Residual Platelet Aggregation Research Articles

High on-thienopyridine platelet reactivity in elderly coronary patients: the SENIOR-PLATELET study

The aim of this study was to compare on-thienopyridine platelet reactivity of elderly patients (≥75 years) vs. younger patients (<75 years). Elderly patients represent a growing and challenging segment of the coronary population for whom the effect of dual antiplatelet therapy on platelet inhibition has not been specifically addressed. The SENIOR-PLATELET study included 1331 coronary patients chronically (>14 days) treated with aspirin and a thienopyridine (clopidogrel 75 mg, n= 1027; clopidogrel 150 mg, n= 139; or prasugrel 10 mg, n= 165). Platelet response to clopidogrel and prasugrel was assessed by the VerifyNow assay and light transmission aggregrometry (LTA). Response to treatment, rate of high platelet reactivity (HPR), and inhibition (HPI) were compared in the two age categories. On-treatment platelet reactivity with clopidogrel 75 mg, 150 mg or prasugrel 10 mg was higher in elderly patients (n= 205) than in younger patients (n= 1126) whichever the test used. The difference in P2Y(12) reaction units (PRU) between the two populations was +45 in patients treated with clopidogrel 75 mg (P< 0.0001), +30 in patients treated with clopidogrel 150 mg (P= 0.17), and +20 with prasugrel 10 mg (P= 0.10). Differences in residual platelet aggregation were consistent when measured by LTA. Elderly patients treated with clopidogrel 75 mg were more likely to have HPR than younger patients (38.2 vs. 18.2%, OR: 2.58, 95% CI: 1.76-3.79; P< 0.0001) even after adjustment for potential confounders (adj OR: 1.83, 95% CI: 1.16-2.87; P= 0.009). Elderly patients present an impaired response to clopidogrel with a high rate of HPR. Clopidogrel 150 mg or prasugrel 10 mg blunt, but do not eliminate the difference in response observed between old and young patients.

Determination of cut-off levels for on-clopidogrel platelet aggregation based on functional CYP2C19 gene variants in patients undergoing elective percutaneous coronary intervention

Introduction Carriers of reduced-function CYP2C19 allele on antiplatelet therapy show diminished platelet inhibition and higher rate of clinical risk. The purpose of this study was to determine cut-off levels of VerifyNow P2Y12 system associated with effective inhibition of on-clopidogrel platelet aggregation to predict carriers of CYP2C19 reduced-function allele among patients undergoing percutaneous coronary intervention (PCI). Materials and Methods We enrolled 202 consecutive patients with stable coronary artery disease (CAD) undergoing PCI and treated with clopidogrel. All patients underwent CYP2C19 genotyping and measurement of residual platelet aggregation by VerifyNow system. Results Carriers of CYP2C19 reduced-function allele constituted 131 (65%) of 202 CAD patients. Platelet inhibition measured by P2Y12 reaction units (PRU) and %inhibition was diminished in carriers compared with noncarriers (PRU: 290.0 ± 81.2 vs 217.6 ± 82.4, p < 0.001, %inhibition: 17.9 ± 17.8 vs 35.5 ± 22.8, p < 0.001, respectively). Multiple logistic regression analysis identified PRU and %inhibition as significant predictors of carrier state [odds ratio (OR) 4.95; 95% confidence interval (95%CI): 2.49 to 9.85; p < 0.001, OR 5.55; 95%CI: 2.80 to 10.99; p < 0.001, respectively]. Receiver-operating characteristic analysis showed that PRU and %inhibition were significant predictors of carrier state [area under the curve (AUC) 0.736 (95%CI: 0.664 to 0.808; p < 0.001), AUC 0.727 (95%CI: 0.651 to 0.803; p < 0.001), respectively]. The cut-off levels of PRU and %inhibition were 256 and 26.5% for the identification of carriers. Conclusions Our results suggested that the cut-off levels of PRU and %inhibition to discriminate carriers of CYP2C19 reduced-function allele from noncarriers are potentially useful clinically to provide optimal clopidogrel therapy in patients with stable CAD undergoing PCI.

Paraoxonase-1 Q192R Polymorphism and Antiplatelet Effects of Clopidogrel in Patients Undergoing Elective Coronary Stent Placement

Recently published data indicate that the paraoxonase-1 (PON1) Q192R genotype-and not as previously shown activity of cytochrome P450 (CYP) 2C19-is the major determinant of metabolic bioactivation of clopidogrel and thereby variability of antiplatelet effect of clopidogrel. We sought to investigate whether the PON1 Q192R gene polymorphism affects platelet reactivity in patients undergoing elective coronary stent placement. The study included 760 consecutive patients undergoing elective coronary stent placement after loading with clopidogrel 600 mg. Platelet function was assessed by adenosine diphosphate-induced (ADP 5 and 20 μmol/L) platelet aggregation and by flow-cytometric analysis of platelet surface protein expression before clopidogrel, at the time of coronary stent placement, and before discharge after coronary stent placement. PON1 Q192R genotype [NM_000446.5:c.575A>G single nucleotide polymorphism (rs662)] was analyzed by TaqMan polymerase chain reaction. Residual platelet aggregation (ADP 5 μmol/L) at predischarge was 8.0% (3.0% to 17.0%) [median (interquartile range)] in PON1 QQ192 patients (n=384), 8.0% (3.0% to 15.0%) in PON1 QR192 (n=304), and 11.0% (3.0% to 18.0%) in PON1 RR192 (n=72; P=0.603). By multivariable linear regression, residual platelet aggregation was not associated with PON1 QQ192/QR192 (partial η(2)<0.001, P=0.728) but with CYP2C19*2 loss-of-function allele (partial η(2)=0.045, P<0.001) as well as any CYP2C19*17 gain-of-function allele (partial η(2)=0.012, P=0.004). All other platelet assays also showed no significant association between PON1 Q192R genotype and antiplatelet effect of clopidogrel. The 1-year incidence of death and myocardial infarction did not differ between PON1 Q192R genotypes. On-treatment platelet reactivity in patients undergoing coronary stent placement after loading with clopidogrel 600 mg was not associated with PON1 Q192R genotype. URL: http://www.clinicaltrials.gov. Unique identifier: NCT00457236.

High Doses of Clopidogrel to Overcome Genetic Resistance: The Randomized Crossover CLOVIS-2 (Clopidogrel and Response Variability Investigation Study 2)

This study sought to determine whether the pharmacokinetic (PK) and pharmacodynamic (PD) responses to high or standard clopidogrel loading doses (LDs) differ according to CYP2C19*2 allele. CYP2C19 loss-of-function alleles are associated with reduced responsiveness to standard clopidogrel doses. Young post-myocardial infarction patients heterozygous (wild type [wt]/*2, n = 43) or homozygous (*2/*2, n = 8) for the CYP2C19*2 genetic variant were matched with patients not carrying the variant (wt/wt, n = 58). All patients were randomized to a 300- or 900-mg clopidogrel LD. The relative reduction in residual platelet aggregation (RR-RPA, %) and the area under the plasma concentration time curve of active metabolite from baseline to 6 h after loading (AUC(0-6)) were compared according to both LD and CYP2C19*2 carriage. The 300-mg LD led to a gene-dose effect for RR-RPA (-65.7% ± 35.9% in wt/wt vs. -48.0% ± 38.4% in wt/*2 vs. -14.6% ± 32.4% in *2/*2; overall p value = 0.003, p = 0.03 for wt/wt versus wt/*2, p = 0.04 for wt/*2 versus *2/*2) with minor effect in *2/*2 carriers. After the 900-mg LD, the effect of the CYP2C19*2 variant on platelet inhibition was fully compensated in wt/*2 carriers but not in *2/*2 carriers (-83.6% ± 25.8% in wt/wt vs.-77.2% ± 26.9% in wt/*2 vs. -29.5% ± 26.8% in *2/*2; overall p value = 0.0003, p = 0.20 for wt/wt versus wt/*2, p < 0.001 for wt/*2 versus *2/*2). A similar pattern was observed for the active metabolite AUC(0-6) according to carriage of CYP2C19*2 for both LDs. There was a significant correlation between PK and PD responses irrespective of the LD. Carriers of CYP2C19*2 display significantly lower responses to clopidogrel with a gene-dose effect. Clopidogrel resistance can be overcome by increasing the dose in heterozygous carriers but not in homozygous carriers. (Clopidogrel and Response Variability Investigation Study 2 [CLOVIS-2]; NCT00822666).

060 Resistance to antiplatelet therapy in the elderly, a real concern. Results of the senior platelet study

Dual antiplatelet therapy effect on platelet inhibition in elderly patients (>75 y/o) is unknown as this growing proportion of ACS are often excluded from clinical trials. To compare on-treatment platelet reactivity under dual antiplatelet therapy of elderly (>75 yrs) vs. younger patients (< 75yrs). We included 652 coronary patients treated by aspirin and clopidogrel in whom platelet response was assessed by light transmission aggregrometry with measure of Maximum (MPA) and Residual Platelet Aggregation (RPA) and VerifyNow with PRU. The population was divided in 5 age categories and compared with elderly patients >75 yrs. Rates of non-response were established using admitted definitions. The mean MD of clopidogrel and aspirin were 86.6 mg and 80.6 mg in patients <75 y/o respectively, and 81.8 mg and 78.6 mg in the elderly. On-clopidogrel platelet reactivity was higher in elderly patients when compared to younger patients whatever the test used (figure). The rate of non-responders was 37.1% in the 105 elderly patients when assessed by PRU>235 and 19,01% in the 547 younger patients (<75 y/o; p<0,001). Results were even more striking when RPA was considered with 67.3% non-responders in the elderly patients vs. 22.8% in the 547 younger patients; p<0,001). Mean ARU was similar in both groups with 440 U in patients under 75 y/o vs. 452 U in elderly (p = 0.8), but the mean AA induced MPA was 5.5% in patients under 75 y/o vs. 10.4% in elderly (p = 0.01). The rate of non-response was 6.25% and 15% with LTA (p = 0.001). Elderly patients have higher levels of on-treatment platelet reactivity for both clopidogrel and aspirin and a 2-fold increase in the rate of non-responders to clopidogrel and a 3-fold increase of non-responders to aspirin, suggesting that they should not be undertreated.

Erratum to: Impact of inflammatory state and metabolic control on responsiveness to dual antiplatelet therapy in type 2 diabetics after PCI: prognostic relevance of residual platelet aggregability in diabetics undergoing coronary interventions

Erratum to: Impact of inflammatory state and metabolic control on responsiveness to dual antiplatelet therapy in type 2 diabetics after PCI: prognostic relevance of residual platelet aggregability in diabetics undergoing coronary interventions

Impact of inflammatory markers on platelet inhibition and cardiovascular outcome including stent thrombosis in patients with symptomatic coronary artery disease

Background There is cumulative evidence that the degree of inflammation correlates with prognosis after percutaneous coronary interventions (PCI). Additionally, there is a cross-link between platelet activation and inflammatory pathways. The aim of the present analysis was to evaluate the association of inflammatory markers and effects of dual antiplatelet therapy on platelet function and outcome in patients undergoing PCI. Methods and results In a pilot study, 157 patients with symptomatic coronary artery disease (CAD) undergoing PCI were consecutively evaluated. Platelet response to clopidogrel and acetylsalicylic acid was assessed using whole blood multiple electrode aggregometry (MEA). Baseline levels of IL-6, RANTES and MCP-1 were measured by Bio-Plex Cytokine assay. C-reactive protein (CRP) was determined by Immunoassay. Levels of IL-6, RANTES, and CRP correlated well with ADP and arachidonic acid (AA)-induced MEA. In a second step, a retrospective analysis of a cohort of 903 PCI-patients was performed to evaluate the association of on-treatment residual platelet aggregation (RPA) and baseline CRP levels on the incidence of myocardial infarction (MI), death and stent thrombosis (ST). Patients suffering a subsequent event had a significantly higher level of baseline CRP and higher RPA compared to patients without events. After multivariate adjustment high baseline CRP and high RPA were independent predictors for combined major events and ST after PCI. Conclusion To our knowledge this is the first study linking inflammation, antiplatelet drug responsiveness and outcome in a large CAD-patient cohort. The results suggest a relevant interaction of these parameters and encourage multimodal therapeutic approaches to treat cardiovascular risk after PCI.

Impact of red blood cell transfusion on platelet activation and aggregation in healthy volunteers: results of the TRANSFUSION study

The underlying mechanisms leading to recurrent ischaemic events or mortality after red blood cell (RBC) transfusion in anaemic acute coronary syndrome patients are poorly understood. The aim of this paper is to determine whether RBC transfusion increases platelet activation and aggregation. In vitro transfusions (n = 45) were performed by the addition of RBCs obtained from transfusion packs to fresh whole blood provided by healthy volunteers. Residual platelet aggregation (RPA) and maximal platelet aggregation (MPA) were assessed before and after in vitro transfusion using light transmission aggregometry performed with four different agonists. Flow cytometry was used for the measurement of P-selectin expression and vasodilatator-stimulated phosphoprotein (VASP) platelet reactivity index (PRI). To control for the effect of haemoconcentration, the same experiments were repeated after hematocrit adjustment using volunteer's platelet poor plasma. Transfusion increased platelet aggregation as measured by RPA with ADP 5 µM (57.7 ± 25 vs. 65.7 ± 24%; P = 0.03) or Collagen 2 µg/mL (59.4 ± 28 vs. 69.7 ± 24%; P = 0.03). There were no significant differences with Arachidonic Acid 1.25 mM or Epinephrine 20 µM and results were similar when MPA was considered. Platelet activation was also increased by transfusion as confirmed by an elevation of P-selectin expression induced by 20 µM ADP (12.2 ± 18 vs. 23.9 ± 18%; P = 0.002) or 50 µM ADP (15.4 ± 18.6 vs.26.8 ± 21.2%; P = 0.004) and an increase in VASP PRI (77.8 ± 6 vs. 81.9 ± 3%; P = 0.03). These effects were all independent of hematocrit. Red blood cell transfusion increases platelet activation and aggregation in vitro in healthy volunteers. This effect might be mediated through the P2Y(12) activation pathway.

Impact of inflammatory state and metabolic control on responsiveness to dual antiplatelet therapy in type 2 diabetics after PCI: prognostic relevance of residual platelet aggregability in diabetics undergoing coronary interventions

Type-2 diabetes is accompanied by a prothrombotic state influenced by endothelial dysfunction, inflammatory condition and platelet hyperreagibility. We aimed to characterize the relationship of inflammation and residual platelet aggregability (RPA) under antiplatelet therapy with regard to prognosis in an unselected PCI-cohort of diabetics. In a first step, a consecutive collective of 75 type 2 diabetics compared to 153 non-diabetic controls was evaluated at the time of PCI. Inflammatory markers, Interleukin 6 and C-reactive protein were measured by immunoassays. ADP and Aspirin assays were performed by multiple electrode aggregometry. Then, we consecutively evaluated ADP-induced RPA in 542 diabetics and 1,161 non-diabetics undergoing PCI and treated by standard antiplatelet therapy. Major CV-events were assessed at 30 days after PCI. Inflammatory markers were significantly increased in diabetics with peri-interventional hyperglycemic state and inversely correlated with responsiveness to clopidogrel and aspirin. In a large scale cohort, diabetics showed a higher RPA compared to non-diabetics (median 38.1 vs. 28.8%; p < 0.001). After adjustment for relevant co-factors, diabetes remained a strong predictor for increased RPA (OR 4.39; 95% CI 1.95-6.83; p < 0.001). Furthermore, diabetics with high RPA had an increased risk for 30-day MI and CV-death than diabetics with low RPA (adjusted HR 1.05; 95% CI 1.02-1.07; p < 0.001). We demonstrate that peri-interventional inflammatory degree and glycaemic control correlate with decreased antiplatelet drug responsiveness in diabetics. In addition, we identified high RPA as strong predictor for short-term CV-events in this group. Therefore, approaches to treat these entities are needed to improve outcome in diabetics undergoing PCI.

Impact of Cytochrome P450 2C19 Loss-of-Function Polymorphism and of Major Demographic Characteristics on Residual Platelet Function After Loading and Maintenance Treatment With Clopidogrel in Patients Undergoing Elective Coronary Stent Placement

The aim of this study was to evaluate the relative impact of demographic and clinical variables versus the cytochrome P450 2C19 (CYP2C19) polymorphism on antiplatelet effects of clopidogrel. Platelet responses to clopidogrel show a marked interindividual variability with substantial impact on clinical outcome. Several demographic and clinical characteristics as well as a polymorphism of CYP2C19 have been described as predictors for a low response to clopidogrel. This analysis enrolled 760 patients undergoing elective coronary stent implantation after loading with 600 mg of clopidogrel. Residual platelet aggregation was determined by optical aggregometry (adenosine diphosphate 5 micromol/l) before discharge. We analyzed the predictive value of the CYP2C19*2 polymorphism and baseline variables for an insufficient antiplatelet response by multivariable regression analysis and classification and regression trees analysis and determined the proportion responsible for the antiplatelet response of these predictors by multivariable linear regression analysis. Major independent predictors for an insufficient antiplatelet response to clopidogrel were CYP2C19*2 carrier status (odds ratio [OR]: 2.74; 95% confidence interval [CI]: 1.93 to 3.90) together with age (OR: 1.03; 95% CI: 1.01 to 1.05), diabetes mellitus (OR: 1.75; 95% CI: 1.19 to 2.56), and body mass index (OR: 1.06; 95% CI: 1.02 to 1.11). The classification and regression trees analysis demonstrated that CYP2C19*2 carrier status followed by diabetes mellitus was the best discriminator between a sufficient and an insufficient antiplatelet response to clopidogrel. The full linear regression model including all these parameters could only explain 11.5% of the antiplatelet response (5.2% by CYP2C19*2 carrier status alone). Thus, our study does not suggest that, in patients critically dependent on adequate platelet inhibition, genotyping alone or in combination with clinical factors can replace phenotyping of platelet function. (Effect of Clopidogrel Loading and Risk of PCI [EXCELSIOR]; NCT00457236).

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 …

009 Red Blood Cell Transfusion Increase Platelet Aggregation: a potential mechanism for increased mortality in transfused patients

Erythrocytes transfusion is an independent risk factor for recurrent ischemic events and mortality in patients suffering from acute coronary syndrome. There is no evidence regarding the underlying mechanism of such association. We hypothesized that red blood cell transfusion would activate platelet aggregation and we sought to identify which are the pathway involved in this activation process. Healthy volunteers (n=15) provided blood samples that were mixed with red blood cell (tRBC) obtained from transfusion packs. We explored platelet activation using light transmission agregometry with four different agonist (ADP, Arachidonic Acid (AA), Collagen and Epinephrin) in 10 volunteers and with flow cytometry for P-selectin and VASP in 5 volunteers. Measures were obtained at baseline (whole blood from healthy volunteers), after in vitro transfusion with a 1:4 ratio of tRBC and after in vitro transfusion with a 1:4 ratio of tRBC and hematocrit adjustement with platelet poor plasma. All experiment were performed in duplicates. Theses are preliminary results from the ongoing TRANSFUSION study. Numerical values are given in table 1. 1/ RBC transfusion activates platelet aggregation thought ADP and AA pathway. 2/ This effect was confirmed by increase in P-Selectin platelet content with flow cytometry and is independent of an increase in hematocrit. 3/ P2Y12 activation pathways is involved with an increase in VASP. Red Blood Cell transfusion activates platelet thought ADP and AA pathway in healthy volunteers. This may explain the independent association between transfusion and recurrent ischemic events including mortality in ACS patients. Results of tRBC induced platelet aggregation n=10 n=5 Technique Aggregometry (Residual Platelet Aggregation %) P-Selection % PRI (%) Agonist ADP AA Collagen Epinephrin 20μM ADP 50μm ADP VAS P Baseline 58,0 79,5 61,6 65,0 33,6 40,2 68,4 After tRBC (no adjustement) 70,3 89,1 72,5 59,6 50,5 56,4 83,9 After tRBC (adjusted with PPP) 48,1 54,5 74,8 p value 0,03 * 0,04 * 0,13 0,15 ND ND ND ND=not done * <0,05

The antiplatelet effect of aspirin is reduced by proton pump inhibitors in patients with coronary artery disease

ObjectiveTo evaluate the effect of proton pump inhibitors (PPIs) on the platelet response to aspirin in patients with coronary artery disease (CAD).DesignCase–control study.Patients418 stable patients with CAD, 54 of whom...

Early but not late stent thrombosis is influenced by residual platelet aggregation in patients undergoing coronary interventions

Recent studies suggest a relevant association of post-interventional residual platelet aggregation (RPA) under therapy with oral platelet inhibitors and the occurrence of atherothrombotic events. The influence of post-interventional RPA on the incidence of stent thrombosis (ST) has not been sufficiently evaluated in consecutive unselected cohorts of percutaneous coronary intervention (PCI) patients. The aim of this observational study was to investigate the impact of RPA on the incidence of ST within 3 months in patients treated with dual antiplatelet therapy. The study population included a consecutive cohort of 1019 patients treated with PCI [n = 741 bare-metal stent (BMS) and n = 278 drug-eluting stent (DES)] due to symptomatic coronary artery disease. Residual platelet activity was assessed by adenosine disphosphate (20 micromol/L)-induced PA after 600 mg clopidogrel loading dose. Maximum RPA was measured as peak of aggregation, final RPA was measured 5 min after addition of agonist. The primary endpoint was the occurrence of ST within 3 months defined according to academic research consortium (ARC) criteria. Final and maximum RPA were independent predictors of ST after 3 months. In secondary analysis, the observed effects were independently associated with early ST (HR 1.05, 95% CI 1.01-1.08 and HR 1.05, 95% CI 1.01-1.09, P < 0.01, respectively). However, incidence of 3-month late stent thrombosis (LAT) was not influenced by post-interventional RPA in multivariable analysis. Post-interventional RPA is associated with the occurrence of early ST in patients treated with either BMS or DES; however, there is no predictive value of RPA for the incidence of 3-month LAT, suggesting the involvement of other possible mechanisms like discontinuation of antiplatelet therapy.

Effect of comedication with proton pump inhibitors (PPIs) on post-interventional residual platelet aggregation in patients undergoing coronary stenting treated by dual antiplatelet therapy

Introduction Currently, there is an intense debate about whether comedication with proton pump inhibitors (PPIs) weakens the antiplatelet effect of clopidogrel in patients undergoing coronary stent implantation. Competing mechanisms on the hepatic cytochrome 2C19 level are proposed. The aim of this study was to assess the impact of PPI treatment on clopidogrel response by measuring the ex vivo platelet aggregation in patients with coronary intervention. Methods 1425 consecutive patients with symptomatic coronary artery disease undergoing percutaneous coronary intervention were enrolled in this single centre study. PPI comedication was defined as PPI intake ≥ 1 week prior to a 600 mg clopidogrel loading dose. PPI treatment was based on physician preference. Residual platelet aggregation (RPA) was measured by optical aggregometry. To correct for potential selection bias, propensity score matching was applied. Results RPA was significantly higher in PPI-treated patients compared with non-PPI-users (final aggregation 34.0% vs. 29.8%, p < 0.001). Low responder defined as RPA in the upper tertile were more often found in PPI-users. After adjustment for relevant confounders, PPI treatment was independently associated with higher RPA-levels. Discussion We demonstrated that peri-procedural co-administration of PPIs significantly decreases the effect of clopidogrel on RPA. To assess if clopidogrel-PPI interaction results in a higher susceptibility for cardiovascular events remains subject to further investigations.

Smoking promotes clopidogrel-mediated platelet inhibition in patients receiving dual antiplatelet therapy

Background High on-treatment residual platelet reactivity is associated with an increased risk of adverse events after coronary stenting. Recent data suggest that cigarette smoking might enhance clopidogrel-mediated platelet inhibition. We therefore sought to investigate the influence of cigarette smoking on clopidogrel- and aspirin-mediated platelet inhibition after percutaneous intervention with stent implantation. Patients and methods Platelet aggregation was assessed by the VerifyNow P2Y12 and aspirin assays in 102 patients on dual antiplatelet therapy 24 hours after peripheral, coronary or carotid artery stenting. Among these, there were 33 nonsmokers, 29 former smokers and 40 current smokers. Patients in the fourth quartile of the VerifyNow assays were considered as patients with high on-treatment platelet reactivity. Results Current smokers had significantly lower P2Y12 Reaction Units compared with nonsmokers (p = 0.028). Former smokers also had lower adenosine diphosphate (ADP)-inducible platelet aggregation than nonsmokers, but the difference was not significant (p = 0.52). A high on-treatment residual ADP-inducible platelet aggregation was more common among nonsmokers than among current smokers (14 vs 5; p = 0.004). In a multivariate regression analysis smoking was an independent influencing variable for post-treatment ADP-inducible platelet reactivity (p = 0.026). Aspirin-mediated platelet inhibition showed no significant differences between nonsmokers and former smokers or current smokers (p > 0.3). Conclusion By in vitro testing, cigarette smoking is associated with enhanced clopidogrel- but not aspirin-mediated platelet inhibition. The clinical implications have to be evaluated in large prospective trials.

Platelet count, not oxidative stress, may contribute to inadequate platelet inhibition by aspirin

Background Several patient characteristics have been shown to increase the risk of inadequate platelet inhibition by aspirin, yet underlying mechanisms remain mostly unknown. We explored whether oxidative stress, via isoprostane formation, was associated with inadequate platelet response to aspirin. Additionally, we sought to investigate whether individual pre-selected demographic, hematological or biochemical parameters further increased the risk of inadequate platelet response to aspirin. Methods Two hundred consecutive subjects suffering from stable coronary artery disease and under daily aspirin therapy were enrolled in our study. Inadequate platelet response to aspirin was defined as residual platelet aggregation ≥ 20% per arachidonic acid-induced light transmission aggregometry. Morning urinary samples were used to determine levels of isoprostanes (8-iso-PGF 2α) using an enzyme immunoassay. Results Eight subjects were deemed to present inadequate platelet response to aspirin. Wide intersubject variability was observed in urinary 8-iso-PGF 2α levels. However, levels were similar between aspirin responders and non-responders. Patients with inadequate platelet response to aspirin had higher platelet counts and received the lowest daily aspirin dose when compared to responders, suggesting subtherapeutic aspirin therapy due to increased platelet production. Only platelet count remained independently predictive of inadequate platelet response to aspirin in a multiple logistic regression model. Conclusions Urinary 8-iso-PGF 2α levels, a reflection of systemic oxidative stress, did not appear to contribute to impaired platelet responsiveness to aspirin, while increased platelet production may partly explain this phenomenon.

Individualized antiplatelet therapy

Safeguarding of antiplatelet drug efficacy represents a cornerstone for the optimal treatment of patients with symptomatic coronary artery disease requiring coronary interventions. This means a challenge to modern cardiology since there has been cumulative evidence, that response to common oral antiplatelet therapy is a highly variable phenomenon underlying various mechanisms. It is known, that particular risk groups exhibit a high residual platelet aggregability (RPA) despite conventional antiplatelet therapy. Additionally, a relevant association between high RPA and recurrent ischaemic events after PCI exists. Individualization of antiplatelet therapy by dose increase or alternative application of novel P2Y12-receptor antagonists might lead to improved cardiovascular outcome in patients with poor responsiveness to conventional antiplatelet therapy. Identification of risk patients who might benefit from tailored therapy by increased net benefit without excess of major bleedings means a challenge. Clinical risk scores might help in the process of risk stratification and therapeutic decision. Subsequently, literature on risk assessment for antiplatelet drug responsiveness and different strategies will be discussed to identify patients who might benefit from personalized antiplatelet strategies.

Dose Effect of Clopidogrel Reloading in Patients Already on 75-mg Maintenance Dose

Clopidogrel loading has mostly been studied in clopidogrel-naïve patients. Whether clopidogrel-treated patients readmitted for an acute coronary syndrome or percutaneous coronary intervention can benefit from a new load of clopidogrel and at what dose remain unknown. Our aim was to evaluate the impact of 3 different strategies of administration of a loading dose of 900 mg clopidogrel in patients already treated with a maintenance dose of 75 mg clopidogrel for at least 7 days on residual platelet aggregation. Patients treated long term by clopidogrel 75 mg/d were assigned to receive a first loading dose of 300, 600, or 900 mg clopidogrel and 4 hours later a second loading dose of 600, 300, or 0 mg, respectively, to achieve a total loading dose of 900 mg in all patients. Platelet aggregation was evaluated at baseline, at 4 hours after the initial load (and before second load), and at 24 hours using light transmission aggregometry with 20 micromol ADP and the point-of-care assay VerifyNow P2Y(12). The primary objective of the study was to evaluate the inhibition (relative change) of residual platelet aggregation (percentage of IRPA) between 600- and 900-mg first loading at 4 hours. IRPA at 24 hours also was evaluated as a secondary objective, as well as the rate of suboptimal response at 4 hours defined as IRPA <10%. We included 166 consecutive patients with acute coronary syndromes (n=80, 48%) or stable coronary artery disease (n=86, 52%). Baseline characteristics were similar in the 3 dose groups. A significant stepwise increase was found in percentage IRPA assessed at 4 hours in patients initially assigned to 300 versus 600 versus 900 mg (30.7% versus 40.3% versus 64.0%, respectively; P=0.0024). The difference in percentage IRPA at 4 hours was not significant between 300 and 600 mg but was significant between 600 and 900 mg and between 300 and 900 mg. Percentage IRPA assessed at 24 hours when all patients had received 900 mg did not differ between the 3 loading regimens. The rates of suboptimal response (IRPA <10% at 4 hours) were 23.6%, 20.4%, and 5.3% with 300, 600, and 900 mg, respectively (P=0.02 for all). In patients treated long term with 75 mg clopidogrel, a new loading dose of 900 mg improves IRPA and reduces poor and/or slow response to clopidogrel significantly more than that obtained with 300 or 600 mg.

CYP2C19 and Nongenetic Factors Predict Poor Responsiveness to Clopidogrel Loading dose after Coronary Stent Implantation

To investigate an association of responsiveness to clopidogrel loading dose with genotypes of cytochrome P450 (CYP) 2C19, other CYP isozymes and nongenetic factors in patients with coronary artery disease. Genotyping for CYP2C19 (*2, *3 and *17), CYP3A4*1B and CYP3A5*3 variants was performed in patients (n = 237) who underwent percutaneous coronary intervention. Adenosine diphosphate-induced platelet aggregation was determined after first administration of 600 mg clopidogrel. CYP2C19*2 carriers showed significantly increased residual platelet aggregation (RPA) (OR: 4.6; 95% CI: 2.5-8.7; p < 0.0001) compared with noncarriers. All other polymorphisms had no influence on RPA. For the development of a risk score for better prediction of RPA, CYP2C19*2 genotype and previously identified nongenetic risk factors (age >65 years, Type 2 diabetes mellitus, decreased left ventricular function, renal failure and acute coronary syndrome) were analyzed. Multivariable logistic regression analysis showed a significant correlation of the nongenetic factors (chi (2) = 5.32; p = 0.021) and CYP2C19*2 (chi (2) = 21.31; p < 0.0001) with high RPA, and an even higher association for the combination of both (chi (2) = 25.85; p < 0.0001). Prediction of responsiveness after clopidogrel loading dose may substantially be improved by adding CYP2C19*2 genotype to nongenetic risk factors.