Pharmacokinetics and Tolerance of the Natural Pentasaccharide (SR90107/ORG31540) with High Affinity to Antithrombin III in Man

Carbohydrate-based drugs launched during 2000-2021

Carbohydrates are fundamental molecules involved in nearly all aspects of lives, such as being involved in formating the genetic and energy materials, supporting the structure of organisms, constituting invasion and host defense systems, and forming antibiotics secondary metabolites. The naturally occurring carbohydrates and their derivatives have been extensively studied as therapeutic agents for the treatment of various diseases. During 2000 to 2021, totally 54 carbohydrate-based drugs which contain carbohydrate moities as the major structural units have been approved as drugs or diagnostic agents. Here we provide a comprehensive review on the chemical structures, activities, and clinical trial results of these carbohydrate-based drugs, which are categorized by their indications into antiviral drugs, antibacterial/antiparasitic drugs, anticancer drugs, antidiabetics drugs, cardiovascular drugs, nervous system drugs, and other agents.

Management of antithrombotic agents in patients undergoing flexible bronchoscopy

Bleeding is one of the most feared complications of flexible bronchoscopy. Although infrequent, it can be catastrophic and result in fatal outcomes. Compared to other endoscopic procedures, the risk of morbidity and mortality from the bleeding is increased, as even a small amount of blood can fill the tracheobronchial tree and lead to respiratory failure. Patients using antithrombotic agents (ATAs) have higher bleeding risk. A thorough understanding of the different ATAs is critical to manage patients during the peri-procedural period. A decision to stop an ATA before bronchoscopy should take into account a variety of factors, including indication for its use and the type of procedure. This article serves as a detailed review on the different ATAs, their pharmacokinetics and the pre- and post-bronchoscopy management of patients receiving these medications.

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.

In vitro and in vivo characterization of a reversible synthetic heparin analog

BACKGROUND

The global supply of unfractionated heparin (UFH) and all commercially available low molecular weight heparins (LMWH) remain dependent on animal sources, such as porcine intestine or bovine lung. Recent experience has shown that contamination of the supply chain (with over-sulfated chondroitin sulfates) can result in lethal toxicity. Fondaparinux is currently the only commercially available synthetic analog of heparin. We recently described a new class of chemoenzymatically synthesized heparin analogs. One of these compounds (S12-mer) is a dodecasaccharide consisting of an antithrombin-binding moiety with repeating units of IdoA2S-GlcNS6S and two 3-O-sulfate groups that confer the ability to bind protamine.

OBJECTIVE/METHODS

We sought to further characterize this new compound in vitro using biochemical and global coagulation assays and in vivo using thrombosis and hemostasis assays.

RESULTS

The anticoagulant activities of the Super 12-mer (S12-mer) and Enoxaparin in anti-factor Xa and plasma-based thrombin generation assays were roughly equivalent with a 50% reduction in peak thrombin generation occurring at approximately 325nM. When protamine was titrated against a fixed concentration of S12-mer in plasma or blood, the S12-mer displayed a significant restitution of thrombin generation and clot formation. In vivo, S12-mer inhibited venous thrombosis to a similar extent as Enoxaparin, with similar bleeding profiles.

CONCLUSIONS

These data show that the S12-mer has almost identical efficacy to Enoxaparin in terms of FXa inhibition, while displaying significant reversibility with protamine. Taken together with the ability to ensure purity and homogeneity from batch to batch, the S12-mer is a promising new synthetic heparin analog with a potentially enhanced safety profile.

Heparin-induced thrombocytopenia

Heparin is widely used for the prevention and treatment of thrombotic and particularly cardiovascular disorders. Unfortunately, 0.5 to 3.0% of patients given heparin develop an immune reaction, commonly termed Type II heparin-induced thrombocytopenia (HIT). This is characterized by a moderate thrombocytopenia and in some patients, a venous or arterial thrombosis. This frequently leads to disastrous sequelae, such as limb amputation and death. The pathophysiological basis of this serious adverse drug reaction is the production of an immunoglobulin G antibody that reacts with an antigenic complex consisting of heparin and platelet factor 4. A significant risk factor for the development of HIT is recent surgery, and the frequency of developing an antiheparin-platelet factor 4 or HIT antibody is particularly high in cardiac surgery patients, although surprisingly, only a few of these patients actually develop the clinical syndrome of HIT. This review will discuss the frequency, pathophysiology, clinical features, diagnosis and management of HIT.

Management of heparin-induced thrombocytopenia

BACKGROUND

Heparin-induced thrombocytopenia (HIT) is a rare but severe prothrombotic adverse effect of heparin treatment. The underlying cause is the formation of highly immunogenic complexes between negatively charged heparin and positively charged platelet factor 4 (PF4). Resulting antibodies against these PF4/heparin complexes can activate platelets via the platelet FcγIIa receptor, leading to thrombin generation and thus to the paradox of a prothrombotic state despite thrombocytopenia and application of heparin. Prompt diagnosis of HIT is important in order to change treatment to prevent severe thromboembolic complications. However, this is often difficult as thrombocytopenia is frequent in hospitalized patients and the commercially available laboratory tests for HIT antibodies have a high negative predictive value but only a poor positive predictive value. This leads to overdiagnosis and overtreatment of HIT, which also bear the risk for adverse outcomes.

AREAS COVERED

This review aims at resuming recent data on HIT, thereby focusing on the role of new anticoagulants and providing a framework for diagnosis and treatment. Furthermore, it provides some insights into the pathogenesis of this peculiar adverse drug reaction and ventures a guess at its future relevance in clinical practice.

EXPERT OPINION

New drugs which are strongly negatively charged should be assessed for their capacity to form complexes with PF4. If they do so, they bear the risk of inducing a HIT-like immune response. The immunology of HIT is still largely unresolved. Understanding HIT might provide insights into other immune and autoimmune response mechanisms.

Parenteral anticoagulants: Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines

This article describes the pharmacology of approved parenteral anticoagulants. These include the indirect anticoagulants, unfractionated heparin (UFH), low-molecular-weight heparins (LMWHs), fondaparinux, and danaparoid, as well as the direct thrombin inhibitors hirudin, bivalirudin, and argatroban. UFH is a heterogeneous mixture of glycosaminoglycans that bind to antithrombin via a unique pentasaccharide sequence and catalyze the inactivation of thrombin, factor Xa, and other clotting enzymes. Heparin also binds to cells and plasma proteins other than antithrombin causing unpredictable pharmacokinetic and pharmacodynamic properties and triggering nonhemorrhagic side effects, such as heparin-induced thrombocytopenia (HIT) and osteoporosis. LMWHs have greater inhibitory activity against factor Xa than thrombin and exhibit less binding to cells and plasma proteins than heparin. Consequently, LMWH preparations have more predictable pharmacokinetic and pharmacodynamic properties, have a longer half-life than heparin, and are associated with a lower risk of nonhemorrhagic side effects. LMWHs can be administered once daily or bid by subcutaneous injection, without coagulation monitoring. Based on their greater convenience, LMWHs have replaced UFH for many clinical indications. Fondaparinux, a synthetic pentasaccharide, catalyzes the inhibition of factor Xa, but not thrombin, in an antithrombin-dependent fashion. Fondaparinux binds only to antithrombin. Therefore, fondaparinux-associated HIT or osteoporosis is unlikely to occur. Fondaparinux exhibits complete bioavailability when administered subcutaneously, has a longer half-life than LMWHs, and is given once daily by subcutaneous injection in fixed doses, without coagulation monitoring. Three additional parenteral direct thrombin inhibitors and danaparoid are approved as alternatives to heparin in patients with HIT.

Effect of edoxaban on markers of coagulation in venous and shed blood compared with fondaparinux

Edoxaban, an oral direct factor Xa (FXa) inhibitor, is in phase III clinical development for stroke prevention in atrial fibrillation and treatment of venous thromboembolism. The shed blood model allows for study of activated coagulation at a site of standardised tissue injury due to local release of tissue factor. The objective of this study was to evaluate the effect of three doses of edoxaban on markers of coagulation in shed and venous blood versus placebo and a standard prophylactic dose of fondaparinux. A total of 100 healthy male subjects were randomised to receive single doses of one of five treatments: subcutaneously administered fondaparinux 2.5 mg; orally administered edoxaban 30, 60, or 120 mg; or placebo. The primary objective was measurement of blood coagulation markers prothrombin fragment 1+2 (F1+2) and thrombin-antithrombin (TAT) complex, and platelet activation marker β-thromboglobulin (β-TG), in venous and shed blood. Secondary objectives included pharmacokinetics, shed blood volume, and safety of edoxaban. Single doses of edoxaban caused rapid and significant decreases of F1+2, TAT, and β-TG in the shed blood model, indicating inhibition of thrombin generation and platelet activation. Inhibition was significantly less for fondaparinux versus edoxaban. Baseline-corrected F1+2, TAT, and β-TG values demonstrated sustained inhibition up to 24 hours for shed blood in the edoxaban groups but no significant inhibition in venous blood. Overall, edoxaban treatments were well tolerated. In conclusion, single oral doses of edoxaban 30, 60, or 120 mg caused rapid and sustained inhibition of coagulation up to 24 hours in the shed blood model.

Clinical pharmacology of direct and indirect factor Xa inhibitors

The limitations of conventional anticoagulants have stimulated the development of new anticoagulants. The central position of factor Xa (FXa) at the junction of the intrinsic and extrinsic pathways in the coagulation cascade means that direct and indirect FXa inhibitors have increasingly changed antithrombotic strategies. FXa inhibitors potently and selectively inhibit thrombin formation rather than thrombin activity. Direct FXa inhibitors may directly bind to FXa, whereas indirect inhibitors are dependent on antithrombin. Direct inhibitors may bind free FXa and, in contrast to indirect inhibitors, FXa within the prothrombinase complex or within clots as well. Fondaparinux is the prototype indirect FXa inhibitor and has been extensively studied in the prevention and treatment of thromboembolic diseases, including acute coronary syndromes. Due to a favourable efficacy and safety profile and convenient once-daily dosing without the need for monitoring, fondaparinux is preferentially recommended in recent guidelines dealing with antithrombotic treatment. A number of small-molecule direct FXa inhibitors are currently at different stages of clinical development. After an extensive clinical trial programme demonstrating superior efficacy without a significant increase in major bleeds compared with enoxaparin, rivaroxaban is now available for the prevention of thromboembolic events in patients undergoing orthopaedic surgery. Rivaroxaban also offers the convenience of oral once-daily dosing without the need for monitoring. Whereas most direct FXa inhibitors are orally active, otamixaban is administered intravenously, offering rapid on-off anticoagulant activity. Other compounds under development may offer additional options for tailored antithrombotic strategies according to differing indications, clinical situations and patient variables.

Anticoagulant and antithrombotic drugs in pregnancy: what are the anesthetic implications for labor and cesarean delivery?

Neuraxial anesthetic techniques are commonly used during the peripartum period to provide effective pain relief for labor and anesthesia during cesarean delivery. Major neurologic complications are rare after neuraxial anesthesia; however, spinal hematoma is associated with catastrophic neurologic outcomes (including lower-limb paralysis). Anticoagulant and antithrombotic drugs can increase the risk of spinal hematoma after neuraxial anesthesia, and better understanding of the pharmacokinetics and pharmacodynamics of anticoagulants has led to greater appreciation for withholding anticoagulation before and after neuraxial anesthesia. A number of national anesthetic societies have produced guidelines for performing neuraxial anesthesia in patients receiving anticoagulation. However, there is limited information about anesthetic implications of anticoagulation during the peripartum period. This article will review the risks of spinal hematoma after neuraxial anesthesia in pregnant patients; current guidelines for neuraxial anesthesia for anticoagulated patients; and relevant pharmacological data of specific anticoagulant and antithrombotic drugs in pregnancy.

Regional anaesthesia and anticoagulation

As the life expectancy of our Western population progressively increases, so does the prevalence of cardiovascular disease and thus the use of antithrombotic drugs. The use of central neuraxial anaesthesia techniques in patients treated with these drugs is a major clinical problem as the presence of an impaired coagulation has been found to be the most important risk factor contributing to the formation of a spinal haematoma. The growing number of case reports of spinal haematoma has led many national societies of anaesthetists to come up with guidelines. This article presents an overview of current guidelines on the use of regional anaesthetic techniques in patients treated with various anticoagulants and also describes a possible strategy to deal with new antithrombotic drugs that have recently been introduced in some countries or will be shortly in others.

Fondaparinux in acute coronary syndromes

Antithrombotic therapies form the cornerstone of management of acute coronary syndromes (ACS). An ideal antithrombotic agent should reduce ischemic complications while keeping bleeding events to a minimum. Heparins, both unfractionated and low molecular weight, reduce ischemic outcomes but also significantly increase the risk of major and minor bleeding. Moreover, they do not reduce mortality. Therefore, there is a need for newer agents that preserve the benefits of ischemia reduction while decreasing mortality and bleeding risk. Fondaparinux is a synthetic pentasaccharide which specifically targets factor Xa of the coagulation cascade. It has been effectively used in the prevention of and treatment of venous thromboembolic disease. Two large randomized controlled trials of fondaparinux compared to unfractionated and low molecular weight heparins, among patients with ACS have recently been completed. These studies have shown a significantly lower risk of bleeding with fondaparinux compared to heparins, with equivalent or greater reductions in ischemic outcomes. A small but definite increase in the risk of catheter-related thrombosis has been found among patients undergoing coronary interventions, which is ameliorated by the administration of unfractionated heparin. This review outlines the pharmacological properties of fondaparinux and critically examines the available clinical trial data for fondaparinux in ACS.

Severe bleeding secondary to misuse of fondaparinux: a case report

Venous thromboembolism (VTE) remains a great challenge because of its frequency and of its potential severity. However, VTE treatment can also lead to iatrogenic complications. We report a case of thigh haematoma by a 83-year-old woman under fondaparinux for a solear thrombosis. Then we discuss the indications of Unfractionated Heparin (UFH), Low-Molecular-Weight Heparins (LMWH) and Fondaparinux, which are the three classes of rapidly acting anticoagulant treatments nowadays available. As their efficacy is comparable, the choice between these classes relies on the risk of adverse effects, which depends on some patient's characteristics. LMWH and fondaparinux are contra-indicated by the patients with a renal clearance under 30 ml/min. Only UFH are authorized during the whole pregnancy even though LMWH are more and more used. Fondaparinux has proven its safety by patients over 100 kg. UFH requires a daily biological management whereas it is optional for LMWH and fondaparinux, as long as their contra-indications are taken into account. No Heparin-induced-thrombocytopenia Syndrome (HIT-Sd) has been proven yet under fondaparinux so that platelets management seems not necessary, contrary to UFH and LMWH which require a twice-weekly platelets count. The accuracy of the therapeutic indication should result in the best benefit/risk assessment.

Anticoagulation with argatroban in a parturient with heparin-induced thrombocytopenia

Unfractionated heparin and low-molecular-weight heparin are currently the anticoagulants of choice for the prevention of recurrent thromboembolic disease during pregnancy. However, heparin-induced thrombocytopenia contraindicates the use of unfractionated heparin and low-molecular-weight heparin. We describe a patient who was admitted to our hospital with deep vein thrombosis at 18 weeks of gestation and who developed heparin-induced thrombocytopenia during her antenatal care. Therapeutic anticoagulation was initially achieved with argatroban, then changed to fondaparinux. During early labor, fondaparinux was discontinued and intravenous argatroban was substituted. Argatroban was discontinued during transition to active labor. After return of a normal partial thromboplastin time, combined spinal-epidural analgesia was induced for routine completion of labor and vaginal delivery. We discuss the decisions made in the maintenance of this patient's anticoagulation during the peripartum period as well as timing of her neuraxial labor analgesia.

Spotlight on fondaparinux sodium in 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 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.

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 antithrombotic drugs: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines (8th Edition)

This chapter focuses on new antithrombotic drugs that are in phase II or III clinical testing. Development of these new agents was prompted by limitations of existing antiplatelet, anticoagulant, or fibrinolytic drugs. Addressing these unmet needs, this chapter (1) outlines the rationale for development of new antithrombotic agents, (2) describes the new antiplatelet, anticoagulant, and fibrinolytic drugs, and (3) provides clinical perspectives on the opportunities and challenges faced by these novel agents.

Treatment of thrombosis with fondaparinux (Arixtra) in a patient with end-stage renal disease receiving hemodialysis therapy

Treatment of thrombosis in children with end-stage renal disease (ESRD) is extremely challenging owing to the underlying risk of bleeding. Fondaparinux (Arixtra, Sanofi-Synthélabo), a synthetic pentasaccharide, is contraindicated in patients with compromised renal function as it is excreted via kidneys. We describe a unique case with ESRD and pulmonary embolism who was treated with fondaparinux owing to the toxicity and poor compliance with low-molecular-weight heparin. Despite regular hemodialysis, a gradual rise in drug levels was observed without significant bleeding complications. This report implies that although low dose fondaparinux can be an option in patients with ESRD under special circumstances, guidelines for laboratory monitoring and appropriate dose adjustments are urgently required to ensure the safety of the patient.

Latest medical treatment strategies for venous thromboembolism

Anticoagulant therapy with unfractionated heparin (UFH) followed by warfarin prevents thrombus extension, reduces the risk of recurrent thrombosis and prevents death in patients with venous thromboembolism (VTE). Low-molecular-weight heparin (LMWH) has replaced UFH as the preferred initial anticoagulant therapy for VTE because it is as effective and safe as UFH, but does not require laboratory monitoring and is less likely to cause immune thrombocytopenia and osteoporosis. More recently, fondaparinux has been shown to be an effective and safe alternative to LMWH and several new parenteral anticoagulants are being evaluated. The most important unmet need in the anticoagulant management of VTE is a replacement for warfarin. New oral anticoagulants that selectively target individual steps in the coagulation cascade have been shown to be effective for the long-term treatment of VTE in Phase II and III trials and are likely to become available in the near future.

Fondaparinux prevents venous thromboembolism after joint replacement surgery in Japanese patients

Venous thromboembolism (VTE) is an important complication of major orthopaedic surgery of the lower limbs. Fondaparinux, a synthetic pentasaccharide and highly selective inhibitor of activated Factor Xa, is the first in a new class of antithrombotic agents. To determine the optimal dose in Japanese patients, double-blind, placebo-controlled, dose-ranging studies of fondaparinux were conducted in patients undergoing total knee replacement (TKR) or total hip replacement (THR) surgery. Patients were randomly assigned to receive a once-daily subcutaneous injection of fondaparinux (0.75, 1.5, 2.5, or 3.0 mg) or placebo in Study 1 (TKR) and Study 2 (THR). In Study 1, the incidence of VTE was 65.3% in the placebo group and was 34.2%, 21.3%, 16.2%, and 9.5% in the groups receiving 0.75, 1.5, 2.5, and 3.0 mg fondaparinux respectively. In Study 2, the incidence of VTE was 33.8% in the placebo group and was 24.2%, 4.6%, 7.4%, and 14.4% in the 0.75, 1.5, 2.5, and 3.0 mg fondaparinux groups respectively. Dose-response effects were observed in both studies; however, no statistically significant differences in major bleeding events were found among any groups. Fondaparinux proved to be a potent anticoagulant with a favourable benefit-to-risk ratio in the prevention of VTE in these study patients.

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.

Synthesis and Evaluation of 1-Arylsulfonyl-3-piperazinone Derivatives as Factor Xa Inhibitors VI. A Series of New Derivatives Containing N,S- and N,SO2-Spiro Acetal Scaffolds

In the course of development of factor Xa (FXa) inhibitors, we have found unique compounds containing an N,O- and an N,N-spiro acetal structure. It appeared that the difference in overall conformation due to the N,X-spiro acetal structure might be important for FXa inhibitory activity. Therefore, other N,X-spiro acetal structures, an N,S- and an N,SO2-spiro acetal, were developed as analogues of the N,X-spiro acetal structure. Compound 7b (N,S-spiro acetal structure) was found to have the strongest activity in these series of N,X-spiro acetal compounds, which had ever been synthesized.(4,5)).

Effect of fondaparinux on coagulation assays: results of College of American Pathologists proficiency testing

CONTEXT

Fondaparinux, a factor Xa inhibitor, is approved for thromboprophylaxis after orthopedic surgery and for treatment of venous thromboembolism. It may also be efficacious, safe, and cost-effective for other patients; thus, more widespread use of fondaparinux is likely. The effect of fondaparinux on coagulation testing needs to be thoroughly examined.

OBJECTIVE

To report the effects of fondaparinux on coagulation tests (prothrombin time, activated partial thromboplastin time, fibrinogen, antithrombin, factor VIII, thrombin time, anti-factor Xa) across diverse methodologies.

DESIGN

Samples with different concentrations of fondaparinux (0, 0.4, 0.8, and 2.0 microg/mL) were sent to laboratories participating in the College of American Pathologists Comprehensive Coagulation proficiency survey (N = 898). Laboratory-specific methods were used to assay coagulation parameters.

RESULTS

Prophylactic or therapeutic fondaparinux prolonged the prothrombin time by approximately 1 second and the activated partial thromboplastin time by 4 to 5 seconds, and reduced factor VIII from 119% to 107% and 102%, respectively. Supratherapeutic fondaparinux reduced factor VIII to 85%. The activated partial thromboplastin time was prolonged in 19%, 29%, and 52% of laboratories with prophylactic, therapeutic, and supratherapeutic fondaparinux levels, respectively. Fibrinogen, antithrombin, and thrombin time assays did not show clinically significant changes. When measuring fondaparinux concentration using an anti-factor Xa assay, the most accurate results were obtained when fondaparinux was used as the calibrator.

CONCLUSIONS

Fondaparinux, even in prophylactic doses, slightly prolongs the prothrombin time and activated partial thromboplastin time and can interfere with factor VIII assays, but it has no clinically relevant effect on fibrinogen, antithrombin, or thrombin time. A fondaparinux standard curve should be used for reporting fondaparinux levels using an anti-factor Xa assay.

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.

Development and Clinical Evaluation of Two Chromogenic Substrate Methods for Monitoring Fondaparinux Sodium

This study was designed to develop methods for monitoring of the selective factor Xa inhibitor fondaparinux sodium (ARIXTRA) based on standard laboratory methods for the chromogenic determination of the anti-factor Xa activity of low molecular weight heparin. To examine the biologic activity of fondaparinux in comparison to its plasma concentration, 2 methods were investigated: 1 working with the addition of antithrombin (AT), the other without exogenous AT. Both methods showed a linear relationship of fondaparinux concentration and OD/min on a log-lin scale in the range from 0.1 to 2 microg/mL. Inter- and intra-assay variability was <6% in all cases. The results of spiked samples from patients on vitamin K antagonists (VKA) were in good agreement with both methods, and the determination of the fondaparinux concentration was not influenced by reduced levels of factor X in plasma caused by VKA-intake. Ex vivo samples from orthopedic patients (n=18) on prophylactic treatment with fondaparinux showed concentrations between 0.2 to 0.7 microg/mL 3 hours after s.c. injection. No significant differences were detected between both methods with these samples. The presented methods are suitable tools for monitoring of fondaparinux. The linear calibration curve in the range 0.1 to 2 microg/mL is suitable for determination of prophylactic and therapeutic application of fondaparinux. Both methods, with and without addition of AT, can be performed fully automated in clinical routine on an automated coagulation analyzer (STA coagulation analyzer). No significant differences were detected between both methods with these samples.

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.

Low-molecular-weight heparins for the treatment of acute coronary syndrome and venous thromboembolism in patients with chronic renal insufficiency

The clinical management of patients with renal insufficiency who develop an acute coronary syndrome or venous thromboembolism is a common clinical scenario that is problematic because of the lack of well-designed randomized trials assessing management strategies in such patients. Impaired renal function is common in patients who develop thromboembolic disorders, particularly in elderly patients in whom renal insufficiency is under-recognized. Low-molecular-weight heparins (LMWHs), which are the most widely used anticoagulant for the treatment of patients with an acute coronary syndrome or venous thromboembolism, are eliminated primarily by the kidney and, therefore, pose treatment challenges in patients with impaired renal function. However, there is emerging evidence regarding the use of LMWHs in patients with impaired renal function suggesting that some preparations may be safe in such patients. The objective of this review is to discuss the clinical management of patients with renal insufficiency who develop an acute coronary syndrome or venous thromboembolism, and to explore similarities and differences of LMWHs when used in this clinical setting.

New Anti-thrombotic Agents: Emphasis on Hemorrhagic Complications and Their Management

Our advanced knowledge of coagulation has led to the synthesis of novel procoagulant substances, such as recombinant activated factor VII (rFVIIa; NovoSeven, Novo Nordisk, Bagsvaerd, Denmark). Similarly, in-depth understanding of the interaction between anticoagulant proteins and their natural inhibitors has led to the synthesis of various novel anticoagulants. Novel anticoagulants are characterized by highly specific coagulation-inhibiting activities and, frequently, a complete lack of effective antidotes. This lack of antidotes is particularly important in the case of novel inhibitors with extended half-lives; for example, idraparinux may produce effective anticoagulation for as long as one week after subcutaneous administration. As novel anticoagulants complete licensing evaluations and are used in clinical practice, the likelihood of anticoagulant-associated hemorrhage will increase. This will require physicians to have an understanding of the mechanism of action of these anticoagulants, and to have an advanced degree of knowledge of the potential specific and nonspecific inhibitors of these anticoagulant agents. This paper will briefly review the biochemistry of coagulation, focusing on the complexes inhibited by currently available and novel anticoagulants. Specific and nonspecific prohemostatic agents will be reviewed and discussed. The ability of nonspecific procoagulant agents (particularly rFVIIa) to reverse the effects of novel anticoagulants will also be reviewed.

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.

New anticoagulant therapy

The development of new anticoagulants is expanding the list of drugs that can be used to prevent and treat venous and arterial thrombosis. New parenteral anticoagulants have been developed to overcome the limitations of heparin and low-molecular-weight heparin, whereas novel orally active anticoagulants have been designed to provide more streamlined therapy than vitamin K antagonists. This review identifies the molecular targets of new anticoagulants, describes the results of clinical trials, and provides clinical perspective on the opportunities for new anticoagulants.

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.

Bleeding in Cardiac Surgery: Its Prevention and Treatment—an Evidence-Based Review

Expected and unexpected bleeding occur frequently in patients undergoing cardiac surgery. Bleeding after cardiac surgery can be broadly divided into two groups: surgical (unrecognized bleeding vessel, anastomosis, or other suture line) or nonsurgical bleeding (caused by coagulopathy). Factors influencing both surgical and nonsurgical bleeding can be further broken down into those occurring preoperatively and those that occur intraoperatively and postoperatively. A thorough understanding of these factors is necessary to reduce bleeding. This is a desirable clinical goal, because excessive bleeding is associated with adverse outcomes.