Argatroban and lepirudin: clinical trials to clinical practice.
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Anticoagulants↗
Biomedical subjects
Jawed Fareed
Publications and source records attributed to Jawed Fareed.
Short- and long-acting synthetic pentasaccharides as antithrombotic agents.
Fondaparinux sodium (Arixtra; GlaxoSmithKline) is the first of a new class of antithrombotic agents. It is a chemically synthesised pentasaccharide mimicking the site of heparin that binds to antithrombin. It is purely a factor Xa inhibitor and an inhibitor of thrombin generation that requires binding to antithrombin. Fondaparinux sodium differs from heparin, low-molecular-weight heparin and heparinoids, and cannot be used interchangeably. It has been approved in the US and Europe for the prophylaxis of venous thrombosis after orthopaedic surgery by a fixed dose of 2.5 mg/day without monitoring. Using this pentasaccharide as a backbone, other structures have been synthesised. Idraparinux sodium (Sanofi-Aventis) differs structurally from fondaparinux sodium as it has additional methyl groups, a long half-life, and once-weekly administration. Both drugs are being developed as antithrombotics for venous and arterial thrombosis, acute coronary syndrome, stroke and as adjuncts to thrombolytic therapy.
Animals↗
Small-molecule direct antithrombins: argatroban.
Argatroban represents the first antithrombin agent that was approved for clinical use. It belongs to the peptidomimetic (arginomimetic) group of drugs with multiple pharmacological properties. Unlike the other antithrombin drugs, such as hirudins and hirulogs, argatroban is a reversible antithrombin agent and therefore exhibits a considerably different pharmacological profile. Although argatroban is considered to be a member of the antithrombin family, its mechanisms of action include several other processes that have not been explored fully to date. These include the inhibition of non-thrombin serine proteases, a direct effect on endothelial cells and the vasculature (generation of nitric oxide), and downregulation of various inflammatory and thrombotic cytokines. Due to its lower molecular weight, argatroban is capable of passing through endovascular and cellular barriers and may, therefore, be more effective than heparins and hirudins in the antithrombotic management of microvascular disorders. Argatroban is an effective anticoagulant agent that produces a stronger anticoagulant effect than heparins and hirudins at equivalent anticoagulant levels, as measured by the activated clotting time (ACT) and activated partial thromboplastin time (APTT). At comparable ACT (300 seconds) and APTT (75-90 seconds), argatroban produces stronger inhibition of thrombin generation, as measured by in-vitro assays. Argatroban does not generate any neutralizing or non-neutralizing antibodies, and has predictable antithrombotic effects in different patients. In addition to the inhibition of thrombogenesis, argatroban also facilitates blood flow, inhibition of platelet activation and endothelial cell stimulation, mechanisms that are not necessarily related to thrombin inhibition. Despite these pharmacological advantages, additional clinical investigations are needed to validate the use of argatroban in clinical indications other than those for which it is currently approved, namely, heparin-induced thrombocytopenia and support of percutaneous coronary angioplasty.
Animals↗
Differential prevalence of anti-heparin-PF4 immunoglobulin subtypes in patients treated with clivarin and heparin: implications in the HIT pathogenesis.
Heparin-induced thrombocytopenia (HIT) syndrome is a catastrophic complication of heparin therapy that may result in arterial/venous thromboembolic events. The pathophysiology of HIT is mediated by the generation of a functionally and molecularly heterogeneous group of anti-heparin-platelet factor 4 (AHPF4) antibodies that cause platelet/endothelial cell activation/destruction. These AHPF4 antibodies may be of various subtypes and cause differential pathogenic responses during HIT. This study evaluated the differential prevalence and functionality of AHPF4 Ig subtypes (IgA, IgG, and IgM) in plasma samples obtained from clinically suspected HIT patients (n = 111) and two clinical trials. In these trials, a low-molecular-weight heparin, clivarin and unfractionated heparin (UFH) were used to treat deep-vein thrombosis (CORTES) and for prophylaxis of the orthopedic surgery (ECHOS). In the CORTES study, three randomized groups of patients (n = 312-328) received prophylactic treatment with either UFH or clivarin (o.d. or b.i.d.). In the ECHOS study, there were approximately 600 patients per group. Citrated plasma samples were analyzed for cumulative IgA/IgG/IgM and individual Ig subtypes of AHPF4 utilizing ELISA. Functionality of the ELISA-positive samples was ascertained by 14C-serotonin release assay. In clinically confirmed HIT patients (and UFH-treated CORTES and ECHOS samples), the Ig subtyping revealed a predominance of IgG AHPF4 antibodies in contrast to the asymptomatic high AHPF4 antibody titers, which were found to be mostly IgM and/or IgA subtypes. In the clivarin-treated patients in both trials, the prevalence of AHPF4 antibodies was found to be lower (2-3 fold, p < 0.01) in comparison to UFH group. In addition, the clivarin-treated patients with positive AHPF4 antibodies were found to be predominantly of the non-functional type and were found in the order of IgM > IgA > IgG Together, these observations demonstrate that ELISA-detectable IgG subtype in UFH-treated patients may be more likely to cause functional/pathologic responses during HIT syndrome. Thus, determination of IgG subtype of AHPF4 antibodies during HIT syndrome may be crucial in the diagnosis; however, the relevance of the pathologically non-functional (IgA and/or IgM) antibodies and the overall mechanism(s) of these HIT-associatied antibodies need further investigation.
Anticoagulants↗
Pharmacodynamic considerations in the selection of dosage of tinzaparin for various indications: experimental studies in primates.
Like unfractionated heparin (UFH), low-molecular-weight heparins (LMWHs) are polypharmacologic agents that can modulate the hemostatic system at multiple points. Thus, to select an optimal dose of LMWH for a given indication, it is necessary to consider multiple actions of the drug. In this study, nonhuman primates were treated with intravenous or subcutaneous boluses of the LMWH tinzaparin or UFH. Doses were selected on the basis of the expected prophylactic (75 U/kg) and therapeutic (175 U/kg) dosing of tinzaparin. Blood samples were drawn periodically up to 24 hours after administration. Circulating anti-Xa and anti-thrombin (anti-IIa) activities determined using amidolytic assays were used to estimate plasma tinzaparin (heparin) concentrations. In addition, total tissue factor pathway inhibitor (TFPI) levels were measured in these primates. Subcutaneous administration of 75 U/kg tinzaparin resulted in plasma levels of approximately 0.2 to 0.3 U/mL, concentrations sufficient for DVT prophylaxis. Such drug levels were not associated with a significant release of TFPI. Intravenous administration of the same dose resulted in a peak drug level of approximately 1.5 anti-Xa U/mL. The elimination half-life was approximately 1 hour. Thus, intravenously administered tinzaparin may be useful for providing anticoagulation during coronary interventions. Subcutaneous administration of 175 U/kg resulted in tinzaparin levels of approximately 0.7 anti-Xa U/mL and a significant increase in TFPI levels. Interestingly, the increase in TFPI levels occurred over a different time frame than anticoagulant activity. Intravenous administration of 175 U/kg resulted in peak drug concentrations of almost 5 anti-Xa U/mL. The pharmacokinetic behavior of intravenously administered tinzaparin was comparable to that of UFH. The data show that the pharmacokinetic and pharmacodynamic effects measured using different assays widely differ. For a proper pharmacodynamic analysis, multiple assays should be considered, given that both UFH and LMWHs are polycomponent in nature.
Animals↗
Laboratory analysis of blood samples from patients treated with tinzaparin.
Tinzaparin at two dosages, 175 anti-Xa U/kg subcutaneously administered for 7 days, followed by warfarin, and 175 anti-Xa U/kg subcutaneously given for 90 days was compared with continuous intravenous unfractionated heparin (UFH) for 5 days, followed by warfarin for 3 months, were tested in the treatment of patients with proximal deep vein thrombosis. Several laboratory assays were used to monitor the effects of tinzaparin and UFH. The tinzaparin only study arm produced a 4- to 6-second prolongation of the activated partial thromboplastin time (aPTT). However, in the anti-Xa chromogenic assay and the Heptest assays, there was a prolongation after the administration of all three agents. In the two groups treated for 7 days, the anti-Xa and Heptest values returned to baseline after cessation of therapy. In the patients treated with tinzaparin for 90 days, the anti-Xa and Heptest remained elevated throughout the treatment period. The anti-IIa (anti-thrombin) results were considerably lower values in the tinzaparin-treated groups. Tissue factor pathway inhibitor (TFPI) antigen levels were elevated 2- to 2.5-fold in all three groups. In addition, the thrombin/antithrombin (TAT) complexes were also measured. After treatment, the TAT levels decreased over time. Tinzaparin was more effective in decreasing these levels. These results suggest that both Heptest and anti-Xa assays can be used to monitor patients receiving tinzaparin. TAT may be a useful test in monitoring the resolution of the clots. However, additional clinical validation is required to demonstrate the relevance of these parameters with the clinical outcome.
Biomarkers↗
Heparin to pentasaccharide and beyond: the end is not in sight.
The 87-year history of heparin began in 1916 when a 26-year-old medical student named Jay McLean startled his mentor William Howell, Professor of Physiology at Johns Hopkins University, by proclaiming that he had discovered "antithrombin." This discovery was so surprising to Howell because he had expected McLean to isolate thromboplastin, a clot-promoting substance from animal tissue. In 1928, Charles Best, M.D., in Toronto, Canada, organized a team of chemists, physiologists, and surgeons to focus on the development of heparin. This group determined which animal tissues were the best source, had performed purification and identification, and had determined pharmacologic properties in vitro. By 1935, they were ready for human trials. By 1941, the group reported a series of 700 patients treated with the glycosaminoglycan called heparin. Meanwhile a critical cofactor, antithrombin, had been discovered at the University of Iowa (Brinkhous, et al). Introduction of newer tests for laboratory monitoring enabled refinement of dosages during the 1960s and 1970s. Its use permitted the development of hemodialysis and cardiopulmonary bypass surgery, and the prophylaxis of deep vein thrombosis in surgical patients. The concept of low-molecular-weight heparin occurred to Dr. Choay and others in France in the late 1970s. During the 1980s and 1990s, the development of low-molecular-weight heparins evolved for both prophylaxis and therapy. The first synthetic product was called the pentasaccharide, named for the five critical sugar units in heparin that bind to antithrombin (1983). Since then, this drug has been studied extensively to prove its clinical efficacy and safety.
Heparin↗
Differentiation of low-molecular-weight heparins: impact on the future of the management of thrombosis.
Low-molecular-weight heparins (LMWHs) are now universally accepted as drugs of choice for postsurgical prophylaxis and treatment of deep vein thrombosis (DVT). Currently, these agents are also being developed for the treatment of various cardiovascular conditions. Because of manufacturing differences, each of the LMWHs exhibits distinct pharmacologic and biochemical profiles. The specific activity of these agents in anticoagulant assays ranges from 35 to 45 anti-IIa U/mg, whereas the activity in terms of anti-Xa units is designated as 80 to 145 U/mg. These LMWHs are also capable of producing product-specific dose- and time-dependent antithrombotic effects in animal models of thrombosis. Although the ex vivo effects are initially present at dosages that are antithrombotic, these agents have been found to produce sustained antithrombotic effects without any detectable ex vivo anticoagulant actions. In experimental animal models and various clinical trials, these agents also have been found to release tissue factor pathway inhibitor and von Willebrand factor. In addition, LMWHs have been reported to produce fibrinolytic effects. The effect of repeated administration also exhibits product-based augmentation of the antithrombotic and hemorrhagic effects. Several new agents are being investigated as possible substitutes for heparins. These include anti-thrombin, anti-Xa, anti-TF (tissue factor), heparinoids, oral formulations of heparin, activated protein C, and biotechnologically derived serpins. These agents may not have the broad clinical spectrum as that observed with the heparins. More recently, several pharmaceutical companies have produced generic LMWHs.
Blood Coagulation↗
Epilogue. Expanded role of low-molecular-weight heparins in hematology and oncology.
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Cardiovascular Diseases↗
Generic low-molecular-weight heparins: some practical considerations.
It is now widely accepted that various low-molecular-weight heparins (LMWHs) exhibit specific molecular and structural attributes that are determined by the type of manufacturing process used. For example, enoxaparin, which is prepared by benzylation followed by alkaline hydrolysis of unfractionated heparin (UFH), exhibits a double bond at the nonreducing end and the presence of a unique bicyclic structure namely 1,6 anhydromanno glucose or mannose, or both, at the reducing end. Similarly, the other LMWHs, such as dalteparin, nadroparin, tinzaparin, and parnaparin, exhibit specific structural characteristics that may contribute to their own unique biochemical and pharmacological profiles. These unique features may not exhibit any major influence on the routinely determined anti-Xa and anti-IIa activities. However, these may have an impact on the pharmacokinetics and other biological actions such as the interactions with growth factors, blood components, and vascular cells. This is the reason for the initial caution for the noninterchangeability of the anti-Xa adjusted dosing of the different LMWHs. Although the nonanticoagulant biological effects of these drugs are poorly understood at this time, they are now recognized as contributing significantly to the overall therapeutic effects of these drugs. Because some of these drugs have proved to be effective in the management of cancer-associated thrombosis and exhibit improvements in mortality outcome, these LMWHs may also produce several other effects by modulating inflammatory processes, apoptosis, and other regulatory functions related to cellular functions at different levels. Thus, the interactions of these LMWHs with antithrombin and heparin cofactor II are not the only determinants of their biological actions. Release of tissue factor pathway inhibitor (TFPI), regulation of cytokines, nitric oxide, and eicosanoids contribute to their individuality. Such properties are not only dependent on the oligosaccharide sequence and consensus sites but also depend mainly on microchemical and structural attributes in these drugs. European Pharmacopoeia (EP) and the World Health Organization (WHO) have developed guidelines to characterize these agents in terms of their molecular and biological profile. Regulatory agencies such as the U.S. Food and Drug Administration (FDA) and European Medicines Agency (EMEA) consider each of these drugs as distinct pharmacological agents. This has prompted the requirement for product-specific clinical data for the approval of their use in various clinical indications. There is a clear concern regarding the development of potential generic versions of branded products and the submissions by generic manufacturers for the regulatory approval of generic interchangeability that refers to the substitution of an apparent chemically identical and bioequivalent versions of the branded LMWHs. Currently, there are no regulatory guidelines or consensus opinions on the acceptance of generic versions of the branded products. Because the LMWHs represent not only a biological entity but also product-specific molecular and structural attributes, the acceptance of a generic version must be based on clearly defined guidelines stipulating minimal molecular and structural, biological, and clinical validation requirements. It is therefore to be stressed that each of the LMWHs is a distinct drug entity that characteristically exhibits a product-based therapeutic spectrum in different thrombotic and nonthrombotic disorders. Thus, until the establishment of valid regulatory guidelines for the generic interchangeability of the commercially available LMWHs is completed, generic substitutes are not recommended.
Anticoagulants↗
Molecular and pharmacologic profile of tinzaparin and a comparable low-molecular-weight bacterial sulfaminoheparosan.
Low-molecular-weight heparins (LMWH) represent depolymerized porcine mucosal heparin derivatives, which are commonly used for the management of thrombotic disorders. Because of their widespread usage, the supplies of the raw material namely unfractionated heparin are nearly exhausted. Porcine mucosal tissue is almost exclusively used for the preparation of these agents. Thus, there is a timely need for the production of heparin like drugs from other sources. Fermentation techniques have been used to produce carbohydrates such as dextran and innulin for therapeutic purposes. Bacterial cell wall polysaccharide mimics the linear hexose units, which constitute heparin. Utilizing Escherichia coli cell membranes produced by fermentation technology, chemical sulfation and enzymatic epimerization, sulfaminoheparosan type of polymer mimicking the structure of heparin has been produced. These semi-synthetic sulfaminoheparosans exhibit biologic actions comparable to that observed with heparin. The sulfaminoheparosan core can also be degraded to obtain low-molecular-weight (LMW) derivatives mimicking LMWHs. Using this technique, a novel LMW sulfaminoheparosan derivative (Q93C/239) was produced by Inalco, Milan, Italy. To compare this heparin analogue, a LMWH, namely tinzaparin, was used to determine the relative anticoagulant, antiprotease, and molecular profile. Additional studies were carried out to determine the susceptibility of this agent to heparinase-I. These comparative studies exhibited both antiprotease and anticoagulant properties similar to those of tinzaparin. However LMW sulfaminoheparosan resisted heparinase-I digestion at low heparinase-I concentrations. These studies demonstrate that the sulfaminoheparosan derived LMW components exhibit similar molecular and anticoagulant profile as tinzaparin and warrant additional preclinical and clinical development to determine their potential usefulness as antithrombotic agents.
Anticoagulants↗
Laboratory diagnosis of heparin-induced thrombocytopenia in Asian Indians as investigated with functional and immunologic methods.
Heparin-induced thrombocytopenia (HIT) was looked for in 33 Indian patients undergoing cardiovascular surgery who received unfractionated heparin (UFH). Platelet counts were performed before the initiation of UFH therapy and 5 to 16 days after administration of the therapy. A decrease in patients' platelet count > 35% of the baseline value or < 100,000/microL was considered to be suggestive of HIT syndrome. Heparin-induced platelet aggregation (HIPA) and enzyme-linked immunosorbent assay (ELISA) tests were performed in all the patients to detect antibodies against heparin/PF4 complex. Thrombocytopenia was found to be present in 10 (30%) patients. Of these, two patients were found to be positive as detected by HIPA and ELISA tests. These two patients were considered to have classic HIT syndrome. One of these had bleeding while the other was asymptomatic. Among the 23 non-thrombocytopenic patients and controls, HIT antibodies were not detectable by HIPA test in all but absent by ELISA in only 21 of them. Two of 23 non-thrombocytopenic patients had positive results on the ELISA test. Because the latter had negative test results on HIPA, they were considered to be false-positive results. Thus, HIT syndrome develops in approximately 6% of Indian patients treated with UFH.
Cardiac Surgical Procedures↗
Acute myocardial infarction in a patient with essential thrombocythemia treated with glycoprotein IIb/IIIa inhibitor.
Essential thrombocythemia (ET) rarely causes obstruction of coronary arteries or acute myocardial infarction. Treatment of acute myocardial infarction in patients with ET may be a problem due to the important role of platelets in the pathogenesis of infarction. There is no reported case of acute myocardial infarction with essential thrombocythemia treated with a glycoprotein IIb/IIIa inhibitor. In this report, a 49-year-old woman with essential thrombocythemia, admitted with a diagnosis of acute inferolateral myocardial infarction, was treated with tirofiban, a glycoprotein IIb/IIIa receptor blocker.
Female↗
Erythropoietin-induced thrombosis as a result of increased inflammation and thrombin activatable fibrinolytic inhibitor.
Chronic inflammation is a major cause of morbidity and mortality in end-stage renal disease. The associated anemia in these patients due to renal cortical atrophy and erythropoietin deficiency is treated with recombinant erythropoietin. Recent reports suggest a growing incidence of symptomatic venous thrombosis in cancer patients treated with recombinant erythropoietin. Several investigators have reported on different mechanisms of thrombosis in these patients. We hypothesize that thrombosis in patients with end-stage renal disease due to increased expression of C-reactive protein (CRP) as a result of chronic inflammation promotes the release of thrombin activatable fibrinolytic inhibitor causing fibrinolytic deficit and eventually thrombosis. Furthermore, because endothelial nitric oxide is responsible for the maintenance of the normal vascular function, the decreased levels of nitric oxide in chronic inflammation cause endothelial damage and result in thrombosis. To test this hypothesis, blood samples were collected from 106 patients (49 male and 57 female, aged 59.8+/-15.7 years) with end-stage renal disease undergoing hemodialysis and treated with recombinant erythropoietin at a mean dose of 201.8 U/kg/week. Blood samples were drawn in 5-mL tubes containing 3.2% sodium citrate just before the hemodialysis procedure. These blood samples were immediately centrifuged to obtain platelet-poor plasma, which was aliquoted and frozen at -70 degrees C until further analysis. Erytropoietin antibodies were measured using an anti-EPO enzyme-linked immunosorbent assay (ELISA) method developed in our laboratory. Nitric oxide was measured using a NO analyzer (Sievers 280I, Ionics, Boulder, CO). Plasma CRP levels were measured with a highly sensitive ELISA method IMUNOCLONE CRP ELISA (American Diagnostica, Greenwich, CT). TAFI antigen levels in plasma were analyzed with an IMUCLONE TAFI ELISA kit (American Diagnostica, Greenwich, CT). TAFI functional activity was assayed with an ACTICHROME TAFI activity kit. The measured levels of nitric oxide, CRP, TAFI antigen, and TAFI functional were 37.36+/-36.8 (normal value, 37.49+/-18.96; range, 19.3-102 microM), 12.27+/-10.6 (normal value, < 1 microg/mL), 146.9+/-28.4% NHP (normal, 100% NHP), and 102.55+/-37% NHP (normal range, 22.3-165.7; mean, 89.5% NHP), respectively. The erythropoietin antibody was detected in 9.4% of the patient group. While 20% of the erythropoietin antibody-positive and 27.1% of the erythropoietin antibody-negative patients experienced chest pain, thrombotic events developed in 9.4% of the erythropoietin antibody-negative patients. These data provide the rationale for a novel mechanism of thrombosis through increased activity of CRP, nitric oxide, and TAFI, leading to fibrinolytic deficit and thrombosis in patients treated with erythropoietin.
Adult↗
Studies on the effect of calcium in interactions between heparin and heparin cofactor II using surface plasmon resonance.
Heparin is the most acidic polysaccharide in the human body and as a result interacts with many cationic species, including ions and proteins, giving rise to myriad biologic activities. Heparin cofactor II (HCII) is a serine protease inhibitor that resembles antithrombin (ATIII) in its ability to be activated by heparin. The interaction of heparin with HCII has been the focus of many studies using affinity chromatography and fluorescence spectroscopy. In this study, surface plasmon resonance (SPR) spectroscopy was used to quantitatively measure the interaction of heparin and HCII using a heparin biochip prepared by covalently immobilizing preformed albumin-heparin conjugate. HCII contains multiple EF hand domains that represent putative calcium ion binding sites. The interactions of HCII with heparin, low-molecular-weight heparin, and heparin oligosaccharides (disaccharide, tetrasaccharide, hexasaccharide) were examined in solution competition experiments using SPR. The results also showed while calcium ions enhanced the heparin/HCII interaction, the activity of heparin-HCII complex against thrombin was not calcium dependent but can be enhanced by the presence of calcium.
Amino Acid Sequence↗
Differentiation of low-molecular-weight heparins: practical implications.
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Drug Interactions↗
Anti-Xa and anti-IIa drugs alter international normalized ratio measurements: potential problems in the monitoring of oral anticoagulants.
Several of the newly developed anti-Xa and anti-IIa agents have been shown to influence the International Normalized Ratio (INR) values. During phase I trials with normal healthy volunteers and phase II study patients who were given warfarin and concomitant anti-IIa or anti-Xa agents, it has been reported that INR values were falsely elevated. It is of critical importance to know of the effects of these agents on INR to avoid dosage errors. To study the influence of these agents on INR, we used several anti-IIa agents (argatroban, recombinant hirudin, efegatran, and PEG-hirudin) and anti-Xa drugs (pentasaccharides such as fondaparinux and idraparinux, DX-9065a and JTV-803). The anti-IIa drugs were supplemented in citrated plasma at a concentration of 0 to 1 microg/mL level and anti-Xa drugs in the range of 0 to 25 microg/mL. The IC(50) values for each of these agents were calculated. Four different commercially available prothrombin time (PT) reagents were used to perform the PT assays and to calculate the relative INR values. Direct synthetic factor IIa and Xa inhibitors exhibited a concentration-dependent increase in the INR values. Hirudin, efegatran, and PEG-hirudin showed a weaker effect, whereas argatroban showed a much higher elevation of the INR values. Synthetic indirect anti-Xa agents such as the pentasaccharide did not show any effect on the INR values. Furthermore, prothrombin time reagents with high ISI values exhibited disproportionally higher INR values for both the direct anti-Xa and anti-IIa agents. Elevation of INR values has therapeutic implications when non-oral anticoagulant drugs are used in combination with drugs such as warfarin. Because of the false elevation of INR values with some of the non-oral anticoagulant drugs, patients who are on concomitant warfarin therapy should be carefully evaluated for their corresponding INR values for proper dosing. To avoid dosing errors it is best not to use the INR values in the therapeutic monitoring of anti-Xa and anti-IIa agents either in the monotherapeutic or polytherapeutic modalities. These data also warrant the development clinically relevant methods for the monitoring of the concomitant use of newly developed anti-Xa and anti-IIa drugs with oral anticoagulants.
Adult↗
Tissue factor pathway inhibitor in thrombosis and beyond.
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Angina, Unstable↗