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The optimal duration and cancer risks of antiplatelet therapy following percutaneous coronary intervention (PCI) are unclear. We compared cancer and all-cause mortality after dual antiplatelet therapy (DAPT) for the combination of clopidogrel and aspirin (ASA) versus ASA alone over 18 months follow-up in event-free patients at 12 months DAPT from the Health Insurance Review and Assessment (HIRA) dataset via the Korean Outcomes Registry Evaluating Antithrombotics (KOREA). We selected PCI patients who were event free for 12 months and maintained a consistent antiplatelet regimen for 18 more months. The primary endpoints were any cancer and all-cause mortality at 30 months follow-up after PCI. From 320,351 screened post-PCI patient HIRA records, we excluded 294,413 and qualified 25,938, constituting DAPT (n=10,992) and ASA (n=14,946) groups. The Propensity Score Matching (PSM), and Inverse Probability of Treatment Weighting (IPTW) revealed no significant differences in background demographics and clinical characteristics for DAPT versus ASA patients. At 30-months post-PCI, after massive (>91 %) exclusions, cancer risk was higher for continuous DAPT [455 (4.15 %) vs 606 (4.04 %); HR=1.221; 95 %CI: 1.061-1.405; p=0.005], which remained significant by PSM (p=0.006) or IPTW (p=0.007), while all-cause mortality was similar [136 (1.24 %) vs 192 (1.28 %) HR=0.999; 95 %CI: 0.736-1.135; p=0.993]. This analysis suggests a potential mild excess cancer risk, but no mortality benefit in Korean post-PCI patients treated with DAPT for an additional 18 months beyond conventional 12 months DAPT. These data are not supporting continuing DAPT for more than one year in East Asians. Analysing cancer types and assessing potential cancer association with bleeding are warranted.

Objective: The impact of thienopyridine reloading on clinical outcomes, and residual high platelet reactivity (HPR) is unclear. We sought to compare the HRP-related effect of prasugrel and clopidogrel reloading in the already clopidogrel-loaded patients undergoing percutaneous coronary intervention (PCI)., Materials and Methods: In this prospective, two-center, randomized, open-label study, patients with HPR who had undergone PCI after a clopidogrel (300-600mg) loading dose (LD) were enrolled. Among screened (n=153), HPR was determined in seventy-six patients, who were randomized to either repeated clopidogrel (300mg LD, followed by 75mg MD daily) or prasugrel (20mg LD, followed by 5mg MD daily). The primary endpoint was HPR at 24h after PCI, as determined by the VerifyNow assay. The rates of sustained high and low platelet reactivity, periprocedural myocardial injury (PMI) and 30-day clinical outcomes were also assessed., Results: Higher inhibition of platelet reactive units (PRU) was observed in the prasugrel group than after clopidogrel reloading (Pre-PCI: 284.4±32.0 vs 279.5±32.5, p=0.504; Post-PCI: 100.0±67.0 vs 202.9±65.8, p<0.001; 30days: 170.8±69.8 vs 215.1±62.4, p=0.007). There were less HRP post-PCI after prasugrel compared with the clopidogrel group (2.7 vs 36.1%, p<0.001). However, reloading with prasugrel did not reduce PMI compared to clopidogrel (36.8% vs 39.5%, p=0.813)., Conclusion: Prasugrel reloading led to a greater reduction in HPR, but similar with clopidogrel PMI in post-PCI patients. Larger randomized evidence is needed for optimization of loading strategies with thienopyridines., Clinical Trial Registration Information: NCT01609647., (Copyright © 2016 Elsevier Ireland Ltd. All rights reserved.)

The optimal utilization of antiplatelet therapy in patients with renal impairment (RI) following acute coronary syndromes (ACS) represents an urgent, unmet and yet unsolved need with regards to the choice of agents, duration of treatment and potential dose/regimen adjustment. The lack of any large randomized trials designed and powered specifically in such high-risk patients, absence of the uniformed efficacy and safety data reporting policy to the FDA and endless overoptimistic publications based on post hoc analyses of primary trials sometimes exaggerating benefits and hiding risks, clouds reality. In addition, triaging RI patients is problematic due to ongoing kidney deterioration and the fact that such patients are prone to both vascular occlusions and bleeding. The authors summarize available FDA-confirmed evidence from the latest trials with approved antiplatelet agents, namely clopidogrel (CAPRIE, CURE, CREDO, CLARITY, CHARISMA); prasugrel (TRITON, TRILOGY); ticagrelor (PLATO, and PEGASUS); and vorapaxar (TRACER and TRA2P) in RI patient cohorts on top of aspirin as part of dual antiplatelet therapy (DAPT). We deliberately avoided any results unless they were verified by the FDA, with the exception of the recent PEGASUS, since Agency reviews are not yet available. Despite differences among the trials and DAPT choices, RI patients universally experience much higher (HR = 1.3-3.1) rates of primary endpoint events, and bleeding risks (HR = 1.7-3.6). However, only ticagrelor increases creatinine and uric acid levels above that of clopidogrel; has the worst incidence of serious adverse events, more adverse events, and inferior outcomes in patients with severe (eGFR <30 ml/min), especially in the lowest (eGFR <15 ml/min) RI subsets. Clopidogrel, prasugrel and vorapaxar appear safer. Moreover, less aggressive half dose (5 mg/daily) prasugrel and strict DAPT, are well justified in RI, but not predominantly triple strategies with vorapaxar as tested in TRA2P and especially in TRACER. In conclusion, data from clinical trials, their sub-studies and affiliated FDA reviews indicate that RI cause more vascular occlusions and bleeding in ACS patients treated with DAPT. Among the novel antiplatelet agents, prasugrel and vorapaxar, but probably not ticagrelor, offer advantage in RI patients.

Background: ST-elevated myocardial infarction (STEMI) holds the highest early mortality among patients with acute coronary syndromes. Despite numerous claims of clinical benefits and superiority over clopidogrel, there are no head-to-head outcome randomized clinical trials (RCTs) directly comparing novel antithrombotic agents in STEMI. Moreover, since most regulatory approvals are based on a single RCT's results, their meta-analyses are rare to compare death rates. We analyzed the 30-day mortality in STEMI patients who underwent percutaneous coronary intervention (PCI) and were treated with antithrombotic agents compared to clopidogrel as a reference., Methods and Results: Altogether, 10 RCT's and 1 retrospective study with a total number of 26,658 STEMI patients were included. Random-effects model with Mantel-Heanszel weighting was used to pool outcomes into a meta-analysis. Therapy with clopidogrel was associated with 2.76% 30-day STEMI mortality which was similar to that of ticagrelor (2.6%; OR=0.9395 [CI=0.76 to 1.17; p=0.58]), and for bivalirudin (2.8%; OR=1.02 [CI=0.82 to 1.27; p=0.86]), but was slightly higher for heparin (3.0%; OR=1.08 [CI=0.86 to 1.35; p=0.52]). There was a trend towards lower mortality after tirofiban (2.1%; OR=0.77 [CI=0.52 to 1.13; p=0.20]), and cangrelor (1.7%; OR=0.59 [CI=0.29 to 1.20; p=0.19]), although the sample size for both agents was woefully small. The only agent which offers a significant 30-day mortality benefit in STEMI was prasugrel with significant lowest 1.75% death rate (OR=0.63 [CI=0.46 to 0.86; p=0.03])., Conclusions: Among antithrombotic agents, prasugrel, but not ticagrelor, offers significant 30-day mortality benefit over clopidogrel in PCI-treated STEMI patients justifying short-term use in such a high-risk population., (Copyright © 2015 Elsevier Ireland Ltd. All rights reserved.)

The aim of this study was to triage platelet reactivity and adverse vascular outcomes after dual antiplatelet therapy due to percutaneous coronary intervention (PCI) dependent on CYP2C19*2 and CYP2C19*3 genotypes in patients with coronary artery disease. Fifty-five patients with coronary artery disease were studied serially pre-PCI and post-PCI. Platelet reactivity was assessed by conventional light transmission aggregometry, VerifyNow Analyzer, and thromboelastography with platelet mapping. Genetic testing was performed with allele-specific real-time polymerase chain reaction. Adverse events included vascular death, acute myocardial infarction, repeated PCI, definite stent thrombosis, and angina recurrence. The common genotype (GG) was found in 39 patients, heterozygous polymorphism CYP2C19 (GA) G681A allele was detected in 14 patients, and the rare homozygous polymorphism CYP2C19 (AA) G681A allele was exhibited in 2 patients. There were no CYP2C19*3 (Trp212Ter) carriers among index patients. The platelet reactivity was higher in patients with heterozygous and homozygous carriers compared with GG genotype. The largest differences were observed among GG, GA, and AA genotypes, which correlated with the average values of platelet aggregation (P = 0.02). There was a significant link between adverse events and high platelet reactivity assessed by light transmission aggregometry (P = 0.002). We found a trend between different genotype and VerifyNow readings (P = 0.057); moreover, their cumulative impact on adverse events was significant (P = 0.041). Platelet reactivity is higher in patients with heterozygous and homozygous carriers of CYP2C19*2 versus common genotype and may predict an increased risk of clopidogrel response variability and/or experiencing adverse cardiac events.

Objective: To detect residual platelet aggregation following the switch from generic (GC) to brand clopidogrel (BC) in male patients after ST-elevated myocardial infarction (STEMI)., Methods: The study was designed as an open-label, prospective cohort trial. Thirty-three male STEMI patients were enrolled. All patients received dual antiplatelet therapy with aspirin (100 mg/daily) and one of six GC at a daily dose of 75 mg. After 2 weeks, all patients were switched to BC. Adrenaline- and adenosine diphosphate (ADP)-induced platelet aggregation was assessed twice: on day 14 (before the switch) and on day 21 (after 1 week of BC therapy)., Results: Adrenaline-induced platelet aggregation did not differ among clopidogrel formulations. In contrast, residual 5 µM ADP-induced platelet aggregation after BC differs from GC by 14% (28.0 ± 2.5 vs. 23.9 ± 2.1%; p = 0.03). When 20 µM ADP was used as agonist, the difference was smaller (36.2 ± 2.9 vs. 34.6 ± 2.8%) but still significant (p = 0.04) favoring BC., Conclusions: After 2 weeks of therapy, switching from GC to BC was associated with a mild but significant reduction in ADP-induced platelet aggregation in male post-STEMI patients. The observed differences between GC and BC should be confirmed in a larger randomized study, but may represent a risk in underdeveloped countries, where GC therapy is mandatory for post-MI inpatients.

Administration of a P2Y 12 -receptor antagonist in addition to aspirin is mandatory in patients with acute coronary syndromes (ACS) or undergoing percutaneous coronary intervention (PCI) to reduce the occurrence of thrombotic events; however, their impact on mortality and stroke is unclear. We aimed to evaluate the influence of moderate (clopidogrel) or potent (prasugrel/ticagrelor) P2Y 12 -receptor inhibition on major cardiovascular outcomes among patients with ACS or undergoing PCI. Systematic literature search was performed to find randomised, controlled clinical trials comparing the clinical impact of clopidogrel with placebo or prasugrel/ticagrelor versus clopidogrel. Outcome measures included cardiovascular death, myocardial infarction (MI), total stroke and intracranial haemorrhage (ICH). Random-effects model with Mantel-Heanszel weighting was used to pool outcomes into a meta-analysis. Four studies comparing clopidogrel with placebo and five trials comparing clopidogrel with new P2Y 12 -receptor inhibitors were identified including a total of 107,473 patients. Compared to placebo, clopidogrel reduced the risk of cardiovascular death (odds ratio [OR]: 0.93; 95% confidence interval [CI]: 0.87-0.99, p=0.02), MI (OR 0.80; 95%CI 0.74-0.88, p<0.00001) and stroke (OR 0.84; 95%CI 0.72-0.97, p=0.02), without influencing risk for ICH (OR 0.96; 95%CI 0.69-1.33, p=0.79). Treatment with prasugrel/ticagrelor provided additional benefit over clopidogrel regarding cardiovascular mortality (OR 0.86; 95%CI 0.78-0.94, p=0.002) and MI (OR: 0.83; 95%CI 0.74-0.93, p<0.001), but no advantage in stroke (OR: 1.06; 95%CI 0.88-1.26, p=0.55) and in ICH (OR: 1.16; 95%CI 0.75-1.81; p=0.49) was observed. Increased potency of P2Y 12 -receptor inhibition is associated with decreased risk in cardiovascular death and MI; however, this association is not true in case of stroke, where potent P2Y 12 -receptor antagonists have no incremental benefit over clopidogrel.

TRial to assess Improvement in Therapeutic Outcomes by optimizing platelet inhibitioN with prasugrel Thrombolysis In Myocardial Infarction 38 (TRITON-TIMI 38) was a Phase 3, randomized, double blind, parallel-group, multinational head-to-head study of prasugrel vs. clopidogrel both on top of aspirin. The primary end point was the rate of cardiovascular death, nonfatal myocardial infarction (MI), or stroke, and was reached in 12.1% of patients treated with clopidogrel and in 9.9% of patients randomized to prasugrel, suggesting impressive vascular outcome benefit of prasugrel over clopidogrel. However, this overoptimistic interpretation of the trial results was challenged by the Food and Drug Administration (FDA) Secondary Review, which revealed several shortcomings with TRITON design and data interpretation including the front-loaded nature of prasugrel benefit. Recently, following approval with black box warning, the FDA posted the complete documentation set (Action Package), revealing additional information including the timing of loading in TRITON, and how it affects vascular outcomes. The detailed FDA communications revealed highly significant correlation of the loading dose delay and primary efficacy outcomes favoring prasugrel. Indeed, when patients in TRITON were loaded early, or pretreated, the benefit of prasugrel was nonexistent. However, the longer it takes during or especially after PCI to load with thienopyridine, the more prasugrel benefit occurs. Considering that pretreatment with clopidogrel was disallowed; that three quarters of patients in TRITON were loaded during or after intervention; and that prasugrel was used at the 60-mg loading dose, which is over three times more potent than 300 mg clopidogrel, the claim of superiority of prasugrel over clopidogrel is not valid due to inappropriate use of clopidogrel., (Copyright © 2011 Elsevier Inc. All rights reserved.)

Background: A growing number of observational studies suggest that high on-clopidogrel platelet reactivity (HPR) is associated with recurrent thrombotic events after percutaneous coronary intervention. We aimed to perform an updated systematic review and meta-analysis on the clinical relevance of HPR to summarize the available evidence and to define more precise effect estimates., Methods: Relevant observational studies published between January 2003 and February 2010 were searched that presented intent-to-treat analyses on the clinical relevance of HPR measured with an adenosine diphosphate (ADP)-specific platelet function assay. The main outcome measures were cardiovascular (CV) death, definite/probable stent thrombosis (ST), nonfatal myocardial infarction (MI), and a composite end point of reported ischemic events. The outcome parameters were pooled with the random-effect model via generic inverse variance weighting., Results: Twenty studies comprising a total number of 9,187 patients qualified. High on-clopidogrel platelet reactivity appeared to be a strong predictor of MI, ST, and the composite end point of reported ischemic events (odds ratios [95% CI]: 3.00 [2.26-3.99], 4.14 [2.74-6.25], and 4.95 [3.34-7.34], respectively; P < .00001 for all cases). According to the meta-analysis, patients with HPR had a 3.4-fold higher risk for CV death compared with patients with normal ADP reactivity (odds ratio 3.35, 95% CI 2.39-4.70, P < .00001). Although there were large differences in the methodology as well as in the definition of HPR between studies, the predicted risk for CV death, MI, or ST was not heterogeneous (I(2): 0%, 0%, and 12%, respectively; P = not significant for all cases)., Conclusions: High on-clopidogrel platelet reactivity, measured by an ADP-specific platelet function assay, is a strong predictor of CV death, MI, and ST in patients after percutaneous coronary intervention., (2010 Mosby, Inc. All rights reserved.)

The PLATO trial revealed a remarkable advantage of ticagrelor over clopidogrel in ACS patients. Unless the regulatory authorities discover serious flaws with the study, which is unlikely, the drug may substantially change the present landscape of oral antiplatelet therapy, especially in high-risk patients. Despite a somewhat unfavourable safety profile, ticagrelor has a lot of room to compensate for these well-defined side effects based on a documented absolute mortality reduction, solid prevention of MI, and convincing pattern of benefit growing over time.

Background: Clopidogrel, aspirin (ASA), and the fixed-dose combination of extended-release dipyridamole and ASA (ER-DP+ASA) are widely used in post-stroke regimens., Objective: This study compared serial changes in multiple biomarkers of platelet activation with ER-DP+ASA and clopidogrel with or without ASA in patients with type 2 diabetes mellitus and a history of transient ischemic attack (TIA)., Methods: This was a randomized, single-blind pilot study conducted at an outpatient center in the United States. Eligible patients were aged 40 years and had a diagnosis of type 2 diabetes and a history of TIA. Patients were allocated to receive ER-DP+ASA 200/25 mg BID, clopidogrel 75 mg/d, or clopidogrel 75 mg/d plus ASA 81 mg/d. Multiple platelet bio-markers were assessed at baseline, day 15, and day 30 using aggregometry, cartridge-based platelet function analyzers, and flow cytometry. The primary end point was the change in platelet receptor expression after 30 days of therapy. Compliance and tolerability were monitored by measuring plasma dipyridamole levels and recording all episodes of headache and vomiting., Results: The study enrolled 60 consecutive patients (20 per treatment arm), all of whom completed the study. There were no significant differences between treatment arms, although the ER-DP+ASA group had a numerically greater mean age, higher proportion of men, and a greater prevalence of vascular disease and smoking compared with the other groups. There were no deaths or serious adverse events during the study, including symptoms attributable to cerebral ischemia, worsening of diabetes, or cerebral or systemic bleeding. Three patients in the ER-DP+ASA group and 1 in the clopidogrel plus ASA group reported headache during the first several days of therapy; 1 patient in the clopidogrel monotherapy group experienced transitory nausea and vomiting. ER-DP+ASA was associated with a significantly delayed (day 30) reduction in expression of glyco-protein (GP) Ilb/IIIa activity (P = 0.02), platelet-endothelial cell adhesion molecule 1 (PECAM-1) (P = 0.03), GP Ib (P = 0.001), vitronectin (P = 0.001), P-selectin (P = 0.001), lysosome-associated membrane protein 1 (P = 0.001), and cluster of differentiation 40 ligand (P = 0.01), as well as significant inhibition of the intact (P = 0.01) and cleaved (P = 0.01) epitopes of protease-activated receptor 1. Clopidogrel monotherapy, on the other hand, was associated with significant inhibition of adenosine diphosphate-induced platelet aggregation (P = 0.001), closure-time prolongation (P = 0.01), and reduction in measurements on the rapid platelet function assay-ASA at day 15 (P = 0.001). Expression of PECAM-1 (P = 0.03) and GP IIb/IIIa activity (P = 0.01) was reduced at day 15 in clopidogrel-treated patients. The addition of ASA to clopidogrel was associated with significant inhibition of collagen-induced platelet aggregation (P = 0.001) and diminished formation of platelet-monocyte microparticles at days 15 (P = 0.02) and 30 (P = 0.03)., Conclusions: In these patients with type 2 diabetes and a history of TIA, patterns of platelet inhibition differed significantly according to whether treatment was with ER-DP+ASA or clopidogrel with or without ASA. The antiplatelet activity of clopidogrel was more potent and occurred earlier (15 days), whereas ER-DP+ASA was associated with moderate downregulation of multiple activation-dependent platelet receptors that occurred later (30 days).

Background: Clopidogrel is widely used in diabetic patients after vascular events; however, the ability of this thienopyridine to yield additional antiplatelet protection on top of aspirin has never been explored in a controlled study with comprehensive assessment of platelet activity. The objective of this study was to compare the antiplatelet profiles of clopidogrel + aspirin in combination (C + ASA) versus aspirin alone (ASA) in patients with type 2 diabetes mellitus., Methods: Seventy patients with documented diabetes already treated with antecedent aspirin were randomly assigned to receive C + ASA or ASA in the PLUTO-Diabetes trial. Platelet studies included adenosine diphosphate-, collagen-, and arachidonic acid-induced aggregometry; PFA-100 (Dade-Behring, Miami, FL) and Ultegra (Accumetrics, San Diego, CA) analyzers; and expression of 6 major receptors by flow cytometry at baseline and at day 30 after randomization., Results: There were no differences in the baseline clinical and platelet characteristics between the C + ASA and ASA groups, or subsequent significant changes in platelet biomarkers in the ASA group, except for diminished collagen-induced aggregation (P = .02). In contrast, when compared with the ASA group, therapy with C + ASA resulted in significant inhibition of platelet activity assessed by adenosine diphosphate aggregation (P = .0001); closure time prolongation (P = .0003) and reduction of platelet activation units with Ultegra (P = .0001); and expression of platelet/endothelial cell adhesion molecule 1 (P = .002), glycoprotein IIb/IIIa antigen (P = .0002), and activity (P = .0001)., Conclusion: Treatment with C + ASA for 1 month provides significantly greater inhibition of platelet activity than ASA alone in diabetic patients in this small randomized trial. However, despite dual antiplatelet regimen, diabetic patients exhibit high residual activity of some platelet biomarkers, including unaffected protease-activated receptor 1 receptor expression.

The ability of clopidogrel to inhibit platelet function in patients with congestive heart failure (CHF) was proved by the PLUTO-CHF trial. We retrospectively analyzed platelet characteristics with respect to CHF etiology, class, and ejection fraction in patients enrolled in the PLUTO-CHF study. Twenty-five patients were divided by CHF etiology, severity, and ejection fraction. All patients received aspirin 325 mg for at least 1 month prior to screening. Platelet function studies were performed at baseline and after 30 days of therapy. There were no differences in platelet parameters dependent on clinical characteristics of CHF, except for a significant (P = 0.023) decrease in platelet/endothelial cell adhesion molecule 1 (PECAM-1) expression in the New York Heart Association class III-IV due to the higher baseline values. Therapy with clopidogrel resulted in a significant inhibition of platelet activity assessed by ADP-induced and epinephrine-induced aggregation, closure time, expression of PECAM-1, glycoprotein Ib, glycoprotein IIb/IIIa antigen, glycoprotein IIb/IIIa activity with PAC-1, CD151, and reduced formation of platelet-leukocyte conjugates when compared with baseline. Clopidogrel provides antiplatelet protection in the broad spectrum of patients with CHF independently of its etiology, severity, or myocardial contractility. This uniform platelet inhibition with clopidogrel may be an important consideration in designing future large-scale clinical trials.

Background: Numerous reports have dichotomized responses after clopidogrel therapy using varying definitions and platelet tests in patients immediately after acute vascular events; however, no large study has assessed platelet characteristics in outpatients receiving long-term treatment for more than 30 days with the maintenance dose (75 mg/d) of clopidogrel. The aim of this study was to describe the responses of ex vivo measures of platelet aggregation and activation to long-term clopidogrel therapy in a large population of outpatients after coronary stenting or ischemic stroke., Methods: We conducted a secondary post hoc analysis of a data set represented by presumably compliant patients after coronary stenting (n = 237) or a documented ischemic stroke (n = 122) treated with clopidogrel-and-aspirin combination antiplatelet therapy., Results: The mean duration of treatment was 5.8 months (range 1-21 months). Every patient exhibited a significant inhibition of adenosine diphosphate-induced platelet aggregation (mean 52.9%, range 36%-70%) as compared with the preclopidogrel measures. Inhibition of aggregation strongly correlated with a diminished expression of PECAM-1 (platelet/endothelial cell adhesion molecule 1, r = 0.75), glycoprotein IIb/IIIa (r = 0.62), and PAR-1 (protease-activated receptor 1, r = 0.71). None of the patients developed hyporesponsiveness (reduction from the baseline <15%) or profound inhibition (residual platelet activity <10%)., Conclusions: In contrast to the wide variability of responses that exists in the acute setting, long-term therapy with clopidogrel leads to consistent and much less variable platelet inhibition. Lack of nonresponse and profound inhibition with clopidogrel allow for the maintenance of a delicate balance between proven efficacy and acceptable bleeding risks for long-term secondary prevention in outpatients after acute vascular events.

Background: Numerous randomized studies have shown that the combination of clopidogrel with aspirin yields better clinical outcomes than monotherapy in patients with acute vascular events. However, the impact of the aspirin dose on the antiplatelet potency of clopidogrel is unclear. We sought to compare the antiplatelet profile of aspirin 81 mg (n = 252) versus aspirin 325 mg (n = 459) before and during conventional clopidogrel loading (300 mg), and/or clopidogrel maintenance (75 mg/daily) therapy., Methods: Secondary post hoc analysis of an existing dataset consisting of 711 patients after coronary stenting (n = 601) and ischemic stroke (n = 110) treated previously with aspirin for at least 1 month, and then with aspirin + clopidogrel for at least 7 days was performed. Platelet assessments include conventional and whole blood aggregometry, rapid cartridge-based analyzers, and expression of platelet/endothelial cell adhesion molecule-1, P-selectin, and GPIIb/IIIa activity by flow cytometry measured before and after addition of clopidogrel., Results: There was a small but consistent yet non-significant trend towards more potent platelet inhibition with aspirin 325 mg compared to aspirin 81 mg for every platelet activation parameter before addition of clopidogrel. However, after loading and/or 1 week of chronic treatment with clopidogrel + aspirin, measured platelet parameters became very similar between the groups, and identical for collagen-induced aggregation and PFA-100 analyzer readings., Conclusions: Before addition of clopidogrel, aspirin 325 mg has a tendency to provide stronger platelet inhibition than aspirin 81 mg. However, when clopidogrel and aspirin are used in combination, the higher aspirin dose does not translate into superior antiplatelet action. Given that the existing body of evidence supports the comparable efficacy and, particularly, superior safety of lower versus higher doses of aspirin, aspirin 81 mg should be the dose used in combination with clopidogrel., (2007 S. Karger AG, Basel)

Background and Purpose: Clopidogrel is widely used in patients after recent ischemic stroke; however, its ability to yield additional antiplatelet protection on top of aspirin has never been explored in a controlled study. To determine whether clopidogrel with aspirin (C+ASA) will produce more potent platelet inhibition than aspirin alone (ASA) in patients after ischemic stroke, we conducted the Plavix Use for Treatment of Stroke trial., Methods: Seventy patients after ischemic stroke were randomly assigned to C+ASA or ASA groups. Platelet studies included aggregometry; cartridge-based analyzers; expression of PECAM-1, P-selectin, GP IIb/IIIa (antigen and activity), vitronectin receptor, and formation of platelet-leukocyte microparticles by flow cytometry. Platelet tests were performed at baseline and after 30 days after randomization., Results: There were no deaths, hospitalizations, or serious adverse events. There were no differences in the baseline platelet characteristics between C+ASA and ASA groups, or significant changes in platelet parameters in the ASA group, except diminished collagen-induced aggregation (P=0.001). In contrast, therapy with C+ASA resulted in a significant inhibition of platelet activity assessed by ADP- (P=0.00001) and collagen-induced (P=0.02) aggregation; closure time prolongation (P=0.03), and reduction of platelet activation units with Ultegra (P=0.00001); expression of PECAM-1 (P=0.01), and GP IIb/IIIa activity with PAC-1 (P=0.02) when compared with ASA group. Therapy with C+ASA also resulted in the reduced formation of platelet-leukocyte microparticles (P=0.02)., Conclusions: Treatment with C+ASA for 1 month provides significantly greater inhibition of platelet activity than ASA alone in patients after recent ischemic stroke in the frame of the small randomized trial.

Objectives: We sought to describe the responses of patients to clopidogrel using ex vivo measures of platelet aggregation and activation in a large, heterogeneous population., Background: Recently, a number of reports, using various definitions, have dichotomized patients who are treated with clopidogrel into a minority of "non-responders" and a majority of "responders." Such classifications imply that treatment leads to an all-or-none response, with potentially important clinical implications., Methods: We conducted secondary post-hoc analyses of a dataset consisting of volunteers (n = 94) and patients after coronary stenting (n = 405), with heart failure (n = 25), and after stroke (n = 20)., Results: The response of subjects to clopidogrel followed a normal, bell-shaped distribution, with a mean and standard deviation of 41.9 +/- 20.8% when aggregation was induced by 5 mumol/l of adenosine diphosphate. When hyporesponsiveness and hyper-responsiveness to clopidogrel were considered to be two standard deviations less than and greater than the mean, respectively, the prevalence of hyporesponsiveness and hyper-responsiveness in these patients was 4.2% and 4.8%, respectively. Pretreatment platelet activity and clinical characteristics were not associated with responsiveness to clopidogrel., Conclusions: Individuals receiving clopidogrel exhibit a wide variability in response that follows a normal distribution. The clinical implications of this variability are unknown but potentially are important. Clinical trials are needed to define whether hyporesponders to clopidogrel are at increased risk for thrombotic events and whether hyper-responders are at increased risk for bleeding. If so, the individualization of antiplatelet therapy, including clopidogrel dosing, may be possible in the future but will require the ability to easily and reproducibly measure responsiveness by a method that has been proven to be predictive of clinical events.

Background: Some, but not all, post hoc analyses have suggested that the antiplatelet effects of clopidogrel are inhibited by atorvastatin. We sought to address this issue prospectively by performing serial measurements of 19 platelet characteristics using conventional aggregometry, rapid analyzers, and flow cytometry., Methods: The Interaction of Atorvastatin and Clopidogrel Study (Interaction Study) was designed for patients undergoing coronary stenting. All patients (n = 75) received 325 mg of aspirin daily for at least 1 week and 300 mg of clopidogrel immediately prior to stent implantation. They had been taking atorvastatin (n = 25), any other statin (n = 25), or no statin (n = 25) for at least 30 days prior to stenting. The main outcome measure was comparison of platelet biomarkers 4 and 24 hours after clopidogrel administration between study groups., Results: At baseline, patients from both statin groups exhibited diminished platelet aggregation and reduced platelet expression of G-protein-coupled protease-activated thrombin receptor (PAR)-1. There were no significant differences in measured platelet characteristics among the study groups 4 and 24 hours after clopidogrel intake, with the exception of a lower collagen-induced aggregation at 24 hours and a constantly diminished expression of PAR-1 in patients treated with any statin., Conclusions: Statins in general, and atorvastatin in particular, do not affect the ability of clopidogrel to inhibit platelet function in patients undergoing coronary stenting. These prospective data also suggest that statins may inhibit platelets directly via yet unknown mechanism(s) possibly related to the regulation of the PAR-1 thrombin receptors.

Background: Persistent platelet activation may contribute to thrombotic events in patients with congestive heart failure (CHF). Chronic use of mild platelet inhibitors could therefore represent an independent avenue to improve morbidity, mortality, and quality of life in this expanding population. Although clopidogrel is widely used in patients with acute coronary syndromes and ischemic stroke, the ability of this novel ADP-receptor antagonist to inhibit platelet function in patients with CHF is unknown. We assessed antiplatelet properties of clopidogrel with aspirin (C+A) versus aspirin alone (A) in patients with CHF with heightened platelet activity., Methods: Patients with left ventricular ejection fraction <40%, or CHF symptoms in the setting of preserved systolic function and New York Heart Association class II-IV were screened. Patients were considered to have platelet activation when 4 of the following 5 parameters were met: ADP-induced platelet aggregation >60%; collagen-induced aggregation >70%; whole blood aggregation >18 ohms; expression of GP IIb/IIIa >220 log MFI; and P-selectin cell positivity >8%. All patients were treated with 325 mg of acetylsalycilic acid (ASA) for at least 1 month. Patients receiving an antithrombotic agent other than ASA were excluded. Patients meeting clinical and laboratory criteria were randomly assigned to C+A (n=25), A (n=25) groups, or represent screen failures (n=38). Platelet studies (conventional and whole blood aggregometry, shear-induced activation, expression of 10 major receptors and formation of platelet-leukocyte microparticles) were performed at baseline and after 30 days of therapy., Results: There were no deaths, hospitalizations, or serious adverse events. There were no changes in platelet parameters in the A group. In contrast, therapy with C+A resulted in a significant inhibition of platelet activity assessed by ADP-induced (P =.00001), and epinephrine-induced (P =.0016) aggregation, closure time (P =.04), expression of PECAM-1 (P =.009), GP Ib (P =.006), GP IIb/IIIa antigen (P =.0001), GP IIb/IIIa activity with PAC-1 (P =.0021), and CD151 (P =.0026) when compared with the A group. Therapy with C+A also resulted in the reduced formation of platelet-leukocyte microparticles (P =.021). Collagen-induced aggregation in plasma and in whole blood, expression of vitronectin receptor, P-selectin, CD63, CD107a, and CD107b did not differ among groups., Conclusions: Treatment with C+A for 1 month provides significantly greater inhibition of platelet activity than ASA alone in patients with CHF. Patients with CHF with heightened platelet activity represent a potential target population in which addition of clopidogrel may decrease mortality rates by reducing the incidence of thrombotic vascular events.

Background: Statins primarily metabolized by cytochrome P450 3A4 (CYP3A4) reportedly reduce clopidogrel's metabolism to active metabolite, thus attenuating its inhibition of platelet aggregation ex vivo. However, the clinical impact of this interaction has not been evaluated., Methods and Results: Clopidogrel for the Reduction of Events During Observation (CREDO) was a double-blind, placebo-controlled, randomized trial comparing pretreatment (300 mg) and 1-year (75 mg/d) clopidogrel therapy (clopidogrel) with no pretreatment and 1-month clopidogrel therapy (75 mg/d) (control) after a planned percutaneous coronary intervention. All patients received aspirin. The 1-year primary end point was a composite of death, myocardial infarction, and stroke. We performed a post hoc analysis to evaluate the clinical efficacy of concomitant clopidogrel and statin administration, categorizing baseline statin use to those predominantly CYP3A4-metabolized (atorvastatin, lovastatin, simvastatin, and cerivastatin) (CYP3A4-MET) or others (pravastatin and fluvastatin) (non-CYP3A4-MET). Of the 2116 patients enrolled, 1001 received a CYP3A4-MET and 158 a non-CYP3A4-MET statin. For the overall study population, the primary end point was significantly reduced in the clopidogrel group (8.5% versus 11.5%, RRR 26.9%; P=0.025). This clopidogrel benefit was similar with statin use, irrespective of treatment with a CYP3A4-MET (7.6% clopidogrel, 11.8% control, RRR 36.4%, 95% CI 3.9 to 57.9; P=0.03) or non-CYP3A4-MET statin (5.4% clopidogrel, 13.6% control, RRR 60.6%, 95% CI -23.9 to 87.4; P=0.11). Patients given atorvastatin or pravastatin had similar 1-year event rates. Additionally, concomitant therapy with statins had no impact on major or minor bleeding rates., Conclusions: Although ex vivo testing has suggested a potential negative interaction when coadministering a CYP3A4-metabolized statin with clopidogrel, this was not clinically observed statistically in a post hoc analysis of a placebo-controlled study.

Our understanding of the pathogenesis of congestive heart failure (CHF) has improved remarkably in recent years. However, despite better knowledge and novel pharmaceutical strategies, this disease is still one of the most brutal killers in the Western world. The pathophysiology of CHF is complex, and much of our comprehension revolves strictly around the neurohormonal and mechanical mechanisms involved. It has been suggested that CHF is associated with altered hemostasis, but whether a prothrombotic state contributes to the pathogenesis and progression of the disease is still not well known. The purpose of this review article is to discuss our current knowledge of platelet activation in patients with CHF and the potential role of antiplatelet agents in preventing these hemostatic abnormalities. Clopidogrel is an established medication that reduces the incidence of stroke, myocardial ischemia, or vascular death. It is currently the drug of choice in the prophylaxis of subacute stent thrombosis and postischemic stroke treatment. Promising results of the most resent trials (Clopidogrel versus Aspirin in Patients at Risk of Ischemic Events [CAPRIE] and Clopidogrel in Unstable angina to prevent Recurrent Events [CURE]) may expand future indications of this ADP receptor antagonist for prevention of thrombotic complications in the CHF population. Currently conducted clinical trials (Warfarin and Antiplatelet Therapy in Chronic Heart Failure [WATCH] and Plavix Use for Treatment of Congestive Heart Failure [PLUTO-CHF] should clarify the role of clopidogrel in these patients.

Background: Despite the common practice of clopidogrel loading for coronary stenting, the time dependence and degree of platelet inhibition after this therapy are not well defined. We sought to establish an optimal clopidogrel dosing regimen for sustained platelet inhibition in stented patients., Methods and Results: Platelets were assessed by conventional aggregation with 5 micromol/L adenosine diphosphate (ADP), 1 microg/mL collagen (COLL), and 750 micromol/L arachidonic acid; whole blood aggregation by 1 microg/mL collagen (WBA); shear-induced closure time (CT); contractile force (CF); and expression of 9 surface receptors by flow cytometry in 100 patients undergoing elective stent placement without glycoprotein (GP) IIb/IIIa receptor antagonists. Blood was obtained at baseline and serially over 5 days poststenting after different clopidogrel loading regimens: 300 mg 24 hours before (Group A), 12 hours before (Group B), 3 to 6 hours before (Group C), and 75 mg at the time of intervention (Group D). Before stenting, ADP, COLL, CT, and WBA were reduced by clopidogrel loading (P <.05). CF was not affected by clopidogrel. Before stenting, GP IIb/IIIa expression increased in groups A through C (P <.05), whereas PECAM-1 and CD107a were reduced (P <.05). At 2 hours and 2 days poststenting, platelets, in general, exhibited an increase in activity that was most inhibited by clopidogrel loading. Clopidogrel inhibited GP Ib, platelet/endothelial cell adhesion molecule-1, CD 107a, CD 151, and GP IIb/IIIa expression at day 5 poststenting., Conclusion: A 300 mg clopidogrel load given 3 to 24 hours before stenting inhibits platelets at the time of the procedure and reduces poststent activity more than a 75 mg dose given at the time of the procedure. The inhibition of adhesive molecule expression may also contribute an antithrombotic effect. Poststent activation of platelets may warrant higher periprocedural dosing.