Combination therapy with tirofiban and enoxaparin in acute coronary syndromes

A Novel Platelet-Repellent Polyphenolic Surface and Its Micropattern for Platelet Adhesion Detection

Surface patterning provides a powerful tool to the diagnosis of platelet adhesion. However, the current methodologies of constructing platelet-patterned surfaces require laborious and complicated steps. Herein, a novel and simple platelet-repellent surface was reported by metal (Fe³⁺ ions)-polyphenol (tannic acid, TA) coordination interaction. The platelet-repellent effect was significantly better than that of poly(ethylene glycol) (PEG) in a long-term. Moreover, the platelet-repellent behavior could extend to other polyphenols-functionalized surfaces. On the basis of these observations, a TA-based micropattern was fabricated in situ by one-step microcontact printing for well-defined platelet adhesion, which can effectively avoid the traditional introduction of inert hydrophilic polymers and bioactive ligands. Afterward, the TA-based micropattern was applied to monitor the adhesion of defective platelets treated with an antiplatelet drug (tirofiban). This work provided a facile, versatile, and environmentally friendly strategy to construct platelet-repellent polyphenolic surfaces and their micropattern. We expect that this simple micropattern could act as a low-cost and label-free platform for biomaterials and biosensors, and could be widely used in the clinical diagnoses of platelet adhesive functions and the evaluation of antiplatelet therapies.

Enoxaparin in acute coronary syndromes

Enoxaparin is a low-molecular-weight heparin (LMWH) derivative that exerts its anticoagulant activity through antithrombin III, an endogenous inhibitor of factor Xa and thrombin IIa. Unlike its unfractionated heparin (UFH) counterparts, enoxaparin has a greater bioavailability, lower incidence of heparin-induced thrombocytopenia and more stable and predictable anticoagulation, allowing fixed dosing without the need for monitoring. These advantages make it an attractive anticoagulant to be used in acute coronary syndrome management. Indeed, several clinical trials and meta-analyses have consistently demonstrated the efficacy of enoxaparin in reducing cardiovascular events and mortality in this population. Although initial clinical trials with enoxaparin during the early conservative approach suggested superior efficacy without differences in safety compared with UFH, emerging data in the current era of early revascularization approach indicate that superior effects of enoxaparin over heparin in reducing clinical events should be balanced against an increase in major hemorrhagic complications. Enoxaparin is a rational alternative to UFH in patients presenting with either unstable angina/non-ST-elevation myocardial infarction or ST-elevation myocardial infarction, with a clinically modest increase in bleeding complications.

Enoxaparin: a pharmacologic and clinical review

INTRODUCTION

Both arterial and venous thromboembolism constitute a significant disease burden worldwide, leading to major use of healthcare resources. As anticoagulants play a pivotal role in the treatment of these disorders, it is vital for healthcare providers to have sufficient knowledge of their biochemical and clinical attributes.

AREAS COVERED

Enoxaparin is one of the most commonly used low-molecular-weight heparins in a wide variety of thromboembolic disorders and has several advantages over unfractionated heparin. An analysis of its biophysical profile, with special emphasis on pharmacokinetic and pharmacodynamic properties, is undertaken in this article. In addition, most recent major clinical studies elucidating its role in common thromboembolic conditions are discussed, while keeping the historical perspective at hand. Readers will be able to understand the pharmacologic properties of enoxaparin with their clinical relevance for day-to-day use and critically analyze the amount and weight of scientific evidence behind its use in various disorders.

EXPERT OPINION

In summary, enoxaparin has been shown, by a vast amount of scientific data, to be a safe and effective agent in the treatment of a whole spectrum of acute coronary syndromes, with similar efficacy and safety in the prevention and treatment of venous thromboembolism.

Mechanism of platelet functional changes and effects of anti-platelet agents on in vivo hemostasis under different gravity conditions

Serious thrombotic and hemorrhagic problems or even fatalities evoked by either microgravity or hypergravity occur commonly in the world. We recently reported that platelet functions are inhibited in microgravity environments and activated under high-G conditions, which reveals the pathogenesis for gravity change-related hemorrhagic and thrombotic diseases. However, the mechanisms of platelet functional variations under different gravity conditions remain unclear. In this study we show that the amount of filamin A coimmunoprecipitated with GPIbalpha was enhanced in platelets exposed to modeled microgravity and, in contrast, was reduced in 8 G-exposed platelets. Hypergravity induced actin filament formation and redistribution, whereas actin filaments were reduced in platelets treated with modeled microgravity. Furthermore, intracellular Ca2+ levels were elevated by hypergravity. Pretreatment of platelets with the cell-permeable Ca2+ chelator BAPTA-AM had no effect on cytoskeleton reorganization induced by hypergravity but significantly reduced platelet aggregation induced by ristocetin/hypergravity. Two anti-platelet agents, aspirin and tirofiban, effectively reversed the shortened tail bleeding time and reduced the death rate of mice exposed to hypergravity. Furthermore, the increased P-selectin surface expression was obviously reduced in platelets from mice treated with aspirin/hypergravity compared with those from mice treated with hypergravity alone. These data suggest that the actin cytoskeleton reorganization and intracellular Ca2+ level play key roles in the regulation of platelet functions in different gravitational environments. The results with anti-platelet agents not only further confirm the activation of platelets in vivo but also suggest a therapeutic potential for hypergravity-induced thrombotic diseases.

Glycoprotein IIb/IIIa inhibitors and low-molecular-weight heparins: a combined role in coronary interventions?

Management strategies for acute coronary syndromes (ACS) are making increasing use of both low-molecular-weight heparins (LMWHs) and glycoprotein (GP) IIb/IIIa inhibitors. To date, however, relatively few studies have assessed the clinical potential of these two classes of agents in combination. There are theoretical grounds to expect LMWHs to be more effective than unfractionated heparin (UFH) in combination with GP IIb/IIIa inhibitors, since UFH, but not LMWH, activates platelets. The antiplatelet effects of GP IIb/IIIa inhibitors are therefore likely to be both more potent and more predictable when combined with LMWH. A recent study in more than 100 patients has demonstrated that a combination of dalteparin and the GP IIb/IIIa inhibitor abciximab provided effective anticoagulation in patients undergoing percutaneous coronary intervention (PCI), without causing significant bleeding or adverse events. Similar results were demonstrated in the National Investigators Collaborating on Enoxaparin (NICE-4) study using a combination of abciximab and enoxaparin in patients undergoing PCI. Of importance is the fact that there were no cases of severe thrombocytopenia in either LMWH study, although this is a recognized potential complication when UFH and abciximab are used in combination. Further studies are now warranted to confirm the efficacy of LMWH and GP IIb/IIIa inhibitors in combination, both for PCI and medical stabilization.

Relative antithrombotic and antihemostatic effects of protein C activator versus low-molecular-weight heparin in primates

The anticoagulant and anti-inflammatory enzyme, activated protein C (APC), naturally controls thrombosis without affecting hemostasis. We therefore evaluated whether the integrity of primary hemostasis was preserved during limited pharmacological antithrombotic protein C activator (PCA) treatment in baboons. The double-mutant thrombin (Trp215Ala/Glu217Ala) with less than 1% procoagulant activity was used as a relatively selective PCA and compared with systemic anticoagulation by APC and low-molecular-weight heparin (LMWH) at doses that inhibited fibrin deposition on thrombogenic segments of arteriovenous shunts. As expected, both systemic anticoagulants, APC (0.028 or 0.222 mg/kg for 70 minutes) and LMWH (0.325 to 2.6 mg/kg for 70 minutes), were antithrombotic and prolonged the template bleeding time. In contrast, PCA at doses (0.0021 to 0.0083 mg/kg for 70 minutes) that had antithrombotic effects comparable with LMWH did not demonstrably impair primary hemostasis. PCA bound to platelets and leukocytes, and accumulated in thrombi. APC infusion at higher circulating APC levels was less antithrombotic than PCA infusion at lower circulating APC levels. The observed dissociation of antithrombotic and antihemostatic effects during PCA infusion thus appeared to emulate the physiological regulation of intravascular blood coagulation (thrombosis) by the endogenous protein C system. Our data suggest that limited pharmacological protein C activation might exhibit considerable thrombosis specificity.

Acute postoperative compromise in cardiovascular function after chest surgery

Attention to preoperative cardiovascular risk factors, appropriate preparation, early recognition, and treatment are essential to prevent potential catastrophic cardiac events from leading to life-threatening situations in the postoperative period.

Administration of eptifibatide to acute coronary syndrome patients receiving enoxaparin or unfractionated heparin: effect on platelet function and thrombus formation

OBJECTIVES

The goal of this study was to compare the antithrombotic effects of enoxaparin versus unfractionated heparin (UFH) when combined with eptifibatide in acute coronary syndrome (ACS) patients.

BACKGROUND

An increasing number of high-risk ACS patients are treated with low-molecular-weight heparin and a glycoprotein (GP) IIb/IIIa inhibitor. There is a paucity of data regarding the antithrombotic properties of such a combination as compared with UFH and GP IIb/IIIa inhibitors.

METHODS

Twenty-six ACS patients scheduled to undergo coronary angiography were treated with subcutaneous enoxaparin (n = 13) or intravenous UFH (n = 13). All patients received eptifibatide just before coronary angiography. Antithrombotic effects were assessed as changes in platelet-thrombus formation using the Badimon ex vivo perfusion chamber. Perfusions were carried out at a high shear rate (HSR) and a low shear rate (LSR). Patients underwent two perfusion studies: at baseline (under enoxaparin or UFH) and 10 min after the eptifibatide bolus. Platelet function was evaluated by ADP-induced platelet aggregation and the rapid platelet function analyzer.

RESULTS

Both therapeutic combinations achieved a marked reduction in platelet aggregation after eptifibatide (83% to 89.7% reduction in the enoxaparin-eptifibatide group and 77.8% to 85.5% reduction in the UFH-eptifibatide group, inter-group differences not significant). Both groups also demonstrated marked reductions in thrombus formation, but the reductions achieved in the enoxaparin-eptifibatide group were significantly higher than those achieved in the UFH-eptifibatide group (HSR: 75.6% reduction vs. 63.9%, respectively, p = 0.01; LSR: 79.7% reduction vs. 66.1%, respectively, p = 0.0001).

CONCLUSIONS

The combination of eptifibatide with enoxaparin appears to have a more potent antithrombotic effect than that of eptifibatide and UFH in the doses tested.

Is the use of unfractionated heparin in acute coronary syndrome outmoded?

Because of the key role of thrombin in the pathogenesis of acute coronary syndrome (ACS), the appropriate selection of antithrombotic therapy is important. Unfractionated heparin (UFH) has been the agent of choice for decades. Unfortunately, UFH has a number of limitations related to its pharmacokinetic and pharmacodynamic properties. Low molecular weight heparins (LMWHs) are attractive alternatives to UFH for several reasons, including predictable anticoagulation and ease of administration. Two LMWHs (dalteparin and enoxaparin) have been approved as alternatives to UFH in patients presenting with unstable angina and non-ST-segment elevation myocardial infarction. Randomized, controlled trials, in addition to open-label series, indicate that LMWH can safely be the agent of choice with or without glycoprotein IIb/IIIa in the medical and upstream management of patients with ACS. Although the data are not definitive, several trials suggest that given intravenously, enoxaparin is safe as the sole antithrombotic agent in the catheterization laboratory.

Low molecular weight heparin and atherosclerosis

Low molecular weight heparin (LMWH) has dramatically impacted the treatment of venous thromboembolic disease and acute coronary syndromes. Recent studies help define the role of these agents for patients undergoing percutaneous coronary interventions and for patients treated with thrombolytic agents for ST-segment elevation myocardial infarction. Recent studies also suggest potential usefulness of LMWH for patients with peripheral vascular disease and its limits of utility in stroke. This review summarizes the evidence about the use of LMWH in these clinical situations.

The role of enoxaparin in interventional management of patients with acute coronary syndromes

Interventional management strategies involving early angiography and percutaneous coronary intervention (PCI) are increasingly widespread in the management of patients with acute coronary syndromes (ACS). Notwithstanding the benefits of early intervention, there is a significant risk of postprocedural thrombotic complications and a need to optimize antithrombotic regimens for use before and during PCI. It is clear that the current standard therapy with unfractionated heparin (UFH) and aspirin can be improved upon, in terms of both efficacy and safety. The low-molecular-weight heparin(s) (LMWHs) offer pharmacologic and practical advantages over UFH. The LMWH enoxaparin has recently emerged as the anticoagulant of choice for the acute management of ACS. Enoxaparin has also demonstrated sustained benefits over UFH in patients proceeding to PCI, and as a procedural anticoagulant. Combination therapy with enoxaparin and a glycoprotein IIb/IIIa inhibitor may further improve the efficacy and safety of antithrombotic treatment during coronary interventions, as a result of the drugs' complementary mechanisms of action. Early clinical evidence supports the use of enoxaparin in combination with glycoprotein IIb/IIIa inhibitors in high-risk patients with ACS. Ongoing, large-scale, randomized controlled studies will help to clarify the role of enoxaparin in interventional cardiology, either as the primary anticoagulant or as part of a combination regimen, and to define optimal regimens for treatment.

Combining enoxaparin and glycoprotein IIb/IIIa antagonists for the treatment of acute coronary syndromes: final results of the National Investigators Collaborating on Enoxaparin-3 (NICE-3) study11Guest Editor for this manuscript was David A. Vorchheimer, MD, Mount Sinai Medical Center, New York, NY

BACKGROUND

In high-risk patients with acute coronary syndromes (ACS), there have been concerns relating to the safety of using low molecular weight heparins (LMWH) in combination with a glycoprotein (GP) IIb/IIIa antagonist, and the continued use of LMWH in patients brought to the cardiac catheterization laboratory for percutaneous coronary intervention (PCI).

METHODS

The National Investigators Collaborating on Enoxaparin-3 (NICE-3) study was an open-label observational study of enoxaparin in combination with any 1 of 3 available GP IIb/IIIa antagonists in patients presenting with non-ST-elevation ACS. The primary end point was the incidence of major bleeding not related to coronary artery bypass graft (CABG) surgery. Data were also recorded on the incidence of death, myocardial infarction (MI), and urgent revascularization for repeat ischemia.

RESULTS

A total of 671 patients with validated data were treated with enoxaparin; 628 of these patients also received a GP IIb/IIIa antagonist (tirofiban, n = 229; eptifibatide, n = 272; abciximab, n = 127); 283 of 628 underwent percutaneous coronary intervention (PCI). The 30-day incidence of non-CABG major bleeding was 1.9%, and was not significantly higher than a prespecified historical control rate of 2.0%. Outcome events included death (1.0% at hospital discharge and 1.6% at 30 days), MI (3.5% and 5.1%, respectively), and urgent revascularization (2.7% and 6.8%, respectively).

CONCLUSIONS

The safety of enoxaparin plus a GP IIb/IIIa antagonist was comparable to that of unfractionated heparin plus a GP IIb/IIIa antagonist, as reported in other recent major trials. Patients undergoing PCI can be safely managed with enoxaparin and a GP IIb/IIIa antagonist, without supplemental use of unfractionated heparin.

The safety and efficacy of subcutaneous enoxaparin versus intravenous unfractionated heparin and tirofiban versus placebo in the treatment of acute ST-segment elevation myocardial infarction patients ineligible for reperfusion (TETAMI)

OBJECTIVES

The aims of the Safety and Efficacy of Subcutaneous Enoxaparin Versus Intravenous Unfractionated Heparin and Tirofiban Versus Placebo in the Treatment of Acute ST-Segment Elevation Myocardial Infarction Patients Ineligible for Reperfusion (TETAMI) study were to demonstrate that enoxaparin was superior to unfractionated heparin (UFH) and that tirofiban was better than placebo in patients with acute ST-segment elevation myocardial infarction (STEMI) who do not receive timely reperfusion.

BACKGROUND

An optimal treatment strategy has not been identified for the many STEMI patients ineligible for acute reperfusion.

METHODS

A total of 1224 patients were enrolled in 91 centers in 14 countries between July 1999 and July 2002. Patients with STEMI ineligible for reperfusion were randomized to enoxaparin, enoxaparin plus tirofiban, UFH, or UFH plus tirofiban. All patients received oral aspirin. The primary efficacy end point was the 30-day combined incidence of death, reinfarction, or recurrent angina; the primary analysis was the comparison of the pooled enoxaparin and UFH groups.

RESULTS

The incidence of the primary efficacy end point was 15.7% enoxaparin versus 17.3% for UFH (odds ratio 0.89 [95% confidence interval CI = 0.66 to 1.21]) and 16.6% for tirofiban versus 16.4% for placebo (odds ratio 1.02 [95% CI 0.75 to 1.38]). The Thrombolysis In Myocardial Infarction (TIMI) major hemorrhage rate was 1.5% for enoxaparin versus 1.3% for UFH (odds ratio 1.16 [95% CI 0.44 to 3.02]) and 1.8% versus 1% for tirofiban versus placebo (odds ratio 1.82 [95% CI 0.67 to 4.95]).

CONCLUSIONS

This study did not show that enoxaparin significantly reduced the 30-day incidence of death, reinfarction, and recurrent angina compared with UFH in non-reperfused STEMI patients. However, enoxaparin appears to have a similar safety and efficacy profile to UFH and may be an alternative treatment. Additional therapy with tirofiban did not appear beneficial.

Pharmacokinetics of enoxaparin in patients undergoing percutaneous coronary intervention with and without glycoprotein IIb/IIIa therapy

The pharmacokinetic profile of enoxaparin was established in a substudy involving 1054 patients undergoing percutaneous coronary intervention. Patients enrolled in the National Investigators Collaborating on Enoxaparin 1 (NICE-1) trial received enoxaparin as a 1.0-mg/kg intravenous bolus. Patients enrolled in the NICE-4 trial received enoxaparin as a 0.75-mg/kg intravenous bolus followed by abciximab as a 0.25-mg/kg bolus and a 0.125-mcg/kg/min 12-hour infusion. Blood samples were collected at six time points over 12 hours and analyzed for plasma anti-Xa, anti-IIa, and Heptest (Haemachem Inc., St. Louis, MO) activity using specific and sensitive assay methods. Data were similar in both trials. Plasma anti-Xa, anti-IIa, and Heptest activity peaked shortly after the enoxaparin bolus and declined in parallel over the ensuing 12 hours. Area under the curve and peak activity were greatest for Heptest activity and least for anti-IIa activity. Values for clearance, volume of distribution, volume of distribution at steady state, and elimination rate constant were on the order of 10 mL/h/kg, 48 mL/kg, 45 mL/kg, and 0.22/h, respectively. These measures suggest that the use of abciximab in combination with enoxaparin during percutaneous coronary intervention is unlikely to affect the pharmacokinetics of enoxaparin.

Glycoprotein IIb/IIIa receptor inhibitors in percutaneous coronary intervention and acute coronary syndrome

OBJECTIVE

To review the contemporary role of the glycoprotein (GYP) IIb/IIIa receptor inhibitors abciximab, eptifibatide, and tirofiban in patients undergoing percutaneous coronary intervention (PCI) and those with an acute coronary syndrome (ACS), and to provide an algorithm based on currently available evidence for specific agents.

DATA SOURCES

Primary articles were identified by a MEDLINE search (1966-January 2003); references cited in these articles provided additional resources.

STUDY SELECTION AND DATA EXTRACTION

All of the articles identified from data sources were considered for relevant information; this article primarily addresses large, controlled or comparative studies, and meta-analyses.

DATA SYNTHESIS

The role of GYP IIb/IIIa inhibitors in patients undergoing PCI and those with ACS has progressed markedly. To date, abciximab has the most robust data in patients undergoing PCI, particularly high-risk individuals. In PCI patients with lower risk (e.g., elective stenting), eptifibatide is a reasonable first-line option. Data do not support tirofiban for routine use in patients undergoing PCI. For individuals with signs and symptoms of ACS, specifically unstable angina or non-ST-segment elevation myocardial infarction (MI), eptifibatide or tirofiban is recommended in high-risk patients when a conservative approach is used (PCI is not planned). Abciximab is not recommended in this situation. In patients with ST-segment elevation MI (STEMI), abciximab is the only GYP IIb/IIIa inhibitor evaluated in large, well-designed investigations. For medical management in combination with a fibrinolytic agent, the role of abciximab remains unclear. For patients undergoing primary PCI for the management of STEMI, the available evidence supports the use of abciximab, albeit further investigation is warranted.

CONCLUSIONS

The role of GYP IIb/IIIa inhibitors in clinical cardiology continues to evolve. Choice of the agent depends on situation of use, patient-specific characteristics and risk stratification, and, in the case of ACS, chosen management strategy (medical management or intervention).

The role of low-molecular-weight heparin in the management of acute coronary syndromes

A substantial number of clinical studies have consistently demonstrated that low-molecular-weight heparin (LMWH) compounds are effective and safe alternative anticoagulants to unfractionated heparins (UFHs). They have been found to improve clinical outcomes in acute coronary syndromes and to provide a more predictable therapeutic response, longer and more stable anticoagulation, and a lower incidence of UFH-induced thrombocytopenia. Of the several LMWH agents that have been studied in large clinical trials, including enoxaparin, dalteparin, and nadroparin, not all have shown better efficacy than UFH. Enoxaparin is the only LMWH compound to have demonstrated sustained clinical and economic benefits in comparison with UFH in the management of unstable angina/ non-ST-segment elevation myocardial infarction (NSTEMI). Also, LMWH appears to be a reliable and effective antithrombotic treatment as adjunctive therapy in patients undergoing percutaneous coronary intervention. Clinical trials with enoxaparin indicate that LMWH is effective and safe in this indication, with or without the addition of a glycoprotein IIb/IIIa inhibitor. The efficacy demonstrated by enoxaparin in improving clinical outcomes in unstable angina/NSTEMI patients has led to investigations of its role in the management of ST-segment elevation myocardial infarction. Initial results are very encouraging, and they indicate that enoxaparin may potentially substitute for UFH as adjunctive therapy in fibrin-specific thrombolytic regimens and improve coronary reperfusion rates in streptokinase-based regimens.

A guide to therapeutic decision-making in patients with non-ST-segment elevation acute coronary syndromes

Recent clinical trial evidence supports an inflammatory etiology in acute ischemic heart disease. When a segment of coronary artery becomes inflamed, important cytokines, such as tissue factor, are released, facilitating thrombosis. Serum inflammatory markers are elevated in most acute coronary syndrome patients at presentation. Mortality risk has been shown to be associated with increased levels of high-sensitivity C-reactive protein (CRP), interleukin 6, and serum vascular cell adhesion molecule. Platelets, which are rich in inflammatory mediators (CD40 and its ligand thrombospondin, and phospholipase A2), also supply important triggers for the inflammatory cascade. In addition, more than 35 platelet-associated messenger ribonucleic acid mediators involved in arterial injury and inflammation have been found. The use of biomarkers of inflammation, such as CRP, and of the sequelae of embolization, such as troponin, provide a window into the underlying pathophysiology of acute ischemic heart disease. New agents from three distinct drug classes have recently flooded the therapeutic armamentarium. Decision-making is further complicated by the choice of an invasive (aggressive) or a medical (conservative) strategy of management with respect to coronary revascularization. For patients at highest risk, aspirin, beta-blockers, nitrates, and a statin should be given, and clopidogrel, enoxaparin, a glycoprotein (GP) IIb/IIIa inhibitor, plus an invasive strategy should be considered. For intermediate- and low-risk patients, a "sliding-scale" approach may be best. Decisions about the three classes of antithrombotics--low-molecular-weight heparins, GP IIb/IIIa inhibitors, and thienopyridines--along with whether to adopt an early invasive strategy, should be made on an individual basis.

Use of low-molecular-weight heparins in the management of acute coronary artery syndromes and percutaneous coronary intervention

CONTEXT

Low-molecular-weight heparins (LMWHs) possess several potential pharmacological advantages over unfractionated heparin as an antithrombotic agent.

OBJECTIVE

To systematically summarize the clinical data on the efficacy and safety of LMWHs compared with unfractionated heparin across the spectrum of acute coronary syndromes (ACSs), and as an adjunct to percutaneous coronary intervention (PCI).

DATA SOURCES

We searched MEDLINE for articles from 1990 to 2002 using the index terms heparin, enoxaparin, dalteparin, nadroparin, tinzaparin, low molecular weight heparin, myocardial infarction, unstable angina, coronary angiography, coronary angioplasty, thrombolytic therapy, reperfusion, and drug therapy, combination. Additional data sources included bibliographies of articles identified on MEDLINE, inquiry of experts and pharmaceutical companies, and data presented at recent national and international cardiology conferences.

STUDY SELECTION

We selected for review randomized trials comparing LMWHs against either unfractionated heparin or placebo for treatment of ACS, as well as trials and registries examining clinical outcomes, pharmacokinetics, and/or phamacodynamics of LMWHs in the setting of PCI. Of 39 studies identified, 31 fulfilled criteria for analysis.

DATA EXTRACTION

Data quality was determined by publication in the peer-reviewed literature or presentation at an official cardiology society-sponsored meeting.

DATA SYNTHESIS

The LMWHs are recommended by the American Heart Association and the American College of Cardiology for treatment of unstable angina/non-ST-elevation myocardial infarction. Clinical trials have demonstrated similar safety with LMWHs compared with unfractionated heparin in the setting of PCI and in conjunction with glycoprotein IIb/IIIa inhibitors. Finally, LMWHs show promise as an antithrombotic agent for the treatment of ST-elevation myocardial infarction.

CONCLUSIONS

The LMWHs could potentially replace unfractionated heparin as the antithrombotic agent of choice across the spectrum of ACSs. In addition, they show promise as a safe and efficacious antithrombotic agent for PCI. However, further study is warranted to define the benefit of LMWHs in certain high-risk subgroups before their use can be universally recommended.

Promise of combined low-molecular-weight heparin and platelet glycoprotein IIb/IIIa inhibition: results from Platelet IIb/IIIa Antagonist for the Reduction of Acute coronary syndrome events in a Global Organization Network B (PARAGON B)

BACKGROUND

Low-molecular-weight heparin (LMWH) has a more predictable anticoagulant effect than unfractionated heparin (UFH), is easier to administer, and does not require monitoring. Minimal data are available on LMWH combined with platelet glycoprotein (GP) IIb/IIIa inhibitors.

METHODS

In the Platelet IIb/IIIa Antagonist for the Reduction of Acute Coronary Syndrome Events in a Global Organization Network B (PARAGON B) trial, patients with an acute coronary syndrome were randomized to receive the IIb/IIIa inhibitor lamifiban or a placebo. To rigorously explore the potential benefits of LWMH and GP IIb/IIIa inhibition, we analyzed the rates of ischemic complications and safety outcomes in PARAGON B.

RESULTS

Approximately one fifth of the patients received LMWH (805 vs 4395 UFH). For the overall cohort, the incidence of death/myocardial infarction (MI)/severe recurrent ischemia (SRI) was 12.2%, and this composite end point was numerically lowest in the lamifiban with LMWH group (10.2%). Similarly, the incidence of death/MI was 11.0% for the entire cohort and lowest in the lamifiban and LMWH group (9.0%). The lower event rate for patients taking LMWH in the lamifiban group was sustained at 6 months, with a lower revascularization rate (51.5% vs 42.8%) and a lower composite of death/MI (13.8% vs 11.9%). Bleeding was comparable in the 2 heparin groups (1.4% with UFH vs 0.9% with LMWH). The propensity adjusted odds ratio for 30-day revascularization was significantly lower with LMWH (odds ratio 0.67, 95% CI 0.57-0.79, P <.001). There were no significant differences in death/MI/SRI at 30 days (P =.465), death/MI at 30 days (P =.264), and stroke at 30 days with the type of heparin use (P =.201) after propensity risk adjustment.

CONCLUSIONS

In the PARAGON B trial, use of LMWH in conjunction with a GP IIb/IIIa inhibitor was safe and associated with a lower revascularization rate. These findings support the rationale and promise for combining GP IIb/IIIa blockers and LMWH for future management of acute coronary syndrome.

Defining the scope of evidence-based practice for low-molecular-weight heparin therapy in high-risk patients with unstable angina and non-ST-elevation myocardial infarction

Various therapies have been utilized for the treatment of unstable angina and non-ST-elevation myocardial infarction (NSTEMI). Each therapy has both advantages and disadvantages with regard to clinical outcomes and an increased risk of bleeding. One emerging primary therapy is low-molecular-weight heparin (LMWH). Concerns have emerged, however, over the use of LMWH in patients going to the catheterization laboratory or who receive platelet glycoprotein IIb/IIIa inhibitors. Available trial data point to the safety and efficacy of LMWH in these patients. Eventually, LMWH will probably replace unfractionated heparin (UFH) for the majority of patients with acute coronary syndromes (ACS). At present, however, practitioners need to consider individually how comfortable they are with the available data.

Safety and effectiveness of combined low molecular weight heparin and glycoprotein IIb/IIIa inhibitors

This study examines the safety and efficacy of low molecular weight heparin (LMWH) in combination with platelet glycoprotein (GP) IIb/IIIa inhibitors in patients with acute myocardial infarction (AMI). LMWH has been shown to be as effective as unfractionated heparin (UFH) in the treatment of acute coronary syndrome (ACS), but there are limited data regarding the safety and efficacy of LMWH in combination with GP IIb/IIIa inhibitors. We studied 37,320 patients in the National Registry of Myocardial Infarction 3 who were treated with GP IIb/IIIa receptor antagonists from April 1998 to September 2000. Using univariate analysis, clinical events were compared between 2,482 patients who received LMWH and 34,838 patients who were treated with UFH. To adjust for confounding covariates, a multivariate regression analysis was also performed. Major bleeding rates were 4.0% in patients on LMWH versus 4.2% in patients who were treated with UFH (odds ratio [OR] 0.99, 95% confidence interval [CI] 0.80 to 1.23, p = 0.92). Similarly, there was no significant difference in the occurrence of recurrent myocardial ischemia (OR 0.93, 95% CI 0.82 to 1.06, p = 0.26), and in-hospital death (OR 0.86, 95% CI 0.71 to 1.05, p = 0.14) between groups. There was a trend toward a decreased risk of recurrent AMI in patients who received LMWH compared with those on UFH (1.5% vs 1.9%, OR 0.74, 95% CI 0.53 to 1.05, p = 0.09). LMWH appears to be a safe and effective alternative to UFH in patients with AMI who receive IIb/IIIa inhibitors.

Defining optimal therapy for the thrombolysis-ineligible patient

Not all patients presenting with acute coronary syndrome (ACS) are able to receive reperfusion therapy. These include patients who present late (after 12 h) or who have bleeding diathesis. Studies have found a number of factors affect the decision to reperfuse. Other treatment options are needed for those patients with acute ST-elevation myocardial infarction (STEMI). Low-molecular weight heparin, such as enoxaparin, now offers these patients the opportunity for successful intervention. Several clinical trials have determined its superiority over unfractionated heparin as an adjunct during thrombolytic therapy. Currently, a trial is underway to determine the effect of enoxaparin in combination with tirofiban in patients with STEMI ineligible for reperfusion therapy. Blinded data for the entire patient cohort shows excellent efficacy and safety in these patients.

Low-molecular-weight heparin therapy for non-ST-elevation acute coronary syndromes and during percutaneous coronary intervention: an expert consensus

BACKGROUND

Therapy with either low-molecular-weight heparin (LMWH) or glycoprotein (GP) IIb/IIIa receptor antagonists is of benefit to patients with acute coronary syndromes (ACSs). However, algorithms that define how LMWH may be used in patients, proceeding from medical management to intervention and in conjunction with GP IIb/IIIa inhibitors, are lacking. The objectives of this task force were to formulate recommendations based on all available data for the use of LMWH, both with and without GP IIb/IIIa receptor antagonists, and to provide seamless integration of care during the transition from medical to interventional management.

METHODS AND RESULTS

An international task force of 14 cardiologists with extensive experience in clinical trials was convened in New York in February 2001 to address issues related to the use of LMWH in patients with non-ST-elevation ACS. Evidence from randomized trials, observational studies, and other reports was discussed, and consensus recommendations were formulated.

CONCLUSIONS

Substantial evidence exists that patients receiving LMWH for an ACS can safely undergo cardiac catheterization and percutaneous coronary intervention. Concerns regarding the transition of these patients from the medical service to the cardiac catheterization laboratory should therefore not impede the upstream use of LMWH. Furthermore, LMWH and GP IIb/IIIa receptor antagonists can be used safely in combination, with no apparent increase in the risk of major bleeding. Consensus algorithms for therapy are presented.

Combination of low molecular weight heparins with antiplatelet agents in non-ST elevation acute coronary syndromes: an update

This article reviews the use of low molecular weight heparin (LMWH) and antiplatelet agents in the treatment of unstable angina and non-ST segment elevation myocardial infarction (NSTEMI), which together account for 1 million hospitalisations annually in the US alone. Mortality and recurrent myocardial infarction (MI) in these conditions is currently approximately 8 to 16% at 1 month, and there is a need to optimise treatment further. Since their introduction, LMWHs have been shown to be successful and well tolerated in the treatment of unstable angina and NSTEMI, but differences have been seen in their efficacy compared with the parent compound, unfractionated heparin (UFH). A meta-analysis of all LMWHs, grouped, versus UFH showed equivalent efficacy and safety. The LMWHs dalteparin sodium and nadroparin calcium have independently been shown to be as effective as UFH. However, enoxaparin sodium has been shown to have greater clinical efficacy than UFH in patients with unstable angina (UA)/NSTEMI. One area of new research is patients with UA/NSTEMI who later undergo percutaneous coronary interventions (PCI), and early data suggest enoxaparin can be safely used as an anticoagulant instead of UFH in these patients. There is a wealth of data for glycoprotein (GP) IIb/IIIa receptor antagonists (abciximab, eptifibatide, lamifiban, and tirofiban), although some are conflicting. Recent meta-analyses suggest that some benefit is conferred by using these compounds, particularly in patients who undergo PCI. Recent trials have focussed on combining GP IIb/IIIa antagonists with LMWH, and although data is still scant, the ACUTE (Anti-thrombotic Combination Using Tirofiban and Enoxaparin) and ACUTE II studies indicate the safety and potential clinical benefit of combining enoxaparin with tirofiban in patients with UA/NSTEMI not undergoing PCI, compared with UFH and tirofiban. The NICE (National Investigators Collaborating on Enoxaparin) 4 study collected data on the combination of enoxaparin and abciximab in patients undergoing PCI, and both safety and efficacy data compared well with historical data collected on the use of UFH with abciximab. The more recent NICE 3 study extended this finding to the combination of enoxaparin with abciximab, tirofiban or eptifibatide. The safety of two doses of dalteparin and abciximab had also been investigated, with the higher dose the efficacious, and also with safety, in patients undergoing PCI. In addition, a GUSTO (Global Use of Strategies to Open Occluded Coronary Arteries in Acute Coronary Syndromes) IV substudy found that dalteparin had equivalent safety to UFH when co-administered with abciximab in patients not undergoing PCI. The NICE 3 and 4 trials were not randomised comparisons, and as such there results must be interpreted with caution. Recently, the CRUISE (Coronary Revascularisation Utilizing Integrelin [eptifibatide] and Single-bolus Enoxaparin) and INTERACT (Integrelin and Enoxaparin randomised assessment of Acute Coronary Syndromes Treatment) studies have provided evidence for both the safety and efficacy of enoxaparin combined with eptifibatide in non-ST elevation patients with acute coronary syndromes. A further study (SYNERGY [Superior Yield of the New strategy of Enoxaparin, Revascularization and GlYcoprotein IIb/IIIa inhibitors]) will investigate the efficacy of the combination of enoxaparin with abciximab versus that of UFH and abciximab in a large cohort of 8000 patients. The use of GP IIb/IIIa agents and LMWH in patients with UA/STEMI has led to their use in those with ST-elevation MI, and studies indicate LMWH is efficacious and can be used safely as an adjunct to thrombolysis. New studies will investigate the use of these agents in patients with STEMI not undergoing thrombolysis and we await the results of these studies.

The role of low-molecular-weight heparin in cardiovascular diseases

Unfractionated heparin continues to have important limitations in clinical practice. It has an inconsistent anticoagulant effect, needs frequent monitoring, and is inactivated by several plasma proteins. Low-molecular-weight heparins have a more predictable anticoagulant effect than unfractionated heparin, are easier to administer, and may not require monitoring. The anticoagulation effect of low-molecular-weight heparins is caused by a combination of inhibition of thrombin generation and inhibition of thrombin activity. Low-molecular-weight heparins have now been evaluated for a number of cardiovascular conditions and have been found to be safe and effective. We review and summarize the existing data regarding the use of low-molecular-weight heparins in cardiovascular diseases, including venous thromboembolism, percutaneous coronary interventions, and acute coronary syndromes such as ST-segment elevation myocardial infarction.

Randomized double-blind safety study of enoxaparin versus unfractionated heparin in patients with non-ST-segment elevation acute coronary syndromes treated with tirofiban and aspirin: the ACUTE II study. The Antithrombotic Combination Using Tirofiban and Enoxaparin

BACKGROUND

In comparison with treatment with unfractionated heparin (UFH) and aspirin (ASA), both tirofiban administered with UFH and ASA, and enoxaparin plus ASA have shown superiority in reducing cardiac ischemic events in patients with unstable angina and non-ST-segment elevation myocardial infarction. Replacing UFH with enoxaparin when tirofiban is administered to patients may offer further therapeutic benefit, but could also increase bleeding.

OBJECTIVE

Our objective was to provide estimates of the frequency of bleeding complications, as defined by means of the Thrombolysis In Myocardial Infarction(TIMI) group, and collect data on clinical efficacy of the combination of tirofiban with enoxaparin plus ASA.

METHODS

Five hundred twenty-five patients with UA/NSTEMI were treated with tirofiban coadministered with ASA and randomized to receive either UFH (n = 210) or enoxaparin (n = 315). Therapy was administered for 24 to 96 hours. Bleeding incidences were assessed until 24 hours after trial therapy was discontinued; other clinical outcomes were assessed for as long as 30 days.

RESULTS

The total bleeding rate (TIMI major + minor + loss-no-site) for the UFH group versus the enoxaparin group was 4.8% vs 3.5% (odds ratio [OR] 1.4, CI 0.6-3.4). The TIMI major and minor bleeding rates for the UFH versus the enoxaparin groups were 1.0% versus 0.3% (OR 3.0, CI 0.3-33.8) and 4.3% versus 2.5% (OR 1.7, CI 0.7-4.6). There was an increase in nuisance cutaneous and oral bleeds (<50 mL of blood loss) in the enoxaparin group. Death or myocardial infarction occurred with similar frequency in the 2 groups (9.0% vs 9.2%). However, refractory ischemia requiring urgent revascularization and rehospitalization because of unstable angina occurred more frequently in the UFH group (4.3% vs 0.6% and 7.1% vs 1.6%, respectively).

CONCLUSIONS

Combination therapy with tirofiban plus enoxaparin appears safe, relative to therapy with tirofiban plus UFH.

Clinical pharmacokinetics of tirofiban, a nonpeptide glycoprotein IIb/IIIa receptor antagonist: comparison with the monoclonal antibody abciximab

Tirofiban is a nonpeptide tyrosine derivative that antagonises platelet glycoprotein IIb/IIIa (GP IIb/IIIa) receptors. It is one of three GP IIb/IIIa antagonists approved by the US Food and Drug Administration for the treatment of patients with acute coronary syndromes. The clinical effect of tirofiban has been shown in large studies such as PRISM (Platelet Receptor Inhibition for Ischemic Syndrome Management), PRISM-PLUS (PRISM - Patients Limited by Unstable Signs and Symptoms) and RESTORE (Randomised Efficacy Study of Tirofiban for Outcomes and Restenosis). Tirofiban is administered as an intravenous infusion. Volume of distribution ranges from 21 to 87 L, and binding to human plasma proteins is modest at 64%. Metabolism in humans is negligible, and most drug is excreted renally with systemic clearance ranging from 4.8 to 25.8 L/h. Renal function may influence the excretion of tirofiban, but concurrent disease or other drugs generally used in patients with ischaemia seem not to do so. This review updates what is known about the pharmacokinetics of tirofiban in humans, especially in comparison with the monoclonal antibody against the IIb/IIIa receptor, abciximab.

[2002 Update of the Guidelines of the Spanish Society of Cardiology for Unstable Angina/Without ST-Segment Elevation Myocardial Infarction]

Since the Spanish Society of Cardiology Clinical Practice Guidelines on Unstable Angina/Non-Q-Wave Myocardial Infarction were released in 1999, the conclusions of several studies that have been published make it advisable to update current clinical recommendations. The main findings are related to the developing role of Chest Pain Units in the management and early risk stratification of acute coronary syndromes in the emergency department; new information concerning the efficacy of glycoprotein IIb/IIIa inhibitors, clopidogrel and low-molecular-weight heparins in the pharmacological treatment of acute coronary syndromes without ST-segment elevation; and the role of early invasive strategy in improving the prognosis of these patients. The published evidence is reviewed and the corresponding clinical recommendations for the management of acute coronary syndromes without persistent ST-segment elevation are updated.

Review of enoxaparin and its clinical applications in venous and arterial thromboembolism

Venous and arterial thromboembolic disorders are common medical conditions that are associated with considerable morbidity and mortality. Unfractionated heparin (UFH) and its derivatives, the low molecular weight heparins (LMWHs), are the anticoagulants of choice when a rapid anticoagulant effect is required. LMWHs have several advantages over UFH, including a longer plasma half-life and higher bioavailability; a predictable dose response, which enables once- or twice-daily dosing; and a more convenient route of administration (subcutaneous instead of intravenous), which enables patients to self-inject in an out-patient setting. Enoxaparin is a LMWH prepared by alkaline hydrolysis of the benzylin ester of UFH. The efficacy of enoxaparin in the management of venous and arterial thromboembolism has been shown in a wide range of patient groups using doses ranging from fixed doses of 20 - 60 mg o.d. and 0.75 - 1.5 mg/kg b.i.d. Other doses, such as 80 mg/day for pregnant women with combined thrombophilic defects, have also been studied. The use of subcutaneous enoxaparin as an effective and safe home treatment for patients with acute proximal deep vein thrombosis (DVT) has been demonstrated. The benefits of preventing venous thromboembolic events with enoxaparin include reducing the costs associated with investigating the symptoms of DVT, acute treatment and hospitalisation, and potentially the development of post-thrombotic syndrome, while improving quality of life and so making the treatment cost effective. In contrast to other LMWHs, enoxaparin has been shown to provide better outcomes than UFH in the treatment of unstable angina and non-ST-segment elevation myocardial infarction, without increasing major bleeding. Adverse events with enoxaparin are infrequent; the most common events are minor bleeding complications. It should be noted that different doses or indications are approved in each country.

Low molecular weight heparins and glycoprotein IIb/IIIa antagonists

The consistent message that emerges from virtually every recent acute coronary syndrome (ACS) trial is that the old "standard" of using aspirin and unfractionated heparin (UFH) can be considerably improved upon. Low molecular weight heparins (LMWHs) (most notably enoxaparin) are emerging as a broad replacement for UFH. Initial safety concerns about combining LMWHs and glycoprotein (GP) IIb/IIIa antagonists have not been borne out; in fact, major bleeding complications may be lower with LMWHs. Clinical outcomes to date suggest that LMWHs may be a better first line therapy than UFH on which to superimpose adjunctive GP IIb/IIIa antagonists. Emerging clinical experience further supports the safety and efficacy of this combination regimen. The forthcoming SYNERGY study will prospectively compare enoxaparin and UFH in high risk patients in whom an invasive management strategy is pursued, with a high coincident use of GP IIb/IIIa antagonists. As the standard of care moves forward, we will see increasing use of LMWHs, with and without GP IIb/IIIa antagonists in conservatively and invasively managed patients.

Low molecular weight heparin and unfractionated heparin in the early pharmacologic management of acute coronary syndromes: a meta-analysis of randomized clinical trials

BACKGROUND

The standard of care in Acute Coronary Syndromes (ACS) includes a full complement of antischemic and antithrombotic therapy. Although aspirin is used widely and concomitant anticoagulation is recommended, the comparative benefits of low molecular weight heparin (LMWH) and unfractionated heparin (UFH) have not been defined.

METHODS/RESULTS

A meta-analysis including all randomized clinical trials comparing LMWH and UFH for the treatment of non-ST segment elevation acute coronary syndromes was performed. Risk ratios (RR), using the DerSimonian-Laird Model, were calculated from a total of 13,320 patients. Death (RR 0.98, 95% CI 0.73-1.31), death and myocardial infarction (MI) (RR 0.86, 95% CI 0.74-1.01), death, MI, recurrent angina or revascularization (RR 0.89, 95% CI 0.74-1.07) and major hemorrhage (RR 1.01, 95% CI 0.81-1.25) occurred with similar frequencies for the anticoagulant-based strategies.

CONCLUSIONS

Fixed dose LMWH therapy given subcutaneously compares favorably with UFH titrated to a target level of anticoagulation and should be considered a safe, effective, and clinically acceptable alternative in the early management of patients with non-ST segment elevation ACS. The superiority of LMWH preparations characterized by high in vitro factor Xa to thrombin inhibitory capacity is supported by clinic trial data but requires further investigation.

The role of low-molecular-weight heparin in the management of acute coronary syndromes

Optimized medical treatment for the non-ST segment elevation acute coronary syndromes (NSTE ACS) should consist of a combined antithrombotic/anti-anginal regimen. Standard antithrombotic treatment is currently unfractionated heparin and aspirin, and in high-risk patients glycoprotein IIb/IIIa inhibitors. However, low-molecular-weight heparins (LMWHs) have practical and clinical advantages over UFH and can be considered an effective alternative in the medical treatment of ACS and in patients proceeding to surgical interventions. Benefits include a more predictable and stable therapeutic response, no need for coagulation monitoring and a reduced incidence heparin-induced thrombocytopenia. In this context, the LMWH enoxaparin has demonstrated sustained clinical and economic benefits compared with UFH, with no increase in major bleeding complications. In addition, recently published studies indicate that LMWHs can improve reperfusion of the arteries and reduce reocclusion when used as adjunctive anticoagulant therapy in patients with ST segment elevation (STE) ACS undergoing thrombolysis with fibrin-specific agents or streptokinase.

Superiority of enoxaparin over heparin in combination with a GPIIb/IIIa receptor antagonist during coronary thrombolysis in dogs

It is known that a low-molecular-weight heparin (LMWH) is more effective than unfractionated heparin in unstable angina/non-Q-wave myocardial infarction (UA/NQMI) and the platelet GPIIb/IIIa receptors play an important role in acute myocardial infarction (AMI). Therefore, enoxaparin might have a similar advantage over heparin when used with a GPIIb/IIIa antagonist (RPR109891) in coronary thrombolysis. After induction of coronary thrombosis in anesthetized dogs, infusion of saline, enoxaparin, heparin, RPR109891, enoxaparin+RPR109891, or heparin+RPR109891 was initiated followed 15 min later by recombinant tissue plasminogen activator (rt-PA). The incidence of reperfusion in the enoxaparin+RPR109891- and the heparin+RPR109891-treated groups was similar, but time to reperfusion tended to be shorter for enoxaparin versus heparin. Only 43% of the vessels reoccluded in the enoxaparin+RPR109891 group, compared to 100% vessels in the heparin+RPR109891 group. Enoxaparin+RPR109891 maintained flow for a significantly longer time compared to saline, enoxaparin, heparin, and heparin+RPR109891. Enoxaparin+RPR109891 and heparin+RPR109891 increased the template bleeding time by 2- and 3-fold and activated partial thromboplastin time (APTT) by 1.3- and 3-fold, respectively. These data suggest that enoxaparin is more effective and potentially safer than heparin when combined with a GPIIb/IIIa receptor antagonist during rt-PA-induced coronary thrombolysis.

2000 ACC/AHA guidelines for the management of patients with unstable angina and non-ST-segment elevation myocardial infarction: a practical summary for emergency physicians

There have been numerous significant clinical advances in both the diagnosis and therapy of acute coronary syndrome during the past several years. Even the term "acute coronary syndrome" is a recent creation meant to expand clinical attention in patients with chest pain of coronary origin beyond identification of ST-segment elevation myocardial infarction and prompt initiation of reperfusion therapy and to include the evaluation and management of those patients with unstable angina (UA) or myocardial injury that does not cause ST-segment elevation. Many of these advances have been studied and first implemented outside the emergency department, leading some emergency physicians to be slow to embrace them, and leaving others without a viable practical option to use them outside of the cardiac catheterization laboratory or the coronary care unit. In September 2000, the American College of Cardiology and the American Heart Association issued practice guidelines for the care of patients with UA and non-ST-segment elevation myocardial infarction. The guidelines specifically address the diagnosis and management of UA and non-ST-segment elevation myocardial infarction in the ED, suggesting evidence-based standards for risk stratification, for the use of biologic markers of myocardial damage and other adjunctive diagnostic tests, and for the appropriate use of antiplatelet and antithrombin therapeutic agents. This article provides an overview of the ED-pertinent analyses and recommendations from the 93-page document. A commentary on the implementation of these recommendations in the ED follows in a separate article.

Pharmacodynamic characterization of the interaction between abciximab or tirofiban with unfractionated or a low molecular weight heparin in healthy subjects

AIMS

The objective of our study was to define the interaction between either unfractionated heparin (UFH) or a low molecular weight heparin, reviparin (REV), and the pharmacodynamic profile of the GPIIb/IIIa-antagonists abciximab (ABC) or tirofiban (T).

METHODS

Two studies each containing 18 healthy subjects were performed, and all were pretreated with aspirin (ASA) for 3 days. Volunteers then received UFH (5000 IU bolus/infusion 7 IU kg(-1) h(-1) for 7 h, n = 6), REV (4200-anti-Xa-IU s.c., n = 6) or placebo (n = 6). One hour later, ABC (study I) or T (study II) were given by i.v. infusion for 6 h. The pharmacodynamic effects measured were bleeding time (BT), fibrinogen-binding at the GPIIb/IIIa-receptor (FIB), expression of the platelet secretion marker CD62, and ADP (20 microM)- and collagen (5 microg ml(-1))-induced platelet aggregation.

RESULTS

After treatment with both GPIIb/IIIa-antagonists, prolongation of BT occurred to a similar magnitude (approximately 25-30 min) and was not affected by UFH or REV-comedication. ABC or T with ASA alone resulted in nearly the same magnitude of reduction in FIB and platelet aggregation. After coadministration with UFH, FIB was significantly higher (thus less inhibited) than after after T + ASA alone (19 +/- 16% vs 55 +/- 36%) or ABC + ASA alone (8 +/- 9% vs 32 +/- 11%). This attenuation of FIB was not seen with REV. Inhibition of ADP-and collagen-induced aggregation tended to be attenuated by treatment with UFH (e.g. ADP-induced aggregation at 0.25 h after ABC + ASA alone =13 +/- 4%; after coadministration with UFH = 40 +/- 26%). No such changes were noted with REV. Minor reductions in CD62-expression were seen in subjects given ABC or T alone, but expression was not affected by UFH or REV.

CONCLUSIONS

Co-medication with UFH attenuated platelet inhibition during treatment with GPIIb/IIIa-antagonists, but these effects were not seen with the low molecular weight heparin reviparin. The results show that administration of reviparin together with abciximab or tirofiban did not adversely affect the pharmacodynamic profile of these GPIIb/IIIa-antagonists.

Advances create opportunities: implementing the major tenets of the new unstable angina guidelines in the emergency department

Of all the clinical syndromes with which emergency physicians must deal, chest pain of coronary cause has benefited from the most striking recent advances both in diagnostic approach (cognitive and technologic) and in therapeutic options. Chest pain evaluation and management have become important foci of research in emergency medicine, and entire units are dedicated to its clinical prosecution in emergency departments and elsewhere in the hospital. New diagnostic tools are proposed and studied on a regular basis. Antiplatelet, antithrombin, and fibrinolytic agents unknown in clinical practice as recently as 5 years ago have secured places in the emergency physician's armamentarium for treating acute coronary syndrome. Many of these diagnostic and therapeutic tools have been developed in the coronary care unit and in the cardiac catheterization laboratory. Although intuitively they may also be useful outside of those settings, they have unreliably been brought to the ED for implementation and resultant appropriate prompt and early care of the coronary patient who does not meet fibrinolytic criteria. As emergency physicians seek to bring accurate chest pain risk stratification into their practice and begin to use new therapeutic agents to minimize myocardial damage before turning the patient's care over to other specialists, it is essential that they are familiar with the data supporting these approaches. In this commentary, we seek to place the American College of Cardiology/American Heart Association unstable angina guidelines into the clinical context of the ED.

Platelet glycoprotein IIb/IIIa-receptor inhibitors in patients with acute coronary syndromes or undergoing percutaneous coronary interventions: a review

BACKGROUND

Over 12.2 million Americans are affected by acute coronary syndromes (ACS) resulting from arterial thrombosis after atherosclerotic plaque rupture. The mechanism of thrombosis is based on the platelet activation pathway, facilitated by expression of the platelet glycoprotein (GP) lIb/Illa receptors. The platelet GP IIb/IIIa-receptor inhibitors represent a new class of drugs, of which abciximab, eptifibatide, and tirofiban have been approved for use in the medical management of ACS and as adjunctive therapy in percutaneous coronary interventions (PCIs).

OBJECTIVE

This article reviews the results of published multicenter, randomized, placebo-controlled, double-blind trials of the efficacy and safety of platelet GP IIb/IIIa-receptor inhibitors in patients with coronary artery disease.

METHODS

To identify articles for this review, a search of MEDLINE for the years 1994 through 2000 was conducted using the key words myocardial ischemia, unstable angina, angioplasty, stent, abciximab, eptifibatide, tirofiban, lamifiban, and platelet aggregation inhibitors. Relevant review articles were consulted as well as reports of clinical studies.

CONCLUSIONS

Three GP IIb/IIIa-receptor inhibitors--abciximab, eptifibatide, and tirofiban-are approved by the US Food and Drug Administration as adjunctive therapy in patients undergoing PCI. Eptifibatide and tirofiban 'are also indicated for the medical management of patients with unstable angina and non-ST-segment-elevation myocardial infarction. The use of GP IIb/IIIa-receptor inhibitors as a component of management with fibrinolytic agents is under investigation. Studies comparing the efficacy of tirofiban and abciximab in patients undergoing planned PCI with intracoronary stent placement are in progress. Until data are available from long-term trials and head-to-head comparisons of these agents, it is not possible to generalize about their overall or comparative efficacy.

The A-to-Z Trial: Methods and rationale for a single trial investigating combined use of low-molecular-weight heparin with the glycoprotein IIb/IIIa inhibitor tirofiban and defining the efficacy of early aggressive simvastatin therapy

BACKGROUND

The A-to-Z Trial is an ongoing international, multicenter, randomized study designed to investigate 2 issues concerning contemporary care of patients with acute coronary syndromes (ACS). The first issue is whether the use of low-molecular-weight heparin versus unfractionated heparin affects outcomes and safety when used as a therapy adjunctive to baseline treatment with tirofiban and aspirin in patients with non-ST-elevation (nSTE) ACS. The second issue is whether early use of an aggressively dosed statin is superior to a current trial-based "accepted care" regimen of a lower-dose statin started 3 to 6 months after an acute event.

METHODS

The study is conceptually and functionally divided into 2 sequential parts-the "A" Aggrastat and "Z" Zocar phases. The primary A-phase end point is a composite of all-cause mortality, myocardial infarction (MI), and documented refractory ischemia at 7 days. Both nSTE-ACS patients from the A phase and patients with ST-elevation ACS who meet specific risk criteria are eligible to enter the subsequent "Z" (Zocor) chronic phase (Z phase). The primary end point of the Z phase is a composite of cardiovascular death, MI, readmission for ACS, and stroke. The trial will continue until 970 primary events have occurred in the Z-phase population.

CONCLUSION

This trial is evaluating 2 temporally connected sequences of phamacotherapy for ACS. At completion, trial results will provide definitive evidence regarding efficacy and safety of early, intensive statin therapy and better define the role of low-molecular-weight heparin in patients with nSTE ACS.

Risk stratification in non-ST segment elevation acute coronary syndromes with special focus on recent guidelines

Patients with unstable angina or non-ST segment elevation (non-Q-wave) myocardial infarction are a heterogeneous group with respect to their risk of developing clinically significant adverse events such as subsequent myocardial infarction and death. Recent guidelines promote risk stratification of these patients, targeting high-risk patients for maximal antithrombotic and antiischemic therapy and low-risk patients for early discharge. We reviewed current and future modalities for risk stratification of patients and the predictive value of these methods in context with available pharmacologic agents. Unfortunately, most of the data identifying a particular pharmacologic regimen as beneficial in high-risk patients are retrospectively derived from large trials. Until prospective studies that use markers to guide therapy are available, clinicians should be familiar with the use of these risk markers and their application to the role of a given management strategy, including pharmacologic therapy.

Low molecular weight heparin therapy for percutaneous coronary intervention: a practice in evolution

Unfractionated heparin (UFH) remains the principal antithrombotic agent during percutaneous coronary intervention (PCI) but is associated with significant limitations including an unpredictable anticoagulation dose response, the requirement for frequent monitoring, and transient rebound hypercoagulability. Low molecular weight heparin (LMWH) represents an attractive alternative due to its predictable dose response relationship, superior antithrombotic efficacy and potential for improved clinical safety, and has been used increasingly in patients with acute coronary syndromes prior to coronary angiography. The rationale and existing data regarding the use of LMWH in PCI is summarized and reviewed. Preliminary clinical guidelines for the use of LMWH in the transition from medical stabilization of patients with acute coronary syndromes to invasive management in the catheterization laboratory are presented.

Clinical use of new antithrombotic therapies for medical management of acute coronary syndromes

Prevention and management of acute coronary syndromes (ACS) are focal points of interest among health care providers. Acute coronary syndromes is an all-encompassing term that refers to unstable angina, non-Q wave myocardial infarction, and Q wave myocardial infarction. These syndromes are usually the result of atherosclerotic plaque rupture leading to thrombus formation in a coronary artery. Heparin and aspirin are traditional antithrombotic treatments. They typically are administered with antiischemic therapies and often with fibrinolytic agents for patients with ST segment elevation associated with acute myocardial infarction. Although aspirin and heparin are important, they have significant limitations that have prompted development of newer antithrombotic approaches. Adenosine diphosphate inhibitors have been evaluated as either alternatives or adjunctive treatment to aspirin. Glycoprotein IIb-IIIa receptor inhibitors, low-molecular-weight heparins, and direct thrombin inhibitors have been studied as concurrent therapy with, or as alternatives to, heparin.