Journal of the American College of Cardiology Vol. 48, No. 7, by the American College of Cardiology Foundation ISSN /06/$32.

Transcription

1 Journal of the American College of Cardiology Vol. 48, No. 7, by the American College of Cardiology Foundation ISSN /06/$32.00 Published by Elsevier Inc. doi: /j.jacc FOCUS ISSUE: CARDIAC INTERVENTION Benefit of a 600-mg Loading Dose of Clopidogrel on Platelet Reactivity and Clinical Outcomes in Patients With Non ST-Segment Elevation Acute Coronary Syndrome Undergoing Coronary Stenting Thomas Cuisset, MD,* Corinne Frere, MD, Jacques Quilici, MD,* Pierre-Emmanuel Morange, MD, PHD, Lyassine Nait-Saidi, MD,* Joseph Carvajal, MD, Agnès Lehmann, Marc Lambert, MD,* Jean-Louis Bonnet, MD,* Marie-Christine Alessi, MD, PHD Marseille, France OBJECTIVES BACKGROUND METHODS RESULTS CONCLUSIONS We analyzed the benefit of a 600-mg clopidogrel loading dose on platelet reactivity and clinical outcomes after stenting for non ST-segment elevation acute coronary syndrome (NSTE ACS). High post-treatment platelet reactivity (HPPR adenosine diphosphate 10 mol l 1 [ADP] induced platelet aggregation 70%) is a marker for low responders to dual antiplatelet therapy with increased risk of recurrent cardiovascular (CV) events after stenting for NSTE ACS. A total of 292 consecutive NSTE ACS patients undergoing coronary stenting were included and randomly received a 300-mg (n 146) or 600-mg (n 146) loading dose of clopidogrel at least 12 h before percutaneous coronary intervention. A single post-treatment blood sample was obtained before percutaneous coronary intervention to analyze maximal intensity of ADP-induced platelet aggregation and platelet surface expression of P-selectin. One-month follow-up CV events were recorded. The ADP-induced platelet aggregation and expression of P-selectin were significantly lower in patients receiving 600 mg than in those receiving 300 mg (mean SD: 50 19% vs %, p and arbitrary units vs arbitrary units; p respectively). Persistence of HPPR was less common in patients receiving 600 mg than in those receiving 300 mg (15 vs. 25%, p 0.03). During the 1-month follow-up, 18 CV events (12%) occurred in the 300-mg group versus 7 (5%) in the 600-mg group (p 0.02); this difference was not affected by adjustment for conventional CV risk factors (p 0.035). In NSTE ACS patients undergoing coronary stenting, a 600-mg loading dose of clopidogrel shows its benefit on platelet reactivity and clinical prognosis. (J Am Coll Cardiol 2006;48: ) 2006 by the American College of Cardiology Foundation Platelet reactivity plays a key role in the pathogenesis of ischemic complications after stenting for non ST-segment elevation acute coronary syndrome (NSTE ACS). Accordingly, platelet inhibition with a thienopyridine (clopidogrel) has significantly reduced recurrent ischemic events in this clinical setting, and in combination with aspirin, clopidogrel is now the treatment of choice for preventing stent thrombosis (1) and reducing major adverse cardiovascular (CV) events after NSTE ACS (2,3). Nevertheless, ischemic events still occur. These recurrences involve a complex and multifactorial process, and low response to antiplatelet therapy could be a major factor. Indeed numerous biological studies, essentially based on adenosine diphosphate (ADP)- induced platelet aggregometry, have reported interindividual variability in platelet response to clopidogrel (4 8); these studies identified patients who did not achieve platelet From the *Department of Cardiology, CHU Timone, Marseille, France; and INSERM, Faculté de Médecine CHU Timone, Marseille, France. This work was supported by the Assistance Publique Hôpitaux de Marseille. Manuscript received March 14, 2006; revised manuscript received May 30, 2006, accepted June 12, inhibition as low responders or resistants. However, antiplatelet effect monitoring would be of limited relevance in the absence of clinical implication. Precisely, as has been shown for aspirin (9), a relationship between clopidogrel resistance and recurrence of clinical outcomes has been reported in several studies (7,10 13). We previously showed that in NSTE ACS patients undergoing coronary stenting, the high post-treatment platelet reactivity (HPPR) (maximal intensity of ADP 10 mol l 1 induced platelet aggregation 70%) identified low responders to dual antiplatelet therapy (aspirin and clopidogrel) at higher risk of CV events during a 1-month follow-up (14). According to these results, other therapeutic approaches should be considered for these low-responder patients, such as higher doses or alternative treatments. Currently, the 300-mg loading dose of clopidogrel given at least 6 h before the procedure represents the conventional antiplatelet regimen before percutaneous coronary intervention (PCI). A higher loading dose of clopidogrel has already shown its capacity to improve platelet reactivity after treatment in healthy volun-

2 1340 Cuisset et al. JACC Vol. 48, No. 7, 2006 Platelet Reactivity and Acute Coronary Syndrome October 3, 2006: Abbreviations and Acronyms ADP adenosine diphosphate CREDO Clopidogrel for Reduction of Events During Observation CV cardiovascular HPPR high post-treatment platelet reactivity NSTE ACS non ST-segment elevation acute coronary syndrome PCI percutaneous coronary intervention PCI-CURE Percutaneous Coronary Intervention- Clopidogrel in Unstable Angina to Prevent Recurrent Events PRP platelet-rich plasma ST stent thrombosis teers and patients (15 21) with an earlier and stronger inhibition of ADP induced platelet activation than the 300-mg loading regimen, and its efficiency for the prevention of periprocedural infarction in stented patients (22). However, to the best of our knowledge, no study has ever tested both platelet parameters and clinical outcomes after increasing the loading dose of clopidogrel, especially in high-risk groups such as stented NSTE ACS patients. Therefore, we conducted a randomized and prospective study to evaluate the benefit of a higher loading dose of clopidogrel on platelet aggregation and recurrent ischemic events for NSTE ACS patients undergoing coronary stenting. METHODS Study population. Consecutive patients admitted for NSTE ACS to the Department of Cardiology of the Timone hospital between June 2004 and October 2005 were eligible for this prospective study if they had undergone successful coronary stenting. We defined NSTE ACS as clinical symptoms compatible with acute myocardial ischemia within 12 h before admission and at least 1 of the following: a new finding of ST-segment depression 0.05 mv, transient ( 20 min) ST-segment elevation 0.1 mv, T-wave inversion 0.3 mv in at least 2 leads, elevated levels of cardiac markers or coronary disease as documented by a history of catheterization, revascularization, or myocardial infarction. The exclusion criteria were a history of bleeding diathesis, persistent ST-segment elevation ACS, New York Heart Association functional class IV, PCI or coronary bypass grafting 3 months, contraindications to antiplatelet therapy, platelet count 100 g l 1, creatinine clearance 25 ml min 1, and use of glycoprotein IIb/IIIa inhibitors before the procedure. Patients were randomly assigned to receive a 300-mg or 600-mg loading dose of clopidogrel at least 12 h before stenting. All patients received aspirin 160 mg daily after a loading dose of 250 mg administered at least 12 h before stenting. The PCI was performed within 48 h after admission. For all patients, anticoagulation was begun before PCI in the intensive care unit and performed with low-molecular-weight heparin (enoxaparin), or unfractionated heparin in patients over 75 years old or with renal insufficiency. The study protocol was approved by the institutional ethics committee of our institution, and patients gave written informed consent for participation. Blood samples. Blood samples for testing platelet reactivity were drawn in the catheterization laboratory from a 6-F arterial sheath before the PCI at least 12 h after the loading dose of clopidogrel and aspirin, and before administration of tirofiban if needed. The initial first millimeters of blood were discarded to avoid platelet activation induced by needle puncture, and blood was immediately collected in Vacutainer tube containing 3.8% trisodium citrate, filled to capacity, and then inverted 3 to 5 times for gentle mixing and drawn immediately to the hemostasis laboratory. Platelet aggregation. The blood citrate mixture was centrifuged at 120 g for 5 min. The resulting platelet-rich plasma (PRP) was kept at room temperature for use within 1 h. The platelet count was determined in the PRP sample and adjusted to ml 1 with homologous plateletpoor plasma. Platelets were stimulated with ADP (10 mol l 1 ), and aggregation was assessed with a PAP4 Aggregometer (Biodata Corporation, Wellcome, Paris, France). Aggregation was expressed as the maximal percentage change in light transmittance from baseline with platelet-poor plasma as a reference. Here we report data on maximal intensity of platelet aggregation with ADP concentrations. The coefficient of variation of maximal intensity of platelet aggregation with ADP was 6.5%. Flow cytometry. The surface expression of the internal alpha-granule membrane protein P-selectin expressed on the surface of ADP activated platelets was determined by flow cytometry with monoclonal antibody. The following antibodies were used: anti-cd62p (Beckman Coulter, Fullerton, California) and antimouse goat immunoglobulin (Ig)G FITC (antimouse goat IgG labeled with fluorescein isothiocyanate; Beckman Coulter). Briefly, PRP was diluted 1:10 in tyrode albumin buffer ( ml 1 ) and gently mixed. Both antibody anti-cd62p (10 l of dilution 1:10) and ADP (final concentration 10 mol ml 1 ) or tyrode albumin buffer were added to 10 l of diluted PRP. After incubation in the dark at room temperature for 15 min, 10 l of antimouse goat IgG FITC (diluted 1:10) were added and again incubated in the dark at room temperature for 15 min. Scatter signals and fluorescence intensity were analyzed on a EPICS XL-MCL flow cytometer (Beckman Coultronics, Margency, France). The light-scattering properties projected on a scattergram identified the platelet cluster. Fluorescence intensity was expressed on individual cytohistograms, with the region of interest limited to the platelet cluster. The mean channel fluorescence intensity was used as an index of antibody binding and P-selectin surface expression. Platelet function end point. We analyzed the mean maximal intensity of ADP-induced platelet aggregation in both groups, receiving 300 mg or 600 mg of clopidogrel. We also reported the rate of persistence of HPPR, defined as

3 JACC Vol. 48, No. 7, 2006 October 3, 2006: Cuisset et al. Platelet Reactivity and Acute Coronary Syndrome 1341 ADP-induced platelet aggregation 70%, in both groups. Finally, we studied the expression of P-selectin to evaluate platelet activation. Clinical end point. The clinical end point included the following CV events: CV death, acute or subacute stent thrombosis, recurrent ACS, and stroke. Follow-up events were prospectively assessed by clinical visit. An ACS was defined by the presence of symptoms compatible with recurrent ischemia needing new hospitalization and coronary angiography, ischemic stroke was defined as a new focal neurologic deficit without bleeding on tomodensitometry and confirmed by a neurologist that as occurring within 1 month of PCI. Drug therapy compliance was assessed. Occurrence of major bleeding defined as intracranial bleeding or clinically overt bleeding associated with a decrease in hemoglobin of 5 g dl 1, according to the Thrombolysis in Myocardial Infarction criteria (23), were reported. The treating physician and the investigators who evaluated the clinical end points were blinded to the results of the platelet testing. Statistical analysis. Statistical analysis was performed with the SAS Software (version 9.01; SAS Institute Inc., Cary, North Carolina). Continuous variables are expressed as mean SD. Categorical variables are expressed as frequencies and percentages. For continuous variables, mean levels were compared between individuals with 300 mg and 600 mg of by analysis of variance, and for categorical variables, proportions were compared by chisquare test. Variables with a skewed distribution were log- or square root-transformed before analysis. The effect of the loading dose of clopidogrel on CV event was performed using logistic regression analysis. Three models were considered successively: Model 1: after adjustment for age and gender; Model 2: additionally adjusted for potential confounders such as conventional CV risk factors, treatment, and inflammatory parameters; Model 3: additionally adjusted for HPPR. RESULTS Patient characteristics. From June 2004 to October 2005, a total of 387 NSTE ACS patients who fulfilled the enrollment criteria were randomized to a 300-mg (n 192) or 600-mg (n 195) loading dose of clopidogrel. After coronary angiography, 95 patients who did not receive successful angioplasty were excluded from the study (72 were treated medically, 20 with elective bypass surgery and 3 with failed PCI). Of the 292 study patients with successful coronary stenting, 146 were randomized to a 300-mg and 146 to a 600-mg loading dose of clopidogrel. Demographic data of the studied population are summarized in Table 1. The demographic, clinical, and therapeutic parameters were similar in the 300-mg and 600-mg groups. The mean time between the loading dose of clopidogrel and blood sampling was h and h, respectively, for patients receiving 300 mg or 600 mg (p 0.56). All patients received 75 mg clopidogrel and 160 mg aspirin during the 1-month follow-up period. Platelet parameters. PLATELET AGGREGATION. We analyzed post-treatment platelet reactivity using the maximal intensity of ADP-induced platelet aggregation. The distribution of this response was consistent with a normal Table 1. Baseline Characteristics of the Patients According to the Loading Dose of Clopidogrel Characteristics 300 mg (n 146) 600 mg (n 146) p Value Age, yrs Men, n (%) 114 (79) 108 (73) 0.34 Hypertension, n (%) 84 (58) 81 (56) 0.67 Diabetes mellitus, n (%) 42 (29) 48 (33) 0.45 Current smoker, n (%) 59 (40) 76 (52) 0.06 Dyslipidemia, n (%) 81 (56) 79 (55) 0.81 Previous ACS, n (%) 65 (44) 66 (45) 0.90 Familial history, n (%) 49 (34) 53 (36) 0.62 Body mass index, kg/m Medications Statins, n (%) 87 (60) 88 (61) 0.90 Beta-blocker, n (%) 71 (49) 62 (42) 0.24 Diuretics, n (%) 24 (16) 24 (16) 1.00 Troponin, n (%) 38 (26) 30 (21) 0.27 ST-segment changes, n (%) 32 (22) 36 (25) 0.58 Left ventricular ejection fraction, % Creatinine, mol l Procedural features Total stent length, mm Tirofiban, n (%) 51 (35) 48 (33) 0.75 Anticoagulation LWMH 95 (65) 99 (68) 0.78 UFH 51 (35) 47 (32) 0.81 Values are mean SD for quantitative variables and n (%) for qualitative variables. For skewed variables, tests were performed on log-transformed values. ACS acute coronary syndrome; LMWH low molecular weight heparin; UFH unfractionated heparin.

4 1342 Cuisset et al. JACC Vol. 48, No. 7, 2006 Platelet Reactivity and Acute Coronary Syndrome October 3, 2006: Figure 1. Maximal intensity of adenosine diphosphate (ADP)-induced platelet aggregation in the 300-mg and 600-mg groups. bell-shaped distribution. Maximal intensity of ADPinduced platelet aggregation was significantly lower in patients who received a 600-mg loading dose of clopidogrel than in those who received 300 mg (mean SD: 50 19% vs %, p ) (Fig. 1). The persistence of HPPR was less common in patients receiving a 600-mg loading dose of clopidogrel (n 22, 15%) than in those receiving 300 mg (n 36, 25%, p 0.04). EXPRESSION OF P-SELECTIN. The mean expression of P-selectin was significantly lower in patients receiving a 600-mg loading dose of clopidogrel than in those receiving 300 mg ( arbitrary units vs arbitrary units; p ) (Fig. 2). Clinical outcomes. One-month follow up was completed in all patients. Twenty-five CV events (8.5%) occurred in the whole population during follow-up. Recurrent ischemic events occurred more frequently in the 300-mg group than in the 600-mg group: 18 (12%) and 7 (5%), respectively (p 0.02). This difference was not affected by adjustment for potential confounders such as age, gender, CV risk factors, troponin elevation, ST-segment changes, left ventricular ejection fraction, or tirofiban use (p 0.035). Distribution of the CV events was 15 hospitalizations for recurrent ACS (2 acute stent thrombosis), 2 strokes, and 1 CV death for the 300-mg group; and 6 hospitalizations for recurrent ACS (1 acute stent thrombosis) and 1 stroke for the 600-mg group (Figs. 3 and 4). Figure 3. Clinical outcomes according to loading dose of clopidogrel. ACS acute coronary syndrome; CV death cardiovascular death; CVE cardiovascular events; ST stent thrombosis. In both groups, HPPR contributed to recurrence of CV events after adjustment for age and gender: (OR [odds ratio] 9.93 [95% confidence interval (CI) 3.19 to 30.90] and OR [95% CI 4.89 to ], respectively, for 300-mg and 600-mg groups). In the 300-mg group, 67% (n 12) of clinical events occurred in patients with HPPR, and 85% (n 6) in the 600-mg group. When including both clopidogrel loading doses and persistence of HPPR as well as potential confounders in a logistic regression analysis, only persistence of HPPR remained independently associated with CV events (OR [95% CI 5.30 to ], p ). No patient in either group had postprocedural major bleeding or required transfusions. DISCUSSION Compared with the 300-mg clopidogrel loading dose, our study shows that a 600-mg bolus allows a superior antiplatelet effect and improves clinical outcomes in patients undergoing coronary stenting for NSTE ACS. Clopidogrel is an antiplatelet agent inhibiting the ADP receptor. Because of its safety profile and the results of clinical trials, clopidogrel has become the standard treatment for ACS and stenting (1 3). Two large studies in patients with ACS have shown that pretreatment with clopidogrel may have beneficial effects. This pretreatment was given a mean of 6 days before intervention in the observational PCI-CURE (Percutaneous Coronary Intervention Clopidogrel in Unstable An- Figure 2. Mean fluorescence intensity of P-selectin expression in the 300-mg and 600-mg groups. AU arbitrary units. Figure 4. Kaplan-Meier analysis for 30-day cardiovascular (CV) events according to loading dose of clopidogrel. Log-rank 9.24, p

5 JACC Vol. 48, No. 7, 2006 October 3, 2006: Cuisset et al. Platelet Reactivity and Acute Coronary Syndrome 1343 gina to Prevent Recurrent Events) (3) and 3 to 24 h in the randomized CREDO (Clopidogrel for the Reduction of Events During Observation) trial (24). Accordingly, current common clinical practice consists of pretreatment with a 300-mg loading dose of clopidogrel at least 6 h before the procedure in patients with ACS, as well as in those undergoing elective intervention. Despite the routine use of dual antiplatelet therapy with loading dose of clopidogrel, recurrent ischemic events occurred and antiplatelet responsiveness involvement emerged in numerous studies as a potential responsible factor. Clopidogrel resistance was initially supported by several biological studies usually based on ADP-induced platelet aggregation, which emphasized high interindividual variability of in vitro platelet response to standard dose of clopidogrel (4 8). Mechanisms involved are not yet clear; variability in intestinal absorption and the hepatic cytochrome P450 3A4 activity were reported as important factors (9). Moreover, several factors could modulate clopidogrel antiplatelet effectiveness. Indeed, a recent study by Saraff et al. (25) showed that the benefit of dual antiplatelet therapy with aspirin and clopidogrel was especially pronounced in smokers, probably because smoking increases platelet reactivity and smokers have poor outcomes after PCI compared with nonsmokers. In the present study, there was a trend toward an increased prevalence of smokers in the 600-mg group. It suggests that the benefit of a higher loading dose could have been greater without this difference between the 300-mg and 600-mg groups. The clinical relevance of the clopidogrel resistance has already been reported in several retrospective studies showing a correlation between platelet parameters and stent thrombosis (7,10 12). Only 2 prospective studies evaluated the relationship between clopidogrel responsiveness and recurrent ischemic events after ACS (13,14). Nevertheless, the lack of a standard definition of resistance as well as the lack of a standard diagnostic modality has hampered the field in identifying and treating this clinical entity. Consequently, some investigators suggested to study post-treatment platelet reactivity rather than antiplatelet responsiveness as a risk marker of clinical outcomes (14). Moreover, recent studies (14,26) proposed the ADPinduced post-treatment platelet aggregation as a means of evaluating the response both to clopidogrel and to aspirin. To determine a useful measurement of platelet reactivity in daily clinical practice, we use one single blood sample testing ADP-induced post-treatment platelet aggregation. We identified HPPR (ADP-induced platelet aggregation 70%), in spite of dual antiplatelet therapy with a 300-mg loading dose of clopidogrel as a risk marker of recurrent ischemic events (14). Therefore, the results of the present study confirmed that the HPPR have a predictive value for recurrent ischemic events in both the 300-mg and the 600-mg groups. Moreover, the multivariable analysis showed that the HPPR was a better predictor of clinical outcomes than the 300-mg or 600-mg loading dose, suggesting that the benefit of higher clopidogrel loading dose on clinical prognosis is directly linked to the decreasing persistence of HPPR. These supplementary data seem to validate the use of this marker in daily clinical practice to identify high-risk patients with persistent HPPR. The dose of 300 mg of clopidogrel derives from dosefinding data on healthy volunteers; however, patients with coronary artery disease may have enhanced platelet reactivity as compared with healthy individuals, and so probably require more aggressive platelet inhibition. Indeed, in an environment of high thrombin activity, it has been shown that clopidogrel might not reduce enough platelet activity because it did not inhibit the platelet aggregation and degranulation after stimulation with the thrombin-related activating peptide (27). Moreover, a study by Soffer et al. (28) has correlated the level of angina class with platelet inhibition by clopidogrel and found that patients with a higher Braunwald angina class had lower inhibition of platelet aggregation. The standard dose of 300 mg is probably not as efficient during ACS as it has been shown in healthy subjects. Plasma concentration of the active drug influences platelet aggregation after first administration in a dose-dependent manner (29). Thus, a more rapid and intense platelet suppression represents the rationale for pretreatment with a 600-mg loading dose of clopidogrel. Several studies have shown a benefit of higher clopidogrel loading on platelet aggregation with a decreased rate of nonresponders and platelet reactivity (15 21), and a previous study showed a benefit of 600 mg of clopidogrel compared with the standard 300-mg regimen on the incidence of periprocedural elevation of markers of myocardial necrosis (22). Even more recently, a dose of 900 mg was tested, although this did not seem to produce any more active metabolite or inhibition of platelet function than the 600-mg dose (20). In the present study, we showed both a biological and a clinical benefit of a higher loading dose of clopidogrel. Moreover, in our study, a higher loading dose of clopidogrel was not associated with important bleeding complications. Elsewhere, other antithrombotic strategies may be useful for these antiplatelet nonresponders at high risk of recurrent ischemic events. First, use in the periprocedural period of GPIIb/IIIa antagonist infusion would be beneficial in these patients. Indeed, a recent study has shown the lower clinical event rate after administration of abciximab in higher-risk NSTE ACS patients in spite of a 600-mg loading dose of clopidogrel (30). Secondly, the emergence of new ADP-antagonists such as prasugrel would probably be helpful in this clinical setting. Clinical studies are required to validate these hypotheses. Study limitations. It should be mentioned that the sample size of the present study is relatively small, and therefore does not allow for definitive conclusions. In our study, timing between the loading dose of clopidogrel and PCI was 12 to 24 h. However, a recent study by Steinhubl et al. (31) from the CREDO study showed that a 300-mg loading dose had no effect if administrated 15 h before PCI, and

6 1344 Cuisset et al. JACC Vol. 48, No. 7, 2006 Platelet Reactivity and Acute Coronary Syndrome October 3, 2006: that the effect was not optimal until approximately 24 h before PCI. Moreover, in the ISAR REACT (Intracoronary Stenting and Antithrombotic Regimen Rapid Early Action for Coronary Treatment) study with a 600-mg loading dose, no relationship was found between the duration of pretreatment (2 to 24 h) and clinical events (32). The design of our study could partially explain the benefit of a higher loading dose for patients pretreated with a 300-mg loading between 12 to 24 h before PCI. Finally, the clinical combined end point chosen in our study is obviously debatable, especially because the usually used periprocedural infarction, defined with elevation of creatine kinase-mb or troponin, was not included. Conclusions. Our study showed that pretreatment with a 600-mg loading dose of clopidogrel given before PCI for NSTE ACS is safe and, as compared with the 300-mg dose, improves periprocedural platelet inhibition and reduces recurrent ischemic events. The low risk and efficiency of this pharmacological regimen may support its routine use in ACS patients before PCI, as recently evoked in the European Society of Cardiology (33) and American College of Cardiology/American Heart association guidelines (34), but larger clinical studies are required. Reprint requests and correspondence: Dr. Marie-Christine Alessi, INSERM, UMR 626 Marseille, F France. Marie-Christine.Alessi@medecine.univ-mrs.fr. REFERENCES 1. Bertrand ME, Rupprecht HJ, Urban P, Gershlick AH, for the CLASSICS Investigators. Double-blind study of the safety of clopidogrel with and without a loading dose in combination with aspirin compared with ticlopidine in combination with aspirin after coronary stenting: the clopidogrel aspirin stent international cooperative study (CLASSICS). Circulation 2000;102: Yusuf S, Zhao F, Mehta SR, Chrolavicius S, Tognoni G, Fox KK. Effects of clopidogrel in addition to aspirin in patients with acute coronary syndromes without ST-segment elevation. N Engl J Med 2001;345: Mehta SR, Yusuf S, Peters RJ, et al. Effects of pretreatment with clopidogrel and aspirin followed by long-term therapy in patients undergoing percutaneous coronary intervention: the PCI-CURE study. Lancet 2001;358: Gurbel PA, Bliden KP, Hiatt BL, O Connor CM. Clopidogrel for coronary stenting: response variability, drug resistance, and the effect of pretreatment platelet reactivity. Circulation 2003;107: Angiolillo DJ, Fernandez-Ortiz A, Bernardo E, et al. Identification of low responders to a 300-mg clopidogrel loading dose in patients undergoing coronary stenting. Thromb Res 2005;115: Jaremo P, Lindahl TL, Fransson SG, Richter A. Individual variations of platelet inhibition after loading doses of clopidogrel. J Intern Med 2002;252: Muller I, Besta F, Schulz C, Massberg S, Schonig A, Gawaz M. Prevalence of clopidogrel non-responders among patients with stable angina pectoris scheduled for elective coronary stent placement. Thromb Haemost 2003;89: Serebruany VL, Steinhubl SR, Berger PB, Malinin AI, Bhatt DL, Topol EJ. Variability in platelet responsiveness to clopidogrel among 544 individuals. J Am Coll Cardiol 2005;45: Wang TH, Bhatt DL, Topol E. Aspirin and clopidogrel resistance: an emerging clinical entity. Eur Heart J 2006;27: Barragan P, Bouvier JL, Roquebert PO, et al. Resistance to thienopyridines: clinical detection of coronary stent thrombosis by monitoring of vasodilator-stimulated phosphoprotein phosphorylation. Catheter Cardiovasc Interv 2003;59: Gurbel PA, Bliden KP, Samara W, et al. Clopidogrel effect on platelet reactivity in patients with stent thrombosis: results of the CREST study. J Am Coll Cardiol 2005;46: Wenaweser P, Hess O. Stent thrombosis is associated with an impaired response to antiplatelet therapy. J Am Coll Cardiol 2005;46: CS Matetzky S, Shenkman B, Guetta V, et al. Clopidogrel resistance is associated with increased risk of recurrent atherothrombotic events in patients with acute myocardial infarction. Circulation 2004;109: Cuisset T, Frere C, Quilici J, et al. High post-treatment platelet reactivity identified low-responders to dual antiplatelet therapy at increased risk of recurrent cardiovascular events after stenting for acute coronary syndrome. J Thromb Haemost 2006;4: Zidar FJ, Moliterno DJ, Bhatt DL, et al. High-dose clopidogrel loading rapidly reduces both platelet inflammatory marker expression and aggregation (abstr). J Am Coll Cardiol 2004;43 Suppl:64A. 16. Kastrati A, von Beckerath N, Joost A, Pogatsa-Murray G, Gorchakova O, Schomig A. Loading with 600 mg clopidogrel in patients with coronary artery disease with and without chronic clopidogrel therapy. Circulation 2004;110: Gurbel PA, Bliden KP, Hayes KM, Young S, Herzog WR, Tantry US. The relation of dosing to clopidogrel responsiveness and the incidence of high post-treatment platelet aggregation in patients undergoing coronary stenting. J Am Coll Cardiol 2005;45: Gurbel PA, Bliden KP, Zaman KA, Yoho JA, Hayes KM, Tantry US. Clopidogrel loading with eptifibatide to arrest the reactivity of platelets: results of the Clopidogrel Loading With Eptifibatide to Arrest the Reactivity of Platelets (CLEAR PLATELETS) study. Circulation 2005;111: Angiolillo DJ, Fernandez-Ortiz A, Bernardo E, et al. High clopidogrel loading dose during coronary stenting: effects on drug response and interindividual variability. Eur Heart J 2004;25: von Beckerath N, Taubert D, Pogatsa-Murray G, Schomig E, Kastrati A, Schomig A. Absorption, metabolization, and antiplatelet effects of 300-, 600-, and 900-mg loading doses of clopidogrel: results of the ISAR-CHOICE (Intracoronary Stenting and Antithrombotic Regimen: Choose Between 3 High Oral Doses for Immediate Clopidogrel Effect) Trial. Circulation 2005;112: Montalescot G. Assessment of the best loading dose of clopidogrel to blunt platelet activation, inflammation, and ongoing necrosis (ALBION) study. Paris, France: EuroPCR, Patti G, Colonna G, Pasceri V, Pepe LL, Montinaro A, DiSciascio G. Randomized trial of high loading dose of clopidogrel for reduction of periprocedural myocardial infarction in patients undergoing coronary intervention. Results From the ARMYDA-2 (Antiplatelet Therapy for Reduction of Myocardial Damage During Angioplasty) study. Circulation 2005;111: Rao AK, Pratt C, Berke A, et al. Thrombolysis in Myocardial Infarction (TIMI) Trial phase I: hemorrhagic manifestations and changes in plasma fibrinogen and the fibrinolytic system in patients treated with recombinant tissue plasminogen activator and streptokinase. J Am Coll Cardiol 1988;11: Steinhubl SR, Berger PB, Mann JT 3rd, et al. Early and sustained dual oral antiplatelet therapy following percutaneous coronary intervention: a randomized controlled trial. JAMA 2002;288: Saraff KY, Steinhubl SR, Hsu AP, Topol EJ, for the CREDO Investigators. Smoking influences the effectiveness of dual antiplatelet therapy on long-term outcomes following percutaneous coronary intervention (abstr). J Am Coll Cardiol 2006;47 Suppl B:36B. 26. Lev EI, Patel RT, Maresh KJ, et al. Aspirin and clopidogrel drug response in patients undergoing percutaneous coronary intervention: the role of dual drug resistance. J Am Coll Cardiol 2006;47: Muller I, Seyfarth M, Rudiger S, et al. Effect of a high loading dose of clopidogrel on platelet function in patients undergoing coronary stent placement. Heart 2001;85: Soffer D, Moussa I, Harjai KJ, et al. Impact of angina class on inhibition of platelet aggregation following clopidogrel loading in

7 JACC Vol. 48, No. 7, 2006 October 3, 2006: Cuisset et al. Platelet Reactivity and Acute Coronary Syndrome 1345 patients undergoing coronary intervention: do we need more aggressive dosing regimens in unstable angina? Catheter Cardiovasc Interv 2003;59: Caplain H, Donat F, Gaud C, Necciari J. Pharmacokinetics of clopidogrel. Semin Thromb Hemost 1999;25 Suppl 2: Kastrati A, Mehilli J, Neumann FJ, et al. Abciximab in patients with acute coronary syndromes undergoing percutaneous coronary intervention after clopidogrel pretreatment: the ISAR-REACT 2 randomized trial. JAMA 2006;295: Steinhubl SR, Berger PB, Brennan DM, Topol EJ, CREDO Investigators. Optimal timing for the initiation of pre-treatment with 300 mg clopidogrel before percutaneous coronary intervention. J Am Coll Cardiol 2006;47: Kandzari DE, Berger PB, Kastrati A, et al. Influence of treatment duration with a 600-mg dose of clopidogrel before percutaneous coronary revascularization. J Am Coll Cardiol 2004;44: Silber S, Albertsson P, Aviles FF, et al. Guidelines for percutaneous coronary intervention. The Task Force for Percutaneous Coronary Intervention of the European Society of Cardiology. Eur Heart J 2005;26: Smith SC Jr., Feldman TE, Hirshfeld JW Jr., et al. ACC/AHA/SCAI 2005 guideline update for percutaneous coronary intervention summary article. A report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (ACC/AHA/SCAI Writing Committee to Update the 2001 Guidelines for Percutaneous Coronary Intervention). J Am Coll Cardiol 2006;47: