20 µmol/L ADP were performed simultaneously in 145 consecutive vulnerable patients. Measurements were performed within 6 months of percutaneous intervention. Patients were considered vulnerable if they had ≥2 risk factors for bleeding or ischaemic events. Window-agreement between PFT pairs was slight to moderate. Multiplate-VerifyNow agreed in 72 patients (50%), κ = 0.41; VerifyNow-LTA agreed in 76 patients (52%), κ = 0.36; and LTA-Multiplate agreed in 64 patients (44%), κ = 0.20. Several variables including the type of P2Y12 inhibitor, aspirin, haemoglobin level, platelet count, age, and previous stroke significantly influenced agreement between PFTs. CONCLUSIONS: Our results suggest that the PFTs, with accompanying therapeutic windows, are not interchangeable when determining the response to antiplatelet therapy in vulnerable coronary artery disease patients on P2Y12 inhibitors. Hence, the type of PFT can directly affect the treatment strategy, which may be especially relevant for patients with multiple factors influencing individual PFTs and thereby test agreement.

The relationship between platelet reactivity and infarct-related artery patency in patients presenting with a ST-elevation myocardial infarction.

Both heightened platelet reactivity and an occluded infarct related artery (IRA) on initial angiography and at the time of primary percutaneous coronary intervention (PCI) are associated with a worsened clinical outcome in patients with ST-elevation myocardial infarction (STEMI). However, the relationship between platelet reactivity and IRA patency has not yet been established. Consecutive STEMI-patients were enrolled in this study. Patients who had TIMI-flow (thrombolysis in myocardial infarction) 0 or 1 on initial angiography constituted the occluded IRA group and patients having TIMI-flow 2 or 3 comprised the IRA patent group. Platelet function measurements were performed using the PFA-100 COL/ADP cartridge and light transmittance aggregometry without agonist (spontaneous) and after stimulation with adenosine diphosphate (ADP) and arachidonic acid (AA). Ninety-nine patients were enrolled, of whom 49 presented with an occluded IRA. Multivariate analysis identified the following independent factors to be associated with an occluded IRA; short COL/ADP closure time (ORper quartile increase=0.60; 95% CI, 0.39-.93; p=0.02), the 20 µM ADP-induced light transmittance aggregometry (ORper quartile increase =1.77; 95% CI, 1.15-2.73; p=0.01) and leukocyte counts (odds ratio [OR]=1.21; 95% CI, 1.05-1.39; p = 0.008). In conclusion, heightened platelet reactivity and elevated leukocyte counts are associated with an occluded IRA upon presentation in STEMI-patients. These results emphasise the importance of potent antithrombotic therapy early after the onset of symptoms, to obtain early recanalisation of the IRA.

Impact of CYP2C19 variant genotypes on clinical efficacy of antiplatelet treatment with clopidogrel: systematic review and meta-analysis.

OBJECTIVE: To evaluate the accumulated information from genetic association studies investigating the impact of variants of the cytochrome P450 (CYP) 2C19 genotype on the clinical efficacy of clopidogrel. DESIGN: Systematic review and meta-analysis with a structured search algorithm and prespecified eligibility criteria for retrieval of relevant studies; dominant genetic model assumptions and quantitative methods for calculating summary effect estimates from study level odds ratios; systematic assessment of bias within and between studies; and grading of the cumulative evidence by consensus criteria. DATA SOURCES: Medline, Embase, the Cochrane Library, online databases, contents pages and bibliographies of general medical, cardiovascular, pharmacological, and genetic journals. Eligibility criteria for selecting studies Original full length reports assessing the cumulative incidence of major adverse cardiovascular events or stent thrombosis over a follow-up period of at least a month in association with carrier status for the loss of function or gain of function CYP2C19 allele in adult patients with coronary artery disease and a clinical presentation of acute coronary syndrome or stable angina pectoris who were taking clopidogrel. RESULTS: 15 studies met the inclusion criteria. The random effects summary odds ratio for stent thrombosis in carriers of at least one CYP2C19 loss of function allele versus non-carriers combining nine studies was 1.77 (95% confidence interval 1.31 to 2.40; P < 0.001). This nominally significant odds ratio was subject to considerable bias across the studies (small study effect bias and replication diversity). The adjustment for these quality modifiers tended to abolish the association. The corresponding random effects summary odds ratio of major adverse cardiovascular events for 12 studies combined was 1.11 (0.89 to 1.39; P = 0.36). The random effects summary odds ratio of stent thrombosis in carriers versus non-carriers of at least one CYP2C19*17 gain of function allele for three studies combined was 0.99 (0.60 to 1.62; P = 0.96), and the corresponding odds ratio of major adverse cardiovascular events in five studies was 0.93 (0.75 to 1.14; P = 0.48). The overall quality of epidemiological evidence was graded as low, which excludes reliable clinical assessments. CONCLUSIONS: Accumulated information from genetic association studies does not indicate a substantial or consistent influence of CYP2C19 gene polymorphisms on the clinical efficacy of clopidogrel. The current evidence does not support the use of individualised antiplatelet regimens guided by CYP2C19 genotype.

High on-treatment platelet reactivity to both aspirin and clopidogrel is associated with the highest risk of adverse events following percutaneous coronary intervention.

AIM: High on-clopidogrel platelet reactivity (HCPR) and high on-aspirin platelet reactivity (HAPR) are associated with atherothrombotic events following coronary stenting. There are, however, few data concerning high on-treatment platelet reactivity to both aspirin and clopidogrel simultaneously. The aim of the present study was to determine the incidence of dual high on-treatment platelet reactivity (DAPR) and its impact on clinical outcome. METHODS: On-treatment platelet reactivity was measured in parallel by ADP- and arachidonic acid-induced light transmittance aggregometry (LTA) (n=921) and the point-of-care VerifyNow system (P2Y12 and aspirin) (n=422) in patients on dual antiplatelet therapy undergoing elective stent implantation. HCPR and HAPR were established by receiver-operator characteristic curve analysis. The primary endpoint was a composite of all-cause death, non-fatal acute myocardial infarction, stent thrombosis and ischaemic stroke at 1-year follow-up. RESULTS: The incidence of DAPR varied between 14.7% and 26.9% depending on the platelet function test used. DAPR, assessed by LTA and the VerifyNow system, was highly associated with an adverse clinical outcome. At 1-year follow-up the primary endpoint occurred more frequently in patients with isolated HCPR (11.7%), isolated HAPR (9.6%) or DAPR (10.7%) compared with patients without high on-treatment platelet reactivity (4.2%, all p<0.01) when platelet function was evaluated with LTA. Using the VerifyNow system, patients exhibiting DAPR had the highest risk for the primary endpoint (17.7% vs 4.1% in patients without high on-treatment platelet reactivity, p=0.001). CONCLUSIONS: In patients undergoing elective percutaneous coronary intervention, DAPR to aspirin and clopidogrel is present in one in five patients and is associated with a high risk for atherothrombotic events. DAPR measured by the point-of-care VerifyNow system has a higher predictability for atherothrombotic events than LTA. CLINICAL TRIAL REGISTRATION INFORMATION: www.clinicaltrials.gov: NCT00352014.

Paraoxonase-1 is a major determinant of clopidogrel efficacy.

Clinical efficacy of the antiplatelet drug clopidogrel is hampered by its variable biotransformation into the active metabolite. The variability in the clinical response to clopidogrel treatment has been attributed to genetic factors, but the specific genes and mechanisms underlying clopidogrel bioactivation remain unclear. Using in vitro metabolomic profiling techniques, we identified paraoxonase-1 (PON1) as the crucial enzyme for clopidogrel bioactivation, with its common Q192R polymorphism determining the rate of active metabolite formation. We tested the clinical relevance of the PON1 Q192R genotype in a population of individuals with coronary artery disease who underwent stent implantation and received clopidogrel therapy. PON1 QQ192 homozygous individuals showed a considerably higher risk than RR192 homozygous individuals of stent thrombosis, lower PON1 plasma activity, lower plasma concentrations of active metabolite and lower platelet inhibition. Thus, we identified PON1 as a key factor for the bioactivation and clinical activity of clopidogrel. These findings have therapeutic implications and may be exploited to prospectively assess the clinical efficacy of clopidogrel.

Variability in on-treatment platelet reactivity explained by CYP2C19*2 genotype is modest in clopidogrel pretreated patients undergoing coronary stenting.

BACKGROUND: An inadequate response to clopidogrel is mainly attributable to the variable formation of its active metabolite. The CYP2C19*2 loss-of-function polymorphism leads to reduced generation of the active metabolite and is, similarly to high on-treatment platelet reactivity (HPR), associated with recurrent atherothrombotic events following coronary stent implantation. AIM: To determine the relative contribution of CYP2C19*2 genotype to HPR. METHODS AND RESULTS: CYP2C19*2 genotyping and platelet function testing using 5 and 20 µmol/l ADP-induced light transmittance aggregometry (LTA), the PlateletWorks assay and the VerifyNow P2Y12 assay, were performed in 1069 clopidogrel pretreated patients undergoing elective coronary stenting (POPular study, http://clinicalTrials.gov/ NCT00352014). The relative contributions of CYP2C19*2 genotype and clinical variables to the interindividual variability of on-treatment platelet reactivity and the occurrence of HPR were established using multivariate regression models. CYP2C19*2 carrier status was associated with a more frequent occurrence of HPR. CYP2C19*2 genotype alone could explain 5.0%, 6.2%, 4.4% and 3.7% of the variability in 5 and 20 µmol/l ADP-induced LTA, the PlateletWorks assay and the VerifyNow P2Y12 assay, respectively, which increased to 13.0%, 15.2%, 5.6% and 20.6% when clinical variables were considered as well. Besides the CYP2C19*2 genotype, multiple clinical variables could be identified as independent predictors of HPR, including age, gender, body mass index, diabetes mellitus, clopidogrel loading dose regimen, use of amlodipine and platelet count. CONCLUSION: The CYP2C19*2 loss-of-function polymorphism is associated with a more frequent occurrence of HPR. However, the part of the interindividual variability in on-treatment platelet reactivity explained by CYP2C19*2 genotype is modest.

Platelet function tests for the monitoring of P2Y12 inhibitors.

IMPORTANCE OF THE FIELD: The individual response to clopidogrel therapy is unpredictable, resulting in high on-treatment platelet reactivity in a substantial number of patients. Moreover, consistent findings across multiple investigations point out that a strong relationship exists between high on-treatment platelet reactivity and the occurrence of atherothrombotic events. AREAS COVERED IN THIS REVIEW: This paper describes the current available methods of platelet function evaluation, including their advantages and drawbacks, reviews the evidence for the relation between high on-treatment platelet reactivity and clinical outcome, and discusses data concerning the clinical implications of platelet function testing in patients treated with thienopyridine therapy. WHAT THE READER WILL GAIN: The reader will be introduced to platelet function testing and its clinical applicability. The reader will gain a better understanding of the techniques used and will learn how to interpret the numerous data on platelet function testing and clinical outcome. TAKE HOME MESSAGE: Although a growing body of evidence demonstrates the promising potential of platelet function tests in predicting atherothrombotic events post stenting, platelet function testing should not yet be used routinely, as adequate treatment of high on-treatment platelet reactivity is unknown.

The Cone-and-Plate(let) analyzer is not suitable to monitor clopidogrel therapy: a comparison with the flowcytometric VASP assay and optical aggregometry.

INTRODUCTION: High on-clopidogrel platelet reactivity has been associated with an increased risk for atherothrombotic events. A new player on the horizon is the IMPACT-R ADP-test using ADP pre-stimulation. We here report the results of a thorough evaluation of this new device. MATERIALS AND METHODS: The IMPACT-R ADP-test was evaluated in different categories of subjects. First, normal range values were determined in healthy subjects (n=46). Second, the effect of 600 mg of clopidogrel was evaluated with the IMPACT-R ADP-test and two other well-validated methods (flowcytometric VASP-analysis and optical aggregometry) in 21 patients. Third, a head-to-head comparison between the IMPACT-R ADP-test and optical aggregometry was performed in a large cohort of patients on dual antiplatelet therapy. RESULTS: The results of the IMPACT-R ADP-test were highly variable throughout healthy subjects. The administration of a high clopidogrel loading dose resulted in a small but significant increase in surface coverage but 61.9% of the patients were still identified as clopidogrel nonresponder. In contrast, optical aggregometry and VASP-analysis identified 24% and 33% of these patients as a clopidogrel nonresponder, respectively. Head-to-head comparison with optical aggregometry in 451 patients showed only a modest correlation between both methods (r approximately 0.20, p<0.0001). CONCLUSIONS: The IMPACT-R ADP-test is relatively insensitive to the effects of clopidogrel and cannot substitute for methods such as flowcytometric VASP-analysis and optical aggregometry. Further studies are required to establish the clinical usefulness of IMPACT-R ADP-test to accurately predict the occurrence of major adverse cardiovascular events in patients with high on-clopidogrel platelet reactivity before it can be implemented in clinical practice.

A comparison between the Plateletworks-assay and light transmittance aggregometry for monitoring the inhibitory effects of clopidogrel.

A simple and rapid point-of-care platelet function assay that guides antiplatelet responses to aspirin and clopidogrel may be of great clinical value for the individual tailoring of therapy. The Plateletworks assay is based on single platelet counting and has been described as a promising point-of-care assay for the monitoring of the effects of the GP IIb/IIIa antagonists. However, data about its utility and reliability in monitoring the effects of thienopyridines is limited. In the present study we assessed reproducibility of the Plateletworks assay over time. In addition, a comparison between the Plateletworks assay and optical aggregometry was performed in a large cohort of patients on maintenance therapy with aspirin and clopidogrel. The Plateletworks assay demonstrated a good agreement with optical aggregometry in measuring the response to clopidogrel. The results of Plateletworks are, however, highly time dependent which implicates that measurements should be performed within 10 min.

Common variation in the platelet receptor P2RY12 gene is associated with residual on-clopidogrel platelet reactivity in patients undergoing elective percutaneous coronary interventions.

BACKGROUND: The clinical efficacy of clopidogrel is hampered by a large interindividual variability in platelet inhibition. Polymorphisms in the P2RY12 receptor gene have been suggested to contribute to this variability, but previous studies included a relatively small number of patients and incompletely covered the common variation in the P2RY12 gene. The aim of this study was to comprehensively investigate the possible association between common variation in the entire P2RY12 locus and the magnitude of residual on-clopidogrel platelet reactivity measured by 2 commonly used platelet function assays in a large cohort of patients. METHODS AND RESULTS: A total of 1031 consecutive patients with coronary artery disease who were scheduled for elective percutaneous coronary interventions were enrolled. Platelet function was assessed by means of ADP-induced light-transmittance aggregometry and the VerifyNow P2Y12 assay. Six haplotype-tagging single nucleotide polymorphisms were carefully selected to comprehensively cover the total common variation in the P2RY12 gene and its flanking regulatory regions. Six common haplotypes were inferred from these haplotype-tagging single nucleotide polymorphisms (denoted A to F). Haplotype F was associated with significantly lower residual on-clopidogrel platelet reactivity compared with the reference haplotype A. The size of this effect per haplotype allele was approximately 5% aggregation in the ADP-induced light-transmittance aggregometry (P<0.05) and 11 P2Y12 reaction units in the VerifyNow P2Y12 assay (P<0.05). CONCLUSIONS: Common variation in the P2RY12 gene is a significant determinant of the interindividual variability in residual on-clopidogrel platelet reactivity in patients with coronary artery disease.