Biochemical and pharmacologic rationale for the development of a synthetic heparin pentasaccharide

Fondaparinux pentasaccharide reduces sepsis coagulopathy and promotes survival in the baboon model of Escherichia coli sepsis

BACKGROUND

Sepsis triggers dysfunction of coagulation and fibrinolytic systems leading to disseminated intravascular coagulation (DIC) that contributes to organ failure and death. Fondaparinux (FPX) is a synthetic pentasaccharide that binds to antithrombin (AT) and selectively inhibits factor (F) Xa and other upstream coagulation proteases but not thrombin (T).

OBJECTIVES

We used a baboon model of lethal Escherichia coli sepsis to investigate the effects of FPX treatment on DIC, organ function, and outcome.

METHODS

Two experimental groups were studied: (a) E. coli challenge (n = 4); and (b) E coli plus FPX (n = 4). Bacteremia was modeled by intravenous infusion of pathogen (1-2 × 1010  CFU/kg). Fondaparinux (0.08 mg/kg) was administered subcutaneously, 3 h prior to and 8 h after bacteria infusion.

RESULTS

Bacteremia rapidly increased plasma levels of inhibitory complexes of AT with coagulation proteases. Activation markers of both intrinsic (FXIa-AT), and extrinsic (FVIIa-AT) pathways were significantly reduced in FPX-treated animals. Factor Xa-AT and TAT complexes were maximal at 4 to 8 h post challenge and reduced >50% in FPX-treated animals. Fibrinogen consumption, fibrin generation and degradation, neutrophil and complement activation, and cytokine production were strongly induced by sepsis. All parameters were significantly reduced, while platelet count was unchanged by the treatment. Fondaparinux infusion attenuated organ dysfunction, prolonged survival, and saved two of four challenged animals (log-rank Mantel-Cox test, P = .0067).

CONCLUSION

Our data indicate that FPX-mediated inhibition of coagulation prevents sepsis coagulopathy; protects against excessive complement activation, inflammation, and organ dysfunction; and provides survival benefit in E. coli sepsis.

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 Ila 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 (DRVVT) proved useful. The drugs were added to a normal human plasma pool ranging in concentration from 0.04 to 10 Ag/mL. Using the two tests named above, DX-9065a and Argatroban showed a dose-related prolongation of TTIT and DRVVT in the concentration range from 0.04 to 5 Amol/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 Amol/mL was the DRVVT. For Argatroban both TTIT and DRVVT 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 DRVVT. 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 Ila inhibitors when suitable controls are used.

Effects of the factor Xa inhibitor, fondaparinux, on the stability of atherosclerotic lesions in apolipoprotein E-deficient mice

BACKGROUND

Atherosclerosis is a progressive inflammatory disease that can lead to sudden cardiac events by plaque rupture and subsequent thrombosis. Factor Xa (FXa) not only occupies a crucial position in the coagulation cascade responsible for thrombin generation, but also has pro-inflammatory effects. The hypothesis that Fondaparinux, the selective FXa inhibitor, attenuates plaque progression and promotes stability of atherosclerotic lesions was assessed.

METHODS AND RESULTS

Fondaparinux (5 mg/kg body weight/day) or 0.9% saline was intraperitoneally administered for 4 weeks to apolipoprotein E-deficient mice (n=12 per group) with established atherosclerotic lesions in the innominate arteries. Fondaparinux did not remarkably decrease the progression of atherosclerosis development in apolipoprotein E-deficient mice, but increased the thickness of fibrous cap (P=0.049) and decreased the ratio of necrotic core (P=0.001) significantly. Moreover, Fondaparinux reduced the staining against Mac-2 (P=0.017), α-SMA (P=0.002), protease-activated receptor (PAR)-1 (P=0.001), PAR-2 (P=0.003), CD-31 (P=0.024), MMP-9 (P=0.000), MMP-13(P=0.011), VCAM-1 (P=0.041) and the mRNA expression of inflammatory mediators (P<0.05) significantly, such as interleukin (IL)-6, MCP-1, IFN-γ, TNF-α, IL-10 and Egr-1.

CONCLUSIONS

Fondaparinux, the selective FXa inhibitor, can promote the stability of atherosclerotic lesions in apolipoprotein E-deficient mice, possibly through inhibiting expression of the inflammatory mediators in plaque and reduced synthesis of MMP-9 and MMP-13.

The mechanisms of nadroparin-mediated inhibition of proliferation of two human lung cancer cell lines

OBJECTIVES

Clinical data suggest that heparin treatment improves survival of lung cancer patients, but the mechanisms involved are not fully understood. We investigated whether low molecular weight heparin nadroparin, directly affects lung cancer cell population growth in conventionally cultured cell lines.

MATERIALS AND METHODS

A549 and CALU1 cells' viability was assessed by MTT and trypan blue exclusion assays. Cell proliferation was assessed using 5-bromo-2-deoxyuridine incorporation. Apoptosis and cell-cycle distribution were analysed by flow cytometry; cyclin B1, Cdk1, p-Cdk1 Cdc25C, p-Cdc25C and p21 expressions were analysed by western blotting. mRNA levels were analysed by real time RT-PCR.

RESULTS

Nadroparin inhibited cell proliferation by 30% in both cell lines; it affected the cell cycle in A549, but not in CALU-1 cells, inducing arrest in the G(2) /M phase. Nadroparin in A549 culture inhibited cyclin B1, Cdk1, Cdc25C and p-Cdc25C, while levels of p-Cdk1 were elevated; p21 expression was not altered. Dalteparin caused a similar reduction in A549 cell population growth; however, it did not alter cyclin B1 expression as expected, based on previous reports. Fondaparinux caused minimal inhibition of A549 cell population growth and no effect on either cell cycle or cyclin B1 expression.

CONCLUSIONS

Nadroparin inhibited proliferation of A549 cells by inducing G(2) /M phase cell-cycle arrest that was dependent on the Cdc25C pathway, whereas CALU-1 cell proliferation was halted by as yet not elucidated modes.

Preincubation in the Prothrombinase-induced Clotting Time test (PiCT) is necessary for in vitro evaluation of fondaparinux and to be avoided for the reversible, direct factor Xa inhibitor, rivaroxaban

INTRODUCTION

There is no clear consensus about tests in vitro that are suitable for evaluating various factor Xa inhibitors. The availability of reversible and irreversible inhibitors further complicates the application of available assays.

METHODS

We evaluated the suitability of the prothrombinase-induced clotting test (PiCT) for fondaparinux and rivaroxaban, as representatives for irreversible and reversible inhibition of factor Xa, with specific attention to preincubation times prior to re-calcification, in the context of automate program limitations.

RESULTS

We demonstrate that the PiCT assay requires a preincubation step to allow inhibitory activity by fondaparinux. Without this step, inhibition in the test is minimal and lacking sufficient dynamic range. In contrast, to measure the reversible inhibition by rivaroxaban, we found any preincubation introduced an artifact in inhibition as exemplified by a biphasic pattern and only the test without a preincubation phase gave informative results.

CONCLUSION

It is concluded that PiCT in its format with two steps is suitable for fondaparinux evaluation, while its format without preincubation (the one-addition format) is suitable for reversible inhibitors such as rivaroxaban. Unfortunately, both types of inhibitors cannot be compared in vitro in a single assay format.

Flavonoids with an oligopolysulfated moiety: a new class of anticoagulant agents

Polysulfated (oligo)flavonoids were synthesized and assayed for their in vitro and in vivo anticoagulant activities. The approach was based on molecular hybridization of two classes of anticoagulants, sulfated polysaccharides and sulfated flavonoids. The synthesis was optimized using microwave-assisted sulfation with triethylamine-sulfur trioxide. The obtained polysulfated flavonosides were highly effective in increasing clotting times and able to completely block the clotting process, in contrast to their corresponding aglycones. The thromboelastography proved that polysulfated flavonosides possess good whole blood anticoagulation activity. The following structure-activity relationships were found: 3-O-rutinosides (10, 13) were direct inhibitors of FXa, while 7-O-rutinosides (7, 8) showed inhibition of FXa by ATIII activation. Furthermore, compounds 7 and 13 were stable in plasma and active in vivo and preliminary toxicity studies would lead us to rule out acute side effects. From the overall results, the polysulfated flavonosides showed the potential as new effective and safe agents for anticoagulant therapy.

Newer anticoagulants in 2009

Several newer anticoagulants are under clinical development. Recently two of them, Dabigatran etexilate/Pradaxa. and Rivaroxaban/Xarelto obtained marketing authorization in Europe and Canada for the prevention of thromboembolic events following major orthopedic surgery such as total hip and knee replacement. The results of Phase III clinical studies in thromboprophylaxis in major orthopedic surgery are highlighted and discussed in detail. Ongoing Phase II and III clinical trials assess their efficacy in the secondary prevention and treatment of deep vein thrombosis and pulmonary embolism, and in the long-term prevention of stroke in patients with non-valvular atrial fibrillation and in combination with aspirin and clopidogrel in patients with acute coronary syndromes. Many other small antithrombotic molecules including a new generation of low molecular weight heparins, are currently in different stages of clinical development. In addition to being administered orally, the newer anticoagulant agents have a more balanced benefit/risk ratio and wider therapeutic window. They have a rapid onset of action, a predictable anticoagulant effect that does not require routine laboratory monitoring. They have minor food and drug interactions, including those with cytochrome P450 and P.gp. They are highly specific and targeted to a single coagulation factor, and could carry similar or less hemorrhagic risks compared to the older anticoagulant agents. Finally, they may be used in a broader variety of patients, especially the medically ill patients with advanced cancer, and the elderly without any dosage adjustment, regardless of the patient age, gender, body weight, or in patients with mild renal impairment. Their use in the general world will hopefully confirm the promising results of clinical trials.

Heparin-induced thrombocytopenia in surgical patients

BACKGROUND

Unfractionated and low-molecular-weight heparin are commonly used in the prevention and therapy of a variety of cardiovascular diseases. Because the major side effects of these drugs are hemorrhagic events, very little attention is paid to another important side effect (ie, heparin-induced thrombocytopenia [HIT]). HIT is an immune-mediated transient prothrombotic state with very severe implications determined by thromboembolic phenomena in both the venous and arterial circulation.

DATA SOURCES

A PubMed search from 1995 to 2008 was performed. Pertinent literature was identified and other references retrieved from bibliographic citations of the articles identified on PubMed. Articles related to the pathogenesis, clinical picture, diagnosis and treatment of HIT were reviewed.

CONCLUSIONS

HIT is a potentially fatal but treatable and largely preventable disease. An increased awareness of the signs and symptoms of the disorder is necessary to prevent its potentially devastating complications.

Fondaparinux sodium: a review of its use in the management of acute coronary syndromes

Fondaparinux sodium (Arixtra) is a synthetic, sulfated pentasaccharide, selective factor Xa inhibitor that is indicated in Europe for preventing thrombus formation in patients with acute coronary syndromes (ACS; the focus of this review), including those with ST-segment elevation myocardial infarction (STEMI), non-STEMI (NSTEMI), or unstable angina.The large (n = 20,078), well designed OASIS-5 trial showed that subcutaneous fondaparinux 2.5 mg/day for <or=8 days was noninferior to subcutaneous enoxaparin 1 mg/kg twice daily (once daily in those with renal dysfunction) in reducing death or ischemic events at 9 days and the efficacy was maintained for up to 6 months (study end) in patients with unstable angina or NSTEMI. During this time, major bleeding occurred in fewer fondaparinux than enoxaparin recipients, resulting in a benefit: risk balance favoring fondaparinux. The incidence of death or reinfarction at 30 days was significantly lower in recipients of subcutaneous fondaparinux 2.5 mg/day than in those who received usual care (including unfractionated heparin [UFH] treatment as indicated) in patients with STEMI in the large (n > 12,000) OASIS-6 trial. There were no differences in the incidence of major bleeding between these groups, resulting in a benefit : risk balance favoring fondaparinux. The specificity and selectivity of fondaparinux, combined with its long half-life and 100% bioavailability, allows once-daily anticoagulation without the need for monitoring activated clotting time. Subcutaneous fondaparinux was noninferior to enoxaparin treatment in patients with unstable angina or NSTEMI, and was more effective than usual care in those with STEMI. Fondaparinux has a favorable tolerability profile, particularly with regard to the risk of major bleeding, and limited data suggest that it is more cost effective than enoxaparin in the short term. Thus, overall, clinical evidence suggests that fondaparinux has a valuable place in the treatment of patients with ACS.

New anticoagulant strategies in ST elevation myocardial infarction: trials and clinical implications

New data have re-established the importance of anticoagulation of patients with ST segment elevation myocardial infarction (STEMI), both as an adjuvant to reperfusion therapy or in patients ineligible for reperfusion. Recent randomized trials have found newer agents to be superior to conventional unfractionated heparin. This article summarizes current understanding of the underlying pathophysiology of STEMI and provides a comprehensive review of emerging trial data for low molecular weight heparins, anti-factor Xa agents and direct thrombin inhibitors in this setting.

Fondaparinux: use in thromboprophylaxis of acute medical patients

Fondaparinux is a synthetic pentasaccharide that inhibits thrombin formation and thrombus development via selective antithrombin mediated inhibition of factor Xa. The complete bioavailability (100%) and elimination half-life of approximately 17 hours allows once-daily administration of fondaparinux. In a well designed trial (ARTEMIS) in acute medical patients aged > or = 60 years, fondaparinux was significantly more effective than placebo in terms of reducing the incidence of venous thromboembolism (VTE) up to day 15. The beneficial effect of fondaparinux therapy was observed in all subgroups of patients irrespective of underlying illness (e.g. acute heart failure or acute respiratory disease) in a predefined subgroup analysis of the ARTEMIS trial. Similarly, in a retrospective analysis of the trial, age and renal function did not appear to affect the incidence of VTE in fondaparinux and placebo recipients. Fondaparinux was generally well tolerated in this clinical trial. In patients receiving fondaparinux, the incidence of major bleeding was similar to that in patients receiving placebo and the incidence of minor bleeding was <3%.

Effects of anticoagulation on wound healing using a tensile test

Wound healing is a complicated and dynamic process. The aim of this study was to determine whether systemic administration of common anticoagulants retards or delays wound healing in an animal model.

[New antitoagulants]

In contrast to older anticoagulant agents vitamin K antagonists and heparins, the new ones are directed towards a single target in general. The main characteristics of the new agents are: their site of action in the coagulation cascade and their mechanism of action which is indirect, antithrombin dependent, most often such as Fondaparinux and Idraparinux or direct such as Dabigatran, Rivaroxaban; the specificity of the new molecules, since they must not interact with other enzymes: trypsin, kallikrein, t-PA, etc...; their mode of administration parenteral and/or oral; their pharmacokinetics and their clearance frequently by the kidney (Hirudin, fondaparinux) or through hepatic metabolism (argatroban); tolerance including for all compounds the bleeding risk or an unexpected hepatic intolerance for Ximelagatran; the availability of a specific antidote and the cost of the drug; one compound is registered in France Arixtra Fondaparinux in major orthopedic surgery and in the treatment of venous thromboembolism and in prophylactic treatment in medical patients. However, the main indications of interest for these new drugs is atrial fibrillation. There is a real need in this indication and the number of patients to treat is growing with the longer life expectancy.

Beyond heparin and warfarin: the new generation of anticoagulants

Heparin and warfarin are widely used for the prevention and treatment of venous and arterial thromboembolism. Although effective, both agents have important limitations; for example, both drugs must be monitored, which is inconvenient for patients and for physicians. Heparin requires parenteral administration and can cause heparin-induced thrombocytopenia, an immune-mediated process that can lead to life-threatening thrombosis. Warfarin also has its limitations. Due to its slow onset of action, warfarin must be overlapped with heparin (or another rapidly acting anticoagulant) when treating patients with established thrombosis or who are at high risk for thrombosis. Warfarin dosing is variable because its activity is influenced by dietary intake of vitamin K, genetic polymorphisms in enzymes that are involved in its metabolism and numerous drug-drug interactions that promote or reduce its activity. New anticoagulants have been developed to overcome these problems. Building on a better understanding of coagulation pathways, advances in structure-based drug design and information derived from natural anticoagulants isolated from hematophagous organisms, most of the new anticoagulants target specific coagulation enzymes. Focussing on drugs that have at least completed Phase II evaluation, this article briefly reviews the coagulation pathways and its natural regulators; outlines the limitations of existing anticoagulants and identifies the opportunities for new ones; highlights the properties of selected new anticoagulants; describes the clinical trial results with these agents; and provides a perspective on their potential strengths and weaknesses.

New anticoagulants for the prevention and treatment of venous thromboembolism

Anticoagulant therapy is effective at preventing the development of venous thromboembolism in high-risk patients, and reduces morbidity and mortality in individuals with established thromboembolic disease. Vitamin K antagonists and heparins are currently the most commonly used anticoagulant drugs, but they have practical limitations. Therefore, new antithrombotic agents with predictable dose-responses (thereby decreasing the need for monitoring without compromising efficacy or safety), ideally available in an oral formulation and with a rapidly reversible anticoagulant effect, are needed. New drugs fulfilling some of the above criteria have been developed and have proven to be effective agents for the treatment and prevention of venous thromboembolism.

Novel factor Xa inhibitors for prevention and treatment of thromboembolic diseases

Novel anticoagulants to replace unfractionated heparins, low molecular weight heparins and vitamin K antagonists, are needed urgently. Coagulation factor Xa is an attractive target for drug development because of its position at the convergence of the intrinsic and extrinsic clotting pathways. There are two differing strategies of inhibiting factor Xa that are being pursued: indirect inhibition by compounds such as fondaparinux and idraparinux, requiring antithrombin as a cofactor; and direct inhibition by compounds such as rivaroxaban (BAY 597939), DX-9065a, otamixaban, LY517717 and YM150. Of these compounds, fondaparinux is approved for the prevention and treatment of venous thromboembolism, and idraparinux is in Phase III for venous thromboembolism treatment and stroke prevention in patients with atrial fibrillation. Rivaroxaban has undergone extensive Phase II studies for venous thromboembolism prevention after orthopaedic surgery, and Phase III studies have begun. In this review, we will discuss the pharmacological effects of factor Xa inhibitors and the latest clinical developments.

The status of new anticoagulants

Currently available anticoagulants include heparin, low-molecular weight heparin, fondaparinux and warfarin. Despite advances with low-molecular weight heparin and fondaparinux, the currently available agents have limitations that have provided the impetus for the development of new drugs for prevention and treatment of both venous and arterial thromboembolism. Novel anticoagulants targeting specific steps in coagulation are in various stages of development. This paper reviews the pharmacology of these new agents and describes the results of clinical trials with new anticoagulants in more advanced stages of clinical testing.

Anticoagulant Treatment of Deep Vein Thrombosis and Pulmonary Embolism

Venous thrombosis is a common disease. As the mean age of the population increases, so does the incidence of venous thromboembolism. Anticoagulant therapy is equally effective in young and older patients, and can reduce substantially the associated morbidity and mortality. When considering long-term oral anticoagulant therapy in older patients, however, careful ongoing evaluation is imperative to ensure that the risk of bleeding does not outweigh the antithrombotic benefits.

Clinical efficacy and safety of fondaparinux in the prevention and treatment of venous and arterial thrombosis

Fondaparinux (Arixtra®) is a synthetic, selective Factor Xa inhibitor. Its pharmacokinetic profile allows once-daily subcutaneous administration of the drug without any laboratory monitoring. The benefit-to-risk ratio of fondaparinux in the prevention of venous thromboembolism has been extensively studied in both surgical and acutely ill medical patients at risk of thrombosis. Its efficacy and safety have also been investigated in the initial treatment of symptomatic deep-vein thrombosis and pulmonary embolism. Finally, a number of Phase II trials investigated the safety and efficacy of fondaparinux in patients with acute coronary syndromes, and a large Phase III program is ongoing in this setting. This review focuses on the use of fondaparinux in the prevention and treatment of thromboembolic disorders.

Unfractionated heparin compared with low-molecular-weight heparin as related to heparin-induced thrombocytopenia

PURPOSE OF REVIEW

Heparin-induced thrombocytopenia is a severe side effect of treatment with unfractionated heparin. The relation of low-molecular-weight heparin to heparin-induced thrombocytopenia is less well understood. This review will summarize what is known about the similarities and differences between thrombocytopenia induced by low-molecular-weight heparin and that induced by unfractionated heparin.

RECENT FINDINGS

The pathophysiology of unfractionated heparin-induced thrombocytopenia, caused by the development of antibodies to heparin/platelet factor 4 complexes, holds true for low-molecular-weight heparin because the molecules of the latter are of the same saccharidic structure as those of unfractionated heparin. Owing to their smaller size, however, low-molecular-weight heparin does not interact with platelet factor 4 and platelets as efficiently as does unfractionated heparin. This translates to a two- to threefold lower risk of immune sensitization (antibody generation and occurrence of clinical heparin-induced thrombocytopenia). Low-molecular-weight heparin-induced thrombocytopenia antibodies are more often immunoglobulin A and immunoglobulin M, in contrast to the immunoglobulin G antibodies generated with unfractionated heparin-induced thrombocytopenia, which tend to be more often associated with clinical heparin-induced thrombocytopenia. The clinical expression of low-molecular-weight heparin-induced thrombocytopenia is generally similar to that of unfractionated heparin-induced thrombocytopenia but can have a slower onset, more severe thrombocytopenia, and slower platelet count recovery. Given that low-molecular-weight heparin, of itself, is linked with heparin-induced thrombocytopenia pathophysiology and it can interact with most preexisting heparin-induced thrombocytopenia antibodies generated after exposure to unfractionated heparin, treatment of heparin-induced thrombocytopenia patients with low-molecular-weight heparin is contraindicated.

SUMMARY

The risk of the development of heparin-induced thrombocytopenia with low-molecular-weight heparin treatment is reduced relative to the frequency of unfractionated heparin-induced thrombocytopenia, but it is not eliminated, and platelet counts should be monitored with treatment.

New anticoagulants

The limitations of heparin and warfarin have prompted the development of new anticoagulant drugs for prevention and treatment of venous and arterial thromboembolism. Novel parenteral agents include synthetic analogs of the pentasaccharide sequence of heparin that mediates its interaction with antithrombin. Fondaparinux, the first synthetic pentasaccharide, is licensed for prevention of venous thromboembolism (VTE) after major orthopedic surgery and for initial treatment of patients with VTE. Idraparinux, a long-acting pentasaccharide that is administered subcutaneously once-weekly, is being compared with warfarin for treatment of VTE and for prevention of cardioembolic events in patients with atrial fibrillation. New oral anticoagulants include direct inhibitors of thrombin, factor Xa and factor IXa. Designed to provide more streamlined anticoagulation than warfarin, these agents can be given without routine coagulation monitoring. Ximelagatran, the first oral direct thrombin inhibitor, is as effective and safe as warfarin for prevention of cardioembolic events in patients with atrial fibrillation. However, ximelagatran produces a three-fold elevation in alanine transaminase levels in 7.9% of patients treated for more than a month, the long-term significance of which is uncertain. Whether other direct thrombin inhibitors or inhibitors of factors Xa or IXa also have this problem is under investigation. After a brief review of coagulation pathways, this paper focuses on new anticoagulants in advanced stages of clinical testing.

[What kind of treatment are available in deep vein thrombosis prevention?]

In order to propose new recommendations concerning deep vein thrombosis prevention in surgery and obstetrics, we identified all the available tools. We performed a Medline search for ten years to review all the studies published in this field. This preliminary stage is mandatory in assessing guidelines able to work out strategies considering each patient in each particular surgical situation. There are no formal guidelines and we outlined a practical approach for the prevention of deep vein thrombosis. Data concerning all available treatment were not classified in an evidence-based strategy.

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.

The safety of fondaparinux for the prevention and treatment of venous thromboembolism

Fondaparinux is the first synthetic selective Factor Xa inhibitor. Along with its antithrombotic efficacy, the safety of fondaparinux has been documented in several Phase II and III clinical trials, including the prevention of venous thromboembolism in patients undergoing major orthopaedic surgery or high-risk abdominal surgery, or in acutely ill medical patients with restricted mobility, and the treatment of patients with deep-vein thrombosis and pulmonary embolism. In all these indications, the safety of fondaparinux used according to its registered regimen was similar to that of reference comparators. In conclusion, due to its superior efficacy and satisfactory safety, fondaparinux may substantially improve the prevention and treatment of venous thrombosis.

New anticoagulants: beyond heparin, low-molecular-weight heparin and warfarin

The limitations of traditional anticoagulants, heparin and warfarin, have prompted the development of new anticoagulant drugs for prevention and treatment of both venous and arterial thromboembolism. After a brief review of thrombogenesis and its regulation, this paper focuses on new anticoagulant agents in more advanced stages of clinical testing.

The synthetic pentasaccharide fondaparinux reduces coagulation, inflammation and neutrophil accumulation in kidney ischemia-reperfusion injury

Ischemia-reperfusion (I/R) injury is associated with activation of coagulation and inflammation. Interestingly, various anticoagulants have been shown to reduce both coagulation and inflammation in animal models of kidney I/R injury. Fondaparinux is a synthetic pentasaccharide that selectively inhibits factor Xa (FXa) in the coagulation cascade. The aim of this study was to investigate the effect of fondaparinux in a lethal murine model of kidney I/R injury. A murine model of kidney I/R was established. In this model, we measured activation of the coagulation cascade and induction of inflammation. Administration of fondaparinux to I/R-injured mice reduced fibrin deposition in the kidney, reduced serum creatinine levels and increased survival from 0 to 44% compared with saline-treated control mice. Fondaparinux also reduced interleukin-6 and macrophage inflammatory protein-2 expression and decreased neutrophil accumulation in the injured kidneys. Finally, we showed that fondaparinux reduced thioglycollate-induced recruitment of neutrophils into the peritoneum and inhibited the binding of U937 cells to P-selectin in vitro. Our data suggest that fondaparinux reduces kidney I/R injury primarily by inhibiting the recruitment of neutrophils.

Unfractionated Heparin, Low Molecular Weight Heparins, and Pentasaccharide: Basic Mechanism of Actions, Pharmacology, and Clinical Use

During the past decade, a large number of new anticoagulant and antithrombotic drugs have been developed. These agents represent a wide variety of substances that are derived using natural sources, biotechnology-based methods, and synthetic approaches. Because of the structural and molecular characteristics, these agents exhibit physicochemical and functional diversities. Thus, each of these classes of drugs controls thrombogenesis by way of distinct mechanisms. The main classes of these new drugs include peptides, peptidomimetics, heparinomimetics, and recombinant proteins. Despite these significant developments, heparin and heparin-derived drugs have continued to play a major role in the management of thrombotic and cardiovascular disorders.

Fondaparinux sodium: a review of its use in the treatment of acute venous thromboembolism

Fondaparinux sodium (fondaparinux) is a synthetic sulfated pentasaccharide anticoagulant developed from the antithrombin binding moiety of heparin. Through the activation of antithrombin it inhibits Factor Xa, the activation of thrombin, and the subsequent coagulation cascade. Fondaparinux is approved in Europe and the US for the treatment of acute venous thromboembolism (VTE), including both deep vein thrombosis (DVT) and pulmonary embolism (PE), when used in conjunction with warfarin. In phase III clinical trials, subcutaneous fondaparinux was noninferior to subcutaneous enoxaparin or intravenous unfractionated heparin (UFH) in the prevention of recurrent symptomatic VTE in patients with acute DVT and PE, respectively, and equally well tolerated. It thus provides a valuable alternative to UFH and low-molecular weight heparins in the treatment of acute VTE, particularly in the outpatient setting.

Pharmacodynamics and pharmacokinetics of C3, a heparin-derived oligosaccharide mixture, in non-human primates

The heparin-derived oligosaccharide C3 (C3) is currently underdevelopment for the prevention and treatment of vascular dementia and senile dementia of Alzheimer's type. C3 exhibits a molecular weight of 2200-2500 Da with a narrow distribution. The objective of the present study was to assess the pharmacodynamics and pharmacokinetics of C3 in non-human primates. C3 was administered as an intravenous or subcutaneous bolus dose of 1.0 or 2.5 mg/kg. Anti-factor Xa activity, Heptest clotting time and activated partial thromboplastin time were measured to determine pharmacodynamic effects of C3 in plasma. The pharmacokinetics of C3 was primarily characterized by measuring plasma anti-factor Xa activity as a surrogate marker. The rate of absorption and elimination of C3 after administration did not change with increasing dose. The volume of distribution of C3 was small, reflecting a major distribution inside the intravascular space (110-130 ml/kg), and was independent of dose. The total clearance (16.0-21.0 ml/h/kg) and half-life (4-6 h) of C3 were also dose-independent. Within the observed dose range, a 2.5 times of the C3 dose resulted in an area under the plasma concentration-time curve that was approximately 16-27% greater than expected on the basis of linear disposition. These differences could be attributed to the endogenous release of tissue factor pathway inhibitor (TFPI) by C3 at higher doses, which is associated with the vascular effects of C3.

Fondaparinux: a suitable alternative in cases of delayed-type allergy to heparins and semisynthetic heparinoids? A study of 7 cases

Hypersensitivity to unfractionated and low-molecular-weight heparins and semisynthetic heparinoids is increasingly common. 7 female patients between 30 and 74 years with delayed-type allergy to heparins and semisynthetic heparinoids were investigated for (cross)-reactivity to fondaparinux, a new pentasaccharide with selective factor Xa inhibition. All patients showed delayed-type reactions to heparins and some additional cross-reaction to a heparinoid on intracutaneous testing. 6/7 tolerated fondaparinux on intradermal testing as well as on subcutaneous challenge testing. However, the 7th patient developed a characteristic delayed-type reaction to both skin tests with fondaparinux. Fondaparinux is a new synthetic pentasaccharide with a molecular weight of 1.728 Da. In some patients with cross-reactivity between various heparins and semisynthetic heparinoids, lepirudin, a recombinant hirudin, may be a safe and effective alternative. However, combined allergy to hirudin and heparins has been reported. Sometimes, intravenous administration of heparins or heparinoids may be tolerated. However, these patients are at risk of developing a systemic reaction. The pathogenesis of heparin hypersensitivity is not fully understood. Heparins may act as haptens by binding to dermal and/or subcutaneous structural proteins. The chemical structures of heparins and fondaparinux are different concerning their alpha- and beta-configuration and the molecular weight. However, some of their functional groups are nearly identical and therefore similar chemical and pharmacological reactivity is to be expected. Fondaparinux seems to be a valuable alternative in most cases of heparin and hirudin hypersensitivity. The clearly rare cross-reaction between fondaparinux and heparins, now confirmed by us, may be due to differences in the response to haptens.

Fondaparinux: a new synthetic and selective inhibitor of Factor Xa

Fondaparinux (Arixtra) is the first synthetic selective Factor Xa inhibitor. Its efficacy and safety in the prevention of venous thromboembolism (VTE) was first studied in patients undergoing major orthopedic surgery, a setting in the highest risk category for postoperative thrombotic complications. Low-molecular-weight heparins are frequently used in this setting, but the rates of VTE still range between 15% and 33%. In large clinical trials, fondaparinux started 6 hours postoperatively was significantly more effective than enoxaparin in preventing VTE in patients undergoing total hip replacement, total knee replacement or hip fracture surgery. The benefit of extended fondaparinux prophylaxis after hip fracture surgery was also investigated. Other trials have demonstrated that fondaparinux is efficacious in the prevention of VTE in other patient populations at risk of thrombosis and in the treatment of symptomatic VTE.

New Pentasaccharides for Prophylaxis of Deep Vein Thrombosis

Fondaparinux is the first of a new class of antithrombotic compounds, the synthetic pentasaccharides. By binding rapidly and strongly to antithrombin, its sole physiologic target in plasma, fondaparinux catalyzes specifically the inhibition of factor Xa, which results in effective and linear dose-dependent inhibition of thrombin generation. Fondaparinux does not bind to platelets. Its antithrombotic effect has been demonstrated in several animal models of arterial and venous thrombosis. At equivalent antithrombotic concentrations, fondaparinux induced less bleeding than unfractionated heparin in experimental bleeding models. Furthermore, it did not cross-react with sera from patients with heparin-induced thrombocytopenia. Administered subcutaneously, the absorption of fondaparinux is complete, rapid, and independent of dose. It has a linear pharmacokinetic profile, and its half-life of approximately 17 h allows for once-daily dosing. Fondaparinux is almost completely excreted by the kidneys. Owing to the limited intrasubject and intersubject variability, routine monitoring and dose adjustments should not be required for most patients. Fondaparinux has been approved for use in thromboprophylaxis after major orthopedic surgery, where it has demonstrated its efficacy compared to a low-molecular-weight heparin. Its clinical development in other indications is ongoing.

Emerging anticoagulant drugs

The limitations of traditional anticoagulants, heparin and warfarin, have prompted the development of new anticoagulant drugs for prevention and treatment of both venous and arterial thromboembolism. After a brief review of thrombogenesis and its regulation, this study focuses on new anticoagulant agents in more advanced stages of clinical testing.

Factor X inhibitors

Factor X plays a central role in coagulation, being the point of convergence of the extrinsic and intrinsic pathways of blood clotting. It may also act as one of the links between the coagulation and inflammatory pathways. These findings suggest that factor X may represent an attractive target for a new antithrombotic drug. Indeed, a factor X inhibitor, fondaparinux, has already been approved for clinical use to prevent post-operative deep vein thrombosis. Factor X inhibitors are also being evaluated for use in the treatment of the acute coronary syndromes, pulmonary embolism and deep vein thrombosis. Oral factor X inhibitors are also being developed, which may be of use in the outpatient prevention and/or treatment of stroke and thromboembolism.

Design, synthesis, and structure-activity relationships of unsubstituted piperazinone-based transition state factor Xa inhibitors

A series of novel transition state factor Xa inhibitors containing a variety of lactam ring systems as central templates was synthesized in an expedient manner and allowed for a great deal of structural variability. Among them, the piperazinone-based inhibitors were found to be not only active against factor Xa but also selective over thrombin. Optimization of the P4 moiety yielded several potent compounds with IC(50) below 1 nM against factor Xa.

Heparin, low-molecular-weight heparins, and heparin pentasaccharide: basic and clinical differentiation

As a result of advanced technology, dramatic developments in the area of new anticoagulant and antithrombotic drugs appear to have made a profound impact on the use of LMWHs. Furthermore, because porcine mucosal heparin is used for the preparation of these agents, it is likely that alternative drugs with comparable pharmacologic and clinical efficacy are sought. Antithrombin drugs such as argatroban and hirudin are already approved for alternative management of heparin-compromised patients. Their efficacy in other indications is less superior. The development of specific anti-Xa drugs is slow. Although these agents may inhibit factor Xa and thrombin generation, none of them are capable of mimicking the polytherapeutic effects of LMWHs and thus can only be given in drug combinations. Synthetic and recombinant protein-derived anti-tissue factor agents have also been developed. These drugs only inhibit the tissue factor-mediated process and are limited in their therapeutic spectrum. Plasma-derived and recombinant serine protease inhibitors (serpins) are also available for the management of thrombotic and inflammatory disorders, but these agents cannot be given subcutaneously. Furthermore, because they are proteins, antibodies to these agents are generated. Nucleic acid derivatives (natural and synthetic aptomers) are developed for intravenous administration, but they are relatively weak antithrombotic agents. Dermatans, heparans, and chondroitin sulfates represent nonheparin GAGs, and, in mono-compositional and polycompositional form, these drugs are mainly used for the intravenous management of DVT prophylaxis. They can be given to patients who are heparin compromised. Synthetic heparinomimetics include heparin consensus-binding oligosaccharides and synthetic oligosaccharides with non-serpin affinity. In addition, binding oligosaccharides are conjugated with antithrombin agents to mimic the anti-Xa/anti-IIa activities of heparin. Biotechnology using bacterial and yeast cultures, aqua cultures for marine products, and plant carbohydrates have been the focus of developing heparin analogues. Development of these agents is in the early phase; however, it is likely that this approach may provide a reasonable alternative to LMWHs. Despite these developments, it is unlikely that any of these drugs will have a profound impact on the use of LMWHs in the near future. Unfractionated heparin and LMWHs collectively represent an important group of polypharmacologic drugs without which the management of thrombosis and vascular disorders would not be possible. The continual development of LMWHs in expanded indications did not comprise the use of unfractionated heparin in surgical and interventional cardiovascular indications. Ever since their introduction in the 1980s, the use of LMWHs has continually increased. This is primarily because of expanded indications and growing awareness among the clinicians. It is likely that once an antidote is developed and additional information is available on the mechanism of action of LMWHs, these drugs may gradualty be used for surgery patients. Despite these developments, it is likely that unfractionated heparin will continue to be used for specific indications. Drug combinations with heparins may necessitate dose adjustments, but it is unclear whether unilateral reduction of heparins will be optimal. The coming years will provide useful clinical and applied data on the improved use of unfractionated heparin. LMWHs, and pentasaccharide in the management of thrombotic and cardiovascular disorders. In addition, use of these drugs will be extended to many conditions, including cancer, inflammation, sepsis, and autoimmune diseases. Polytherapeutic approaches emphasizing LMWHs as primary and secondary drugs will also have an impact on the management of thrombotic and nonthrombotic disorders. Ultra-LMWHs and synthetic heparinomimetics, such as fondaparinux, that exhibit a narrow pharmacologic spectrum will only be useful in specific indications and in combination with other drugs.

New antithrombin-based anticoagulants

Clinically used anticoagulants are inhibitors of enzymes involved in the coagulation pathway, primarily thrombin and factor Xa. These agents can be either direct or indirect inhibitors of clotting enzymes. Heparin-based anticoagulants are indirect inhibitors that enhance the proteinase inhibitory activity of a natural anticoagulant, antithrombin. Despite its phenomenal success, current anticoagulation therapy suffers from the risk of serious bleeding. The need for safer and more effective antithrombotic agents clearly exists. The past decade has seen enormous effort directed toward discovering and/or designing new molecules with anticoagulant activity. These new molecules can be classified into (a). antithrombin and its mutants, (b). natural polysaccharides, (c). synthetic modified heparins and heparin-mimics, (d). synthetic oligosaccharides, and (e). synthetic non-sugar antithrombin activators. This review focuses on these efforts in designing or discovering new molecules that act through the antithrombin pathway of anticoagulation.

Evaluation of the pharmacological properties and clinical results of the synthetic pentasaccharide (fondaparinux)

Fondaparinux (Arixtra) is the first of a new class of selective indirect antithrombin-dependent factor Xa inhibitors, which inhibits thrombin generation. Fondaparinux is a completely synthetic pentasaccharide. It is a single molecular entity with a well-defined pharmacological target. Fondaparinux has nearly complete bioavailability after subcutaneous injection. The pharmacokinetics of fondaparinux appears predictable and consistent. The peak plasma level is obtained about 2 h after the subcutaneous injection, indicating that a rapid onset of antithrombotic activity is obtained on initiation of treatment. The elimination half-life is about 17 h and it is dose-independent, which allows a convenient once-daily dosing regimen. Fondaparinux is eliminated exclusively by the kidneys. Thus, the estimation of the renal function especially in elderly patients is important for the treatment with fondaparinux, whereas it is contraindicated in patients with severe renal insufficiency. Phase II clinical studies have identified a subcutaneous dose of 2.5 mg once daily for prophylaxis of venous thromboembolism in patients undergoing major orthopaedic surgery. Four phase-III clinical trials using bilateral phlebography for the diagnosis of DVT, demonstrated a combined 50% relative risk reduction of asymptomatic venous thromboembolic events in orthopaedic surgery patients in comparison to the low-molecular-weight heparin (LMWH) enoxaparin. Hemorrhagic complications for fondaparinux were either comparable or higher than those for LMWH but the authors did not judge that the increased bleeding was clinically relevant. A dose ranging study led to the selection of the dose of 7.5 mg at a single daily subcutaneous injection as optimal for the treatment of VTE. In two phase III clinical trials, the dose of 7.5 mg/day is expected to be as efficacious and safe as heparin for the treatment of DVT or PE, respectively. Phase II studies show that the efficacy-to-safety ratio of fondaparinux in the treatment of unstable angina or as an adjunct to thrombolysis in acute myocardial infarction is promising. These results demonstrated that a single anti-Xa agent devoid of antithrombin activity is a potent antithrombotic drug. Fondaparinux has obtained FDA and European health authorities approval. Its use on a large scale will allow the evaluation of its efficacy and tolerance in the daily clinical practice. Chemical modifications of the original synthetic pentasaccharide increase the affinity to AT resulting in a more potent inhibition of FXa and longer half-life. Idraparinux is the first of these new oligosaccharides that we named "meta-pentasaccharides." After subcutaneous injection the half-life of idraparinux is about 80 h allowing a single injection per week. A dose-finding study has established the optimal dose given once a week to be compared with warfarin for the treatment of DVT.

Absence of interaction of fondaparinux sodium with aspirin and piroxicam in healthy male volunteers

OBJECTIVE

Patients undergoing major orthopaedic surgery who are being treated with fondaparinux sodium for prevention of venous thromboembolism may be receiving treatment for coronary artery disease or chronic inflammatory disease of the joints or arthritis. Two separate studies assessed any possible interaction between fondaparinux sodium at steady state and aspirin (acetylsalicylic acid) or piroxicam in healthy volunteers.

DESIGN

In the first study a single dose of aspirin 975mg was assessed initially, followed by single doses of aspirin or placebo on the fourth day of an 8-day regimen of subcutaneous fondaparinux sodium (10mg once daily). The second study was a three-way crossover, double-blind, randomised study which investigated fondaparinux sodium 10mg + placebo, fondaparinux sodium 10mg + piroxicam 20mg, or placebo + piroxicam 20mg.

METHODS

Both studies obtained plasma concentration-time profiles of fondaparinux sodium administered alone and with aspirin or piroxicam. Noncompartmental parameters - peak concentration, trough concentration, time to reach peak concentration, and area under the concentration-time curve - were obtained. Both studies measured the pharmacodynamic parameters bleeding time and activated partial thromboplastin time (aPTT). Safety was monitored.

RESULTS AND CONCLUSIONS

Neither aspirin nor piroxicam influenced the pharmacokinetics of fondaparinux sodium at steady state. Two hours after administration, prolongation of bleeding time with aspirin alone or with aspirin plus fondaparinux sodium was significantly greater than with fondaparinux sodium alone (p = 0.003 and p = 0.004, respectively). No significant differences were observed between aspirin alone or aspirin + fondaparinux sodium in effect on bleeding time. A small decrease in collagen-induced platelet aggregation was observed after administration of piroxicam alone or piroxicam + fondaparinux sodium. A small effect on aPTT was observed; it was similar for fondaparinux sodium whether administered alone or in combination with either aspirin or piroxicam. No serious adverse events were reported.

Fondaparinux sodium mechanism of action: identification of specific binding to purified and human plasma-derived proteins

BACKGROUND

Fondaparinux sodium is a novel antithrombotic agent, the first of a new class of selective factor Xa inhibitors. It has favourable pharmacokinetics including 100% bioavailability, low variability and a mean terminal half-life of 17 hours for young and 21 hours for elderly healthy volunteers, enabling once-daily administration. Studies on the prevention of venous thromboembolism (VTE) after orthopaedic surgery demonstrated significantly improved efficacy over the low-molecular-weight heparin enoxaparin, with a >50% reduced risk of VTE and a similar safety profile.

OBJECTIVE

To investigate the in vitro binding of fondaparinux sodium to purified antithrombin III (ATIII) and other plasma proteins.

METHODS

Fondaparinux sodium was incubated with human plasma, antithrombin-depleted plasma or purified human plasma proteins, including antithrombin, alpha1-acid glycoprotein, serum albumin and immunoglobulin. Non-protein-bound fondaparinux sodium was determined using a validated chromogenic assay method, enabling the calculation of the free fraction of fondaparinux sodium and its binding parameters.

RESULTS

At steady state, fondaparinux sodium at therapeutic concentrations [i.e. those attainable in the prevention (0.14 to 0.50 mg/L) and treatment (up to approximately 2 mg/L) of VTE] was extensively bound (>97%) to plasma proteins and specifically bound (>94%) to purified ATIII. The specific binding parameters B(max) (binding capacity) and K(D )(dissociation constant) were similar for human plasma (B(max) = 2072 nmol/L, K(D) = 28 nmol/L) and purified ATIII (B(max) = 1627 nmol/L and K(D) = 32 nmol/L). There was no specific binding of fondaparinux sodium to other purified plasma proteins.

CONCLUSION

At clinically relevant concentrations, fondaparinux sodium is highly and specifically bound to ATIII in human plasma, suggesting that potential interaction with drugs via albumin or alpha1-acid glycoprotein displacement is unlikely.

Fondaparinux sodium is not metabolised in mammalian liver fractions and does not inhibit cytochrome P450-mediated metabolism of concomitant drugs

OBJECTIVE

To investigate the in vitro metabolism of the antithrombotic agent fondaparinux sodium in mammalian liver fractions and to evaluate its potential inhibitory effect on human cytochrome P450 (CYP)-mediated metabolism of other drugs.

METHODS

Metabolism was evaluated by incubating radioisotope-labelled fondaparinux sodium with postmitochondrial liver fractions of rat, rabbit, monkey or human origin (three subjects). Human liver microsomal preparations and an NADPH-generating system were incubated with phenacetin, coumarin, tolbutamide, S-mephenytoin, bufuralol, chlorzoxazone or nifedipine. These are selectively metabolised by CYP isoforms: CYP1A2, CYP2A6, CYP2C9, CYP2C19, CYP2D6, CYP2E1 or CYP3A4, respectively. Experiments were designed to determine apparent K(i) (inhibitory constant) values for fondaparinux sodium against each CYP isoform, by varying concentrations of fondaparinux sodium and the selective substrate. Each experiment included control reaction mixtures containing an isoform-selective inhibitor. After incubation, the mixtures were analysed by LC-MS/MS or with fluorometric detection.

RESULTS

All liver fractions were enzymatically active, as demonstrated by degradation of [(14)C]testosterone. No metabolism of fondaparinux sodium was detectable in postmitochondrial liver fractions. Apparent K(i) values for fondaparinux sodium against the CYP isoforms could not be determined because the oxidative metabolism of the isoform-selective CYP substrates was not significantly inhibited in pooled microsomal reaction mixtures. In the presence of selective CYP inhibitors, metabolism of each substrate was significantly reduced, confirming that inhibition could be observed in these assays.

CONCLUSION

The demonstrated lack of mammalian hepatic metabolism of fondaparinux sodium is consistent with animal and human studies. The absence of inhibition of the human CYP isoforms commonly involved in the metabolism of drugs suggests that clinical treatment with fondaparinux sodium is unlikely to interfere with the pharmacokinetics and metabolism of a wide range of other drugs which are associated with CYP inhibition.

Preparation and anticoagulant activity of the phosphosulfomannan PI-88

A yeast-derived phosphomannan mixture was chemically sulfonated and the composition and structure of the product mixture was studied. This phosphosulfomannan mixture, PI-88, is currently under clinical evaluation as an anti-cancer agent. Analysis using capillary electrophoresis demonstrated that PI-88 was a multi-component mixture. Gel permeation chromatography provided four fractions of PI-88 that contained components which differed in size from disaccharide to hexasaccharide, and by degree of sulfation. These fractions were characterised by spectroscopic and chromatographic methods and the structure of PI-88 is that expected based on the structure of the phosphomannan starting material. The anticoagulant activity of these fractions was evaluated and the structural requirements for activity are described.

Fondaparinux sodium

black triangle Fondaparinux sodium, a selective factor Xa inhibitor, is the first in a new class of antithrombotics. It binds selectively with high affinity to antithrombin III and specifically catalyses the inactivation of factor Xa. The elimination half-life of fondaparinux sodium permits once daily treatment. black triangle A randomised, double-blind, parallel-group, dose-ranging, multicentre phase IIb study in 933 eligible patients established that a subcutaneous dose of between 1.5 and 3mg of fondaparinux sodium has the optimum efficacy and safety profile for prophylaxis of venous thromboembolism in patients undergoing major orthopaedic surgery. black triangle Fondaparinux sodium, given to more than 3600 patients undergoing major orthopaedic surgery who participated in prospective, randomised, double-blind, multicentre phase III clinical trials, significantly reduced the incidence of venous thromboembolism, with an overall risk reduction of 55.2% compared with enoxaparin. black triangle Fondaparinux sodium was well tolerated by patients undergoing major orthopaedic surgery, and at the recommended clinical dose of 2.5mg has a similar tolerability profile, including bleeding events, to standard enoxaparin regimens. Fondaparinux sodium has not been reported to cause antibody-induced thrombocytopenia.