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Debra A Hoppensteadt

Publications and source records attributed to Debra A Hoppensteadt.

At least 19 recordsLinked to original sources
PubMed2007

Relative neutralization of the biological actions of sulfaminoheparosans (K5 derivatives) and heparins by protamine sulfate.

Biosynthetic, semisynthetic, and synthetic analogues of heparins are currently developed as substitute antithrombotic agents for heparin. Sulfaminoheparosan (SAH) represents a bacterial polysaccharide (K5)-derived antithrombotic polymer from which pharmacologically active products with varying molecular weights (5-25 kDa) can be derived. These agents have been shown to exhibit pharmacologic effects comparable to heparins. The objective of this investigation is to determine the relative neutralization profile of various SAH derivatives, also called as bioheparins, by protamine sulfate. Four SAH fractions with varying molecular weights (20, 9, 7, and 6 kDa), a low molecular weight heparin (LMWH), tinzaparin, and unfractionated heparin (UFH) were supplemented to normal human pool plasma over a concentration range of 6.2 to 100 microg/mL. A fixed amount of protamine sulfate at 25 microg/mL (final concentration) was supplemented to determine the neutralization profile by performing tests such as prothrombin time (PT), activated partial thromboplastin time (APTT), Heptest, prothrombin-induced clotting time (PiCT), and amidolytic anti-Xa and anti-IIa assays. Protamine sulfate produced varying degrees of neutralization of all bioheparin fractions in the clotting assays. In the amidolytic anti-IIa assay relatively stronger inhibition was noted for all agents than inhibition of FXa. On a cumulative basis the neutralization profile of SAHs was comparable with heparins. These results suggest that the anticoagulant activities of SAH derivatives can be antagonized by protamine sulfate. These studies warrant further in vivo investigation to validate the relative neutralization profile of sulfaminoheparosans.

Bacterial Capsules↗
PubMed2006

Modulatory effects of Escherichia coli capsular-derived sulfaminoheparosans and heparins on tissue factor-mediated activation of platelets: flow cytometric analysis.

Sulfaminoheparosans (alternatively known as bioheparins) represent sulfated derivatives obtained from the K5 capsular polysaccharide of Escherichia coli. Previous studies have shown that these agents are structurally comparable to heparins and capable of exerting anticoagulant and antiprotease effects like heparins. Furthermore they are also able to release tissue factor pathway inhibitor (TFPI). Tissue factor (TF) plays a vital role in the pathogenesis of thrombotic and cardiovascular disorders. Anticoagulants such as heparins and bioheparins inhibit this thrombogenic mediator and thereby downregulate the activation of prothrombin and factor X. This study was carried out to determine the effects of several bioheparin fractions and heparins on TF-mediated platelet activation and their direct effect on platelets using human whole blood flow cytometry. Four different sulfaminoheparosan fractions with mean molecular weights of 20, 9, 7, and 6 kDa were tested for their inhibitory effects on platelet activation at two different concentrations (100 and 10 microg/mL). Unfractionated heparin and a low-molecular-weight heparin, tinzaparin, were also tested under the same experimental conditions for comparative modulatory responses. Fresh whole blood from healthy female and male volunteers (n = 5) was mixed with each of these agents and incubated with TF (diluted thromboplastin C) to activate platelets. Platelets were labeled with the antibodies CD61 FITC (GP IIIa) and CD62 PE (P-selectin). The data were analyzed in terms of percent platelet aggregation and platelet P-selectin expression. At 100 microg/mL, all of these agents strongly and significantly inhibited (approximately 40%) the platelet activation induced by TF in comparison to saline control. The inhibitory effects of each of these agents were slightly weaker (approximately 24% inhibition) at 10 microg/mL. The inhibitory effects of these agents on P-selectin expression correspond to their effects on platelet aggregation. At 100 microg/mL all the agents produced greater than 80% inhibition of P-selectin expression whereas at 10 microg/mL, the inhibition is greater than 70% except for bio-20 kDa, which produced less than 50% of inhibition. No molecular weight dependence was observed with bioheparin fractions in terms of inhibitory effects on platelet aggregation or P-selectin expression. None of the bioheparins and heparins exhibited any direct effects on platelets. These observations suggest that both the bioheparins and heparins are capable of inhibiting TF-mediated activation of platelets. Thus the therapeutic effects of bioheparins in the TF-mediated pathogenesis of platelet activation may be similar to those of heparins.

Anticoagulants↗
PubMed2006

Product individuality of commercially available low-molecular-weight heparins and their generic versions: therapeutic implications.

The currently available brand-name low-molecular-weight heparins (LMWHs) in the United States include dalteparin (Pfizer), enoxaparin (Aventis), and tinzaparin (Pharmion). Other products available, in Europe, include certoparin (Novartis), reviparin (Abbott), nadroparin (GlaxoSmithkline), and parnaparin (Alpha-Wasserman). Each of these LMWHs has a characteristic molecular weight profile and biological activity in terms of an anti-FXa and anti-FIIa potency. The mean molecular weight of these drugs ranges from 4.0 kDa to 7.0 kDa and the anti-FXa:anti-FIIa ratio ranges from 1.5 to 3.5. These agents may also be characterized by the presence of specific chemical end groups such as 2-O-sulfo-4-enepyranosuronic acid at the nonreducing terminus (enoxaparin) or 2,5-anhydro-D-mannose at the reducing terminus (dalteparin). Further, the component oligosaccharide chains exhibit product-specific distribution profiles. It is now widely accepted that individual LMWHs are chemically unique agents and cannot be interchanged therapeutically. Each commercial LMWH has been individually developed for specific clinical indications, which are dose and product dependent. Recently, several generic LMWHs have become available in India (Cutenox and Markaparin) and South America (dilutol, clenox, dripanina), and three companies have filed for regulatory approval of a generic version of enoxaparin in the United States. As the primary aim of a generic drug is to reduce cost without compromising patient care, a generic drug is required to be chemically and biologically equivalent to the pioneer drug. Because LMWHs represent complex natural mucopolysaccharide drugs that have undergone chemical and enzymatic modifications, physicochemical and biological information in addition to molecular weight and anti-FXa:anti-FIIa ratio should be used to determine generic equivalency to the branded drug. We have utilized a previously reported approach to systematically compare three generic versions of enoxaparin obtained from India and Brazil with the branded enoxaparin (Lovenox) available in the United States. Testing included molecular and structural profiling, evaluation in clot-based and amidolytic anti-FXa and anti-FIIa assays, and heparinase-I digestion profiles. While the molecular profiles (4.8 +/- 1.8 kD) and anticoagulant potencies as determined by activated partial thromboplastin time (APTT) were comparable for all four agents, the generic products showed variations in the thrombin time (TT) and Heptest assays. Two generic and the branded enoxaparin were readily digested by heparinase-I, losing most of their anticoagulant activity, but one generic product resisted digestion. This may have been due to a unique structural feature in this product. These studies show that, while generic LMWHs may exhibit acceptable molecular weight and anti-FXa profiles, they can exhibit assay-based differences and digestion profiles. Testing in animal models to determine safety, efficacy, and pharmacodynamic parameters may be important to verify equivalence. In order to assure that the generic LMWHs are equivalent to branded LMWHs such that equivalent clinical results are obtained, there is a need to develop clear stepwise guidelines that will establish equivalency in terms of physical, chemical, biochemical, pharmacokinetic, and pharmacodynamic properties for these anticoagulant drugs.

Blood Coagulation Tests↗
PubMed2005

Development of generic low molecular weight heparins: a perspective.

It is clear that the introduction of generic versions of low molecular weight heparins (LMWHs) is inevitable; however, it is important that the generic products are manufactured in strict compliance with the manufacturing specification of the branded product. Furthermore, regulatory agencies should require additional data on the chemical biologic, pharmacologic/toxicologic, and dose-response relationship in specific settings. Although there is strong opposition to stop the introduction of these drugs, their development will reduce cost and permit availability to all patients who need them. Some objective guidelines for the proper development of these drugs are needed. Only expert groups and advisory panels to the regulatory bodies can develop these guidelines.

Drug Approval↗
PubMed2005

Functional characterization of antibodies against heparin-platelet factor 4 complex in heparin-induced thrombocytopenia patients in Asian-Indians: relevance to inflammatory markers.

Occurrence of heparin-induced thrombocytopenia (HIT) was investigated for 33 Indian patients undergoing cardiovascular surgery who received unfractionated heparin (UFH). Platelet counts were performed prior to the initiation of UFH therapy and 5-16 days post therapy. Heparin-induced platelet aggregation, C-serotonin release assay, and enzyme-linked immmunosorbent assay (ELISA) tests were performed in all the patients to detect the antibodies formed against the complex of heparin and platelet factor 4 (HPF4). Levels of inflammatory markers/mediators such as CD40 ligand (CD40L) and C-reactive protein (CRP) were also measured in the patient plasmas utilizing ELISA tests. Based on clinical observations and laboratory diagnoses, five patients (15%) were considered to have confirmed HIT. Despite wide variations in the titers of inflammatory markers, patients who tested ELISA-positive for HPF4 antibodies showed markedly elevated levels of both soluble CD40L and C-reactive protein. Most strikingly, the C-serotonin release assay-positive patients showed up to a 10-fold increase in the level of CD40L. It is concluded that approximately 15% Asian-Indian patients receiving UFH during cardiovascular surgery develop functional HPF4 antibodies, which are associated with the increased levels of inflammatory markers/mediators in this catastrophic HIT syndrome.

Adolescent↗
PubMed2004

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↗
PubMed2004

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↗
PubMed2004

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↗
PubMed2004

Monitoring the new antithrombotic drugs.

Today there is a diverse group of anticoagulant and antithrombotic drugs available that includes warfarin derivatives, heparin, low-molecular-weight heparins, thrombin inhibitors, factor Xa inhibitors, and various antiplatelet agents. Many of these new drugs do not alter measurable blood coagulation parameters, yet they are effective antithrombotic agents through their actions on vascular endothelial cells and proteins. Thus, these new agents do not affect the traditional clot-based prothrombin time/International Normalized Ratio (PT/INR) and activated partial thromboplastin time (aPTT) tests, and monitoring and standardization require the development of new methods. In addition to clot-based assays, chromogenic assays, enzyme-linked immunosorbent assay (ELISA), high-performance liquid chromatography (HPLC), flow cytometry, and other techniques have been used to monitor these new drugs. On the other hand, some of the new antithrombotic drugs do affect the PT, aPTT, and activated clotting time (ACT); however, they behave differently from the warfarin derivatives and heparin. The traditionally used relationship of target time to clot values and INR to clinical effect cannot necessarily be transferred to the new drugs. Unfortunately, monitoring is not as simple as it was for warfarin and heparin. Although the new antithrombotic drugs have been approved for clinical use, assay systems for monitoring most of them are still in development or have not been clinically validated. This applies to each of the clinical settings targeted for prophylaxis, treatment, or interventional procedures (i.e., high- and low-dosing regimens typically require different monitoring methods). In addition to basic monitoring, other issues such as sensitivity of the drug to different laboratory monitoring reagents and instrumentation, drug combination monitoring, and patient-related factors that contribute to the variability of the results still need to be addressed.

Chromatography, High Pressure Liquid↗
PubMed2004

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↗
PubMed2004

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↗
PubMed2004

Prevalance of heparin-dependent platelet-activating antibodies in preterm newborns after exposure to unfractionated heparin.

Heparin is frequently used in preterm infants to prolong the patency of intravascular catheters. The aim of this study was to evaluate the prevalence of heparin-dependent platelet-activating antibodies in newborns. A cross-section of all preterm newborn infants expected to require heparin to maintain patency of a central venous access line were enrolled. A blood sample was obtained soon after birth before heparin exposure to exclude the possibility of placental transfer of maternal heparin-dependent platelet-activating antibodies. A second sample was obtained at termination of heparin use (mean duration of heparin exposure was 23 +/- 13 days; range, 6-67). Paired samples, at birth and after heparin use, were available for 42 infants with a mean gestational age of 27.8 +/- 2.2 weeks and birth weight of 1036 +/- 267 g. Thrombocytopenia developed in 57% (24/42) of the infants. None of these infants had clinical suspicion of thrombosis during the study period. The etiology of thrombocytopenia was confirmed sepsis in six, presumed sepsis in three, necrotizing enterocolitis in one, and unclear in 14 infants. Anti-heparin/platelet factor 4 antibodies measured using the standard assays for heparin-induced thrombocytopenia (two commercially available enzyme-linked immunosorbent assay tests and the functional platelet serotonin release assay) were negative on all infants. Although it could be related to the poor ability of these infants to mount an immunologic response, further research is necessary to fully understand this lack of response to heparin and to elucidate further the reasons for thrombocytopenia in very-low-birth-weight infants.

Autoantibodies↗
PubMed2003

Management of thrombotic and cardiovascular disorders in the new millenium.

Anticoagulants and antithrombotic drugs have played a key role in the prophylaxis, treatment and surgica/interventional management of thrombotic and cardiovascular disorders. There are several newer drugs which are currently developed for the anticoagulant management of cardiovascular diseases in both the medical and surgical indications. These include the low molecular weight heparins (LMWHs), antithrombin agents such as the Hirudin, Hirulog and Argatroban and indirect and direct anti-Xa drugs, represented by Pentasaccharide (Arixtra) and DX 9065a, respectively. Several other agents such as the natural and recombinant anti-Xa drugs and anti-tissue factor agents are also developed. The antiplatelet agents include Clopidogrel, Cilostazol, Anplag and GP IIb/IIIa inhibitors. For the subcutaneous indications, unfractionated heparin is gradually replaced by the low molecular weight heparins (LMWHs). LMWHs such as the Enoxaparin and Dalteparin are commonly used for the management of acute coronary syndrome. These drugs have been approved for the treatment of unstable angina and are currently undergoing rigorous trials for interventional indications. Arixtra is also developed for various subcutaneous indications. However, it exhibits lower anticoagulant effects and may not be optimal for intravenous and interventional purposes. At a higher dosage when administered intravenously the LMWHs produce varying degrees of anticoagulation at relatively lower activated clotting times (150-200). Several studies in vascular and cardiovascular interventions have shown that even at a relatively lower anticoagulant level the LMWHs are as effective as unfractionated heparin at the recommended dosages which produce a relatively higher level of anticoagulation (ACT > 200 secs.). Thus, these agents are currently developed for interventional and surgical indications. It should be emphasized that different LMWHs produce different degrees of anticoagulation and should therefore be individually optimized for a given interventional or surgical purposes. At a relatively high dosage the levels of LMWHs can be measured by using the ACT and APTT. When administered with such GP IIb/IIIa inhibitors as the Abciximab, Aggrastat or Eptifibratide, these drugs may require dosage adjustment However, since the introduction of the front loading of Clopidogrel, the unqualified use of GP IIb/IIIa is debated. LMWHs will find expanded indications in both the medical and surgical management of patients with cardiovascular disorders including atrial fibrillation and congestive heart failure. The only approved anti-Xa drug is represented by a synthetic heparinomimetic, namely, Arixtra. This drug is given for the prophylaxis of post orthopedic indications. This agent is undergoing additional clinical trials in the management of coronary artery diseases. Because of the dependence on antithrombin III (AT) and the sole anti-Xa effects, it has a narrow therapeutic index and its efficacy in this indication may be limited. Additional clinical trials are needed at this time to validate the clinical potential of this drug. The antithrombin agents (Hirudin, Hirulog and Argatroban) were initially developed for arterial indications. However, these agents are approved as a substitute anticoagulant in patients with heparin induced thrombocytopenia (HIT) and PCI. Currently an of these agents are being developed for surgical and interventional use. However, since there is no available antidote at this time, the development is somewhat limited. The antithrombin agents may be useful in patients with HIT which require further clinical validation. Many other anti-Xa agents are also developed. Most of these can be given parenterally. However, the clinical data is somewhat limited. Similarly, several of the new antiplatelet drugs can be administered parenterally and may be useful in CAD. Since most of these newer anticoagulant and antithrombotic drugs are mono-therapeutic their therapeutic index is rather limited. Only in combination these agents can mimic heparins. At this time it is safe to state that heparin and its LMW derivatives will remain the anticoagulant of choice for cardiovascular indications until these newer agents have been validated in extended clinical trials in polytherapeutic settings.

Anticoagulants↗
PubMed2003

Differential effects of DX-9065a, argatroban, and synthetic pentasaccharide on tissue thromboplastin inhibition test and dilute Russell's viper venom test.

New synthetic direct and indirect factor Xa or factor IIa inhibitors are increasingly used for the prevention and treatment of thrombotic disorders, including patients suffering from antiphospholipid syndrome. In this study, the effects of the synthetic direct factor Xa inhibitor DX-9065a, the indirect synthetic heparinomimetic pentasaccharide, and the direct factor IIa inhibitor Argatroban were studied. These two widely used assays for the detection of lupus anticoagulant, namely the tissue thromboplastin inhibition (TTIT) and the dilute Russell viper venom tests (DRWT) proved useful. The drugs were added to a normal human plasma pool ranging in concentration from 0.04 to 10 microg/mL. Using the two tests named above, DX-9065a and Argatroban showed a dose-related prolongation of TTIT and DRWT in the concentration range from 0.04 to 5 micromol/mL, but the pentasaccharide only slightly prolonged the clotting times of these assays even at high concentrations. Argatroban had the more pronounced effect on both tests when compared with DX-9065a (p < 0.001). The most responsive assay for DX-9065a up to a concentration of 2.5 micromol/mL was the DRWT. For Argatroban both TTIT and DRWT were equally responsive. Patients whose plasma was tested for suspected lupus anticoagulant and who have been given DX-9065a or Argatroban may have false-positive results with the TTIT tests and DRWT. This effect should be considered during patient management. These results indicate that these assays could be used for the effective quantitation of the direct factor Xa or factor IIa inhibitors when suitable controls are used.

Anticoagulants↗
PubMed2003

Investigations of the immunoglobulin subtype transformation of anti-heparin-platelet factor 4 antibodies during treatment with a low-molecular-weight heparin (clivarin) in orthopedic patients.

CONTEXT: It is now widely accepted that the pathophysiology of heparin-induced thrombocytopenia (HIT) syndrome is mediated by the generation of a wide array of functional and molecularly heterogeneous anti-heparin-platelet factor 4 (AHPF4) antibodies that may mediate platelet and/or endothelial cell activation/destruction. OBJECTIVE: We investigated the differential prevalence and functionality of AHPF4 immunoglobulin subtypes (IgA, IgG, and IgM) in plasmas obtained from orthopedic patients immobilized with Plaster-Cast and treated with clivarin (a low-molecular-weight heparin) in comparison to a placebo for the prophylaxis of deep-vein thrombosis. DESIGN AND METHODS: Clivarin was administered subcutaneously at a fixed daily dosage of 1750 U without any adjustment or loading dosage. Citrated plasmas were obtained at baseline, at 10 to 14 days, and at postbrace procedure (5-12 weeks). An enzyme-linked immunosorbent assay (ELISA) was used to quantitate the AHPF4 antibody titers. The functionality of the ELISA-positive samples was determined by a 14C-serotonin release assay (SRA). RESULTS: In the ELISA test, 16 of 1073 samples (1.5%; 6 in clivarin and 10 in placebo groups) were positive for AHPF4 antibodies (mean optical density [OD] = 0.46 +/- 0.02). None of the ELISA-positive samples for AHPF4 antibodies could mediate platelet activation responses as determined by the SRA (0%-3% serotonin release, P >.10, n = 16). Through differential immunoglobulin subtype analysis of the samples positive for (cumulative) AHPF4 antibodies, we determined that their relative prevalence in plasma were as follows: IgM (mean OD = 0.71 +/- 0.13) > IgG (0.31 +/- 0.08) > IgA (0.14 +/- 0.02). Although there was no significant difference in the total antibody titers between clivarin and placebo groups, the antibody subtyping data showed conversion trends (ie, IgA [clivarin to placebo], IgG [placebo to clivarin], and IgM [clivarin to placebo]). CONCLUSION: These observations indicate that even at reduced dosages, clivarin can shift the immunogenic up-regulation toward the IgG subpopulation; however, the IgG subtype is of a nonfunctional type of AHPF4 antibody and thus may not cause any HIT-related pathogenic responses.

Adolescent↗
PubMed2002

Differential effects of clivarin and heparin in patients undergoing hip and knee surgery for the generation of anti-heparin-platelet factor 4 antibodies.

The pathophysiology of heparin-induced thrombocytopenia (HIT) syndrome is mediated via a heterogeneous group of heparin(s)-platelet factor 4 (H-PF4) complexes bound to their antibodies. These anti-H-PF4 (AHPF4) antibodies that are capable of binding to the FcgammaRIIA receptor [cluster of differentiation (CD) 32] on platelets, resulting in platelet activation, widely vary in their specific activities as platelet activation (functionality). Predisposing factors related to specific pathologic conditions may also contribute to the generation of these antibodies and their relative functionality during HIT syndrome. To understand this phenomenon, a sub-study was carried out in patients undergoing elective total hip and knee replacement surgery (ECHOS Study) and who were treated with unfractionated heparin (UFH) and a low-molecular-weight heparin (LMWH; Clivarin). Approximately 600 patients per arm [UFH=7,500 anti-Xa U twice a day (b.i.d.) subcutaneous (s.c.) and clivarin=4200 U once daily (o.d.) s.c.], age >40 years, received prophylactic treatment for a minimum of 11-14 days. Plasma samples were collected at pre-dose, days 2-4, days 11-14 and at follow-up 6-8 weeks after discharge and were analyzed for AHPF4 antibody titers. Functionality of the enzyme-linked immunosorbant assay (ELISA)-positive AHPF4 antibodies to cause platelet activation was tested by 14C-serotonin release assay (SRA). Both UFH and clivarin treatments in orthopedic surgical patients resulted in a progressive generation of AHPF4 antibodies. The relative prevalence/functionality of AHPF4 antibodies in clivarin arm was markedly lower (two- to threefold, p<0.001) as compared to UFH at each time point. Most of the samples in clivarin group were found to be SRA negative, suggesting the presence of AHPF4 antibodies that did not activate platelets (nonfunctional). Within the UFH arm, the relative prevalence/functionality of AHPF4 antibodies was much higher (p<0.002) in knee group compared to the corresponding hip group. This study, for the first time, reports on the elevated levels of AHPF4 antibodies generated by heparin associated with the pathogenesis of knee surgery. Clinical significance of the differential generation of HIT-associated antibodies remains unexplored at this time.

Adult↗