Initial experience with a direct antithrombin, Hirulog, in unstable angina. Anticoagulant, antithrombotic, and clinical effects

Heparin-Induced Thrombocytopenia: A Comprehensive Clinical Review

Heparin-induced thrombocytopenia is a profoundly dangerous, potentially lethal, immunologically mediated adverse drug reaction to unfractionated heparin or, less commonly, to low-molecular weight heparin. In this comprehensive review, the authors highlight heparin-induced thrombocytopenia's risk factors, clinical presentation, pathophysiology, diagnostic principles, and treatment. The authors place special emphasis on the management of patients requiring procedures using cardiopulmonary bypass or interventions in the catheterization laboratory. Clinical vigilance of this disease process is important to ensure its recognition, diagnosis, and treatment. Misdiagnosis of the syndrome, as well as misunderstanding of the disease process, continues to contribute to its morbidity and mortality.

Anticoagulation Monitoring

Optimal management of anticoagulant therapy requires an understanding of the laboratory tests often employed to guide therapy. The activated partial thromboplastin time (aPTT) can detect abnormalities in the intrinsic and common clotting pathways. Despite numerous limitations in the aPTT test, it remains the gold standard for monitoring unfractionated heparin and direct thrombin inhibitor therapy. The aPTT can be performed in the central laboratory or at the bedside (point of care [POC] testing). The activated clotting time (ACT) is a POC test that is routinely employed to monitor high-dose heparin during invasive and surgical procedures. The ACT therapeutic range will depend on the specific procedure or surgery being performed. Heparin levels are becoming more routinely available and are used to establish the aPTT therapeutic range for heparin therapy as well as for direct monitoring of heparin and low-molecular-weight heparin therapy. The international normalized ratio (INR) is the gold standard for monitoring warfarin patients. The target INR depends on the indication for anticoagulation. POC monitoring for warfarin is becoming increasingly used. Clinicians should have a thorough understanding of the benefits as well as the limitations of warfarin POC monitoring.

New Approaches to the Role of Thrombin in Acute Coronary Syndromes: Quo Vadis Bivalirudin, a Direct Thrombin Inhibitor?

The pathophysiology of acute coronary syndrome (ACS) involves platelet activation and thrombus formation after the rupture of atherosclerotic plaques. Thrombin is generated at the blood-plaque interface in association with cellular membranes on cells and platelets. Thrombin also amplifies the response to the tissue injury, coagulation and platelet response, so the treatment of ACS is based on the combined use of both antiplatelet (such as aspirin, clopidogrel, prasugrel and ticagrelor) and antithrombotic drugs (unfractionated heparin, enoxaparin, fondaparinux and bivalirudin). Bivalirudin competitively inhibits thrombin with high affinity, a predictable response from its linear pharmacokinetics and short action. However, a present remarkable controversy exists between the latest main Guidelines in Clinical Practice and the key trials evaluating the use of bivalirudin in ACS. The aim of this review is to update the development of bivalirudin, including pharmacological properties, obtained information from clinical trials evaluating efficacy and safety of bivalirudin in ACS; as well as the recommendations of clinical Guidelines.

Activated clotting time test alone is inadequate to optimize therapeutic heparin dosage adjustment during post-cardiopulmonary resuscitational extracorporeal membrane oxygenation (e-CPR)

BACKGROUND

We conducted an observational study to evaluate the relationship between activated clotting time (ACT) and activated partial thromboplastin time (aPTT) tests, anticipating the possibility that the ACT will become a substitute test for the aPTT in post-CPR extracorporeal membrane oxygenation (e-CPR).

PATIENTS AND METHODS

Three hundred and fifteen paired ACT and aPTT samples were derived from 60 in-hospital e-CPR patients and were divided into three groups according to the observed ACT value: low level (ACT < 170 s, Group A), intended target level (ACT 170-210 s Group B) and high level (ACT > 210 s, Group C). The relationship of aPTT in each group was analyzed.

RESULTS

The mean ACT and aPTT values were 189.39 ± 48.27 s (IQR, 163-202) and 71.85 ± 45.32 s (IQR, 44.5-81.8), respectively. Although the observed mean ACT value of 189.39 s was similar to the intended mean target value of 190 s (p = 0.823), the observed mean aPTT value (71.85 s) was significantly lower than the predicted mean target value (77.5 s, p = 0.027). Despite the mean ACT values being significantly different in each group (p < 0.0001), the mean aPTT values were not statistically different between Groups A and B (p = 0.317). Of the Group B samples (n = 139), only 31 samples (22.3%) met the optimal therapeutic aPTT range. Pearson's correlation coefficient for Group B showed only a weak correlation between ACT and aPTT (r = 0.177; p = 0.037).

CONCLUSIONS

Our study demonstrates that the ACT test alone does not seem to be enough to optimize therapeutic heparin dosage adjustment during e-CPR.

Bivalirudin as an adjunctive anticoagulant to heparin in the treatment of heparin resistance during cardiopulmonary bypass-assisted cardiac surgery

Heparin resistance (unresponsiveness to heparin) is characterized by the inability to reach acceptable activated clotting time values following a calculated dose of heparin. Up to 20% of the patients undergoing cardiothoracic surgery with cardiopulmonary bypass using unfractionated heparin (UFH) for anticoagulation experience heparin resistance. Although UFH has been the "gold standard" for anticoagulation, it is not without its limitations. It is contraindicated in patients with confirmed heparin-induced thrombocytopenia (HIT) and heparin or protamine allergy. The safety and efficacy of the use of the direct thrombin inhibitor bivalirudin for anticoagulation during cardiac surgery has been reported. However, there have been no reports on the treatment of heparin resistance with bivalirudin during CPB. In this review, we report the favorable outcome of our single-center experience with the alternative use of bivalirudin in the management of anticoagulation of heparin unresponsive patients undergoing coronary artery bypass graft surgery.

Bivalirudin: an anticoagulant option for percutaneous coronary intervention

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

Evaluation of a multifunctional staphylokinase variant with thrombin inhibition and antiplatelet aggregation activities produced from salt-inducible E. coli GJ1158

Reocclusion is one of the major root causes for secondary complications that arise during thrombolytic therapy. A multifunctional staphylokinase variant SRH (staphylokinase (SAK) linked with tripeptide RGD and didecapeptide Hirulog) with antiplatelet and antithrombin activities in addition to clot specific thrombolytic function, was developed to address the reocclusion problem. We preferred to use Escherichia coli GJ1158 as the host in this study for economic production of SRH by osmotic (0.3 mol/L sodium chloride) induction, to overcome the problems associated with the yeast expression system. The therapeutic potential of SRH was evaluated in the murine model of vascular thrombosis. The SAK protein (1 mg/kg body mass) and SRH protein (1 mg/kg and 2 mg/kg) were administered intravenously to the different treatment groups. The results have shown a dose-dependent antithrombotic effect in carrageenan-induced mouse tail thrombosis. The thrombin time, activated partial thromboplastin time, and prothrombin time were significantly prolonged (p < 0.05) in the SRH-infused groups. Moreover, SRH inhibited platelet aggregation in a dose-dependent manner (p < 0.05), while the bleeding time was significantly (p < 0.05) prolonged. All of these results inferred that the osmotically produced multifunctional fusion protein SRH (SAK-RGD-Hirulog) is a promising thrombolytic agent, and one which sustained its multifunctionality in the animal models.

Percutaneous coronary intervention in patients with acute coronary syndrome: focus on bivalirudin

Previously, indirect thrombin inhibitors such as unfractionated heparin or low-molecular-weight heparin were used as a standard anticoagulation during percutaneous coronary intervention to prevent procedural thrombotic complications but at a risk of hemorrhagic complications. More recently, bivalirudin, a member of the direct thrombin inhibitor class, has been shown to have 1) predictable pharmacokinetics, 2) ability to inhibit free- and clot-bound thrombin, 3) no properties of platelet activation, 4) avoidance of heparin-induced thrombocytopenia, and 5) a significant reduction of bleeding without a reduction in thrombotic or ischemic endpoints compared to heparin and glycoprotein IIbIIIa inhibitors when used in patients presenting with acute coronary syndrome who are planned for an invasive treatment strategy.

Antibodies against lepirudin are polyspecific and recognize epitopes on bivalirudin

Bivalirudin is a synthetic antithrombin sharing a sequence of 11 amino acids with the recombinant hirudin lepirudin. We investigated whether antilepirudin antibodies recognize epitopes on bivalirudin. Antilepirudin antibody–positive sera of 43 patients, treated with lepirudin for heparin-induced thrombocytopenia, were analyzed. Lepirudin- and bivalirudin-coated microtiter plates were used for antibody testing in an enzyme-linked immunosorbent assay (ELISA) system. Of the 43 sera-containing antibodies binding to lepirudin, 22 (51.2%) contained antibodies that also recognized bivalirudin. Binding of these antibodies to bivalirudin was inhibited by more than 70% by preincubation with high doses of bivalirudin. However, if lepirudin-coated microtiter plates were used, high concentrations of bivalirudin inhibited only 2 of the 43 positive sera by more than 30%. Therefore antihirudin antibodies must be polyspecific. The clinical consequences of this cross-reactivity are unknown but bivalirudin, targeted by antibodies of patients treated with lepirudin previously, could potentially boost antibody titers in such patients or even trigger an immune response by itself. Clinically significant antibody formation in response to bivalirudin monotherapy has not been observed, however. Yet, as lepirudin and antilepirudin antibodies have recently been implicated in severe anaphylactic reactions, caution is warranted when using bivalirudin in patients previously treated with lepirudin.

The evolving role of direct thrombin inhibitors in acute coronary syndromes

The central role of thrombin in the initiation and propagation of intravascular thrombus provides a strong rationale for direct thrombin inhibitors in acute coronary syndromes (ACS). Direct thrombin inhibitors are theoretically likely to be more effective than indirect thrombin inhibitors, such as unfractionated heparin or low-molecular-weight heparin, because the heparins block only circulating thrombin, whereas direct thrombin inhibitors block both circulating and clot-bound thrombin. Several initial phase 3 trials did not demonstrate a convincing benefit of direct thrombin inhibitors over unfractionated heparin. However, the Direct Thrombin Inhibitor Trialists' Collaboration meta-analysis confirms the superiority of direct thrombin inhibitors, particularly hirudin and bivalirudin, over unfractionated heparin for the prevention of death or myocardial infarction (MI) during treatment in patients with ACS, primarily due to a reduction in MI (odds ratio, 0.80; 95% confidence interval, 0.70 to 0.91) with little impact on death. The absolute risk reduction in the composite of death or MI at the end of treatment (0.8%) was similar at 30 days (0.7%), indicating no loss of benefit after cessation of therapy. Supportive evidence for the superiority of direct thrombin inhibitors over heparin derives from the recently reported Hirulog and Early Reperfusion or Occlusion (HERO)-2 randomized trial with ST-segment elevation ACS, which demonstrated a similar benefit of bivalirudin over heparin for the prevention of death or MI at 30 days (absolute risk reduction 1.0%), again primarily due to a reduction in MI during treatment (odds ratio, 0.70; 95% confidence interval, 0.56 to 0.87), with little impact on death. Further evaluation of hirudin and bivalirudin in the antithrombotic management of patients with ACS is warranted.

Pharmacology and clinical use of bivalirudin

OBJECTIVE

To review the primary literature describing the pharmacology and clinical uses of bivalirudin.

DATA SOURCES

A MEDLINE search (January 1966-May 2001) was conducted that used bivalirudin, hirulog, and direct thrombin inhibitor as key words. References from retrieved articles and unpublished information acquired from the manufacturer and the Internet were also used.

STUDY SELECTION

All acquired articles that discussed the pharmacology, pharmacokinetics, and clinical efficacy of bivalirudin were reviewed.

DATA EXTRACTION

Articles were selected based on content regarding the pharmacology and clinical use of bivalirudin. Given the paucity of data pertaining to the clinical use of bivalirudin, most articles were used, including abstracts and communications with the manufacturer.

DATA SYNTHESIS

Bivalirudin is a direct thrombin inhibitor that inactivates both unbound and fibrin-bound thrombin. Bivalirudin rapidly induces anticoagulation and has a relatively short duration of action. Bivalirudin displays linear kinetics and is primarily eliminated renally. Bivalirudin was proven effective in preventing postprocedural ischemic complications in patients with unstable or postinfarction angina who received percutaneous transluminal coronary angioplasty (PTCA). Yet, further investigations that include less critically ill patients and use the current clinical practice of administering glycoprotein IIb/IIIa antagonists and/or inserting intracoronary stents are needed to fully evaluate its efficacy. Bivalirudin has also induced early patency in patients with myocardial infarction in combination with streptokinase, but its use with newer thrombolytics needs to be studied. Bivalirudin has been used in patients with immunologically mediated, heparin-induced thrombocytopenia (HIT) without complications. Bleeding is the major adverse effect and occurs more commonly in patients with renal dysfunction.

CONCLUSIONS

At present, bivalirudin is worthy of consideration in patients requiring PTCA who have HIT. Advocating the routine use of bivalirudin in patients experiencing an acute coronary syndrome or HIT is premature.

Bivalirudin: a direct thrombin inhibitor

BACKGROUND

Studies of the anticoagulant effects of hirudin, which is derived from the saliva of the leech Hirudo medicinalis, led to the development of compounds that can directly inhibit thrombin activity without the need for additional cofactors. One of these is the direct thrombin inhibitor bivalirudin, which has recently been approved by the US Food and Drug Administration for use as an anticoagulant in patients with unstable angina undergoing percutaneous transluminal coronary angioplasty.

OBJECTIVE

This is a review of the pharmacologic properties, efficacy, tolerability, and potential cost-effectiveness of bivalirudin in the treatment of ischemic coronary syndromes.

METHODS

Articles were identified by searches of MEDLINE (1966-September 2001), International Pharmaceutical Abstracts (1970-September 2001), and the Iowa Drug Information Service (1966-September 2001) using the terms bivalirudin and Hirulog. The reference lists of retrieved articles were also reviewed for relevant articles.

RESULTS

Bivalirudin is a synthetic polypeptide that directly inhibits thrombin by binding simultaneously to its active catalytic site and its substrate recognition site. After intravenous administration, peak plasma concentrations occur in 2 minutes. In patients given a 1.0-mg/kg bolus followed by a 2.5-mg/kg per hour infusion, a median activated clotting time of 346 seconds is achieved with little interpatient or intrapatient variability. Clearance of bivalirudin occurs through a combination of renal elimination and proteolytic cleavage, and doses may need to be decreased in the presence of renal dysfunction. In patients undergoing percutaneous coronary interventions, bivalirudin has been associated with equivalent efficacy but lower bleeding rates (P < 0.001) than unfractionated heparin (UFH). Data from the Hirulog Early Reperfusion/Occlusion-2 study suggest no reduction in mortality with bivalirudin compared with heparin when either is added to aspirin and streptokinase in patients with acute myocardial infarction, despite a lower reinfarction rate (P < 0.001). Experience with bivalirudin in patients with unstable angina and heparin-induced thrombocytopenia (HIT), as well as in patients receiving glycoprotein IIb/IIIla inhibitors, is limited. The differences in bleeding rates between bivalirudin and heparin in published clinical trials probably reflect differences in levels of anticoagulation achieved in comparator groups.

CONCLUSIONS

Given its high cost, bivalirudin should be reserved for use as an alternative to UFH, primarily in patients with HIT, until clinical trials have more clearly demonstrated its benefits in terms of efficacy or safety.

Bivalirudin for percutaneous coronary intervention and in acute coronary syndromes

This review focuses on the use of bivalirudin as a replacement anticoagulant for heparin in patients undergoing percutaneous coronary intervention, or who are being treated for unstable angina pectoris, ST-elevation, or non-ST-elevation myocardial infarction. Potential advantages of bivalirudin include a lack of dependence on antithrombin III for anticoagulant activity, the ability to inactivate both fibrin-bound and soluble thrombin, a lack of aggregatory effects on platelets, a predictable anticoagulant response without monitoring, and a wider therapeutic window. Clinical trial results to date suggest that bivlirudin is at least as effective as heparin with superior safety due to lower bleeding rates.

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.

Bivalirudin: a new approach to anticoagulation

Bivalirudin is one of the first of a new class of anticoagulants known as direct thrombin inhibitors. These drugs are able to overcome many of the shortcomings of traditional heparin anticoagulation by virtue of this unique mechanism of action. Bivalirudin is a semisynthetic derivative of hirudin, a modified component of leech saliva. Hirudin has been plagued by bleeding complications, likely due to its high affinity for thrombin. Bivalirudin has lower thrombin affinity than hirudin and therefore is believed to be a much safer compound. Bivalirudin has been shown to be a very effective anticoagulant in laboratory models, though its clinical efficacy remains to be fully proven. Bivalirudin has been studied in the setting of coronary angioplasty, unstable angina, and acute myocardial infarction and has shown some promise in many of these settings, particularly in preventing complications of percutaneous coronary interventions. Bivalirudin has consistently shown less major bleeding compared with standard heparin, although limitations in study methodologies somewhat hinder an accurate interpretation of this finding. Larger-scale studies are indicated and are currently being performed, the results of which will more definitively define the role of bivalirudin for the treatment of cardiovascular disease.

Newer antithrombotic strategies in the initial management of non-ST-segment elevation acute coronary syndromes

OBJECTIVE

To review the place in therapy of currently available antithrombotic agents in the non-ST-segment elevation acute coronary syndromes, that is, unstable angina and non-Q-wave myocardial infarction (MI). Recommendations are made based on currently available data.

DATA SOURCE

English-language clinical studies, position statements, and review articles pertaining to the management of unstable angina and non-Q-wave MI with currently available products.

STUDY SELECTION

Selection of prospective clinical studies was limited to those focusing on the management of the non-ST-segment elevation acute coronary syndromes, unstable angina, and non-Q-wave MI.

DATA SYNTHESIS

It has yet to be determined which combination of agents (dalteparin, enoxaparin, lepirudin, clopidogrel, ticlopidine, abciximab, eptifibatide, tirofiban) and procedural strategies most significantly reduces mortality and serious events in these patients. The relevant pathophysiology, diagnostic criteria, and risk-stratifying procedures are reviewed in context with information from clinical studies regarding currently available agents for the management of non-ST-segment elevation acute coronary syndromes.

CONCLUSIONS

A large number of new therapeutic classes and agents are available for the treatment of unstable angina and non-Q-wave MI. Although the diagnoses of unstable angina or non-Q-wave MI identify risk, treatment decisions are often based on the presence or absence of ST-segment elevations. Limited prospective evidence delineates the proper utilization of resources to best manage these patients. Efforts should be aimed at identifying particular patients who will best benefit from recently available therapies.

Clotting for the Clinician: An Overview of Thrombosis and Antithrombotic Therapy

The use of antithrombotic therapy has taken on central importance in the field of cardiovascular disease. Currently, anticoagulants and antiplatelet drugs are central to the treatment and the primary and secondary prevention of coronary artery disease. New insights into the "revised" coagulation cascade have highlighted new targets for intervention. In addition, the interactions between the coagulation system and platelets demonstrate ways that anticoagulants may affect platelet function and how antiplatelet agents may have anticoagulant effects. This overview will describe the present understanding of primary and secondary hemostasis, and current and future therapeutic approaches to modify these systems for therapeutic effects in cardiovascular medicine.

Novel Antithrombotic Strategies for the Treatment of Coronary Artery Thrombosis: A Critical Appraisal

Large-scale clinical trials have demonstrated that treatment of patients with acute myocardial infarction and unstable angina with antithrombotic agents significantly improves outcome. Despite the proven benefit of current therapies, there is a widespread perception that outcome could be enhanced further with novel antithrombotic agents. Enthusiasm for novel antithrombotic strategies has been stimulated by recent advances in the understanding of the mechanisms responsible for coronary artery thrombosis, which has led to the development of diverse inhibitors of platelet function and coagulation factors. In experimental models of coronary artery thrombosis, aspirin and heparin have been ineffective in preventing recurrent thrombosis after coronary thrombolysis and in preventing the progression of thrombosis in response to strong thrombogenic stimuli. In contrast, inhibitors of the platelet fibrinogen receptor, direct-acting thrombin inhibitors, and inhibitors of coagulation factors that promote elaboration of thrombin have been shown to be effective in attenuating arterial thrombosis in a variety of experimental preparations. Initial clinical trials with these agents have also documented efficacy in attenuating thrombotic events in patients treated with coronary thrombolysis and in those with unstable angina. However, optimal doses of novel antithrombotic agents, the degree to which combination antiplatelet and anticoagulant therapies are needed, and the risk/benefit ratio associated with specific novel antithrombotic drugs are still relatively undefined. With regard to the latter, it is possible that the large-scale clinical trials now in progress may show an increase in bleeding complications with novel anticoagulants compared with conventional therapy. Nonetheless, there are considerable data that suggest that treatment with aspirin and heparin is not completely effective in preventing the progression of thrombosis or its recurrence after interventions in high-risk subgroups of patients with coronary artery thrombosis and unstable coronary artery disease. Accordingly, continued investigation of a large variety of antithrombotic agents, both currently available and in development, should improve the treatment of high-risk patients with coronary disease if regimens with appropriate efficacy but without serious hemorrhagic effects can be designed.

Optimizing the Treatment of Unstable Angina

Unstable angina and non--Q-wave myocardial infarction (MI) are at the center of the spectrum of myocardial ischemia, which ranges from stable angina to acute Q-wave MI. In addition to clinical evaluation, cardiac specific markers such as troponin T or I can assist in early diagnosis, triage, and risk stratification. Antithrombotic therapy with aspirin and heparin have been shown to improve the outcome of patients with acute ischemic syndromes. Thrombolytic therapy does not appear to be beneficial in these syndromes. Antiischemic therapy remains an important component of the overall therapy. A strategy of early coronary angiography and revascularization leads to a similar long-term outcome as compared with a more conservative strategy of revascularization for recurrent ischemia, but the early invasive strategy is more expeditious as a large number of conservatively treated patients have recurrent ischemia. At present, many new antithrombotic agents are under active investigation, with the hope that they will lead to further improvement in the clinical outcome of patients with acute ischemic syndromes.

Antithrombins and the importance of good control

The generation of thrombin and the formation of platelet rich intra-coronary thrombus in response to atherosclerotic plaque rupture is pathognomonic of acute coronary syndromes. An understanding of the process of thrombin generation and the unique relationship between the structure and function of thrombin is essential to developing more effective anti-thrombotic strategies than the use of standard unfractionated heparin in the acute coronary syndromes. The mechanisms of action of heparin, low molecular weight heparins (LMWHs) and the newer direct anti-thrombins, recombinant hirudin and Hirulog, are reviewed. Evidence from the currently available phase 2 and 3 trials of these drugs regarding their efficacy in the acute coronary syndromes is also reviewed.

Anticoagulant therapy in unstable angina

The goal of anticoagulant therapy in unstable angina is to prevent progression of a subocclusive coronary thrombus to complete occlusion of the coronary artery, thereby preventing myocardial infarction and death. Although these have been many advances in therapy with anticoagulants, considerable morbidity and mortality remains. Also, although combination therapy with potent novel anticoagulants and antiplatelet agents may be an alternative strategy, this needs to be balanced against the risks of hemorrhagic complications. More precise and biologically relevant methods of monitoring anticoagulant effect, along with appropriately modified doses given in combination offers promise.

Antithrombotic therapy of unstable angina and non-Q-wave myocardial infarction

Unstable angina and non-Q-wave myocardial infarction still represent an unsolved problem for clinicians, owing to their unpredictable evolution and high incidence of coronary events in the follow-up. Traditional antithrombotic agents, unfractionated heparin and aspirin, have been proved to be highly effective, but show some important limitations. New potent antithrombotic therapy have been studied to improve their efficacy, with encouraging results. Among these drugs, low molecular weight heparins (for subcutaneous administration) and inhibitors of platelet glycoprotein receptor IIb/IIIa (for intravenous, and possibly oral, administration) are the most promising and are now under extensive investigation.

Therapeutic inhibition of thrombin activities, receptors, and production

Thrombin mediates acute vascular thrombosis following mechanical denuding injury or spontaneous rupture of atherosclerotic plaques. In the process of generating thrombin, factor VII/VIIa binds avidly with tissue factor exposed on cellular membranes, leading to sequential activation of coagulation serine proteases via macromolecular catalytic complexes on phospholipid surfaces. At sites of disrupted arteries thrombin activates platelets, blood leukocytes, endothelium, and vascular SMCs by cleaving G protein-coupled TRs, mediating SMC intimal proliferation in the formation of neointimal vascular lesions. Therapeutic strategies targeting thrombin include inactivation of bound thrombin, inhibition of TR activation by thrombin, and interruption of thrombin production. In patients having orthopedic surgery, inactivating bound thrombin with direct antithrombins markedly reduces venous thromboembolism as compared with heparin or its derivatives, without significant impairment of hemostasis. Antithrombotic effects in arterial thromboembolism, such as acute coronary syndrome, are not conclusively benefitted by systemic direct antithrombins when administered at safe levels, because interrupting TR-dependent platelet thrombosis demands systemic levels of direct antithrombins that compromise hemostatic function. Alternative safer strategies evolving from preclinical studies include (1) inhibiting thrombin activation of TRs, thereby abolishing platelet recruitment in arterial thrombogenesis, while sparing fibrin formation in hemostatic plugs; (2) enhancing the formation of endogenous activated protein C by protein C-selective thrombin mutants; and (3) preventing thrombin production by inhibiting precursor serine protease function and interrupting the formation of both acute thrombosis and vascular lesion formation. Tissue factor pathway antagonists are particularly promising because they exhibit both efficacy and safety in the prevention of thrombosis and vascular lesions.

A randomized comparison of bivalirudin and heparin in patients undergoing coronary angioplasty for postinfarction angina. Hirulog Angioplasty Study Investigators

The outcome of coronary angioplasty performed for unstable angina is determined, in part, by the acuteness and severity of the clinical presentation. The risk of abrupt vessel closure is increased in patients with postinfarction angina. The Hirulog Angioplasty Study compared the efficacy and safety of bivalirudin with weight-adjusted heparin in patients undergoing percutaneous transluminal coronary angioplasty (PTCA) for unstable or postinfarction angina. We report the results of the intent-to-treat analysis using adjudicated data for the prespecified group of 741 patients who underwent angioplasty within 2 weeks of documented myocardial infarction. Patients received either bivalirudin or heparin immediately before angioplasty. The primary efficacy endpoint was procedural failure defined as abrupt vessel closure, death, myocardial infarction, or revascularization during hospitalization. Bivalirudin significantly (p = 0.004) decreased the incidence of procedural failure compared with heparin (5.1% vs 10.8%, odds ratio 0.45; 95% CI 0.25-0.79). The improved efficacy of bivalirudin was replicated for each individual clinical endpoint. The incidence of major bleeding was significantly (p = 0.001) lower in bivalirudin-treated patients compared with heparin-treated patients (2.4% vs 11.8%, respectively). The benefits observed with bivalirudin are of similar magnitude as those reported for platelet glycoprotein (GP) IIb/IIIa inhibitors, such as abciximab. Bivalirudin may be a more effective foundation anticoagulant than heparin in patients undergoing coronary angioplasty for postinfarction angina.

New antithrombotics for the treatment of acute and chronic arterial ischemia

The established antithrombotic agents are effective but they have limitations which have provided opportunities for the development of new antithrombotic compounds. Of these new agents, the antithrombin III-independent thrombin inhibitors and the platelet GPIIb/IIIa receptor antagonists are the most advanced in their development. Other new antithrombotic agents include the antithrombin III-independent factor Xa inhibitors, activated protein C, soluble thrombomodulin and tissue factor pathway inhibitor. Of the GPIIb/IIIa antagonists, the humanized 7E3 antibody and integrin have been evaluated in phase III studies. The 7E3 antibody was effective in preventing both short-term and longer-term complications of coronary angioplasty. The antithrombin III-independent thrombin inhibitors hirudin and hirulog have also been evaluated in phase III studies. The studies with hirudin as an adjuvant to coronary thrombolysis had to be terminated and restarted at lower dosages because of an unacceptable incidence at intracranial hemorrhage and the study with hirulog produced equivocal results.

Thrombin generation, inhibition and clinical outcomes in patients with acute myocardial infarction treated with thrombolytic therapy and heparin: results from the GUSTO-I Trial. GUSTO-I Hemostasis Substudy Group. Global Utilization of Streptokinase and TPA for Occluded Coronary Arteries

OBJECTIVES

We sought to assess the effects of antithrombotic therapy after thrombolysis for acute myocardial infarction on markers of thrombin generation and activity and to determine the relation of these markers with clinical outcomes.

BACKGROUND

Thrombin activation and generation often occur with thrombolysis for acute myocardial infarction. Antithrombotic regimens have been developed to reduce the resulting thrombotic complications.

METHODS

We sampled plasma markers of thrombin generation and activity after thrombolysis in 292 patients. We assessed the relations of these markers with clinical outcomes at 30 days.

RESULTS

Fibrinopeptide A (FPA), a marker of thrombin activity toward fibrinogen, was elevated at baseline (12.3 ng/ml) and increased to 18.4 ng/ml by 90 min after streptokinase and subcutaneous heparin treatment. With intravenous heparin, this increase was attenuated, but intravenous heparin did not prevent thrombin generation, as measured by prothrombin fragment 1.2 (F1.2). Heparin level, measured by anti-Xa activity, correlated with activated partial thromboplastin time (aPTT, r = 0.62 to 0.67). Thrombin activity, measured by FPA, was as closely related to aPTT as to the heparin level. Baseline levels of F1.2 were significantly related to the risk of death or reinfarction at 30 days (p = 0.008); values 12 h after enrollment also were related to 30-day mortality (p = 0.05).

CONCLUSIONS

Although intravenous heparin partly suppresses the increased thrombin activity associated with thrombolysis, it does not inhibit thrombin generation. The aPTT was as good a measure of suppression of thrombin activity as the heparin level itself. Hematologic markers of thrombin generation were found to be related to the subsequent risk of thrombotic events.

Inhibition by hirulog-1 of generation of plasminogen activator inhibitor-1 from vascular smooth-muscle cells induced by thrombin

Hirulog-1 effectively prevents thrombosis in coronary artery disease and is associated with a low incidence of bleeding complications. Our study characterized the effect of Hirulog-1 on thrombin-induced production of plasminogen activator inhibitor-1 (PAI-1) in cultured baboon aortic smooth-muscle cells (BASMCs). Thrombin increased the steady-state levels of PAI-1 messenger RNA (mRNA) and the release of PAI-1 antigen from BASMCs. Treatments with 10-20 mg/L of Hirulog-1 inhibited >80% of thrombin-induced PAI-1 generation from BASMCs. Hirulog-1 alone did not significantly alter PAI-1 production in the absence of thrombin. Significant reduction of thrombin-induced PAI-1 release was observed in cultures treated with Hirulog-1 for 1 h. The maximal effect of Hirulog-1 on thrombin-induced PAI-1 release was achieved in cultures treated with thrombin plus Hirulog-1 for 3 to 6 h, associated with the normalization of PAI-1 mRNA levels induced by thrombin treatment. Strong inhibition by Hirulog-1 on thrombin-induced PAI-1 release remained in cultures with 8 h of the treatment, but the effect was attenuated 16 h after a single addition of the inhibitor. Our study demonstrates that Hirulog-1 effectively inhibited thrombin-induced PAI-1 production in cultured vascular SMCs at mRNA and protein levels. Vascular SMCs may be exposed to high concentrations of thrombin when endothelium is injured. The information generated from this study suggests that Hirulog-1 potentially prevents intravascular thrombogenesis through inhibiting thrombin-induced PAI-1 production in vascular SMCs, especially when hypercoagulation and endothelial injury occurs.

Local treatment with an antithrombotic drug reduces thrombus size in coronary and peripheral thrombosed arteries

Since the treatment of thrombotic disease by antithrombotic drugs may be associated with bleeding complications, a local delivery technique for administration of the drug may be useful. The efficacy of low-dose local delivery of an antithrombotic drug on thrombosis was investigated in 73 dogs. The antithrombotic drug (heparin, 25 U/kg, antithrombin: argatroban, 0.05 mg/kg, or defibrinogenating agent: batroxobin, 0.05 U/kg) was infused locally to a 1-h-old thrombus, and no drug was given in controls. The effect of the local delivery on the thrombus was evaluated. Low- and high-dose systemic drug delivery was also evaluated. The mean reduction in thrombotic coronary stenosis observed by angiography was 30.3% with argatroban, 22% with heparin, and 20.8% with batroxobin (P < 0.005 vs controls). Systemic delivery of low-dose heparin or argatroban did not induce any change in thrombus size. With high-dose systemic drug delivery (heparin 250 U/kg, argatroban 0.5 mg/kg), the mean reduction of thrombotic stenosis was 15.2% with heparin and 32.8% with argatroban (P < 0.005 vs controls). In the iliac arterial thrombosis, after local delivery of the drugs, the mean reduction of thrombotic stenosis observed by angiography was 24.4% in the argatroban group, and 19.2% in the heparin group (P < 0.05 vs controls, respectively). With high-dose systemic heparin delivery, the mean reduction of the thrombotic stenosis was 13.2% (P < 0.01 vs control). Angioscopy also demonstrated a similar trend. The high-dose drug delivery reduced systemic coagulability. Thus, local delivery of an antithrombotic agent can reduce the thrombus size in the coronary and iliac arteries without having any significant influence on coagulability.

Induction of thrombolysis and prevention of thrombus formation by local drug delivery with a double-occlusion balloon catheter

The efficacy of the local delivery of an antithrombotic drug in preventing thrombosis and enabling thrombolysis was investigated in 29 dogs. An antithrombotic drug (heparin, 25 U/kg), or an antithrombin (argatroban, 0.05 mg/kg) was infused into injured canine iliac arteries, using a double-occlusion balloon catheter, and the preventive effect of the drug was evaluated. Local delivery of low-dose tissue-type plasminogen activator (t-PA; Tisokinase, 50,000 U; Kowa, Nagoya and Asahi Chemical Industries, Fuji, Japan) into thrombosed canine iliac arteries, using the same catheter, or intravenous infusion of low-dose or high-dose t-PA (30,000 U/kg) was also performed. Angiographically, stenotic thrombosis was 2% by local delivery of argatroban and 7% by local delivery of heparin (P < 0.01 vs each control; 47% and 51% respectively). Thrombotic stenosis, as observed by angiography, decreased from 91% to 9% after local delivery of t-PA, and from 94% to 52% in controls. Local delivery of t-PA effectively reduced the thrombus size (P < 0.01 vs control). After systemic intravenous delivery of low-dose t-PA, no reduction of residual thrombotic stenosis, was observed. Reduction of residual thrombotic stenosis after intravenous delivery of high-dose t-PA, was similar to that achieved by local delivery of the drug. Angioscopy demonstrated a similar trend. High-dose drug delivery reduced systemic coagulability. Local delivery of an antithrombotic drug, using a double-occlusion balloon catheter, effectively prevented thrombus formation, and local delivery of t-PA induced thrombolysis without exerting a significant influence on coagulability.

Pharmacological properties of hirudin and its derivatives. Potential clinical advantages over heparin

Hirudin and its derivatives represent the first parenteral anticoagulants introduced since the discovery of heparin in the early 1900s. Hirudin, the naturally occurring anticoagulant of the leech, is a single peptide chain of 65 amino acids with a molecular weight of about 7000. Recombinant technology has developed methods to produce recombinant forms of hirudin (r-hirudin) in sufficient quantities for therapeutic use. Hirudin is a potent thrombin-specific inhibitor that forms equimolar complexes with thrombin. It represents a new anticoagulant agent in a field in which heparin has been the only available drug for many years. In contrast to heparin, hirudin does not require antithrombin III as a cofactor, is not inactivated by antiheparin proteins, has no direct effects on platelets and may also inactivate thrombin bound to clot or the subendothelium. In humans, experience with r-hirudin in preventing or treating venous thromboembolism is very preliminary. However, r-hirudin achieved promising results in patients with unstable angina, or following coronary angioplasty. In patients with acute myocardial infarction, 3 important clinical trials were stopped because of an excess of bleeding complications. At present, the discovery of a r-hirudin regimen that is more efficacious than heparin and at least as safe needs a reappraisal of the drug in further trials.

Relation between systemic anticoagulation as determined by activated partial thromboplastin time and heparin measurements and in-hospital clinical events in unstable angina and non-Q wave myocardiaL infarction. Thrombolysis in Myocardial Ischemia III B Investigators

Although coronary thrombosis is thought to play a pivotal role in the pathogenesis of unstable angina and non-Q wave myocardial infarction and antithrombotic therapy is a mainstay in the early management of these patients, the relation between measures of systemic anticoagulation and clinical events has not been defined clearly. In the Thrombolysis in Myocardial Ischemia III trial, 1473 patients with ischemic chest pain at rest evaluated within 24 hours of symptom onset were randomized to (1) tissue plasminogen activator (TPA) or placebo and (2) an early invasive or an early conservative strategy. All patients received a full complement of anti-ischemic medication, aspirin, and continuous intravenous heparin titrated to an activated partial thromboplastin time (aPTT) of 1.5 to 2.0 times control for 72 to 96 hours. The median aPTT in all study groups exceeded the minimum threshold (45 seconds) by 24 hours and remained within the designated range during the protocol-directed heparin infusion. No differences in median aPTT values for the 72- to 96-hour study period were observed between groups (p=not significant). Median 12-hour heparin concentrations were >0.2 U/ml in all groups; however, values <0.2 U/ml were common thereafter, particularly in TPA-treated patients. Time-dependent covariate analyses failed to identify statistically significant differences in either aPTT or heparin levels between patients with in-hospital clinical events (spontaneous ischemia, myocardial infarction, or death) and those without events (p=0.27). Furthermore, early clinical events occurred in a similar percentage of patients with optimal anticoagulation (all aPTTs >60 seconds, all heparin levels>0.2 U/ml), and those with aPTTs or heparin levels below these thresholds. Aggressive (high-intensity) anticoagulation with heparin to achieve aPTTs >2.0 times control does not appear to offer additional clinical benefit to lower levels (1.5 to 2.0 times control) among patients with unstable angina and non-Q wave myocardial infarction receiving intravenous heparin and oral aspirin. Therefore, the optimal level of anticoagulation in this common clinical setting is between 45 and 60 seconds when heparin is included in the treatment strategy. Direct plasma heparin measurement does not offer an advantage to routine aPTT monitoring. The occurrence of spontaneous ischemia, myocardial infarction, and death in spite of antischemic therapy and optimal anticoagulation (as it is currently defined) with heparin supports ongoing efforts to develop more effective antithrombotic agents.

Sustained-release local hirulog therapy decreases early thrombosis but not neointimal thickening after arterial stenting

Adventitial heparin delivery has been shown to inhibit thrombosis and neointimal thickening in a rat carotid injury model. To determine whether sustained, local delivery of hirulog, a potent antithrombin agent, inhibits thrombus formation and neointimal thickening after arterial stenting, silicone polymers containing hirulog were formulated at a concentration of 5.8% by weight and were tested in vitro to determine the rate of drug release. An oversized metallic stent was implanted in the carotid artery of 18 juvenile farm pigs. Hirulog-impregnated silicone polymers were placed around the adventitial surface of one stented segment of each animal and a control polymer was placed contralaterally. Intravenous hirulog (4 mg/kg/hr) was infused for the duration of the procedure to maintain the activated clotting time of > 300 sec. Ex vivo testing estimated the release of hirulog to be 1.54 micrograms/mg matrix/day with no loss of anticoagulant activity of the released peptide. In four pigs killed on days 3 through 5, macroscopic thrombus was very faintly visible on the stent struts of one arterial segment treated with sustained-release hirulog but was readily evident in all control arteries. However, electron microscopy showed platelet adhesion and microscopic thrombus formation on each stent of both treated and untreated sides. Fourteen pigs were killed 32 +/- 4 days after stenting. Histologic analysis showed no difference between hirulog-treated and control sides in the volume of neointima (540 +/- 129 units vs 357 +/- 95 units, p = 0.27) or in the average intima to media ratio (0.44 +/- 0.12 vs 0.34 +/- 0.24, p = 0.47) over the length of the stented segment. Late thrombotic occlusion occurred in two hirulog-treated and two control arteries. In this model, local adventitial hirulog delivery at the dose and delivery rate used may reduce, but does not prevent, thrombus formation and does not reduce the severity of neointimal thickening after carotid stent implantation.

Local treatment with antithrombotic drugs can prevent thrombus formation: an angioscopic and angiographic study

OBJECTIVES

This study was designed to evaluate the efficacy of local versus systemic treatment of thrombosis with various antithrombotic drugs.

BACKGROUND

Local use of low dose antithrombotic drugs has been proposed as being effective and safe.

METHODS

Heparin (30 U/kg), an antithrombin agent (argatroban, 0.05 mg/kg body weight) or a defibrinogenating drug (batroxobin, 0.05 U/kg) was locally infused into one side of the canine iliac artery after injury by balloon inflation. The other side was injured as a control. The efficacy of systemic delivery of high dose (heparin [300 U/kg] and argatroban [0.5 mg/kg]) and low dose drugs was also assessed.

RESULTS

Sixty minutes after local treatment in 22 dogs, no thrombotic stenosis was observed by angiography in locally treated arteries (p < 0.005 vs. mean thrombotic stenosis of 27% in control segments for heparin, 25.3% in control segments for argatroban and 32% in control segments for batroxobin). Angioscopy demonstrated the same trend. In locally treated arteries, thrombus weight was significantly lower in the treated than control side. In the systemic high dose group (n = 10), angiographic thrombotic stenosis was < 5% after high dose drug delivery (p < 0.05 vs. control segments, 37.4% for heparin, 43% for argatroban). In another 10 dogs, low dose systemic delivery was not effective in inhibiting thrombus formation. Activated partial thromboplastin time and fibrinogen levels did not change with local treatment.

CONCLUSIONS

Compared with systemic administration of antithrombotic drugs, local treatment is a safer and more effective method of preventing thrombosis.

Novel antithrombotic drugs in development

Platelet activation plays a critical role in thromboembolic disorders, and aspirin remains a keystone in preventive strategies. This remarkable efficacy is rather unexpected, as aspirin selectively inhibits platelet aggregation mediated through activation of the arachidonic-thromboxane pathway, but not platelet aggregation induced by adenosine diphosphate (ADP), collagen and low levels of thrombin. This apparent paradox has stimulated investigations on the effect of aspirin on eicosanoid-independent effects of aspirin on cellular signalling. It has also fostered the search for antiplatelet drugs inhibiting platelet aggregation at other levels than the acetylation of platelet cyclo-oxygenase, such as thromboxane synthase inhibitors and thromboxane receptor antagonists. The final step of all platelet agonists is the functional expression of glycoprotein (GP) IIb/IIIa on the platelet surface, which ligates fibrinogen to link platelets together as part of the aggregation process. Agents that interact between GPIIb/IIIa and fibrinogen have been developed, which block GPIIb/IIIa, such as monoclonal antibodies to GPIIb/IIIa, and natural and synthetic peptides (disintegrins) containing the Arg-Gly-Asp (RGD) recognition sequence in fibrinogen and other adhesion macromolecules. Also, some non-peptide RGD mimetics have been developed which are orally active prodrugs. Stable analogues of prostacyclin, some of which are orally active, are also available. Thrombin has a pivotal role in both platelet activation and fibrin generation. In addition to natural and recombinant human antithrombin III, direct antithrombin III-independent thrombin inhibitors have been developed as recombinant hirudin, hirulog, argatroban, boroarginine derivatives and single stranded DNA oligonucleotides (aptanes). Direct thrombin inhibitors do not affect thrombin generation and may leave some 'escaping' thrombin molecules unaffected. Inhibition of factor Xa can prevent thrombin generation and disrupt the thrombin feedback loop that amplifies thrombin production.

Inhibition of platelet deposition by combined hirulog and aspirin in a rat carotid endarterectomy model

PURPOSE

Hirulog, a thrombin-specific inhibitor, has shown efficacy in reducing arterial thrombosis in patients treated with aspirin who require angioplasty or have unstable angina. In this study, the effect of hirulog on reducing deposition of indium 111-labeled platelets was assessed in a surgical model of aspirin-treated rats undergoing carotid endarterectomy.

METHODS

Animals were randomly assigned to one of five groups: control (no aspirin or hirulog); aspirin alone (10 mg/kg); aspirin plus low-dose hirulog (0.2 mg/kg bolus followed by 0.5 mg/kg/hr); aspirin plus medium-dose hirulog (0.4 mg/kg bolus followed by 1.0 mg/kg/hr); or aspirin plus high-dose hirulog (0.6 mg/kg bolus followed by 1.5 mg/kg/hr). Hirulog was infused before surgery and continued until termination of the experiment 30 minutes after endarterectomy.

RESULTS

Platelet deposition in rats receiving aspirin alone was reduced by 19% +/- 23% SE (p = 0.26) compared with controls. Deposition in aspirin-treated groups receiving low-, medium-, and high-dose hirulog decreased in a dose-dependent manner by 37% +/- 20% (p = 0.048), 44% +/- 19% (p = 0.061), and 56% +/- 13% (p = 0.022), respectively. As the dose of hirulog was increased, the plasma hirulog levels and activated partial thromboplastin time ratios (final:initial) also increased in a dose-dependent manner. The mean plasma hirulog levels ranged from 0.74 +/- 0.08 micrograms/ml in the low-dose hirulog group to 2.55 +/- 0.08 micrograms/ml in the high-dose hirulog group, and the corresponding activated partial thromboplastin time ratios were 1.5 +/- 0.12 (p = 0.001) and 3.3 +/- 0.63 (p = 0.001). Bleeding was easily controlled by local hemostatic measures for all experimental groups.

CONCLUSION

Hirulog causes significant decrease in 111In-labeled platelet deposition in aspirin-treated rats subjected to microsurgical endarterectomy at doses that allow surgical hemostasis to be easily established.

Activation of blood coagulation by plaque rupture: mechanisms and prevention

Inhibition of thrombosis is proving to be an important treatment goal in many clinical situations, including coronary thrombolysis, angioplasty, and unstable angina. Heparin is a potent inhibitor of thrombin and thrombin generation, but its ability to accelerate thrombolysis, prevent acute reocclusion after vascular injury in angioplasty, and prevent myocardial infarction in unstable angina is relatively limited, possibly because clot-bound thrombin plays an important role in these clinical situations. Thus, when thrombin binds to fibrin, it remains enzymatically active and relatively impervious to inactivation by heparin or other fluid-phase inhibitors. However, direct thrombin inhibitors--such as D-Phe-L-Pro-L-Arg-CH2Cl (PPACK), hirudin, hirugen, and hirulog--inhibit free and clot-bound thrombin with equal efficacy, presumably because their sites of interaction are not masked when thrombin binds to fibrin. Advanced clinical trials suggest that the direct thrombin inhibitors and 7E3, an inhibitor of platelet glycoprotein IIb/IIIa, will soon be incorporated into the armamentarium against arterial thrombosis.

Novel antithrombotic approaches to coronary artery disease

Current prevention or treatment of coronary thrombosis relies on antiplatelet agents (aspirin), antithrombin agents (heparin), and plasminogen activators (t-PA). The purpose of this review is to describe novel antithrombotic agents in each of these classes and to discuss recent and future clinical trials with the new agents. Whereas aspirin is a cyclo-oxygenase inhibitor, the most promising new antiplatelets are directed at an integrin cell surface receptor--glycoprotein (GP) IIb/IIIa--which represents the final common pathway for platelet aggregation. The monoclonal F(ab) antibody c7E3, a chimeric murine-human immunoglobulin G (IgG) fragment, is the most intensively studied to date. c7E3 was assessed by the Evaluation of Platelet Monoclonal Antibody to Prevent Ischemic Complications (EPIC) trial in which 2,099 high-risk angioplasty patients were randomized to bolus (placebo) plus infusion (placebo), bolus (c7E3, 0.25 mg/kg) plus infusion (placebo), and bolus (c7E3, 0.25 mg/kg) plus infusion (c7E3, 10 micrograms/min; 12 hours). The overall event rate at 30 days was significantly decreased from 12.8% (placebo) to 8.3% (c7E3), a 36% relative reduction (p = 0.009). Integrelin is a cyclic heptapeptide with marked specificity for GP IIb/IIIa integrin. It was studied during the Integrelin to Manage Platelet Aggregation to Prevent Coronary Thrombosis (IMPACT) trial, which enrolled 150 routine coronary intervention patients. At endpoint, overall event rate was reduced from 11.9% (placebo) to 5.6% (integrelin). The much larger (4,010 patients) IMPACT-II trial has just completed enrollment to confirm and extend these encouraging results. Hirudin is the prototype of the direct antithrombins; it binds to the active catalytic site and the substrate recognition site (exosite) of thrombin.(ABSTRACT TRUNCATED AT 250 WORDS)

Use of a direct thrombin inhibitor (argatroban) during pulse-spray thrombolysis in experimental thrombosis

PURPOSE

To evaluate the effectiveness of intravenous and intrathrombic injection of the thrombin inhibitor argatroban during pulse-spray pharmacomechanical thrombolysis (PSPMT) in experimental venous thrombosis.

MATERIALS AND METHODS

Clots were produced in the inferior vena cava in 52 rabbits by placement of steel coils and balloon injury to the vessel wall. Two days later, clots were treated with PSPMT. Several treatment methods were used: intrathrombic saline, intrathrombic tissue plasminogen activator (t-PA), intrathrombic t-PA with intrathrombic and intravenous heparin, intrathrombic t-PA with intravenous argatroban, and intrathrombic t-PA with intrathrombic and intravenous argatroban at two different doses. After treatment, the rabbits were killed and residual clot was weighed. Pretreatment clot weight was estimated and clot lysis was assessed.

RESULTS

PSPMT with t-PA and adjunctive intrathrombic heparin resulted in greater lysis than PSPMT with only t-PA (percentage of residual clot, 59% +/- 14 vs 81% +/- 28; P = .02). Addition of intravenous argatroban did not increase lysis, but adjunctive intrathrombic argatroban significantly increased lysis at low doses (37% +/- 16; P = .02) and high doses (34% +/- 6; P = .006) compared with t-PA and intrathrombic heparin.

CONCLUSION

In a rabbit model of venous thrombosis, the use of intrathrombic argatroban during PSPMT with t-PA significantly improved clot lysis.