GLYCOPROTEIN IIB/IIIA ANTAGONISTS: DO THEY HAVE A ROLE IN THE MANAGEMENT OF UNSTABLE ANGINA?

Plaque rupture, platelet aggregation and thrombosis have central roles in the pathogenesis of acute coronary syndromes. Despite several trials showing the benefit of aspirin and heparin in patients presenting with unstable angina and acute myocardial infarction, these patients are still at risk. This has prompted the development and evaluation of several new therapeutic agents including low molecular weight heparin, new antiplatelet drugs (e.g. ticlopidine and clopidogrel), direct thrombin inhibitors, and intravenous and oral glycoprotein IIb/IIIa antagonists. The IIb/IIIa receptor is the final common pathway involved in platelet aggregation. Thus, whatever the stimulus for platelet activation, subsequent aggregation is mediated by the IIb/IIIa receptor binding fibrinogen. A variety of antibody, peptide and non-peptide compounds that block the IIb/IIIa receptor have been developed, and several studies have investigated the role of these agents in patients with acute coronary syndromes both within and outside the setting of percutaneous intervention. This article summarises the studies to date using IIb/IIIa antagonists, and discusses their role in patients with non-ST segment elevation acute coronary syndromes.     

Tirofiban in acute coronary syndromes

Acute coronary syndromes represent a major health problem in terms of incidence and mortality. Intracoronary platelet-rich thrombi may develop in response to plaque rupture, and are involved in the pathogenesis of all acute coronary syndromes. The glycoprotein IIb/IIIa receptor, a platelet surface integrin, plays a key role in platelet aggregation once it has been activated by specific ligands. The development of glycoprotein IIb/IIIa inhibitors has revolutionized the management of acute coronary syndromes. Tirofiban is one of three parenteral glycoprotein IIb/IIIa inhibitors in clinical use, and many trials have demonstrated its clinical efficacy and low rate of adverse effects in patients with non-ST-segment elevation acute coronary syndrome. This article reviews the data concerning its use in the clinical settings of acute coronary syndromes and percutaneous coronary angioplasty, and discusses its benefits in different treatment strategies and in association with other drugs. In particular, the role of early, upstream tirofiban coupled with early aggressive revascularization in the management of high-risk non-ST-segment elevation acute coronary syndromes is emphasized.     

Early Glycoprotein IIb/IIIa Inhibitor Use for Non–ST-segment Elevation Acute Coronary Syndrome: Patient Selection and Associated Treatment Patterns

Objectives: The authors analyzed contemporary use of glycoprotein (GP) IIb/IIIa inhibitors in patients with non–ST-segment elevation acute coronary syndrome (NSTE ACS) to determine patient selection patterns with early (<24 hours) GP IIb/IIIa inhibitor use and the relationship between GP IIb/IIIa inhibitor therapy and use of other guidelines-recommended therapies for NSTE ACS. Methods: Using the CRUSADE Quality Improvement Initiative database, patient characteristics, in-hospital treatments, and outcomes for 65,424 patients with ischemic chest pain of <24 hours' duration and either positive cardiac markers or ischemic electrocardiographic changes were analyzed. Data were collected from 443 U.S. hospitals from January 2001 to June 2003. Results: Only 35% of eligible patients received GP IIb/IIIa inhibitors <24 hours after hospital admission. Approximately one third of patients received GP IIb/IIIa inhibitors in the emergency department, one third in the coronary care unit, and one third in the catheterization laboratory. Admission to a cardiologist's care was the most significant associated factor with early GP IIb/IIIa inhibitor use, along with elevated cardiac markers or ST-segment deviation. Patients at high risk for adverse cardiac events due to advanced age, congestive heart failure, or female gender were less likely to receive early GP IIb/IIIa inhibitor therapy. Patients who received early GP IIb/IIIa inhibitor therapy were more likely to receive other guidelines-recommended therapies. Conclusions: Despite the American College of Cardiology/American Heart Association (ACC/AHA) guidelines recommendations, early GP IIb/IIIa inhibitor therapy remains underutilized in patients with NSTE ACS and administration of early GP IIb/IIIa inhibitors is directed toward lower-risk patients. Early GP IIb/IIIa inhibitor therapy is associated with improved overall adherence to the ACC/AHA guidelines.     

Update on acute coronary syndromes and ST-elevation myocardial infarction

PURPOSE: The goal of modern therapy of acute myocardial infarction is twofold: to achieve rapid reperfusion of ischemic myocardium and to decrease subsequent remodeling, which can have deleterious effects on ventricular function and prognosis. The current paradigm for treatment of most patients with acute coronary syndromes is the consideration of an 'early invasive' strategy. RECENT FINDINGS: Studies published this year have reinforced the importance of early reperfusion, solidified the evidence for early institution of aggressive adjunctive treatment, and added newer therapies to the existing armamentarium. This review evaluates published data from the past year encompassing advancements in percutaneous coronary intervention, drug-eluting stents, glycoprotein IIb/IIIa antagonists, thienopyridines, HMG-CoA reductase inhibitors, aldosterone blockade, low-molecular-weight heparins, direct thrombin inhibitors, implantable cardioverter-defibrillators, and beta-blockade in the treatment of acute coronary syndrome and ST-segment elevation myocardial infarction. In addition to patency of the epicardial coronary arteries, the role of the microvascular has become an area of recent interest. SUMMARY: As novel modalities and approaches are put to the test of clinical trials, evidence-based therapies may help to lessen the adverse effects of myocardial ischemia and reduce future cardiovascular events.     

Antiplatelet therapy in acute coronary syndromes: the emergency physician's perspective

The platelet plays a central role in the pathogenesis of coronary thrombosis after atherosclerotic plaque rupture, and its active inhibition forms a cornerstone of the management of acute coronary syndromes (ACS). Early treatment with clopidogrel in addition to aspirin is more effective than aspirin alone in reducing recurrent ischemic events in patients presenting with ACS, and is a useful adjunct to percutaneous coronary intervention, especially with stenting. There is a potential for increased bleeding complications in patients on clopidogrel therapy who subsequently undergo urgent coronary artery bypass graft surgery. Consequently, many emergency physicians withhold clopidogrel treatment until it is clear that urgent coronary artery bypass graft surgery will not be required. The potential untoward effects seem to be minimized by withholding antiplatelet therapy 3-5 days before surgery. Intravenous glycoprotein (GP) IIb/IIIa receptors inhibitors are also particularly useful in patients who undergo percutaneous coronary intervention, and may have some utility in the medical management of patients with high-risk non-ST-segment elevation ACS, starting in the emergency department. For patients presenting to the emergency department with ACS, the benefits and risks of initiating clopidogrel or GP IIb/IIIa inhibitor therapy need to be considered on an individual basis.     

Present and evolving role of eptifibatide in the treatment of acute coronary syndromes

Platelet-dependent thrombosis plays a central role in the pathophysiology of myonecrosis in both percutaneous coronary interventions (PCIs) and acute coronary syndromes (ACS). Extensive data from randomized clinical trials support the use of acute therapies that interfere with platelet aggregation to provide clinical benefit to patients presenting with ACS and undergoing PCI. Glycoprotein (GP) IIb/IIIa receptor antagonists represent a major advance in the therapy of patients undergoing PCI and those with non-ST segment elevation (NSTE) ACS. Eptifibatide, a small molecule GP IIb/IIIa receptor antagonist, is one such agent. A more consistent platelet-inhibitory effect over time and the short half-life of eptifibatide represent potential pharmacologic advantages compared with other drugs within this class. Large, randomized clinical trials have demonstrated the benefits of eptifibatide for treating patients with NSTE ACS and patients undergoing PCI, establishing its central role in modern management of these conditions. However, recent new advances in the pharmacotherapy of ACS and PCI are requiring us to reconsider the role of GP IIb/IIIa inhibitors; therefore, ongoing and future randomized clinical trials will re-examine GP IIb/IIIa inhibition and establish the role of GP IIb/IIIa inhibitors for the next decade.     

Glycoprotein IIb/IIIa inhibitor-induced thrombocytopenia

Summary Thrombocyte glycoprotein IIb/IIIa inhibitors prevent fibrinogen binding and thereby thrombocyte aggregation. The inhibition of thrombocyte activation at the damaged coronary plaque is the target of the new therapeutic strategies in treating acute coronary syndrome. This reduces the ischemic complications associated with the non-STelevation myocardial infarction (NSTEMI) and percutaneous coronary intervention (PCI). Thrombocytopenia is a known complication of glycoprotein (GP) IIb/IIIa inhibitors. Although, in general, GP IIb/IIIa inhibitor-induced thrombocytopenia is a harmless side effect which responds readily to thrombocyte transfusion, it can occasionally be a very serious complication associated with serious bleeding. In addition patients developing thrombocytopenia have unfavorable outcome (e.g., death, myocardial infarction, bypass surgery or additional PCI) in comparison to patients without thrombocytopenia. Advanced age (> 65 years), low BMI and a low initial thrombocyte count (<180 000/μl) are independent risk factors of thrombocytopenia. The risk of bleeding is higher with this form of thrombocytopenia not only due to the low thrombocyte count but also to the impaired function of the remaining thrombocytes. It is important to closely monitor platelet count during GP IIb/IIIa antagonist treatment. Platelet count monitoring two, six, twelve and 24 hour after starting the treatment reveals most cases of acute thrombocytopenia. Side effects can be avoided by the early discontinuation of the GP IIb/IIIa antagonist treatment. This article reviews the diagnosis and treatment of glycoprotein IIb/IIIa inhibitor-induced thrombocytopenia and summarizes the differential diagnosis from heparin-induced thrombocytopenia and laboratory-related pseudothrombocytopenia.     

Antiplatelet therapy from clinical trials to clinical practice

A platelet-rich clot at the site of severe coronary stenosis, plaque erosion, or a recent plaque rupture is the common etiology of acute ischemic syndromes. Thus, antiplatelet therapy is the cornerstone in the management of these conditions. Aspirin in a dose ranging from 160 to 325 mg once daily should be administered to virtually all patients. In patients with severe disease, particularly those who have no acute angiography, clopidogrel (Plavix, Bristol-Myers Squibb/Sanofi Pharmaceuticals) in a dose of 75 mg once daily should add to the benefit of aspirin for up to a year after the event. Clopidogrel also is an alternative to aspirin where a true aspirin allergy exists. Intravenous platelet glycoprotein IIb/IIIa receptor inhibitors demonstrated a robust benefit when used in conjunction with coronary intervention and thus far have no role in medical therapy alone. Oral platelet glycoprotein IIb/IIIa receptor inhibitors are of no clinical value.     

Selection of glycoprotein IIb/IIIa inhibitors for upstream use in patients with diabetes experiencing unstable angina or non‐ST segment elevation myocardial infarction. What have we learned in the last 10 years?

Coronary disease accounts for the majority of deaths among patients with diabetes and the thrombotic milieu accelerated by diabetes results in unstable angina (UA), non-ST segment elevation myocardial infarction (NSTEMI) or ST-segment elevation myocardial infarction (STEMI) or death. Upstream use of a glycoprotein IIb/IIIa (GP IIb/IIIa) inhibitor with percutaneous coronary intervention (PCI) as part of an early invasive approach is preferred. However substantial numbers of patients present to rural or non-teaching hospitals without immediate access to a catheterization laboratory. Enhanced GP IIb/IIIa receptor mobilization, TXA2 production and platelet activation together present an extensive thrombotic challenge that may not be overcome with current doses of GP IIb/IIIa inhibitors when used without PCI. Heterogeneity of platelet aggregometric analysis may have identified GP IIb/IIIa doses used in clinical trials that may not fully overcome the thrombotic challenge in patients with diabetes. GUSTO-IV ACS failed to demonstrate a difference in mortality when used without PCI. The PURSUIT trial provided evidence that eptifibatide decreases death or non-fatal myocardial infarction (MI) in the main group and in the diabetic subgroup. Reductions in this primary endpoint were driven by the reduction in non-fatal MI. The PRISM and PRISM-PLUS trials demonstrated a reduction in death, MI or refractory ischaemia at 48 h or 7 days in the main cohort but not specifically in patients with diabetes. Data supporting use of GP IIb/IIIa inhibitors are inconsistent, raising the question of whether these agents should be used at all without PCI. Variability in experimental methodology of platelet aggregometry and selection of anticoagulant used during dose finding studies may have generated doses that are insufficient to overcome the thrombotic burden. A new marker of active inflammation, sCD40L is found to be upregulated at subtherapeutic doses of GP IIb/IIIa inhibitors, suggesting that rebound inflammatory processes may partially account for absence of clear evidence of benefit with some GP IIb/IIIa inhibitors in patients with diabetes experiencing UA/NSTEMI.     

Abciximab and atherosclerotic heart disease: use in percutaneous coronary intervention,acute coronary syndromes and acute myocardial infarction

Abciximab irreversibly binds to the glycoprotein IIb/IIIa receptor on both activated and unactivated platelets inhibiting platelet aggregation. It has been studied in a variety of clinical settings including percutaneous coronary intervention (PCI), ST-elevation myocardial infarction, and non ST-elevation acute coronary syndromes. Abciximab has been demonstrated to reduce acute ischaemic events in the setting of percutaneous intervention with both percutaneous transluminal coronary angioplasy and stenting. It has been shown to be particularly effective when used in patients with acute myocardial infarction undergoing primary PCI. The data for its effective use in the medical phase of therapy for patients with acute coronary syndromes, however, is not as consistent. In this article we review the major trials evaluating the use of abciximab in these clinical scenarios compared with placebo and alternative glycoprotein IIb/IIIa inhibitors.     

The platelet in diabetes: focus on prevention of ischemic events

Accelerated atherosclerosis and the increased risk of thrombotic vascular events in diabetes may result from dyslipidemia, endothelial dysfunction, platelet hyperreactivity, an impaired fibrinolytic balance, and abnormal blood flow. There is also a correlation between hyperglycemia and cardiovascular (CV) events. The importance of platelets in the atherothrombotic process has led to investigation of using antiplatelet agents to reduce CV risk. A meta-analysis conducted by the Antiplatelet Trialists' Collaboration demonstrated that aspirin reduced the risk of ischemic vascular events as a secondary prevention strategy in numerous high-risk groups, including patients with diabetes. Based on results from placebo-controlled randomized trials, the American Diabetes Association recommends low-dose enteric-coated aspirin as a primary prevention strategy for people with diabetes at high risk for CV events. Clopidogrel is recommended if aspirin allergy is present. There is occasionally a need for an alternative to aspirin or for additive antiplatelet therapy. Aspirin in low doses inhibits thromboxane production by platelets but has little to no effect on other sites of platelet reactivity. Agents such as ticlopidine and clopidogrel inhibit ADP-induced platelet activation, whereas the platelet glycoprotein (Gp) IIb/IIIa complex receptor antagonists block activity at the fibrinogen binding site on the platelet. These agents appear to be useful in acute coronary syndromes (ACSs) in diabetic and nondiabetic patients. A combination of clopidogrel plus aspirin was more effective than placebo plus standard therapy (including aspirin) in reducing a composite CV outcome in patients with unstable angina and non-ST segment elevation myocardial infarction. In a meta-analysis of six trials in diabetic patients with ACSs, intravenous GpIIb-IIIa inhibitors reduced 30-day mortality when compared with control subjects. Results from controlled prospective clinical trials justify the use of enteric-coated low-dose aspirin (81-325 mg) as a primary or secondary prevention strategy in adult diabetic individuals (aged >30 years) at high risk for CV events. Recent studies support the use of clopidogrel in addition to standard therapy, as well as the use of GpIIb-IIIa inhibitors in ACS patients.     

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The glycoprotein (GP) IIb/IIIa receptor serves as the final common pathway of platelet-thrombus formation. Thus, the GP IIb/IIIa receptor has been identified as a target for the prevention of thrombus formation during acute coronary syndromes and/or percutaneous coronary intervention. While there are several intravenous GP IIb/IIIa inhibitors available, abciximab has proven to be a dependable agent with unique properties. Based on American College of Cardiology, American Heart Association and Society for Angiography and Interventions guidelines, compared with the other available intravenous GP IIb/IIIa inhibitors, abciximab receives the highest recommendation for use in patients with ST-elevation myocardial infarction undergoing primary percutaneous coronary intervention. Abciximab is also unique in that there is no need for renal dosing and its effects are mostly reversible with platelet transfusions.     

Abciximab: a review and update for clinicians

The glycoprotein (GP) IIb/IIIa receptor serves as the final common pathway of platelet-thrombus formation. Thus, the GP IIb/IIIa receptor has been identified as a target for the prevention of thrombus formation during acute coronary syndromes and/or percutaneous coronary intervention. While there are several intravenous GP IIb/IIIa inhibitors available, abciximab has proven to be a dependable agent with unique properties. Based on American College of Cardiology, American Heart Association and Society for Angiography and Interventions guidelines, compared with the other available intravenous GP IIb/IIIa inhibitors, abciximab receives the highest recommendation for use in patients with ST-elevation myocardial infarction undergoing primary percutaneous coronary intervention. Abciximab is also unique in that there is no need for renal dosing and its effects are mostly reversible with platelet transfusions.     

The effects of platelet inhibitors on blood use in cardiac surgery

Platelet inhibition via glycoprotein (GP) IIb/IIIa receptor antagonists has greatly reduced the need for emergent cardiac surgery. However, this change has come at a cost to both the patient and the cardiac surgical team in terms of increased bleeding risk. Current guidelines for patients requiring coronary artery bypass surgery include: 1) cessation of GP IIb/IIIa inhibitor; 2) delay of surgery for up to 12 h if abciximab, tirofiban, or eptafibitide is used; 3) utilization of ultrafiltration via zero balance technique; 4) maintenance of standard heparin dosing despite elevated bleeding times; and 5) transfusion of platelets as needed, rather than prophylactically. These agents present cardiac surgery teams with increased risk during CABG, although overall risk may be diminished by the substantial benefits to patients with acute coronary syndromes and percutaneous interventions, i.e., reduced infarction rates and improved vessel patency. With judicious planning, urgent coronary artery bypass can be safely performed on patients who have been treated with GP IIb/IIIa receptor inhibitors.     

Antithrombotic therapy for non-ST segment elevation myocardial infarction

Non-ST segment elevation myocardial infarction (NSTEMI) is an acute life-threatening event which has a high rate of recurrence. Combined antithrombotic therapy (including cacetylsalicylic acid, clopidogrel, heparins and glycoprotein IIb/IIIa receptor antagonists) substantially reduced major coronary events during the acute phase of coronary heart disease with a good tolerance because of the short duration of such aggressive strategy. The combined antithrombotic strategy also allows to increase the benefit of an early invasive strategy including coronary angiogram with stent percutaneous coronary angioplasty which recent trials have shown that to be preferable to a conservative approach in these high risk patients. Antithrombotic and antiplatelet therapy in association with coronary revascularization play an important role in the prevention of an adverse outcome. Recently, clopidogrel has been shown reduce recurrent ischaemic events, both early and during the first year after non-ST-segment elevation myocardial infarction. An ideal antithrombotic and antiplatelet strategy will reduce events before revascularization, enhance the revascularization procedure without excessive bleeding.     

Bivalirudin for primary percutaneous coronary intervention in acute myocardial infarction: the HORIZONS-AMI trial

The combination of unfractionated heparin (UFH) plus glycoprotein IIb/IIIa inhibitors (GPIs) has been a frequently used anti-thrombotic treatment strategy for acute coronary syndrome patients, including those with ST-segment elevation myocardial infarction undergoing primary percutaneous coronary intervention. However, the ischemic benefit of the UFH plus GPI combination came at the expense of high rates of bleeding complications and thrombocytopenia, both of which have been independently associated with increased mortality. By contrast, bivalirudin monotherapy compared with the combination of UFH plus GPI resulted in improved net clinical outcomes, based on similar ischemic protection with significant reductions in bleeding complications in randomized trials including patients with stable angina, those with unstable angina and those with non-ST-segment elevation myocardial infarction. More recently, the HORIZONS-AMI randomized, open-label, multicenter trial has compared the efficacy and safety of bivalirudin alone versus UFH plus a GPI in 3602 patients with ST-segment elevation myocardial infarction undergoing primary percutaneous coronary intervention. Clinical results derived from this large study, including the final 3-year follow-up data, will be reviewed in the present clinical trial report.     

Bivalirudin: an anticoagulant option for percutaneous coronary intervention

Coronary artery thrombosis is usually triggered by platelet-rich thrombus superimposed on a spontaneously or mechanically disrupted atherosclerotic plaque. Thrombin and platelets both play a role in this process. Unfractionated heparin and aspirin have served as cornerstones in the prevention and treatment of intracoronary thrombus, but unfractionated heparin has several limitations that necessitate the use of adjunctive therapies, such as glycoprotein IIb/IIIa receptor inhibitors and clopidogrel, in order to reduce the risk of ischemic events. These combination therapies, however, typically increase the risk for bleeding complications, as well as the cost and complexity of treatment. Bivalirudin (Angiomax, The Medicines Company), a thrombin-specific anticoagulant, does not share heparin's limitations. Bivalirudin appears to provide clinical advantages over unfractionated heparin therapy in acute coronary syndrome patients and those undergoing percutaneous coronary intervention, without increasing cost or complexity of treatment for most patients.     

Antiplatelet medications and their indications in preventing and treating coronary thrombosis

Platelets play a pivotal role in the pathophysiology of unstable angina, acute myocardial infarction, and complications following percutaneous coronary intervention. Three classes of platelet-inhibiting drugs, aspirin, thienopyridines and platelet glycoprotein IIb/IIIa inhibitors, are now commonly used for the prevention and treatment of disorders of coronary artery thrombosis. For the last several decades aspirin has been the sole option for antiplatelet therapy in the treatment and prevention of the manifestations of cardiovascular disease. However, a wider selection of antiplatelet agents, including the thienopyridines (ticlopidine and clopidogrel) and the platelet glycoprotein (GP)IIb/IIIa receptor antagonists, are now available and provide clinicians with the opportunity to potentially improve upon the previous gold standard of aspirin. This review summarizes these drugs and the scientific data that have led to their use in primary and secondary prevention, unstable angina, myocardial infarction, and percutaneous coronary intervention.     

Antiplatelet medications and their indications in preventing and treating coronary thrombosis

Platelets play a pivotal role in the pathophysiology of unstable angina, acute myocardial infarction, and complications following percutaneous coronary intervention. Three classes of platelet-inhibiting drugs, aspirin, thienopyridines and platelet glycoprotein IIb/ IIIa inhibitors, are now commonly used for the prevention and treatment of disorders of coronary artery thrombosis. For the last several decades aspirin has been the sole option for antiplatelet therapy in the treatment and prevention of the manifestations of cardiovascular disease. However, a wider selection of antiplatelet agents, including the thienopyridines (ticlopidine and clopidogrel) and the platelet glycoprotein (GP)IIb/IIIa receptor antagonists, are now available and provide clinicians with the opportunity to potentially improve upon the previous gold standard of aspirin. This review summarizes these drugs and the scientific data that have led to their use in primary and secondary prevention, unstable angina, myocardial infarction, and percutaneous coronary intervention.     

ST-elevation myocardial infarction: the role of adjunctive antiplatelet therapy

Antiplatelet therapy to reduce the risks of recurrent myocardial infarction and restenosis after primary percutaneous coronary intervention is critically important to optimize the early treatment of ST-segment elevation myocardial infarction (STEMI). Traditionally, acetylsalicylic acid (ASA; aspirin) has been recommended for patients with suspected STEMI, but this agent targets only one of several pathways of platelet aggregation. Antiplatelet agents with different inhibitory mechanisms may act synergistically with ASA. Glycoprotein IIb/IIIa inhibitors are generally not used with fibrinolytic agents in acute STEMI management; indeed, glycoprotein IIb/IIIa inhibitors plus bolus fibrinolytics increase the risk of intracranial hemorrhage. Aggressive antiplatelet therapy with clopidogrel reduces mortality in STEMI patients and offers significant clinical benefits, without an associated increase in major bleeding events. Recent trials support the development of an early and aggressive approach to more complete platelet inhibition using clopidogrel, in combination with ASA, for patients with STEMI.