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

Factors Affecting the Formation and Treatment of Thrombosis by Natural and Synthetic Compounds

Venous thromboembolism (VTE) refers to deep vein thrombosis (DVT), whose consequence may be a pulmonary embolism (PE). Thrombosis is associated with significant morbidity and mortality and is the third most common cardiovascular disease after myocardial infarction and stroke. DVT is associated with the formation of a blood clot in a deep vein in the body. Thrombosis promotes slowed blood flow, hypoxia, cell activation, and the associated release of many active substances involved in blood clot formation. All thrombi which adhere to endothelium consist of fibrin, platelets, and trapped red and white blood cells. In this review, we summarise the impact of various factors affecting haemostatic disorders leading to blood clot formation. The paper discusses the causes of thrombosis, the mechanism of blood clot formation, and factors such as hypoxia, the involvement of endothelial cells (ECs), and the activation of platelets and neutrophils along with the effects of bacteria and reactive oxygen species (ROS). Mechanisms related to the action of anticoagulants affecting coagulation factors including antiplatelet drugs have also been discussed. However, many aspects related to the pathogenesis of thrombosis still need to be clarified. A review of the drugs used to treat and prevent thrombosis and natural anticoagulants that occur in the plant world and are traditionally used in Far Eastern medicine has also been carried out.

Characterization of active anticoagulant fraction and a fibrin(ogen)olytic serine protease from leaves of Clerodendrum colebrookianum, a traditional ethno-medicinal plant used to reduce hypertension

ETHNOPHARMACOLOGICAL RELEVANCE

Cardiovascular diseases are the major cause of mortality and morbidity, causing over 17.9 million deaths a year worldwide. Currently used therapy is often having side effects and expensive, dietary interventions and alternative medicines are required. Clerodendrum colebrookianum has been used to treat cardiac hypertension but anticoagulant potency was not evaluated.

AIM OF THE STUDY

To characterize an active anticoagulant fraction (AAFCC) and a 30 kDa fibrin(ogen)olytic serine protease (clerofibrase) isolated from aqueous leave extract of C. colebrookianum.

MATERIALS AND METHODS

AAFCC/clerofibrase was subjected to extensive biochemical and pharmacological characterization including LC-MS/MS, amino acid compositional and GC-MS analyses. Interaction between clerofibrase with fibrinogen was studied by spectrofluorometric analysis. In vitro thrombolytic, antiplatelet and cytotoxicity assay were performed. In vivo toxicity, anticoagulant, defibrinogen and antithrombotic activities were determined on Swiss albino mice.

RESULTS

The in vitro anticoagulant activity of AAFCC was found to be superior to heparin and clerofibrase and comparable to Nattokinase and warfarin. The proteomics and amino acid composition analyses suggest that clerofibrase is a previously uncharacterized novel plant protease capable of degrading the -αβ chains of fibrinogen/fibrin. AAFCC/clerofibrase exerts their anticoagulant action via fibrinogenolytic activity and partially by antiplatelet activity albeit they have no effect on thrombin and FXa inhibition. The spectrofluorometric analysis revealed the binding of clerofibrase to fibrinogen but not to thrombin and FXa. The phytochemical constituents and bioactive components of AAFCC were characterized by biochemical, and GC-MS analyses. The AAFCC and clerofibrase inhibited collagen/ADP-induced mammalian platelet aggregation, showed in vitro thrombolytic activity, and non-cytotoxic to mammalian cells. The AAFCC showed and dose-dependent in vivo plasma defibrinogenating and anticoagulant activities and inhibited k-carrageen-induced thrombus formation in the tails of mice.

CONCLUSION

The potent in vivo anticoagulant and antithrombotic effects of AAFCC suggests its pharmacological significance as herbal anticoagulant drug for the prevention and/or treatment of hyperfibrinogenemia- and thrombosis associated cardiovascular disorders.

Identification and characterisation of novel inhibitors on extrinsic tenase complex from Bungarus fasciatus (banded krait) venom

Snake venoms are excellent sources of pharmacologically active proteins and peptides, and hence are potential sources of leads for drug developments. It has been previously established that krait (Bungarus genus) venoms contain mainly neurotoxins. A screening for anticoagulants showed that Bungarus fasciatus venom exhibits potent anticoagulant effect in standard clotting assays. Through sequential fractionation of the venom by size exclusion and high performance liquid chromatographies, coupled with functional screening for anticoagulant activities, we have isolated and purified two anticoagulant proteins, termed BF-AC1 ( Bungarus fasciatus anticoagulant 1) and BFAC2. They have potent inhibitory activities (IC50 of 10 nM) on the extrinsic tenase complex. Structurally, these proteins each has two subunits covalently held together by disulfide bond(s). The N-terminal sequences of the individual subunits of BF-AC1 and BF-AC2 showed that the larger subunit is homologous to phospholipase A2, while the smaller subunit is homologous to Kunitz type serine proteinase inhibitor. Functionally, in addition to their anticoagulant activity, these proteins showed presynaptic neurotoxic effects in both in vivo and ex vivo experiments. Thus, BF-AC1 and BF-AC2 are structurally and functionally similar to β-bungarotoxins, a class of neurotoxins. The enzymatic activity of phospholipase A2 subunit plays a significant role in the anticoagulant activities. This is the first report on the anticoagulant activity of β-bungarotoxins and these results expand on the existing catalogue of haemostatically active snake venom proteins.

Clinical Application of Prothrombin Complex Concentrate in Blood Management in Patients

Management of patients receiving anticoagulants is a major factor in achieving better outcomes. Anticoagulant therapy may need to be discontinued or rapidly reversed before urgent surgery or invasive procedures. In these situations, treatment with concentrated vitamin K, fresh frozen plasma, and/or clotting factors can achieve more rapid anticoagulant reversal than can drug discontinuation alone. Activated prothrombin complex concentrate is used to treat hemophiliac patients with acquired factor VIII inhibitors. Nonactivated prothrombin complex concentrates are used for anticoagulant reversal. The concentrates are effective within minutes of dosing, providing a nearly immediate decrease in the international normalized ratio. The concentrates are lyophilized powders that can be quickly reconstituted, do not require ABO blood typing before use, and contain 25 times the concentration of vitamin K-dependent clotting factors compared with fresh frozen plasma. Studies suggest that the concentrates are associated with better clinical end points than is fresh frozen plasma.

The evolution of anticoagulant therapy

Arterial and venous thromboembolism are leading causes of morbidity and mortality around the world. For almost 70 years, heparins (unfractionated heparin and low molecular weight heparins) and vitamin K antagonists have been the leading therapeutic medical options for the treatment and prevention of thromboembolic disorders. Nevertheless, the many limitations of these traditional anticoagulants have fuelled the search for novel agents over the past 15 years, and a new class of oral anticoagulants that specifically target activated factor X and thrombin has been developed and is now commercially available. In this narrative review, the evolution of anticoagulant therapy is summarised, with a focus on newer oral anticoagulants.

Venous Thromboembolism (VTE) Prophylaxis for Hip and Knee Arthroplasty: Changing Trends

Venous thromboembolism (VTE) has been identified as an immediate threat to patients undergoing major orthopedic procedures such as total hip arthroplasty (THA) and total knee arthroplasty (TKA). Given the known dangers of VTE, arthroplasty surgeons are sensitive to the need for VTE thromboprophylaxis. However, the modalities of thromboprophylaxis used to minimize the risks to patients have been variable. Clinical practice guidelines have been published by several professional organizations, while some hospitals have established their own protocols. The 2 most popular guidelines are those published by the Academy of Orthopaedic Surgeons (AAOS) and American College of Chest Physicians (ACCP), both from North America. Prior to 2012, these recommendations varied depending on underlying definitions, methodology, and goals of the 2 groups. For the first time, both groups have similar recommendations that focus on minimizing symptomatic VTE and bleeding complications. The key to determining the appropriate chemoprophylaxis for patients is to balance efficacy of a prophylactic agent, while being safe in regards to bleeding complications. However, a multimodal approach that focuses on early postoperative mobilization and the use of mechanical prophylaxis, in addition to chemoprophylaxis, is essential.

Effect of Food, an Antacid, and the H2Antagonist Ranitidine on the Absorption of BAY 59-7939 (Rivaroxaban), an Oral, Direct Factor Xa Inhibitor, in Healthy Subjects

To investigate the influence of food and administration of an antacid (aluminum-magnesium hydroxide) or ranitidine on the absorption of BAY 59-7939 (rivaroxaban), 4 randomized studies were performed in healthy male subjects. In 2 food interaction studies, subjects received BAY 59-7939, either as two 5-mg tablets (fasted and fed), four 5-mg tablets (fasted), or one 20-mg tablet (fasted and fed). In 2 drug interaction studies, BAY 59-7939 (six 5-mg tablets) was given alone or with ranitidine (150 mg twice daily, preceded by a 3-day pretreatment phase) or antacid (10 mL). Plasma samples were obtained to assess pharmacokinetic and pharmacodynamic parameters of BAY 59-7939. In the presence of food, time to maximum concentration (t(max)) was delayed by 1.25 hours; maximum concentration (C(max)) and area under the curve (AUC) were increased, with reduced interindividual variability at higher doses of BAY 59-7939. Compared with baseline, BAY 59-7939 resulted in a relative increase in maximum prothrombin time (PT) prolongation of 44% (10 mg) and 53% (20 mg) in the fasted state, compared with 53% and 83% after food. Time to maximum PT prolongation was delayed by 0.5 to 1.5 hours after food, with no relevant influence of food type. No significant difference in C(max) and AUC was observed with coadministration of BAY 59-7939 and ranitidine or antacid.

Old and new anticoagulant drugs: a minireview

Abstract The limits of traditional anticoagulants, such as heparin and warfarin, have prompted the search for new agents for prophylaxis and treatment of arterial and venous thromboembolism, including factor Xa and thrombin inhibitors. These agents can be given orally, and their most significant advantage is that no laboratory monitoring is needed. The anti-Xa inhibitor rivaroxaban and the direct thrombin inhibitor dabigatran etexilate are licensed for prophylaxis of venous thromboembolism (VTE) in high-risk orthopedic surgery. They are at least as safe and effective as heparins but much more expensive. Dabigatran, rivaroxaban, and other agents currently in the pipeline of clinical development have the potential to replace warfarin in the two most frequent indications for anticoagulation, i.e. secondary prophylaxis of VTE and atrial fibrillation. Prevention and treatment of coronary artery thrombosis in patients with ischemic heart disease is another area of investigation for the role of new anticoagulants. These drugs have the potential to meet some currently unmet needs of traditional anticoagulants, but available clinical data warrant confirmation and expansion. Lack of specific antidotes for anticoagulation reversal and the high cost are important limitations of their use.

Update on Rivaroxaban

Anticoagulants are recommended for the prevention and treatment of venous thromboembolism (VTE). The new anticoagulants which target specific factors in the coagulation cascade offer the advantage that they can be administered orally. These drugs seek to offer safe anticoagulation without the need for regular monitoring and frequent dose adjustment. Some of these newer drugs are in the advanced stages of clinical trials or have already completed them and thereby aim to provide more options in the management of thromboembolism. In the present review we discuss the currently available evidence supporting the use of these new anticoagulants, in particular rivaroxaban.

M118, a novel low-molecular weight heparin with decreased polydispersity leads to enhanced anticoagulant activity and thrombotic occlusion in ApoE knockout mice

Heparin and low-molecular weight heparin (LMWH) are complex, heterogeneous polysaccharides used in the treatment of arterial and venous thrombosis. M118 is a novel LMWH with low polydispersity and pronounced anti-Xa and anti-thrombin (IIa) activity as compared to current LMWHs. To determine if M118 is effective in preventing thrombosis in the setting of a vascular plaque, apolipoprotein E knockout mice fed a high fat diet were injected with M118, enoxaparin, unfractionated heparin, or saline control and examined for arterial thrombosis using a rose bengal laser induced carotid artery injury model. M118 significantly increased the time to occlusion as compared to control and unfractionated heparin but not compared to enoxaparin although fewer M118 treated animals had any vascular occlusion present at the time of protocol completion. Platelet-neutrophil aggregates were studied by flow cytometry and were found to be decreased with M118 as compared to enoxaparin. This is the first published report examining M118, a novel LMWH designed to have low polydispersity and enhanced anticoagulant activity. In an animal model of vascular plaque, M118 is a potent inhibitor of arterial thrombosis and, despite lower in vivo anti-Xa and anti-IIa activity levels, M118 was superior to UFH in the prevention of arterial thrombosis.

Case files of the Medical Toxicology Fellowship at Banner Good Samaritan Medical Center in Phoenix, AZ: a non-warfarin anticoagulant overdose

A 50-year-old man presented to the emergency department (ED) following an overdose of his "blood thinners." The patient had become increasingly depressed over financial concerns, prompting a suicide attempt. He declined to provide any details regarding his current medications or his past medical history. A review of the computerized medical record, however, revealed he had a Factor V Leiden mutation with multiple venothromboembolic events. He previously had an inferior vena cava filter placed, and had received tissue plasminogen activator (tPA) for a cerebrovascular accident. A toxicology consult was obtained in the ED.

A new era for anticoagulants

Selective inhibitors of specific coagulation factors represent a new class of antithrombotic agents, designed to overcome the limitations of traditional anticoagulants. Available clinical studies indicate that the most promising new anticoagulants are those selectively targeting factor Xa and thrombin. Typically, the standard steps for clinical evaluation of new anticoagulants are thromboprophylaxis in high risk orthopedic surgery, followed by treatment of established venous thromboembolism, nonvalvular atrial fibrillation and acute coronary syndromes. These agents - that have the potential to be more effective and easier to use than conventional drugs such as heparins and vitamin K antagonists - will greatly expand our armamentarium for the prevention and treatment of arterial and venous thromboembolism. The current knowledge on these antithrombotic agents is summarized in this review, particularly focusing on the early results of clinical trials.

Blood coagulation: hemostasis and thrombin regulation

Perioperative bleeding is a major challenge particularly because of increasing clinical use of potent antithrombotic drugs. Understanding current concepts of coagulation is important in determining the preoperative bleeding risk of patients, and in managing hemostatic therapy perioperatively. The serine protease thrombin plays pivotal roles in the activation of additional serine protease zymogens (inactive enzymatic precursors), cofactors, and cell-surface receptors. Thrombin generation is closely regulated to locally achieve rapid hemostasis after injury without causing uncontrolled systemic thrombosis. During surgery, there are major disturbances in coagulation and inflammatory systems because of hemorrhage/hemodilution, blood transfusion, and surgical stresses. Postoperative bleeding often requires allogeneic blood transfusions, which support thrombin generation and hemostasis. However, procoagulant activity and inflammation are increased postoperatively; thus, antithrombotic therapy may be required to prevent perioperative thrombotic complications. There have been significant advances in the management of perioperative hemostasis and thrombosis because of the introduction of novel hemostatic and antithrombotic drugs. However, a limitation of current treatment is that conventional clotting tests do not reflect the entire physiological processes of coagulation making optimal pharmacologic therapy difficult. Understanding the in vivo regulatory mechanisms and pharmacologic modulation of thrombin generation may help control bleeding without potentially increasing prothrombotic risks. In this review, we focus on the regulatory mechanisms of hemostasis and thrombin generation using multiple, simplified models of coagulation.

Antithrombotic potential of GW813893: a novel, orally active, active-site directed factor Xa inhibitor

BACKGROUND

Factor Xa (FXa) has been a target of considerable interest for drug development efforts aimed at suppressing thrombosis. In this report, a new orally active, small molecule, active-site directed FXa inhibitor, GW813893, has been profiled in a succession of in vitro and in vivo assays involved in its preclinical characterization as a potential antithrombotic therapeutic.

METHODS

In vitro profiling of GW813893 consisted of assessing its inhibitory potential against FXa and a broad panel of related and unrelated enzymes and receptors. Additionally, the FXa inhibition potential of GW813893 was assessed in prothrombinase and plasma-based clotting assays. In vivo characterization of GW813893 consisted of thrombosis studies in a rat inferior vena cava model, a rat carotid artery thrombosis model, and a rabbit jugular thrombosis model. Bleeding studies were conducted in a rat tail transection model. Ex vivo determinations of compound effects on FX and clotting activity were also undertaken.

RESULTS

GW813893 was more than 90-fold selective over all enzymes tested, and it inhibited FXa and prothrombinase activity with a Ki of 4.0 nM and 9.7 nM, respectively. In vivo, GW813893 concentration-dependently suppressed thrombotic activity in all models tested. The antithrombotic activity correlated with the suppression of plasma-based clotting activity and the inhibition of plasma FX activity (P < 0.02). Over the antithrombotic dose-range, an increased bleeding diathesis was not observed.

CONCLUSION

These experiments demonstrate that GW813893 is a potent, selective, orally active inhibitor of FXa. The data suggest that GW813893 has robust antithrombotic potential at doses that have no detectable hemostasis liability. Collectively, the profile suggests that GW813893 has the preclinical pharmacology underpinnings of an oral antithrombotic therapeutic.

Structure-activity relationships of anthranilamide-based factor Xa inhibitors containing piperidinone and pyridinone P4 moieties

Introduction of the phenyl piperidinone and phenyl pyridinone P4 moieties in the anthranilamide scaffold led to potent, selective, and orally bioavailable inhibitors of factor Xa. Anthranilamide 28 displayed comparable efficacy to apixaban in the rabbit arteriovenous-shunt (AV) thrombosis model.

Dalteparin vs low-dose unfractionated heparin for prophylaxis against clinically evident venous thromboembolism in acute traumatic spinal cord injury: a retrospective cohort study

BACKGROUND

When venous thromboembolism (VTE) includes deep-vein thrombosis (DVT) and pulmonary embolism (PE), patients with acute traumatic spinal cord injury (SCI) have the highest incidence of VTE among all hospitalized groups, with PE the third most common cause of death. Although low-molecular-weight heparin (LMWH) outperforms low-dose unfractionated heparin (LDUH) in other patient populations, the evidence in SCI remains less robust.

OBJECTIVE

To determine whether the efficacy for LMWH shown in previous SCI surveillance studies (eg, routine Doppler ultrasound) would translate into real-world effectiveness in which only clinically evident VTE is investigated (ie, after symptoms or signs present).

METHODS

A retrospective cohort study was conducted of 90 patients receiving LMWH dalteparin (5,000 U daily) or LDUH (5,000 U twice daily) for VTE prophylaxis after acute traumatic SCI. The incidence of radiographically confirmed VTE was primarily analyzed, and secondary outcomes included complications of bleeding and heparin-induced thrombocytopenia.

RESULTS

There was no statistically significant association (p = 0.7054) between the incidence of VTE (7.78% overall) and the type of prophylaxis received (LDUH 3/47 vs dalteparin 4/43). There was no significant differences in complications, location of VTE, and incidence of fatal PE. Paraplegia (as opposed to tetraplegia) was the only risk factor identified for VTE.

CONCLUSIONS

There continues to be an absence of definitive evidence for dalteparin (or other LMWH) over LDUH as the choice for VTE prophylaxis in patients with SCI. Novel approaches to VTE prophylaxis are urgently required for this population, whose risk of fatal PE has not decreased over the last 25 years.

A phase II study of the oral factor Xa inhibitor LY517717 for the prevention of venous thromboembolism after hip or knee replacement

BACKGROUND

LY517717 is an oral direct inhibitor of activated factor X that is currently under clinical development.

OBJECTIVES

The aims of this proof-of-concept study in patients undergoing total knee replacement (TKR) or total hip replacement (THR) were to determine whether LY517717 can safely reduce the risk of venous thromboembolism (VTE) and to identify at least one dose of LY517717 that is non-inferior to enoxaparin.

METHODS

In a double-blind, parallel-arm, dose-ranging study, patients undergoing TKR or THR were randomly allocated to receive once-daily oral LY517717 (25, 50, 75, 100, 125 or 150 mg), started 6-8 h after wound closure, or s.c. enoxaparin, 40 mg, started in the evening before surgery. The primary efficacy endpoint was the composite of deep venous thrombosis (DVT), detected by mandatory bilateral venography performed at the end of the study treatment (between days 5 and 9), and objectively confirmed symptomatic DVT and/or pulmonary embolism (PE), occurring during the treatment period. The combination of major and minor bleeding was the primary safety endpoint.

RESULTS

Five hundred and seven patients received at least one dose of LY517717 or enoxaparin (safety population). Three hundred and ninety-one patients had evaluable bilateral venography or experienced a clinical DVT and/or PE (primary efficacy population). LY517717 treatment resulted in a dose-dependent decrease in the incidence of thromboembolic events (P = 0.0001). The incidences of VTE with 100, 125, and 150 mg of LY517717 were 19%, 19% and 16%, respectively, compared to 21% with enoxaparin. The efficacies of 100-mg, 125-mg and 150-mg doses of LY517717 were non-inferior to that of enoxaparin according to prespecified criteria. Bleeding events were uncommon in both LY517717 and enoxaparin patients.

CONCLUSIONS

Doses of 100, 125 and 150 mg of LY517717 are non-inferior to enoxaparin for the prevention of VTE after TKR or THR, and are associated with similar low rates of bleeding.

Regulation of Thrombin Activity—Pharmacologic and Structural Aspects

Thrombin is an essential serine protease for survival. Since the discovery of heparin in the early twentieth century, significant advances have been made in the understanding of thrombin structure and function in coagulation system. Endogenous anticoagulant proteins in blood tightly regulate thrombin generation, but additional anticoagulant agents may be necessary to suppress excessive thrombin formation or defective anticoagulant proteins. Despite the availability of an array of anticoagulant agents based on chemical and biological engineering technologies, anticoagulation therapy remains a challenge for clinicians in terms of balancing bleeding and thrombosis. The aim of this article is to review endogenous serine protease inhibitors and novel antithrombotic agents in relation to pharmacologic regulation of thrombin.

Exploration of potential prodrugs of RWJ-445167, an oxyguanidine-based dual inhibitor of thrombin and factor Xa

Compound 2 (RWJ-445167; 3DP-10017), a dual inhibitor of thrombin and factor Xa, was advanced into human clinical studies. However, its oral bioavailability in humans proved to be below acceptable limits. To address this issue, we explored a prodrug approach involving numerous guanidine derivatives. Prodrug candidates of classes A (carbamate derivatives), B (imidate derivatives), and C (alkyl and acyl derivatives), compounds 3-6, were synthesized and evaluated for anticoagulant activity at 2 h after oral administration to rats. In comparison to the parent drug (2), little worthwhile improvement was observed for the prodrug candidates.

Serum amyloid A in autoimmune thrombosis

The objectives of this study were (1) to determine how levels of serum amyloid A (SAA), high sensitivity C-reactive protein (CRP) and interleukin-6 (IL-6) correlate to autoimmune diseases in patients with or without thrombosis, and (2) to discuss the parameters that influence the relative SAA values. SAA, CRP and IL-6 concentrations were determined by enzyme linked immunosorbent assay (ELISA). 84 patients with secondary antiphospholipid syndrome (SAPS), primary antiphospholipid syndrome (PAPS), systemic lupus erythematosus with antiphospholipid antibodies (SLE+aPL), SLE, venous thrombosis (VT), arterial thrombosis (AT) were compared to healthy donors (n=60). The percentages of patients above cut-off were highest in the SAPS, SLE and SLE+aPL groups. Significant differences were observed between healthy donors and inflammatory groups of patients (SAPS and SLE+aPL) in all three measured parameters. SAA and CRP were shown to be correlated to a greater extent in SAPS patients than SLE+aPL patients. In summary, this cross-sectional, retrospective, small study and accompanying clinical considerations limit the ability to make definite conclusions. SAA would not serve as a useful marker for venous, arterial thrombosis or PAPS (pro-coagulant events). It could however, be a good predictor of progression from a non-inflammatory thrombotic condition to an inflammatory one.

Oral Anticoagulants in Development

Current anticoagulant provision is dominated by parenteral heparin and oral warfarin, which act by inhibiting several steps of the coagulation pathway indirectly. Recent research efforts have focused on the identification of small molecule inhibitors of the coagulation enzymes as novel therapies for thrombotic disorders. There has been particular success in developing nonpeptidic, orally available, small molecules to directly inhibit the key proteases, factor IIa and factor Xa. Of the new oral anticoagulants in development, the two agents in the most advanced stage are dabigatran etexilate (BIBR 1048) and rivaroxaban (BAY 59-7939), which inhibit factor IIa and factor Xa, respectively. Other agents in the early stages of development include several Xa inhibitors (LY-517717, YM150, DU-176b and apixaban [BMS-562247]), a factor IXa inhibitor (TTP889), and an orally active glycosaminoglycan enhancer (odiparcil [SB-424323]), which indirectly enhances thrombin inhibition via heparin cofactor II. Results have been reported from important, phase II dose-finding studies, and a number of registration-track phase III studies have been initiated, reflecting the drive towards potentially more effective, but primarily safer and more convenient therapies for the prevention and treatment of venous and arterial thrombosis. Indeed, two unmet needs for anticoagulation that can be easily identified are safety and ease of use. Safety relates primarily to the incidence of major bleeding and this remains the key concern of orthopaedic surgeons, over and above any efficacy advantage, and convenience of use, which centres on oral administration replacing the need for injections. The clinical development of these new anticoagulants is following the well tested strategy of dose-ranging and registration studies in major orthopaedic surgery, prior to development in arterial indications. There are a number of subtle issues, including the timing of the first perioperative dose, duration of prophylactic treatment and definition/assessment of study endpoints that can influence study outcome and require careful consideration when evaluating study results with new agents and in the comparison with established agents, and which are considered in this review. It is anticipated that over the next 3 years, at least one of these agents will be successfully licensed for the prevention of venous thromboembolism after major orthopaedic surgery, which will act as a springboard for the gradual replacement of current anticoagulants.

Oral, direct Factor Xa inhibition with BAY 59-7939 for the prevention of venous thromboembolism after total hip replacement

BACKGROUND

Joint replacement surgery is an appropriate model for dose-ranging studies investigating new anticoagulants.

OBJECTIVES

To assess the efficacy and safety of a novel, oral, direct factor Xa (FXa) inhibitor--BAY 59-7939--relative to enoxaparin in patients undergoing elective total hip replacement.

METHODS

In this double-blind, double-dummy, dose-ranging study, patients were randomized to oral BAY 59-7939 (2.5, 5, 10, 20, or 30 mg b.i.d.), starting 6-8 h after surgery, or s.c. enoxaparin 40 mg once daily, starting on the evening before surgery. Treatment was continued until mandatory bilateral venography was performed 5-9 days after surgery.

RESULTS

Of 706 patients treated, 548 were eligible for the primary efficacy analysis. The primary efficacy endpoint was the incidence of any deep vein thrombosis, non-fatal pulmonary embolism, and all-cause mortality; rates were 15%, 14%, 12%, 18%, and 7% for BAY 59-7939 2.5, 5, 10, 20, and 30 mg b.i.d., respectively, compared with 17% for enoxaparin. The primary efficacy analysis did not demonstrate any significant trend in dose-response relationship for BAY 59-7939. The primary safety endpoint was major, postoperative bleeding; there was a significant increase in the frequency of events with increasing doses of BAY 59-7939 (P = 0.045), but no significant differences between individual BAY 59-7939 doses and enoxaparin.

CONCLUSIONS

When efficacy and safety were considered together, the oral, direct FXa inhibitor BAY 59-7939, at 2.5-10 mg b.i.d., compared favorably with enoxaparin for the prevention of venous thromboembolism in patients undergoing elective total hip replacement.

New treatment options for stroke prevention in atrial fibrillation

Atrial fibrillation (AF) is the most common arrhythmia requiring treatment. Its most devastating consequence is thromboembolic stroke. Therapy with warfarin is indicated in most patients, as it has been shown conclusively to reduce the risk of stroke. Aspirin is an inferior alternative except in certain low-risk patients or for patients with an absolute contraindication to warfarin. Guidelines have been published for the administration of antithrombotic therapy in AF, but many patients who are candidates for anticoagulation do not receive this therapy. Even as this therapy is under-utilized, the indication for anticoagulation is expanding. Indefinite continuation of anticoagulation should be considered in higher-risk patients despite the appearance that sinus rhythm has been restored because asymptomatic (or silent) AF occurs frequently. Newer agents that offer substantial benefit over warfarin are being developed and would enhance compliance with anticoagulation in AF if these novel therapies prove to be safe and equivalent to warfarin in efficacy.