Clopidogrel Platelet Reactivity Research Articles

Increased risk of adverse events in patients with low-on clopidogrel platelet reactivity after percutaneous coronary intervention: A systematic review and meta-analysis.

Clinical evidence has been controversial regarding the influence of low platelet reactivity (LPR), ischemic and bleeding outcomes among patients receiving coronary stent implantation. Hence, the present study performed a meta-analysis to systematically evaluate the significance of LPR on adverse cardiovascular events. MEDLINE, EMBASE and CENTRAL databases were searched up to November 2020 for relevant studies including patients with acute coronary syndrome undergoing percutaneous coronary intervention. LPR was the exposed arm while the non-LPR group represented the control. The primary outcome of interest was bleeding risk including major and minor bleeding events. Secondary outcomes included all-cause mortality, repeated revascularization, nonfatal myocardial infarction, and stent thrombosis. Study-level outcomes were evaluated in random-effect models. A total of 20 studies with 19,064 patients were included. Pooled analysis showed that LPR was associated with an increased bleeding risk (relative risk [RR] 2.80, 95% confidence interval [CI] 1.95-4.02, p < 0.01). Patients with LPR had a lower risk of non-fatal myocardial infarction (RR 0.59, 95% CI 0.38-0.91, p < 0.05) and of serious vascular events (RR 0.50, 95% CI 0.30-0.84, p < 0.01). Low platelet reactivity is associated with an increased bleeding risk of patients who underwent coronary stent implantation. The results suggest possible benefits of this marker in risk stratification, with potential improvement in risk prediction. There are potential advantages using combinations with other factors in prediction models, however, they require further study. PROSPERO registration number: CRD42019136393).

Decreased Platelet Inhibition by Thienopyridines in Hyperuricemia

PurposeHyperuricemia carries an increased risk of atherothrombotic events in acute coronary syndrome (ACS) patients undergoing percutaneous coronary intervention (PCI). This may at least in part be due to inadequate P2Y12 inhibition. The aim of this study was to prospectively investigate the potential association between hyperuricemia and decreased platelet inhibition by P2Y12 antagonists.MethodsLevels of uric acid as well as on-treatment residual platelet reactivity in response to adenosine diphosphate (ADP) were assessed in 301 clopidogrel-treated patients undergoing elective angioplasty and stenting, and in 206 prasugrel- (n = 118) or ticagrelor-treated (n = 88) ACS patients following acute PCI. Cut-off values for high on-treatment residual ADP-inducible platelet reactivity (HRPR) were based on previous studies showing an association of test results with clinical outcomes.ResultsHyperuricemia was significantly associated with increased on-treatment residual ADP-inducible platelet reactivity in clopidogrel- and prasugrel-treated patients in univariate analyses and after adjustment for differences in patient characteristics by multivariate regression analyses. In contrast, ticagrelor-treated patients without and with hyperuricemia showed similar levels of on-treatment residual platelet reactivity to ADP. HRPR occurred more frequently in clopidogrel- and prasugrel-treated patients with hyperuricemia than in those with normal uric acid levels. In contrast, hyperuricemic patients receiving ticagrelor did not have a higher risk of HRPR compared with those with normal uric acid levels.ConclusionHyperuricemia is associated with decreased platelet inhibition by thienopyridines but a normal response to ticagrelor. It remains to be established if lowering uric acid increases the antiplatelet effects of clopidogrel and prasugrel in hyperuricemic patients with HRPR.

Diurnal Variability of On-Treatment Platelet Reactivity in Clopidogrel versus Prasugrel Treated Acute Coronary Syndrome Patients: A Pre-Specified TROPICAL-ACS Sub-Study.

Long-term evidence supports a clustering of cardiovascular events in the early morning and smaller mechanistic studies in aspirin-treated patients have shown increased platelet reactivity at the end of the dosing interval. Comparative pharmacodynamic analyses for different adenosine diphosphate (ADP) receptor inhibitors in percutaneous coronary intervention-treated acute coronary syndrome (ACS) patients are lacking and this pre-specified analysis from the randomized Testing Responsiveness To Platelet Inhibition On Chronic Antiplatelet Treatment For Acute Coronary Syndromes (TROPICAL-ACS) trial aimed for the first time at investigating diurnal variability of on-treatment platelet reactivity in clopidogrel versus prasugrel treated patients. TROPICAL-ACS randomized 2,610 ACS patients to either treatment with prasugrel (control group) or to a platelet function testing-guided de-escalation of anti-platelet treatment with a switch to clopidogrel (guided de-escalation group). This study design enabled a diurnal comparison of on-prasugrel versus on-clopidogrel treatment platelet reactivity under steady-state conditions. For 2,526 patients (97%), both the exact time of blood sampling and the ADP-induced platelet aggregation value (in units, Multiplate analyser) were available. Platelet reactivity in patients on clopidogrel (n = 1,265) was higher and subject to significant diurnal variability (p = 0.019) with a peaking of platelet reactivity in the early morning (5-10 a.m.). In prasugrel-treated patients (n = 1,261), there was no sign for diurnal variability (p = 0.174) or a peaking of platelet reactivity in the morning. The potent ADP receptor inhibitor prasugrel is not subject to diurnal variability while we observed a significant diurnal variability of on-clopidogrel platelet reactivity. The clinical impact of this observation may differ for patients with and without an adequate response to clopidogrel treatment and the issue of diurnal variability of platelet reactivity in ACS patients warrants further investigation.

Clopidogrel utilization in patients with coronary artery disease and diabetes mellitus: should we determine CYP2C19*2 genotype?

Clopidogrel non-responsiveness is multifactorial; several genetic and non-genetic factors may contribute to impaired platelet inhibition. The goal of this study is to determine the effect of the cytochrome P450 CYP2C19*2 polymorphism on the platelet response to clopidogrel in patients with and without diabetes mellitus (DM). We conducted an observational study in patients with coronary artery disease and consequent exposure to clopidogrel therapy (75mg/day for at least 7 consecutive days). We have analyzed two groups of patients: group I (DM patients) and group II (non-diabetes mellitus patients). Platelet reactivity was assessed by the VerifyNow P2Y12 assay and high on clopidogrel platelet reactivity (HPR) was defined as P2Y12 reaction units (PRU) ≥ 208. Genotyping for CYP2C19*2 polymorphism was performed by PCR-RFLP. We have included 150 subjects (76 DM and 74 non-diabetes mellitus patients). The carriage of CYP2C19*2 allele, in DM patients, was significantly associated to HPR (odds ratio (OR) 4.437, 95% confidence interval (CI) 1.134 to 17.359; p= 0.032). Furthermore, 8.4% of the variability in percent inhibition by clopidogrel could be attributed to CYP2C19*2 carrier status. However, in non-diabetes mellitus patients, there was no significant difference in platelet response to clopidogrel according to the presence or absence of CYP2C19*2 allele carriage (OR 1.260, 95% CI 0.288 to 5.522; p = 0.759). Our study suggests that the carriage of CYP2C19*2 polymorphism, in DM patients, might be a potential predictor of persisting HPR in these high-risk individuals. Clinical Trials.gov NCT03373552 (Registered 13 December 2017).

5915Diurnal variability of on-treatment platelet reactivity in clopidogrel vs. prasugrel treated acute coronary syndrome patients: a pre-specified TROPICAL-ACS sub-study

5915Diurnal variability of on-treatment platelet reactivity in clopidogrel vs. prasugrel treated acute coronary syndrome patients: a pre-specified TROPICAL-ACS sub-study

Association between high on-treatment platelet reactivity to clopidogrel and hepatosteatosis in patients undergoing elective stent implantation.

The present study is an investigation of the association between high on-treatment platelet reactivity to clopidogrel (HTPRC) and hepatosteatosis in patients who had elective stent implantation due to coronary artery disease. A total of 190 consecutive patients who underwent an elective coronary stent implantation due to coronary artery disease were prospectively enrolled in the study. Eligible patients were given a 300 mg loading dose of clopidogrel before percutaneous coronary intervention. All of the patients underwent an ultrasound assessment for fatty liver. The patients were divided into 2 groups according to the detection of HTPRC: patients with HTPRC and patients without HTPRC. HTPRC was present in 54.2% (103 of 190 patients) of the total study population. The age and body mass index data were similar between the 2 groups. In all, 111 (58.6%) patients had hepatosteatosis. The HTPRC ratio was statistically higher in female patients (p=0.032). Hepatosteatosis was significantly greater in patients with HTPRC (p<0.001); 84 (81.6%) patients with HTPRC had hepatosteatosis (p=0.001). There was also a statistically significant association between the hepatosteatosis grade and HTPRC (p<0.001). The percentage of HTPRC was greater in patients with ≥grade 2 hepatosteatosis than grade 1 (p<0.001). Logistic regression analysis indicated that hepatosteatosis (odds ratio: 9.403, 95% confidence interval: 4.519-19.566; p<0.001), fasting blood glucose, and hypertension were independent predictors of HTPRC. To the best of our knowledge, this is the first study to demonstrate a relationship between hepatosteatosis and HTPRC.

The role of platelet reactivity assessment in dual antiplatelet prophylaxis after transcatheter aortic valve implantation

Dual antiplatelet therapy (DAPT) is recommended prophylaxis after transcatheter aortic valve implantation (TAVI). The usefulness of platelet reactivity (PLTR) tests in predicting the safety of periprocedural DAPT in the TAVI population is unknown. To analyze the value of aspirin/clopidogrel PLTR testing in predicting the risk of in-hospital TAVI-related bleeding. PLTR, expressed as P2Y12/aspirin reaction units (PRU/ARU), was performed using optical aggregometry with the VerifyNow® device, in the 24h before and on the sixth day after TAVI. Follow-up was by telephone. Bleeding was defined according to VARC-2, and comprised in-hospital, major and life-threatening events. Overall, 100 patients undergoing TAVI were included; 30 (30%) had bleeding. Clopidogrel PLTR before TAVI (area under the curve [AUC] 0.686, 95% confidence interval [CI] 0.542-0.808; P=0.02) and after TAVI (AUC 0.970, 95% CI 0.904-0.995; P<0.001) correlated with bleeding, with PRU cut-off values of ≤204 and ≤124 as bleeding predictors, respectively. A significant periprocedural decrease in clopidogrel PLTR was noted, with a PRU drop of >78 as bleeding predictor (AUC 0.851, 95% CI 0.725-0.935; P<0.001). Only postprocedural aspirin PLTR was associated with bleeding (AUC 0.697, 95% CI 0.585-0.794; P=0.008). Follow-up (359±73 days after TAVI) included 85 patients (85%) (after exclusion for in-hospital death [n=4] and lack of contact [n=11]). Major bleeding was noted in four patients (4.7%), all on combined prophylaxis. TAVI-related bleeding occurs mainly during the procedure or in the early postprocedural period. Testing of periprocedural clopidogrel PLTR, but not aspirin PLTR, seems useful because of its predictive value for TAVI-related bleeding. PLTR testing suggests that premedication with clopidogrel, enhanced response to clopidogrel early after TAVI and significant periprocedural drop in clopidogrel PLTR might increase the risk of TAVI-related bleeding.

A comparison of reduced-dose prasugrel and standard-dose clopidogrel in elderly patients with acute coronary syndromes undergoing early percutaneous revascularization: Design and rationale of the randomized Elderly-ACS 2 study

Elderly patients display higher on clopidogrel platelet reactivity as compared with younger patients. Treatment with prasugrel 5mg has been shown to provide more predictable and homogenous antiplatelet effect, as compared with clopidogrel, suggesting the possibility of reducing ischemic events after an acute coronary syndrome (ACS) without increasing bleeding. The Elderly-ACS 2 study is a multicenter, randomized, parallel-group, open-label trial designed to demonstrate the superiority of a strategy of dual antiplatelet treatment using a reduced 5-mg daily dose of prasugrel over a standard strategy with a daily clopidogrel dose of 75mg in patients older than 74years with ACS (either ST- or non-ST-elevation myocardial infarction) undergoing early percutaneous revascularization. The primary end point is the composite of all-cause mortality, myocardial reinfarction, disabling stroke, and rehospitalization for cardiovascular causes or bleeding within 1 year. Taking advantage of the planned size of 2,000 patients, the secondary objective is to assess the prognostic impact of selected prerandomization variables (age, sex, diabetic status, serum creatinine level, electrocardiogram changes, abnormal troponin levels, basal and residual SYNergy between percutaneous coronary intervention with TAXus and cardiac surgery [SYNTAX] score). The Elderly-ACS 2 study is a multicenter, randomized trial comparing a strategy of dual antiplatelet therapy with a reduced dose of prasugrel with a standard dose of clopidogrel in elderly patients with ACS undergoing percutaneous revascularization (the Elderly ACS 2 trial: NCT01777503).

Point-of-care genetic profiling and/or platelet function testing in acute coronary syndrome.

Our aim was to demonstrate that the sequential use of the Verigene® rapid CYP2C19 test for genetic profiling and the VerifyNowTM bedside test for platelet function measurement in ACS patients may optimise P2Y12 inhibition. "Rapid" (CYP2C19*1/*1 or CYP2C19*17 carriers, n=211) and "slow" metabolisers (CYP2C19*2 carriers, n=58) were first put on clopidogrel and prasugrel for ≥ 2 weeks, respectively. Patients with low platelet reactivity (PRU<30) on prasugrel or high platelet reactivity (>208 PRU) on clopidogrel were then switched to clopidogrel and prasugrel, respectively. Our objectives were (i) to demonstrate that the proportion of "rapid" metabolisers on 75 mg of clopidogrel within 30-208 (PRU) of P2Y12 inhibition is non-inferior to "slow" metabolisers on prasugrel 10 mg and (ii) to evaluate the same end-point after switching drugs. The proportion of "rapid" and "slow" metabolisers within 30-208 PRU of P2Y12 inhibition was 71% and 56.9%, respectively, an absolute difference of +14.1% (95% CI, -0.05% to 28.28%) with a non-inferiority margin greater than the predefined margin of -10%. Among patients out of target, all but one "slow" metabolisers displayed low-on prasugrel platelet reactivity while the majority of "rapid" metabolisers (68%) displayed high-on clopidogrel platelet reactivity. After switching, the proportion of patients within 30-208 PRU of P2Y12 inhibition was 83.6% and 79.3% in "rapid" and "slow" metabolisers, respectively (+4.3%, 95% CI -7.3% to 15.9%). In conclusion, this study demonstrates a loose relationship between genotype and platelet function phenotype approaches but that they are complementary to select prasugrel or clopidogrel MD in stented ACS patients.

The first six-month clinical outcomes and risk factors associated with high on-treatment platelet reactivity of clopidogrel in patients undergoing coronary interventions

Objective:This study attempted to fill the gaps in evidence related to response to clopidogrel treatment in the Turkish population. The study aimed to determine the prevalence, associated risk factors, and clinical outcomes of high on-treatment platelet reactivity (HTPR) of clopidogrel in patients undergoing percutaneous coronary intervention (PCI) in a tertiary cardiovascular hospital in Turkey.Methods:In this prospective studied a total of 1.238 patients undergoing PCI were included in the present study. Blood samples were analyzed using a Multiplate analyzer. All patients were examined in the outpatient clinics at the end of the first and sixth months for recording drug therapy compliance and study endpoints.Results:Among the study population, 324 (30.2%) patients were found to have HTPR (mean age 58.03±11.88 years, 71.7% men). The incidence of HTPR was higher amongst females than amongst males (38.3% vs. 27%, p=0.010). Hypertension and diabetes mellitus were more frequently observed in the HTPR group (57.7% vs. 48.7%, p=0.004; 35% vs. 29.1%, p=0.040, respectively). When the recorded data were analyzed using multinomial regression analysis, hypertension, hemoglobin level, platelet, lymphocyte, and eosinophil count were independently associated with HTPR.Conclusion:On the basis of the results obtained from our study, we conclude that 30.2% of the Turkish population has HTPR. Our results also led us to believe that hypertension is an associated risk factor and decreased hemoglobin level as well as increased platelet counts are laboratory parameters that are strongly associated with the presence of HTPR. However, no differences were observed with regard to cardiovascular mortality and stent thrombosis. (Anatol J Cardiol 2016; 16: 967-73)

Influence of Cyp2c19*2 Gene Variant on Therapeutic Response During Clopidogrel Treatment in Patients with Carotid Artery Stenosis.

SummaryBackgroundDespite the proven clinical effect of oral antiplatelet drugs, a considerable number of patients do not have an adequate response to clopidogrel. The aim of our study was to determine the influence of CYP2C19*2 loss-of-function variant allele on clopidogrel responsiveness in patients with carotid artery stenosis.MethodsOne hundred and twelve patients with carotid artery stenosis undergoing endarterectomy were included in this one-year prospective study. All of them received clopidogrel (75 mg daily) for at least 30 days after the intervention. They were followed from the moment of hospital admission. CYP2C19*2 genotyping was performed by TaqMan Assay. The influence of CYP2C19*2 variant allele on clopidogrel platelet reactivity was determined using multiple-electrode aggregometry (MEA).ResultsGenotyping results showed that 82 (73.2%) patients were homozygous for wild type, 29 (25.9%) were heterozygous for the CYP2C19*2 allele and 1 (0.9%) was CYP2C19*2 homozygous. After 24 hours, among those with the wild type 29.3% were clopidogrel responders, and in those with the CYP2C19*2 alleles 10%. In the wild type group, 74.4% were clopidogrel responders after 7 days of taking the drug; 82.9% after 30 days of clopidogrel introduction, respectively. In patients with the CYP2C19*2 alleles the number of responders increased up to 46.7% after 7 days; 53.3% after 30 days of taking the drug, respectively. The risk for being a low-responder is higher for the patients heterozygous for the CYP2C19*2 allele vs. wild-type (OR 4.250, 95% CI 1.695-10.658, P<0.01).ConclusionsThe CYP2C19*2 loss-of-function variant allele has significant influence on clopidogrel response in patients with carotid artery stenosis undergoing endarterectomy.

0466: Point-of-care genetic profiling in acute coronary syndrome

Our aim was to examine the hypothesis that the sequential use of the Verigene® rapid CYP2C19 test for genetic profiling and the VerifynowTM bedside test for platelet function measurement in ACS patients may improve P2Y 12 inhibition. “Rapid” (CYP2C19*1/*1 or CYP2C19*17 carriers, n=211) and “slow” metabolizers (CYP2C19*2 carriers, n=58) were first put on clopidogrel and prasugrel MD for ≥2 weeks, respectively. Patients with low inhibition >80% on prasugrel or high inhibition <30% on clopidogrel were then switched to clopidogrel and prasugrel, respectively. Our objectives were to demonstrate that the proportion of “rapid” metabolizers on 75mg MD of clopidogrel within 30%-80% of P2Y 12 inhibition is non-inferior to “slow” metabolizers on prasugrel 10mg MD and (ii) to evaluate the same end-point after switching drugs. The proportion of “rapid” and “slow” metabolizers within 30%-80% of P2Y 12 inhibition was 58.5% and 44.8%, respectively, an absolute difference of +13.6% (95% CI (confidence interval), –0.8% to 28.1%) with a non-inferiority margin greater than the predefined margin of –10%. Among patients out of target, all but one “slow” metabolizers displayed low-on prasugrel platelet reactivity while the majority of “rapid” metabolizers (70%) displayed high-on clopidogrel platelet reactivity. After switching, the proportion of patients within 30%-80% of P2Y 12 inhibition was 74.4% and 65.5% in “rapid” and “slow” metabolizers, respectively (+8.9%, 95% CI –4.7% to 22.5%). This study demonstrates a loose relationship between genotype and platelet function phenotype approaches but that they are complementary to select prasugrel or clopidogrel MD in stented ACS patients.

Evaluation of platelet response to different clopidogrel dosing regimens in patients with acute coronary syndrome in clinical practice

High-post clopidogrel platelet reactivity in acute coronary syndrome (ACS) patients is associated with adverse outcomes and may be related to clopidogrel dosing. Clinical studies evaluating different clopidogrel doses have resulted in conflicting conclusions. Clopidogrel dosing regimens have evolved over time, enabling us to evaluate platelet reactivity in real-life ACS patients undergoing percutaneous coronary intervention and treated with three different clopidogrel doses. Platelet reactivity was assessed with light transmitted aggregometry on the third day post clopidogrel loading in 404 consecutive ACS patients. Of them, 198 were treated with a standard regimen (300 mg loading, 75 mg/day maintenance dose), 95 with a high loading regimen (600 mg loading, 75 mg/day maintenance dose) and 111 with a high loading/high maintenance regimen (600 mg loading, 150 mg/day maintenance). Compared with the standard regimen, the high loading regimen resulted in significantly lower mean platelet reactivity to adenosine diphosphate (ADP) with a lower proportion of patients exhibiting clopidogrel non-responsiveness (11% vs. 28%, p = 0.004). Compared with the high loading regimen, the high loading/high maintenance regimen resulted in significantly lower mean platelet reactivity to ADP, but without a further drop in the number of non-responders (8.1% vs. 11%, p = 0.16). In conclusion, greater overall inhibition can be achieved with higher loading and maintenance doses in ACS patients. However, despite high clopidogrel doses, a sizable proportion of patients remained “resistant” to the effects of clopidogrel.

Safety and efficacy of policosanol to improve high on clopidogrel platelet reactivity after percutaneous coronary stent implantation

Safety and efficacy of policosanol to improve high on clopidogrel platelet reactivity after percutaneous coronary stent implantation

Genetic determinants of high on-treatment platelet reactivity in clopidogrel treated Chinese patients

IntroductionCytochrome P450 (CYP), ATP-binding cassette transporters (ABCB1), and paraoxonase-1 (PON1) play crucial roles in clopidogel absorption and bioactivation. Genetic polymorphisms in these genes have been associated with the variability of the response to clopidogrel, however their contribution to high on-treatment platelet reactivity (HPR) in clopidogrel treated Chinese patients is less known. Materials and methodsFive-hundred Chinese-Han patients treated with clopidogrel for acute coronary syndrome (ACS) were consecutively recruited from the Department of Geriatric Cardiology, General Hospital of Chinese People’s Liberation Army, from September 2010 to September 2012. We assessed the relations of CYP2C19*2 (rs4244285), CYP2C19*3 (rs4986893), CYP2C19*17 (rs12248560), PON1Q129R (rs662) and ABCB1C3435T (rs1045642) to the platelet aggregation after 5days maintenance dose of clopidogrel administration, and the risk for HPR. The cutoff of HPR was defined as 20μmol/L adenosine diphosphate (ADP)-induced platelet aggregation>50%. ResultsBoth CYP2C19*2 and *3 alleles were significantly associated with higher platelet aggregation after 5days maintenance dose of clopidogrel administration (P<0.00001and P=0.042, respectively). The platelet aggregation in carriers of at least one CYP2C19 loss-of-function allele (*2 or *3, accounted for 58% of the study population) was obviously higher than that in non-carriers (P<0.00001). Patients with the CYP2C19*2 allele had a higher risk of HPR than those with the CYP2C19 wild-type genotype [adjusted hazard ratio (HR), 1.56; 95% confidence interval(CI), 1.04–2.33, P=0.03]. The carriers of at least one CYP2C19 loss-of-function allele could also predict significantly greater risk of HPR compared with non-carriers (adjusted HR1.79,95% CI: 1.33–2.4,P=0.003). However, the carriage of CYP2C19*3 alone could not predict the risk of HPR significantly (adjusted HR, 1.5; 95% CI: 0.83–3, P=0.16). Significant relation of CYP2C19*17, PON1Q129R and ABCB1C3435T to the platelet aggregation was not found. ConclusionIn clopidogrel treated Chinese patients with ACS, carriers of at least one CYP2C19 loss-of-function allele could predict greater risk of HPR, with the impact mainly attributing to CYP2C19*2. Neither ABCB1 nor PON1 genotype could influence the antiplatelet response of clopidogrel in the cohort of Chinese patients.

Prasugrel Versus High Dose Clopidogrel to Overcome Early High on Clopidogrel Platelet Reactivity in Patients with ST Elevation Myocardial Infarction

There is a paucity of data regarding the early effectiveness of the proposed 600 mg clopidogrel loading dose (LD) on platelet reactivity (PR) in ST elevation myocardial infarction (STEMI) patients. If high on-treatment platelet reactivity (HTPR) is present, prasugrel reloading and subsequent maintenance dose (MD), might offer faster and stronger platelet inhibition than high clopidogrel MD. In 93 STEMI patients treated by primary percutaneous coronary intervention we assessed PR using the VerifyNow P2Y12 platelet function test, 2 h following 600 mg LD of clopidogrel. All the 60 (64.5 %) patients exhibiting HTPR (defined as PR ≥ 235 P2Y12 reaction units), were randomized to 1 of 2 therapeutic strategies: reloading with prasugrel 60 mg/10 mg MD or high (150 mg) clopidogrel MD. The primary endpoint of PR at 24 h post randomization was lower in the prasugrel compared to the clopidogrel group (51.3, 25.7-77.0 versus 242.4, 215.8-268.9 P2Y12 reaction units, least square estimates, 95 % confidence intervals, p < 0.001). PR at 2 h and 5 days post randomization was lower in the prasugrel compared to the clopidogrel group (117.2, 70.9-163.4 and 101.6, 70.1-133.2 least square mean difference, 95 % confidence intervals, p < 0.001 for both). At all the time points of PR assessment, HTPR rates were lower in prasugrel than in clopidogrel group. HTPR is commonly observed early post 600 mg clopidogrel LD in STEMI patients. In this case, prasugrel 60 mg LD/10 mg MD provides faster and stronger platelet inhibition than a high clopidogrel MD regimen.

Suboptimal response to clopidogrel and the effect of prasugrel in acute coronary syndromes

BackgroundHigh on clopidogrel platelet reactivity (HPR) has been associated with adverse outcomes following acute coronary syndromes (ACS). This study investigated the rate of HPR in a New Zealand ACS population and examined the effectiveness of prasugrel in reducing platelet reactivity in those with HPR. MethodsIn this prospective cohort study, 250 patients with ACS were pretreated with aspirin and clopidogrel and residual platelet reactivity was measured using whole blood multiple electrode platelet aggregometry. Twenty-seven of the patients with HPR were treated with prasugrel at the discretion of their physician, and platelet reactivity retested. ResultsNinety-five patients (38%) had HPR. Maori and Pacific Island patients had a higher rate of HPR compared to Europeans (57% versus 35.9%, p=0.013). Additionally, patients with diabetes were also found to have higher rate of HPR compared to non-diabetics (50% versus 34.8%, p=0.045). Patients treated with a low dose clopidogrel regimen had significantly higher rates of HPR (45.4%) compared to those treated with intermediate (25.4%) or high dose regimens (26.8%, p=0.009). All of the 27 patients with HPR who were subsequently treated with prasugrel (60mg) had a significant decrease in platelet reactivity (660AU∗min (565–770) before versus 230AU∗min (110–345) after, p<0.001), and was reduced to below the HPR cutoff in 24 (88.9%) of the patients. ConclusionsEthnicity, diabetes and clopidogrel dose contributed to HPR. The use of prasugrel in those with HPR resulted in a consistent and marked reduction in platelet reactivity.

High on Treatment Platelet Reactivity and Stent Thrombosis

Stent thrombosis (ST) remains a major adverse outcome of percutaneous coronary intervention (PCI). We examined potential associations between high on treatment platelet reactivity and the risk of ST and assessed the effects of increased antiplatelet dosage on platelet inhibition. Differences in clinical characteristics and the effect of aspirin and clopidogrel on platelet reactivity were determined after angiographically proven ST in 16 patients and in 40 patients without ST. Platelet reactivity was determined using the VerifyNow assays (Accumetrics Inc., San Diego, CA). Patients found with high on treatment platelet reactivity (P2Y12 Reaction Units ≥ 235 and/or Aspirin Reaction Units ≥ 550) returned following two weeks of double dose antiplatelet therapy for further analyses. High post aspirin and/or clopidogrel platelet reactivity was significantly more common in patients with ST versus controls (75% vs. 2.5%, p = < 0.001). Overall, ST patients were younger (52.8 ± 10.5 vs. 59 ± 9.6 years; p = 0.039), had more pre-existing coronary artery disease (75% vs. 42%; p = 0.028) and smaller reference vessel diameters (2.9 ± 0.36 vs. 3.2 ± 0.54 mm; p = 0.047) when compared to controls. After double dose therapy, antiplatelet reactivity improved significantly in ten out of 12 subjects on clopidogrel (83.3%) and the two patients on aspirin who initially had high on treatment platelet reactivity. This study demonstrates that high on treatment platelet reactivity with aspirin and/or clopidogrel is common amongst patients who develop stent thrombosis. Additionally this resistance can be improved with doubling the prior dose of antiplatelet therapy.

Genotyping, Clopidogrel Metabolism, and the Search for the Therapeutic Window of Thienopyridines

It is somewhat remarkable to note that not until recently, nearly 12 years and tens of millions of treated patients after its initial approval, has the metabolism of clopidogrel, an inactive prodrug, begun to be more fully understood. Although this lack of knowledge may not be unique among common cardiovascular drugs, there are 4 characteristics of clopidogrel therapy that make this gap in understanding disconcerting: The potential for life-threatening complications (bleeding or thrombosis) at both ends of its therapeutic spectrum; the fact that 1 dose is supposed to fit all; the lack of a measureable, proven end point (such as blood pressure for antihypertensive drugs) that allows for titration to a target response; and the nearly mandatory need by many patients for clopidogrel, with no acceptable alternative until recently. Article see p 512 Historically, understanding the metabolism of a drug has been critical in identifying those patients most likely to benefit from and, more important, potentially be harmed by that drug. This is especially true for drugs with relatively narrow therapeutic windows, such as phenytoin, warfarin, and others. Although it seems safe to assume, on the basis of our extensive clinical experience, that the therapeutic window of clopidogrel is unlikely to be narrow, this certainly does not represent the depth of knowledge we would hope for after so much clinical experience and research. What we do know is that P2Y12 inhibition with thienopyridines is beneficial in preventing arterial thrombotic events, presumably requiring the achievement of some minimal level of receptor inhibition that may or may not vary on the basis of the patient and clinical scenario. We also know that it is associated with a significant increase in serious bleeding events, with higher levels of inhibition associated with greater bleeding. In the present and future practice environment, with a growing …

Cytochrome P450 2C19 681G>A Polymorphism and High On-Clopidogrel Platelet Reactivity Associated With Adverse 1-Year Clinical Outcome of Elective Percutaneous Coronary Intervention With Drug-Eluting or Bare-Metal Stents

We investigated whether the loss of function CYP2C19 681G>A *2 polymorphism is associated with high (>14%) residual platelet aggregation (RPA) on clopidogrel and whether high on-clopidogrel RPA impacts clinical outcome after elective coronary stent placement. The cytochrome P450 (CYP)-dependent conversion of clopidogrel to its active metabolite may contribute to the variability in antiplatelet effect of clopidogrel. The study included 797 consecutive patients undergoing percutaneous coronary intervention, who were followed-up for 1 year. Adenosine-diphosphate-induced (5 mumol/l) RPA was assessed after a 600-mg loading dose and after the first 75-mg maintenance dose of clopidogrel before discharge. CYP2C19 genotype was analyzed by real-time polymerase chain reaction. Of the patients included, 552 (69.3%) were CYP2C19 wild-type homozygotes (*1/*1) and 245 (30.7%) carried at least one *2 allele. Residual platelet aggregation at baseline did not differ significantly between genotypes. On clopidogrel, RPA was significantly (p < 0.001) higher in *2 carriers than in wild-type homozygotes (23.0% [interquartile range (IQR) 8.0% to 38.0%] vs. 11.0% [IQR 3.0% to 28.0%] after loading; 11.0% [IQR 5.0% to 22.0%] vs. 7.0% [IQR 3.0% to 14.0%] at pre-discharge). Between *2 carriers and wild-type homozygotes, we found significant (p < 0.001) differences in the proportion of patients with RPA >14%, both after loading (62.4% vs. 43.4%) and at pre-discharge (41.3% vs. 22.5%). Residual platelet aggregation >14% at pre-discharge incurred a 3.0-fold increase (95% confidence interval 1.4 to 6.8; p = 0.004) in the 1-year incidence of death and myocardial infarction. Patients carrying at least one CYP2C19*2 allele are more prone to high-on clopidogrel platelet reactivity, which is associated with poor clinical outcome after coronary stent placement (Effect of Clopidogrel Loading and Risk of PCI [EXCELSIOR]; NCT00457236).