Low molecular weight heparin in acute coronary syndrome: evidence for superior or equivalent efficacy compared with unfractionated heparin?

Heparin versus placebo for non-ST elevation acute coronary syndromes

BACKGROUND

Non-ST elevation acute coronary syndromes (NSTEACS) represent a spectrum of disease including unstable angina and non-ST segment myocardial infarction (NSTEMI). Despite treatment with aspirin, beta-blockers and nitroglycerin, unstable angina/NSTEMI is still associated with significant morbidity and mortality. Although evidence suggests that low molecular weight heparin (LMWH) is more efficacious compared to unfractionated heparin (UFH), there is limited data to support the role of heparins as a drug class in the treatment of NSTEACS. This is an update of a review last published in 2008.

OBJECTIVES

To determine the effect of heparins (UFH and LMWH) compared with placebo for the treatment of patients with non-ST elevation acute coronary syndromes (unstable angina or NSTEMI).

SEARCH METHODS

For this update the Cochrane Heart Group Trials Search Co-ordinator searched the Cochrane Central Register of Controlled Trials on The Cochrane Library (2013, Issue 12), MEDLINE (OVID, 1946 to January week 1 2014), EMBASE (OVID, 1947 to 2014 week 02), CINAHL (1937 to 15 January 2014) and LILACS (1982 to 15 January 2014). We applied no language restrictions.

SELECTION CRITERIA

Randomized controlled trials of parenteral UFH or LMWH versus placebo in people with non-ST elevation acute coronary syndromes (unstable angina or NSTEMI).

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed quality of studies and independently extracted data.

MAIN RESULTS

There were no new included studies for this update. Eight studies (3118 participants) were included in this review. We found no evidence for difference in overall mortality between the groups treated with heparin and placebo (risk ratio (RR) = 0.84, 95% confidence interval (CI) 0.36 to 1.98). Heparins compared with placebo, reduced the occurrence of myocardial infarction in patients with unstable angina and NSTEMI (RR = 0.40, 95% CI 0.25 to 0.63, number needed to benefit (NNTB) = 33). There was a trend towards more major bleeds in the heparin studies compared to control studies (RR = 2.05, 95% CI 0.91 to 4.60). From a limited data set, there appeared to be no difference between patients treated with heparins compared to control in the occurrence of thrombocytopenia (RR = 0.20, 95% CI 0.01 to 4.24). Assessment of overall risk of bias in these studies was limited as most of the studies did not give sufficient detail to allow assessment of potential risk of bias.

AUTHORS' CONCLUSIONS

Compared with placebo, patients treated with heparins had a similar risk of mortality, revascularization, recurrent angina, and thrombocytopenia. However, those treated with heparins had a decreased risk of myocardial infarction and a higher incidence of minor bleeding. Overall, the evidence assessed in this review was classified as low quality according to the GRADE approach. The results presented in this review must therefore be interpreted with caution.

Attributable Cost and Length of Stay for Patients with Enoxaparin-Associated Bleeding

OBJECTIVES

Patients receiving enoxaparin are at risk of bleeding. The study of the economic impact of enoxaparin-associated bleeding in Asian population, however, is limited. This study aimed to estimate the attributable costs and length of stay (LOS) of patients experiencing enoxaparin-associated bleeding compared with nonbleeding patients in the setting of acute coronary syndrome.

METHODS

We conducted a retrospective cohort study of hospitalized patients with acute coronary syndrome who received enoxaparin in a large university-affiliated hospital. Cost and LOS were compared among three groups of patients according to the status of bleeding event. The attributable cost and LOS were estimated by using multiple linear regressions with log-transformed model and adjusted by confounders. The adjusted means of cost and LOS estimates were retransformed to their natural values by using Duan's smearing estimator. The differences of costs and LOS were presented as mean with 95% confidence intervals (CIs).

RESULTS

Out of 346 patients, 134 experienced enoxaparin-associated bleeding (28 and 106 patients experienced major and minor bleeding, respectively). The average age and gender in both groups were similar. Compared to the nonbleeding group, the attributable cost and LOS were 108,226 Thai baht (95% CI: 87,068-129,386) and 8 days (95% CI: 7.1-9.0) for major bleeding and 72,997 Thai baht (95% CI: 57,822-88,172) and 3.1 days (95% CI: 2.5-3.7) for minor bleeding, respectively.

CONCLUSIONS

Bleeding is significantly associated with increased cost and LOS among enoxaparin users. These findings suggest that strategies aiming to reduce bleeding events may potentially help reduce the cost of care among patients with acute coronary syndrome receiving enoxaparin therapy.

A critical review of clinical trials for low-molecular-weight heparin therapy in unstable coronary artery disease

Unstable angina and non-ST-segment elevation myocardial infarction (MI) are collectively referred to as unstable coronary artery disease (UCAD). They are conditions that share a common pathophysiology and represent frequently encountered, potentially life-threatening clinical manifestations of advanced atherosclerosis. Therefore, treatment of UCAD is a major focus for practicing clinicians, and although pharmacologic agents have been developed that impact on patient outcome, recent data suggest that a further reduction in ischemic complications is possible. Acute-phase treatment with aspirin is associated with a significant reduction in death and nonfatal MI in patients with UCAD. This benefit is enhanced by the addition of unfractionated heparin (UFH) to the treatment strategy; however, UFH requires careful monitoring and titration. In contrast, low-molecular-weight heparins (LMWHs), produced by chemical or enzymatic depolymerization of UFH, yield a predictable and consistent pharmacokinetic profile and anticoagulant response, making them an attractive treatment alternative to UFH in patients with UCAD. The optimal duration of treatment with LMWH is an important question influenced by the observation that reactivation of coagulation occurs following the early and abrupt discontinuation of heparin treatment. Early trials, such as FRISC and FRIC, demonstrated the benefit of acute therapy with dalteparin sodium; however, the results of extended treatment with dalteparin were inconclusive. The extended phase of these studies included relatively low-risk patients, and a once-daily, relatively low-dose strategy was employed. The findings derived from the FRISC II trial, which used a twice-daily dose of dalteparin, suggest a benefit for at least 60 days with extended treatment in high-risk patients with UCAD. Although an early-invasive treatment strategy is particularly beneficial, patients in whom early revascularization is not possible should be considered for extended treatment with dalteparin for up to 45 days, especially those awaiting percutaneous coronary intervention. Extended treatment with dalteparin therefore provides a protective "bridge" to enhance the outcome of patients with UCAD awaiting revascularization.

The low-molecular-weight heparin dalteparin as adjuvant therapy in acute myocardial infarction: the ASSENT PLUS study

Rapid reperfusion of an infarct-related artery reduces the extent of myocardial damage and improves survival in acute myocardial infarction (AMI). Currently, anticoagulant treatment with unfractionated heparin (UFH) is used as adjuvant therapy to fibrinolytic treatment. The low-molecular-weight heparin (LMWH) dalteparin is at least as effective as UFH in unstable coronary artery disease. The ASSENT PLUS trial was carried out to evaluate whether dalteparin is as effective as UFH as an adjunct to recombinant tissue-plasminogen activator (rt-PA) and aspirin in obtaining patency and Thrombolysis in Myocardial Infarction (TIMI)-3 flow in patients with AMI. The primary assessment of this phase II trial was TIMI flow, determined by coronary angiography. Patients with ST-elevation MI were randomized to receive aspirin and either rt-PA and UFH for 48 h, or rt-PA and dalteparin for 4 to 7 days. Evaluation was by TIMI flow after 4 to 7 days and clinical events (death, reinfarction, or revascularization) up to 30 days. There was a clear trend toward greater TIMI 3 flow with dalteparin compared with UFH. There was significantly less TIMI 0-1 flow or thrombus in the dalteparin group. Bleeding rates were similar. The occurrence of reinfarction was reduced during dalteparin treatment. These findings suggest that dalteparin could be substituted for UFH as an adjunct to rt-PA/aspirin in the management of patients with AMI.

Reduced factor VII and factor VIII levels and prolonged thrombin-generation times during a healthy diet in middle-aged women with mild to moderate cardiovascular disease risk

BACKGROUND

No experimental study has investigated the effect of whole-diet therapies on a wide range of hemostatic parameters, and their relationship with metabolic and inflammatory markers. Such information was sought in middle-aged women with moderate cardiovascular disease (CVD) risk subjected to an integrated healthy diet.

METHODS

Forty-nine premenopausal women were screened for C-reactive protein levels > or =1 mg L(-1) and at least one additional CVD risk factor. Sixteen women (age: 43-54 years) were selected and received a 12-week diet (four phases) integrating National Cholesterol Education Program-Adult Treatment Panel-III recommendations with components of a Mediterranean-style diet.

RESULTS

We observed a reduction in body mass index (BMI) (P = 0.001), waist circumference (P = 0.005), total (P = 0.011) and low-density lipoprotein (LDL) cholesterol levels (P = 0.035). Antigen levels of coagulation factor (F)VII (P = 0.003) and FVIII (P = 0.005) were clearly reduced by dietary intervention, which also appeared to decrease circulating tissue factor but not fibrinogen and von Willebrand factor (VWF) antigen levels. Levels of FVIII and tumor necrosis factor-alpha, among the inflammation markers, showed the highest correlation, particularly before the intervention (r = 0.55, P = 0.032). Only this cytokine influenced FVIII variation over time, thus highlighting new relations between coagulation and cellular components of inflammation. The functional effect of diet on coagulation was indicated by markedly prolonged thrombin generation initiation and propagation times (lag time, P = 0.002; time to peak, P = 0.005).

CONCLUSIONS

The changes observed in coagulation initiation and amplification phases, body composition and lipid profile could translate into a remarkable decrease in the risk for cardiovascular disease. Our observations suggest novel relationships between coagulation and inflammatory components.

Heparin versus placebo for acute coronary syndromes

BACKGROUND

Acute coronary syndromes (ACS) represent a spectrum of disease including unstable angina (UA) and non-ST segment myocardial infarction (NSTEMI). Despite treatment with aspirin, beta-blockers and nitroglycerin, UA/NSTEMI is still associated with significant morbidity and mortality. Although emerging evidence suggests that low molecular weight heparin (LMWH) is more efficacious compared to unfractionated heparin (UFH), there is limited data to support the role of heparins as a drug class in the treatment of ACS.

OBJECTIVES

To determine the effect of heparins (UFH and LMWH) compared with placebo for the treatment of patients with ACS.

SEARCH STRATEGY

We searched the Cochrane Central Register of Controlled Trials on The Cochrane Library (issue 4, 2002), MEDLINE (1966 to May 2002), EMBASE (1980 to May 2002) and CINAHL (1982 to May 2002). Authors of included studies and pharmaceutical industry representatives were contacted to determine if unpublished studies which met the inclusion criteria were available.

SELECTION CRITERIA

Randomized controlled trials of parenteral UFH or LMWH versus placebo in people with ACS (UA or NSTEMI).

DATA COLLECTION AND ANALYSIS

Two reviewers independently assessed quality of studies. Data were extracted independently by two reviewers. Study authors were contacted to verify and clarify missing data.

MAIN RESULTS

Eight studies (3118 participants) were included in this review. We found no evidence for difference in overall mortality between the groups treated with heparin and placebo (RR = 0.84, 95% CI 0.36 to 1.98). Heparins reduced the occurrence of MI (RR = 0.40, 95% CI 0.25 to 0.63, NNT = 33). An increase in the incidence of minor bleeds (RR = 6.80, 95% CI 1.23 to 37.49, NNH = 17).

AUTHORS' CONCLUSIONS

Compared to placebo, patients treated with heparins had similar risk of mortality, revascularization, recurrent angina, major bleeding and thrombocytopenia. However, those treated with heparins had decreased risk of MI and a higher incidence of minor bleeding.

Development of a dosage strategy in patients receiving enoxaparin by continuous intravenous infusion using modelling and simulation

AIM

To develop an appropriate dosing strategy for continuous intravenous infusions (CII) of enoxaparin by minimizing the percentage of steady-state anti-Xa concentration (C(ss)) outside the therapeutic range of 0.5-1.2 IU ml(-1).

METHODS

A nonlinear mixed effects model was developed with NONMEM for 48 adult patients who received CII of enoxaparin with infusion durations that ranged from 8 to 894 h at rates between 100 and 1600 IU h(-1). Three hundred and sixty-three anti-Xa concentration measurements were available from patients who received CII. These were combined with 309 anti-Xa concentrations from 35 patients who received subcutaneous enoxaparin. The effects of age, body size, height, sex, creatinine clearance (CrCL) and patient location [intensive care unit (ICU) or general medical unit] on pharmacokinetic (PK) parameters were evaluated. Monte Carlo simulations were used to (i) evaluate covariate effects on C(ss) and (ii) compare the impact of different infusion rates on predicted C(ss). The best dose was selected based on the highest probability that the C(ss) achieved would lie within the therapeutic range.

RESULTS

A two-compartment linear model with additive and proportional residual error for general medical unit patients and only a proportional error for patients in ICU provided the best description of the data. Both CrCL and weight were found to affect significantly clearance and volume of distribution of the central compartment, respectively. Simulations suggested that the best doses for patients in the ICU setting were 50 IU kg(-1) per 12 h (4.2 IU kg(-1) h(-1)) if CrCL < 30 ml min(-1); 60 IU kg(-1) per 12 h (5.0 IU kg(-1) h(-1)) if CrCL was 30-50 ml min(-1); and 70 IU kg(-1) per 12 h (5.8 IU kg(-1) h(-1)) if CrCL > 50 ml min(-1). The best doses for patients in the general medical unit were 60 IU kg(-1) per 12 h (5.0 IU kg(-1) h(-1)) if CrCL < 30 ml min(-1); 70 IU kg(-1) per 12 h (5.8 IU kg(-1) h(-1)) if CrCL was 30-50 ml min(-1); and 100 IU kg(-1) per 12 h (8.3 IU kg(-1) h(-1)) if CrCL > 50 ml min(-1). These best doses were selected based on providing the lowest equal probability of either being above or below the therapeutic range and the highest probability that the C(ss) achieved would lie within the therapeutic range.

CONCLUSIONS

The dose of enoxaparin should be individualized to the patients' renal function and weight. There is some evidence to support slightly lower doses of CII enoxaparin in patients in the ICU setting.

[Platelet activation and hypercholesterolemia in the pathogenesis of deep vein thrombosis]

Currently it is accepted that deep vein thrombosis is a multifactorial event in which the presence of activated platelets and also plasmatic lipids seems to play a pivotal role that it is not well established in the scientific bibliography. Due to the non consensus state about these topics between the different groups working in these aspects, the topic involving deep vein thrombosis-platelets-lipids, and also their interactions, still is an interesting area of investigation, in which it is necessary to carry out studies with the aim of establishing risk factors, initial diagnostic methods and clinical assays to probe the efficacy of new therapies.

Low-molecular-weight heparin compared with unfractionated heparin for patients with non–ST-segment elevation acute coronary syndromes treated with glycoprotein IIb/IIIa inhibitors: Results from the CRUSADE initiative

BACKGROUND

Both heparin and glycoprotein (GP) IIb/IIIa inhibitor therapy and early invasive management strategies are recommended by the American College of Cardiology (ACC)/American Heart Association (AHA) guidelines for the treatment of patients with non-ST-segment elevation acute coronary syndromes (NSTE ACS). However, controversy exists about which form of heparin-unfractionated (UF) or low-molecular-weight (LMW)-is preferable. We sought to compare the efficacy and safety of these treatment strategies in a large contemporary population of patients with NSTE ACS.

METHODS

Using data from the CRUSADE Initiative, we evaluated LMWH and UFH in high-risk NSTE ACS patients (positive cardiac markers and/or ischemic ST-segment changes) who had received early (< 24 hours) GP IIb/IIIa inhibitor therapy and underwent early invasive management. In-hospital outcomes were compared among treatment groups.

RESULTS

From a total of 11,358 patients treated at 407 hospitals in the US from January 2002-June 2003, 6881 (60.6%) received UFH and 4477 (39.4%) received LMWH. Patients treated with UFH were more often admitted to a cardiology inpatient service (73.6% vs. 65.5%, P < 0.0001) and more frequently underwent diagnostic catheterization (91.8% vs. 85.9%, P < 0.0001) and percutaneous coronary intervention (PCI) (69.7% vs. 56.9%, P < 0.0001) than patients treated with LMWH. The point estimate of the adjusted risk of in-hospital death or reinfarction was slightly lower among patients treated with LMWH (odds ratio [OR] 0.81, 95% confidence interval [CI] 0.67-0.99) and the risk of red blood cell transfusion was similar (OR 1.01, 95% CI 0.89-1.15). Among patients who underwent PCI within 48 hours, adjusted rates of death (OR 1.14, 95% CI 0.71-1.85), death or reinfarction (OR 0.93, 0.67-1.31), and transfusion (OR 1.16, 0.89-1.50) were similar. Patients who underwent PCI more than 48 hours into hospitalization had reduced rates of death (OR 0.64, 0.46-0.88), death or reinfarction (OR 0.57, 0.44-0.73), and transfusion (OR 0.66, 0.52-0.84).

CONCLUSIONS

In routine clinical practice, patients treated with GP IIb/IIIa inhibitors have slightly improved outcomes and similar bleeding risks with LMWH than with UFH. These findings are consistent with current ACC/AHA guidelines but raise important questions about the safety and effectiveness of antithrombotic therapy in real-world clinical practice. Using data from the CRUSADE Initiative, we evaluated low-molecular-weight heparin (LMWH) and unfractionated heparin (UFH) in high-risk patients with non-ST-segment elevation acute coronary syndromes (NSTE ACS) who received early (<24 hours) glycoprotein (GP) IIb/IIIa inhibitors and early invasive management. In-hospital outcomes were compared among treatment groups. LMWH was associated with slightly improved clinical outcomes and similar rates of transfusion compared with UFH. Our results support the current ACC/AHA guidelines recommendations but raise concerns about the safety and efficacy of UFH in the setting of background use of upstream GP IIb/IIIa inhibitors for patients with NSTE ACS in routine clinical practice.

Some issues with composite endpoints in clinical trials

This article discusses some important issues that may arise in the current usage of composite endpoints as primary endpoints for demonstrating the efficacy of new drugs in clinical trials. The discussion focuses on time-to-event composite endpoints. Issues discussed include validity of a composite endpoint, the often lack of follow-up of patients beyond first event, the analysis of a composite endpoint, its sub-composite and individual component endpoints and their interpretation. Actual published examples in the literature are used to illustrate some of these problems. It is recommended that a clinical trial using a composite endpoint as the primary endpoint should be designed to include patient follow-up beyond the first event if possible. For data collected from such trials, basic formats for tabular presentation of trial data and for results of analysis of the composite endpoint, its sub-composite and individual component endpoints are proposed for transparency and ease of interpretation.

Heparin in interventional radiology: a therapy in evolution

Interventional radiology techniques made possible by the antithrombotic properties of heparin have revolutionized treatment for a myriad of disorders. Newer low-molecular-weight heparins (LMWHs) offer several advantages over unfractionated heparin (UFH), especially in chronic settings. They are increasing in popularity for use during vascular procedures. However, LMWH shares limitations with UFH such as heterogeneity, nonspecificity, and induction of thrombocytopenia. These drawbacks have led to a search for the next generation of antithrombotic agents. Homogeneous drugs targeting specific coagulation cascade molecules are now available. The number of alternative anticoagulant drug combinations presents clinicians with a confusing array of choices. The strengths and weaknesses of UFH, LMWH, and direct antithrombin agents are presented. The promising future of LMWH and hirudins is discussed.

Preoperative use of enoxaparin increases the risk of postoperative bleeding and re-exploration in cardiac surgery patients

OBJECTIVE

The purpose of this study was to investigate if the preoperative use of new platelet inhibitors and low-molecular-weight heparins may contribute to bleeding after cardiac surgery.

DESIGN

Retrospective data review.

SETTING

University teaching hospital.

PARTICIPANTS

One hundred eleven patients divided in 5 groups.

INTERVENTIONS

Patients were grouped according to preoperative antithrombotic regimen: group 1, control, no agents (n=55); group 2, clopidogrel (n=9); group 3, enoxaparin (n=17); group 4, any GP IIb/IIIa inhibitor (n=14); and group 5, any drug combination (n=15). Data included cumulative mediastinal chest tube drainage, allogeneic blood transfusions, total blood donor exposures, and re-exploration.

MEASUREMENTS AND MAIN RESULTS

Use of any drug (groups 2-5) resulted in greater total blood transfusions and donor exposure (p=0.0003) than control, especially red cells (p=0.002) and platelets (p=0.006). A greater percentage of patients on enoxaparin required mediastinal re-exploration for nonsurgical bleeding versus control (3/17 v 0/55, p=0.001). The use of enoxaparin was associated with significantly higher chest tube output after the first 24 hours postoperatively (p=0.048).

CONCLUSION

Newer antithrombotic agents were associated with greater transfusion rates and total donor exposures. Enoxaparin use was associated with greater overall blood loss and with higher incidence of mediastinal re-exploration. The relative risk-benefit ratio of reduced periprocedure morbidity versus increased bleeding complications has yet to be determined.

The role of low-molecular-weight heparins in cardiovascular medicine

Low-molecular-weight heparins (LMWHs) have been shown to be as effective and safe as unfractionated heparin (UFH) for acute phase treatment of acute coronary syndrome in the absence of ST-elevation [unstable angina/non-ST-elevation myocardial infarction (UA/NSTEMI)]. LMWHs have practical advantages over UFH, including usual lack of requirement for laboratory monitoring of the anticoagulant response because of their favourable pharmacokinetic properties, and thus represent a simpler and more cost-effective option in clinical practice. The LMWH dalteparin has been shown to provide extended therapy benefit to high-risk UA/NSTEMI patients and can provide a protective bridge until revascularization. While revascularization procedures are now an established intervention for patients with UA/NSTEMI, a new approach for patients who cannot undergo immediate catheter intervention is to continue with medical treatment until revascularization is possible. LMWHs are currently being investigated for use in the catheterization laboratory, in patients undergoing percutaneous coronary intervention procedures, and in conjunction with thrombolytics for treatment of acute myocardial infarction.

Enoxaparin versus tinzaparin in non-ST-segment elevation acute coronary syndromes: the EVET trial

BACKGROUND

Low-molecular weight heparins have different pharmacokinetic and pharmacodynamic characteristics and may vary in efficacy. We compared the efficacy of enoxaparin with that of tinzaparin in the management of non-ST-segment elevation acute coronary syndromes (NSTACS).

METHODS

A total of 438 patients with NSTACS were randomized to receive subcutaneous treatment with enoxaparin, 100 IU/kg twice daily (equivalent to 1 mg/kg twice daily; n = 220), or tinzaparin, 175 IU/kg once daily, (n = 218) for as long as 7 days. The primary composite end point was recurrent angina, myocardial infarction (or reinfarction), or death at day 7. Secondary end points were the primary end point at day 30 and the occurrence of individual events at days 7 and 30.

RESULTS

The incidence of the primary end point was 12.3% in the enoxaparin group and 21.1% in the tinzaparin group (P =.015). At day 7, the rate of recurrent angina was lower with enoxaparin than with tinzaparin (11.8% vs 19.3%). At day 30, the incidences of the composite end point, recurrent angina, and myocardial infarction were also lower with enoxaparin, 17.7% vs 28.0% (P =.012), 17.3% vs 26.1% and 0.5% vs 2.8%, respectively. The rate of revascularization was lower in the enoxaparin group, 8.6% vs 17.9% (P =.010) at day 7 and 16.4% vs 26.1% (P =.019) at day 30. Rates of bleeding complications were similar in the 2 treatment groups.

CONCLUSIONS

This study indicates a benefit of enoxaparin (100 IU/kg twice daily) as compared with tinzaparin (175 IU/kg once daily) in the treatment of patients with NSTACS, which is sustained for at least 30 days.

A guide to drug use during percutaneous coronary intervention

The past decade has seen major advances in adjunctive pharmacotherapy for percutaneous coronary intervention. Pharmacological therapeutic advances have resulted from a greater understanding of the pathophysiological mechanisms underlying platelet activation and aggregation, thrombin generation and thrombus formation. Specifically, refinements in the use of unfractionated heparin, developments in the use of low molecular weight heparins and direct antithrombin agents as well as improvement in both oral and parenteral adjunctive antiplatelet therapies have occurred and are reviewed herein.

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.

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

In the past few years, several clinical trials with low-molecular-weight heparins in acute coronary syndromes without ST-segment elevation have been published. In the acute phase of treatment, enoxaparin obtained better results than unfractionated heparin, but dalteparin and nadroparin did not. Enoxaparin also obtained better results than tinzaparin. From these results, it can be assumed that the efficacy of enoxaparin is higher than that of dalteparin and nadroparin. However, because low-molecular-weight heparins have not been compared head to head (except in the case of enoxaparin and tinzaparin), and given the differences between studies in patient selection criteria, design, treatment strategies, and efficacy variables, it cannot be concluded that one low-molecular-weight heparin is superior to another in the acute phase of treatment. Prolonged dalteparin treatment suggests a benefit, particularly for patients at high risk (defined as those with high troponin levels), and it can also be useful in patients waiting for invasive procedures.

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.

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.

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.

Head-to-head comparison of two different low-molecular-weight heparins in acute coronary syndrome: a single center experience

Low-molecular-weight heparins (LMWH) of different types have yielded different results when used in the setting of unstable angina (UA) or non Q-wave myocardial infarction (NQMI). We compared the safety and therapeutic efficacy of two different LMWHs, namely dalteparin (Dalt.) and enoxaparin (Enox.), in the acute phase (first 5 days) of UA or NQMI. One hundred and forty-two patients with UA/NQMI were randomly assigned to treatment with either Dalt. [120 IU/kg twice daily by subcutaneous (SC) injection] or Enox. [1 mg/kg twice daily by SC injection]. The occurrence of any one of death, myocardial infarction, or angina recurrence within 5 days of the first LMWH injection was the endpoint of the study. There were 69 patients in the Enox. group (53 males, 16 females, mean age: 60.3+/-11.9) and 73 patients in the Dalt. group (54 males, 19 females, mean age: 59.6 +/-10.3). The baseline characteristics of the patients in the two groups were similar. There were no deaths in either group. Myocardial infarction occurred in two patients in the Dalt. group (4%). Angina recurrence was seen in 11 patients in the Enox. group (16%) and in 11 patients in the Dalt. group (15%). Overall, any of the events that made up the endpoint occurred in 11 (16%) and 14 (19%) patients in the Enox. and Dalt. groups, respectively (P>0.05). The time to occurrence of the first event, however, was significantly longer in the Enox. group (82.3+/-33.2 versus 37.6+/-23.4 hours, P=0.007). Thrombocytopenia and allergic reactions were not detected in any patient. Major bleeding was seen in I patient in the Enox. group. Minor bleeding occurred in 17 (25%) and 21 (29%) patients in the Enox. and Dalt. groups, respectively (P>0.05). Enoxaparin and dalteparin were found to be equally safe and effective for the early management of UA/NQMI, but enoxaparin appeared to delay the occurrence of MI or angina recurrence as compared to dalteparin in this setting.

Efficacy assessment of meloxicam, a preferential cyclooxygenase-2 inhibitor, in acute coronary syndromes without ST-segment elevation: the Nonsteroidal Anti-Inflammatory Drugs in Unstable Angina Treatment-2 (NUT-2) pilot study

BACKGROUND

Despite the use of heparin, aspirin, and other antiplatelet agents, acute coronary syndrome patients without ST-segment elevation remain at risk of cardiovascular thrombotic events. Given the role of inflammation in the pathogenesis of arterial thrombosis, we tested the hypothesis that the combination of meloxicam, a preferential COX-2 inhibitor, and heparin and aspirin would be superior to heparin and aspirin alone.

METHODS AND RESULTS

In an open-label, randomized, prospective, single-blind pilot study, patients with acute coronary syndromes without ST-segment elevation were randomized to aspirin and heparin treatment (n=60) or aspirin, heparin, and meloxicam (n=60) during coronary care unit stay. Patients then received aspirin or aspirin plus meloxicam for 30 days. During the coronary care unit stay, the primary outcomes variable of recurrent angina, myocardial infarction, or death was significantly lower in the patients receiving meloxicam (15.0% versus 38.3%, P=0.007). The second composite variable (coronary revascularization procedures, myocardial infarction, and death) was also significantly lower in meloxicam-treated patients (10.0% versus 26.7%, P=0.034). At 90 days, the primary end point remained significantly lower in the meloxicam group (21.7% versus 48.3%, P=0.004), as did the secondary end point (13.3% versus 33.3%, P=0.015) and the need for revascularization alone (11.7% versus 30.0%, P=0.025). No adverse complications associated with the meloxicam treatment were observed.

CONCLUSIONS

Meloxicam with heparin and aspirin was associated with significant reductions in adverse outcomes in acute coronary syndrome patients without ST-segment elevation. Additional larger trials are required to confirm the findings of this pilot study.

Nasal administration of low molecular weight heparin

The main objective of this study was to determine if the systemic absorption of therapeutic amounts of heparin was possible following nasal administration. Sprague-Dawley rats received nosedrops containing a low molecular weight heparin (LMWH) or unfractionated heparin (UFH) formulated with or without tetradecylmaltoside (TDM). TDM is a nonionic surfactant that has been previously shown to be a potent absorption enhancer in studies with peptide drugs. LMWH/UFH absorption was determined by measuring plasma anti-Factor Xa activity. The inclusion of 0.25% TDM in nasal formulations containing LMWH resulted in a significant increase in the C(max) and area under the curve (AUC) of anti-Factor Xa activity when compared to LMWH formulated in saline alone. The addition of TDM to a nasal formulation containing UFH resulted in a much smaller increase in the C(max) and the AUC of anti-Factor Xa activity. The absolute bioavailability of LMWH was increased from 4.0 +/- 0.4% in the absence of TDM to 19 +/- 0.3% in the presence of TDM. The reversibility of the absorption enhancing effect of TDM was studied by applying LMWH nasally 60 or 120 min after the enhancer. The effect of TDM on the nasal epithelia appeared to be rapidly reversible. In conclusion, nasal delivery of LMWH, but not UFH, was successful when an absorption enhancer was included to increase nasal permeability.

Therapeutic equivalency of low-molecular-weight heparins

OBJECTIVE

To review the recent literature on the approved uses of enoxaparin, dalteparin, ardeparin, and tinzaparin and the evidence for therapeutic equivalence.

DATA SOURCES

A MEDLINE search (1993-January 2001) was conducted to identify English-language literature available on enoxaparin, dalteparin, ardeparin, and tinzaparin.

STUDY SELECTION

All controlled trials evaluating low-molecular-weight heparins (LMWHs) versus standard therapy powered to detect a significant difference were reviewed.

DATA EXTRACTION

Agents were reviewed with regard to safety and efficacy.

DATA SYNTHESIS

As a class, LMWHs have chemical, physical, and clinical similarities. LMWHs have greater bioavailability, longer half-lives, a more predictable pharmacologic response, possible improved safety, and similar or greater efficacy compared with unfractionated heparin (UFH). Because of this, enoxaparin, dalteparin, ardeparin, and tinzaparin are being considered as alternatives to UFH or warfarin, and there is potential for therapeutic interchange. Evaluation of clinical trials is limited because of differing diagnostic methods, drug administration times, dose equivalencies, and outcome measurements.

CONCLUSIONS

Only 1 trial has evaluated 2 LMWHs in a direct comparison in the same study. There is insufficient evidence for determining the therapeutic equivalence of LMWHs.

Antiplatelet therapy: an alternative to heparin for blunt carotid injury

BACKGROUND

Blunt carotid injuries (BCIs) are uncommon. Most single-center studies are small and highlight the use of anticoagulation for treatment. In a retrospective review, we identified 22 patients who presented with BCI and assessed neurologic and survival outcomes on the basis of injury grade and treatment with anticoagulation or antiplatelet therapy.

METHODS

Patient demographics were identified using the trauma registry at a single Level I trauma center. Chart reviews assessed neurologic function, modalities used for diagnosis, and treatment. Neurologic outcomes were graded good (minimal to no deficit), fair (moderate deficit needing some assistance), poor (requiring institutionalization), and dead.

RESULTS

Twenty-two adult trauma patients were diagnosed with BCI, for an incidence of 0.45% in the 8-year study period. All BCI patients underwent head computed tomography and four-vessel cerebral arteriography. Eight patients were not anticoagulated, five because of intracranial injuries, two who had surgical CCA repairs, and one with an aortic injury. Full anticoagulation with heparin was attempted in seven patients, with four major bleeding complications requiring cessation of heparin and blood transfusions. Seven patients received antiplatelet therapy. No difference in neurologic outcome was observed between those receiving anticoagulation and those receiving antiplatelet therapy. Bleeding complications from full anticoagulation were higher than with antiplatelet agents (p = 0.05).

CONCLUSION

Contrary to previous reports, we did not observe improved outcomes with full anticoagulation compared with antiplatelet therapy. Anticoagulation was associated with increased extracranial bleeding complications. The risks and possible benefits, as well as timing, of anticoagulation or antiplatelet therapy for BCI should be carefully weighed by the major care providers of the patient with multiple injuries.

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.

Current management of unstable angina: lessons from the TACTICS-TIMI 18 trial

Patients presenting with unstable angina pectoris or non-Q-wave myocardial infarction (MI), if treated inadequately, are at a high risk of MI and subsequent mortality. The use of intravenous small molecule glycoprotein IIb/IIIa inhibitors along with standard therapeutic management options improves outcome. Since the publication of the Thrombolysis in Myocardial Ischemia IIIB, Veterans Affairs Non-Q-Wave Infarction Strategies In-Hospital (VANQWISH) and Fragmin and Fast Revascularization during InStability in Coronary artery disease II (FRISC II) studies, there is great debate about the advantages of following an early 'invasive' treatment option with coronary angiography and revascularization after initial medical therapy compared with the 'conservative' approach, where angiography is reserved for those who remain symptomatic. The Treat angina with Aggrastat and determine Cost of Therapy with an Invasive or Conservative Strategy--Thrombolysis in Myocardial Infarction 18 (TACTICS-TIMI 18) study has helped to resolve some of the controversies since it was designed with more current medical (early and routine use of tirofiban) and revascularization (use of stents during percutaneous coronary interventions) options as part of the invasive treatment protocol. This study indicated that an early invasive strategy in risk stratified patients combined with early use of tirofiban with standard medical therapy significantly improves outcome and appears well tolerated.

Leukocyte-platelet aggregation, platelet surface P-selectin, and platelet surface glycoprotein IIIa after percutaneous coronary intervention: Effects of dalteparin or unfractionated heparin in combination with abciximab

BACKGROUND

Plaque disruption with resultant platelet activation and leukocyte-platelet aggregation is a pathophysiologic process common to both acute coronary syndromes and percutaneous coronary interventions. Unfractionated heparin is a standard antithrombotic therapy in patients with both acute coronary syndromes and in those undergoing percutaneous coronary interventions. Low-molecular-weight heparins have been reported to cause less platelet activation than unfractionated heparin.

METHODS

Monocyte-platelet aggregates, neutrophil-platelet aggregates, platelet surface P-selectin, and platelet surface glycoprotein (GP) IIIa were measured serially by whole blood flow cytometry in 40 patients with unstable angina (randomly assigned to either unfractionated heparin 70 U/kg or the low-molecular-weight heparin dalteparin 60 IU/kg) undergoing coronary intervention with planned abciximab administration (in 2, one-half-dose boluses). Assays were performed at baseline, 5 minutes after administration of either type of heparin, 10 minutes after the first bolus of abciximab, 10 minutes after second bolus of abciximab, and 8 to 10 and 16 to 24 hours after administration of either heparin.

RESULTS

No significant differences in clinical outcomes were observed between patients receiving either unfractionated heparin or dalteparin. The number of circulating P-selectin-positive platelets was increased by unfractionated heparin but not dalteparin, and abciximab reversed this increase. The number of circulating P-selectin-positive platelets was reduced below baseline levels in both treatment groups 8 to 10 and 16 to 24 hours after study drug administration. At 8 to 10 and 16 to 24 hours after administration of study drug, platelet degranulation in response to iso-thrombin receptor agonist peptide 1.5 mmol/L was significantly reduced by almost 50% (compared with immediately after study drug administration). Both unfractionated heparin and dalteparin significantly increased the numbers of circulating monocyte-platelet and neutrophil-platelet aggregates, which were subsequently reduced to baseline levels after administration of the second abciximab bolus and to below baseline at both 8 to 10 and 16 to 24 hours in all patients. After both unfractionated heparin and dalteparin administration, platelet surface GP IIIa expression was significantly increased compared with baseline at both 8 to 10 and 16 to 24 hours.

CONCLUSIONS

Dalteparin in combination with abciximab in patients with unstable angina undergoing coronary intervention appears to be safe. Unfractionated heparin, but not dalteparin, degranulates platelets in patients with unstable angina. Both heparins increase the number of circulating monocyte-platelet and neutrophil-platelet aggregates. Abciximab therapy during coronary interventions rapidly reduces the number of degranulated platelets and leukocyte-platelet aggregates.

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.

Pharmacology department

Traditionally administered unfractionated heparin (UH) is a heterogeneous mixture of polysaccharide chains of varying length. Heparin is now available in new formulations, most notably the low-molecular-weight heparins (LMWHs), which possess pharmacology that is similar to but distinct from UH. Key advantages of LMWHs include improved bioavailability and longer half-life, more predictable anticoagulation that requires less laboratory monitoring, and fewer serious side effects. The article reviews the pharmacology of heparin and discusses the addition of LMWHs to the family of anticoagulant drugs.

Postoperative anticoagulation in vascular surgery: part 1. A retrospective comparison of clinical outcomes for unfractionated heparin versus low-molecular-weight heparin

The use of postoperative anticoagulation is not uncommon for patients undergoing vascular procedures, whether for adjunctive therapy to the surgical procedure or for resumption of preoperative anticoagulation. Longer postoperative length of stay is necessary to achieve an adequate therapeutic international normalized ratio with traditional protocols that call for the use of unfractionated heparin. We retrospectively examined 195 cases to determine whether low-molecular-weight heparin, specifically enoxaparin, was an effective postoperative replacement for intravenous unfractionated heparin, with the impact on postoperative length of stay. There was no difference in the frequency of complications except for increased incidence of return to surgery for graft thrombosis (n = 11) in patients who received traditional intravenous unfractionated heparin with adjusted-dose warfarin daily (n = 139, P <.02). For all 195 vascular procedures combined, the average postoperative length of stay with use of enoxoparin was shortened with use of enoxaparin (P <.0008). There was a 2-day reduction in the average postoperative length of stay for the femoral-distal procedure group (n = 18, P <.004). In the first part of the article, we summarize our findings and offer new applications and ideas for vascular nurses to consider when postoperative anticoagulation is indicated after vascular procedures. Factors contributing to safe and efficacious postoperative anticoagulation with use of low-molecular-weight heparin, specifically enoxaparin, are presented to the vascular nurse. In the second part, we discuss the roles of members of the vascular team, as well as our experience with use of enoxaparin as implemented in the clinical setting.

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.

Glycoprotein IIb/IIIa antagonists and low-molecular weight heparin in acute coronary syndromes

The glycoprotein (GP) IIb/IIIa antagonists and the low-molecular weight heparins are the newest additions to the armamentarium of antiplatelet drugs for the treatment of acute coronary syndromes. They are extremely potent inhibitors of platelet aggregation and thrombin generation, respectively. There are currently three GP IIb/IIIa inhibitors (abciximab, eptifibatide, and tirofiban) and two low-molecular weight heparins (dalteparin and enoxaparin) approved for use with acute coronary syndromes. Data continue to accumulate outlining the specific roles for these drugs in the treatment of patients with acute coronary syndromes. Clinical trials in patients with acute coronary syndromes have demonstrated that the GP IIb/IIIa antagonists and low-molecular weight heparins offer significant benefit with acceptable safety profiles. Future issues that need to be addressed include refinement of indications for administration and patient selection, comparison between existing agents, evaluation of newer agents, and optimization of dosing to maximize benefit and safety in the use of these powerful new classes of drugs.

Inhibition of tissue factor-activated platelets by low-molecular-weight heparins and glycoprotein IIb/IIIa receptor antagonist

Thrombotic disorders can lead to vascular distress and platelet activation eventually resulting in the rupture of the lesions where a sizable amount of tissue factor (TF) is generated during the pathogenesis of arterial diseases. Since low-molecular-weight heparins (LMWHs) and platelet glycoprotein (GP) IIb/IIIa inhibitors are clinically used for the management of acute coronary syndrome (ACS), studies were taken to determine the effects of these agents on TF-mediated activation of platelets. Freshly drawn native whole blood (WB) from normal healthy volunteers (n = 6) supplemented with a predetermined amount of TF was incubated with equivalent anti-Xa adjusted amounts of various LMWHs at 0.01-1.0 U/ml and tirofiban from 10 to 100 ng/ml. Platelet activation was assessed by measuring the expression of P-selectin (CD62) and the generation of platelet aggregates. At 0.01 U/ml, enoxaparin exhibited a stronger inhibition of TF-induced platelet activation compared to ardeparin and dalteparin. At 0.1 U/ml, these LMWHs produced a comparable inhibition of total P-selectin expression, and at 1.0 U/ml, a marked inhibition was noted. Since enoxaparin produced the best concentration-dependent inhibition of P-selectin expression (saline: 76 +/- 10% vs. 1.0 U/ml enoxaparin: 18 +/- 7%; P < .02) and platelet aggregate formation (saline: 63 +/- 7% vs. 1.0 U/ml enoxaparin: 35 +/- 6%, P < .035), this agent was used for additional studies. Unlike enoxaparin, tirofiban produced a weak concentration-dependent inhibition of platelet activation. At 100 ng/ml, tirofiban produced a 40% inhibition of P-selectin expression and about 60% inhibition of platelet aggregate formation. To elucidate the potential interaction between tirofiban and enoxaparin, the effect of 10 and 100 ng/ml tirofiban was studied with enoxaparin-supplemented WB in a 0.01-1.0 U/ml range. Additive effects between these two agents were noted only at lower concentrations. Thus, at therapeutic concentrations (0.8-1.2 U/ml), enoxaparin itself was capable of inhibiting TF-mediated activation of platelets to > 70%; whereas tirofiban failed to produce such concentration-dependent inhibition. This suggests that the simultaneous administration of GPIIb/IIIa receptor antagonist with LMWH may not have any added benefit in the clinical management of patients with ACS.