Factor Xa or thrombin: is thrombin a better target?

Comparative effectiveness and safety of direct acting oral anticoagulants in nonvalvular atrial fibrillation for stroke prevention: a systematic review and meta-analysis

PURPOSE

To systematically review available evidence of indirect comparisons from RCTs and direct comparisons from observational studies regarding the comparative effectiveness and safety of DOACs in patients with AF.

METHODS

Electronic databases including EMBASE, MEDLINE, and PUBMED were searched up to June 5th, 2020. Primary endpoints included effectiveness (stroke or systemic embolism [SE]) and safety (major bleeding) outcomes. Bucher methods and random-effects models were conducted for indirect and direct comparisons among DOACs, respectively. Ranking probability analyses and the number needed to treat for net effect (NNTnet) were applied.

RESULTS

A total of 36 studies, involving 7 RCTs (n = 60,292 patients) and 29 observational studies (n = 1,164,821 patients), were included for analyses. Regarding the risk of stroke/SE, no significant differences were found from indirect comparisons of RCTs among the DOACs. For major bleeding, apixaban tended to be safer than rivaroxaban and dabigatran based on both direct and indirect comparisons (all p < 0.05; evidence quality: very low to moderate). Ranking probability analysis showed that apixaban had a high probability of being the best treatment in decreased risk of stroke/SE and major bleeding (80.30% and 91.30%, respectively). Likewise, apixaban was found to have the highest net clinical benefit (0.02, 95% CI: 0.014-0.029) and smallest NNTnet (48, 95% CI: 35-74).

CONCLUSIONS

Apixaban appeared to have a favorable effectiveness-safety profile compared with the other DOACs in AF for stroke prevention, based on evidence from both direct and indirect comparisons. However, additional high-quality evidence is needed to support firm recommendations on clinical decision-making.

Prolongation of clot lysis time by a direct thrombin inhibitor melagatran mediated by paradoxical enhancement of thrombin generation: comparison with a direct factor Xa inhibitor edoxaban

Previously, we reported that a direct thrombin inhibitor melagatran paradoxically increased thrombin generation in human plasma in the presence of thrombomodulin. The aim of this study is to test the hypothesis that melagatran may exert a deleterious effect on tissue-type plasminogen activator (t-PA)-induced fibrinolysis via enhancement of thrombin generation and subsequent activation of thrombin-activatable fibrinolysis inhibitor (TAFI) and factor XIII (FXIII). Clot formation in human plasma containing t-PA and thrombomodulin was induced by tissue factor. The absorbance at 405 nm was measured to obtain clot lysis time. Effects of melagatran and a factor Xa inhibitor edoxaban on clot lysis time were determined. In the presence of thrombomodulin, melagatran significantly prolonged clot lysis time, but edoxaban shortened it. In the absence of thrombomodulin, melagatran did not inhibit fibrinolysis. Prolongation of clot lysis time by melagatran was reversed by activated protein C (which suppressed thrombin generation increased by melagatran) and a TAFIa inhibitor. Melagatran significantly suppressed plasmin generation, while edoxaban significantly increased it. However, both melagatran and edoxaban suppressed FXIII activation. In the clot formed in the presence of melagatran and edoxaban, the fibrin fibre was thin compared with control, showing no clear difference in the clot structures between melagatran and edoxaban. These results indicated that melagatran, not edoxaban, prolonged clot lysis time through the paradoxical enhancement of thrombin generation, and subsequent TAFI activation and inhibition of plasmin generation. Neither FXIII activation nor change in fibrin clot structure contributed to the inhibition of fibrinolysis by melagatran.

The direct oral anticoagulants rivaroxaban and dabigatran do not inhibit orthotopic growth and metastasis of human breast cancer in mice

Essentials Factor Xa (FXa)-targeting direct oral anticoagulants (DOACs) reduce venous thromboembolism (VTE) The effects of FXa-targeting DOACs on cancer progression remain to be studied In xenograft models, a FXa-targeting DOAC did not inhibit breast cancer growth and metastasis A thrombin-targeting DOAC, dabigatran, also did not inhibit breast cancer growth and metastasis ABSTRACT: Background Factor Xa-targeting DOACs were recently found to reduce recurrent VTE efficiently in cancer patients when compared to the standard treatment with low-molecular-weight heparins (LMWHs). While the anticancer effects of LMWHs have been extensively studied in preclinical cancer models, the effects of FXa-targeting DOACs on cancer progression remain to be studied. Objective We investigated whether the FXa-targeting DOAC rivaroxaban and the thrombin-targeting DOAC dabigatran etexilate (DE) affected human breast cancer growth and metastasis in orthotopic xenograft models. Methods/results Mice that were put on a custom-made chow diet supplemented with rivaroxaban (0.4 or 1.0 mg/g diet) or dabigatran etexilate (DE) (10 mg/g diet) showed prolonged ex vivo coagulation times (prothrombin time [PT] and activated partial thromboplastin time [aPTT] assay, respectively). However, rivaroxaban and DE did not inhibit MDA-MB-231 tumor growth and metastasis formation in lungs or livers of 7-week-old fully immunodeficient NOD/SCID/ƴC-/- (NSG) mice. Comparable data were obtained for rivaroxaban-treated mice when using NOD-SCID mice. Rivaroxaban and DE treatment also did not significantly inhibit tumor growth and metastasis formation when using another human triple negative breast cancer (TNBC) cell line (HCC1806) in NOD-SCID mice. The FXa and thrombin-induced gene expression of the downstream target CXCL8 in both cell lines, but FXa and thrombin, did not significantly stimulate migration, proliferation, or stemness in vitro. Conclusion Although effectively inhibiting coagulation, the DOACs rivaroxaban and DE did not inhibit orthotopic growth and metastasis of human TNBC. It remains to be investigated whether DOACs exert antitumorigenic effects in other types of cancer.

Design, synthesis and biological evaluation of anthranilamide derivatives as potential factor Xa (fXa) inhibitors

Factor Xa (fXa) is a crucial player in various thromboembolic disorders. Inhibition of fXa can provide safe and effective antithrombotic effects. In this study, a series of anthranilamide compounds were designed by utilizing structure-based design strategies. Optimization at P1 and P4 groups led to the discovery of compound 16g: a highly potent, selective fXa inhibitor with pronounced in vitro anticoagulant activity. Moreover, 16g also displayed excellent in vivo antithrombotic activity in the rat venous thrombosis (VT) and arteriovenous shunt (AV-SHUNT) models. The bleeding risk evaluation showed that 16g had a safer profile than that of betrixaban at 1 mg/kg and 5 mg/kg dose. Additionally, 16g also exhibited satisfactory PK profiles. Eventually, 16g was selected to investigate its effect on hypoxia-reoxygenation- induced H9C2 cell viability. MTT results showed that H9C2 cell viability can be remarkably alleviated by 16g.

Platelet-targeted dual pathway antithrombotic inhibits thrombosis with preserved hemostasis

Despite advances in antithrombotic therapy, the risk of recurrent coronary/cerebrovascular ischemia or venous thromboembolism remains high. Dual pathway antithrombotic blockade, using both antiplatelet and anticoagulant therapy, offers the promise of improved thrombotic protection; however, widespread adoption remains tempered by substantial risk of major bleeding. Here, we report a dual pathway therapeutic capable of site-specific targeting to activated platelets and therapeutic enrichment at the site of thrombus growth to allow reduced dosing without compromised antithrombotic efficacy. We engineered a recombinant fusion protein, SCE5-TAP, which consists of a single-chain antibody (SCE5) that targets and blocks the activated GPIIb/IIIa complex, and tick anticoagulant peptide (TAP), a potent direct inhibitor of activated factor X (FXa). SCE5-TAP demonstrated selective platelet targeting and inhibition of thrombosis in murine models of both carotid artery and inferior vena cava thrombosis, without a significant impact on hemostasis. Selective targeting to activated platelets provides an attractive strategy to achieve high antithrombotic efficacy with reduced risk of bleeding complications.

Design, synthesis and biological evaluation of novel 2,3-dihydroquinazolin- 4(1H)-one derivatives as potential fXa inhibitors

Coagulation factor Xa (fXa) is a particularly attractive target for the development of effective and safe anticoagulants. In this study, novel 2,3-dihydroquinazolin-4(1H)-one derivatives were designed as potential fXa inhibitors based on anthranilamide structure which has been reported in our previous research. The experimental data showed that most of the designed compounds exhibited significant in vitro potency against fXa. Among them, compound 8e displayed the strongest potency against fXa with the IC₅₀ value of 21 nM and highly selectivity versus thrombin (IC₅₀ = 67 μM) and excellent in vitro antithrombotic activity with its 2 × PT value of 1.2 μM and 2 × aPTT value of 0.6 μM. In addition, 8e also displayed excellent in vivo antithrombotic activity in the rat arteriovenous shunt (AV-SHUNT) model. The bleeding risk evaluation showed that 8e had a similar safety profile as that of betrixaban. All results demonstrated that compound 8e could be considered as a potential fXa inhibitor for the prevention and treatment of thromboembolic diseases.

Heparin: Past, Present, and Future

Heparin, the most widely used anticoagulant drug in the world today, remains an animal-derived product with the attendant risks of adulteration and contamination. A contamination crisis in 2007-2008 increased the impetus to provide non-animal-derived sources of heparin, produced under cGMP conditions. In addition, recent studies suggest that heparin may have significant antineoplastic activity, separate and distinct from its anticoagulant activity, while other studies indicate a role for heparin in treating inflammation, infertility, and infectious disease. A variety of strategies have been proposed to produce a bioengineered heparin. In this review, we discuss several of these strategies including microbial production, mammalian cell production, and chemoenzymatic modification. We also propose strategies for creating "designer" heparins and heparan-sulfates with various biochemical and physiological properties.

An Integrative Thrombosis Network: Visualization and Topological Analysis

A comprehensive understanding of the integrative nature of the molecular network in thrombosis would be very helpful to develop multicomponent and multitarget antithrombosis drugs for use in traditional Chinese medicine (TCM). This paper attempts to comprehensively map the molecular network in thrombosis by combining platelet signaling, the coagulation cascade, and natural clot dissolution systems and to analyze the topological characteristics of the network, including the centralities of nodes, network modules, and network robustness. The results in this research advance understanding of functions of proteins in the thrombosis network and provide a reference for predicting potential therapeutic antithrombotic targets and evaluating their influence on the network.

Physician's fear of anticoagulant therapy in nonvalvular atrial fibrillation

Despite the availability of predictive tools and treatment guidelines, anticoagulant therapies are underprescribed and many patients are undertreated for conditions that predispose to thromboembolic complications, including stroke. This review explores reasons for which physicians fear that the risks of anticoagulation may be greater than the potential benefit. The results of numerous clinical trials confirm that patients benefit from judiciously managed anticoagulation and that physicians can take various approaches to minimize risk. Use of stratification scores for patient selection and accurate estimation of stroke risk may improve outcomes; bleeding risk is less important than stroke risk. Adoption of newer anticoagulants with simpler regimens may help physicians allay their fears of anticoagulant use in patients with atrial fibrillation. These fears, although not groundless, should not overtake caution and hinder the delivery of appropriate evidence-based care.

Managing New Oral Anticoagulants in the Perioperative and Intensive Care Unit Setting

Managing patients in the perioperative setting receiving novel oral anticoagulation agents for thromboprophylaxis or stroke prevention with atrial fibrillation is an important consideration for clinicians. The novel oral anticoagulation agents include direct Factor Xa inhibitors rivaroxaban and apixaban, and the direct thrombin inhibitor dabigatran. In elective surgery, discontinuing their use is important, but renal function must also be considered because elimination is highly dependent on renal elimination. If bleeding occurs in patients who have received these agents, common principles of bleeding management as with any anticoagulant (including the known principles for warfarin) should be considered. This review summarizes the available data regarding the management of bleeding with novel oral anticoagulation agents. Hemodialysis is a therapeutic option for dabigatran-related bleeding, while in vitro studies showed that prothrombin complex concentrates are reported to be useful for rivaroxaban-related bleeding. Additional clinical studies are needed to determine the best method for reversal of the novel oral anticoagulation agents when bleeding occurs.

Haemodialysis before emergency surgery in a patient treated with dabigatran

Novel oral anticoagulants (NOAs) which directly inhibit thrombin (dabigatran) or factor Xa (rivaroxaban and apixaban) have recently been developed. We report the first case of perioperative management of a patient treated with dabigatran requiring haemodialysis before emergency surgery. A 62-yr-old woman visited the emergency department for a left bi-malleolar ankle fracture; she had a past medical history of severe ischaemic cardiomyopathy, alcoholic cirrhosis Child B, and moderate chronic renal insufficiency. The patient was treated with dabigatran for a left ventricular aneurysm with thrombus. Cutaneous manifestation of a voluminous haematoma required emergency surgery. Blood tests revealed dabigatran anticoagulant activity of 123 ng ml(-1) (therapeutic values: 85-200 ng ml(-1)), activated partial thromboplastin time of 63 s, and a prothrombin ratio of 68%, indicating that dabigatran disturbed coagulation. We decided to perform emergency haemodialysis before surgery. After 2 h, the anticoagulant activity of dabigatran was 11 ng ml(-1), allowing surgery. Surgery proceeded without any problems and the postoperative period was unremarkable. This case highlights the difficulties for the anaesthesiologist regarding emergency perioperative management of patients treated with NOAs and confirms the efficacy of haemodialysis in cases of dabigatran treatment. NOAs should be prescribed with caution, especially for patients with renal or hepatic disease, at least as long as no antagonist is available. In cases of deferred operative urgency in haemodynamically stable patients treated with dabigatran, haemodialysis should be considered to reverse dabigatran's anticoagulant effects.

Prevention and treatment of venous thromboembolism with new oral anticoagulants: a practical update for clinicians

Traditional anticoagulants, such as warfarin and enoxaparin, have several limitations, including parenteral administration, need for laboratory monitoring, and ongoing dose adjustment, which may limit optimal patient care. Newer oral anticoagulants, such as direct thrombin inhibitors (e.g., dabigatran etexilate) and direct factor Xa inhibitors (e.g., rivaroxaban, apixaban, and edoxaban), have been developed to overcome these drawbacks, and thereby improve patient care. Several of these agents have been approved for use in the prevention and treatment of venous and/or systemic thromboembolism. The objective of this paper is to provide an overview of the available clinical trial data for these new oral anticoagulants in the prevention and treatment of venous thromboembolism and a practical update for clinicians.

[Reversal for heparins and new anticoagulant treatments]

Even with unfractionated heparin or derivates, the reversal of pharmacologic anticoagulation is crucial in anticoagulated patients developing a life-threatening bleeding or scheduled for an emergency procedure. The antagonisation of unfractionated heparin is well codified: each milligram of protamine sulfate antagonizes 100 IU of heparin. Measurement of thrombin time reflects the anti-IIa effect of heparin and has to be monitored immediately and 1hour after the injection of protamine. The required dose of protamine sulfate depends on dosage and time of LMWH administration, although no clinical study supports these data. To date, there is no effective antidote for new anticoagulants (fondaparinux and other pentasaccharides, direct thrombin inhibitors, direct anti-Xa inhibitors). Some preliminary studies suggest the effectiveness of recombinant activated factor VII for pentasaccharides and activated or not Prothrombin Complex Concentrates and recombinant activated factor VII for oral anti-Xa and anti-IIa agents. Therefore, while the characteristics of these new anticoagulants could increase the comfort and improve the compliance, their development needs to ascertain the lack of increase in bleeding complications and the need for a safe and effective antidote.

Acute management of bleeding in patients on novel oral anticoagulants

Novel oral anticoagulants that directly inhibit thrombin (dabigatran) or factor Xa (rivaroxaban, apixaban) are currently available for prevention of venous thromboembolism (VTE) after orthopaedic surgery, treatment of acute VTE, and prevention of arterial thromboembolism in non-valvular atrial fibrillation. These agents offer advantages over VKAs, including rapid onset, shorter half-lives, fewer drug interactions, and lack of need for routine monitoring. However, there are no established agents to reverse their anticoagulant effect. We review the risk of bleeding with the novel oral anticoagulants and the limitations of conventional coagulation assays for measuring anticoagulant effect. We provide an approach to the management of patients with bleeding complications with evidence for various interventions for reversal, where available.

Antithrombotic strategies to reduce adverse clinical outcomes in patients with acute coronary syndrome

Acute coronary syndromes (ACSs), which include ST-segment elevation myocardial infarction, non-ST-segment elevation myocardial infarction, and unstable angina, present a considerable burden to the health care system. Furthermore, many patients with a first ACS event will develop another event within 1 year. To prevent this, higher-risk patients with ACS are revascularized when possible after presentation and then prescribed ongoing treatments to prevent recurrent vascular events. These include agents that prevent platelet aggregation and subsequent coronary thrombosis. However, some patients will develop a recurrent event despite treatment with these drugs, prompting a search for additional strategies to augment the effectiveness of current therapies. One such approach is add-on therapy with oral anticoagulant drugs. These agents may act synergistically with antiplatelet agents in preventing thrombosis. In conclusion, new oral anticoagulants might represent an attractive therapeutic strategy if they do not result in unacceptable bleeding.

Pharmacokinetic and pharmacodynamic effects of comedication of clopidogrel and dabigatran etexilate in healthy male volunteers

Purpose

To evaluate the pharmacokinetic and pharmacodynamic effects of concomitant administration of single loading doses of clopidogrel or multiple doses of clopidogrel with multiple doses of dabigatran etexilate.

Methods

This was an open-label trial in healthy male subjects. In part 1 (pilot, n = 8) and part 3 (n = 12), a single dose of clopidogrel (300 or 600 mg, respectively) was given concomitantly with dabigatran etexilate at steady state; part 2 was a randomized, multiple-dose, crossover study with the test treatment being clopidogrel at steady state [300 mg loading dose on day 1, then 75 mg once daily (qd)] with concomitant dabigatran.

Results

Bioavailability was moderately increased when a loading dose of clopidogrel (300 mg in part 1 and 600 mg in part 3) was administered concomitantly with dabigatran etexilate 150 mg twice daily (bid). Test/reference ratios for AUC_τ,ss were 135% (90% CI 107–169%) and 132% (90% CI 112–156%), respectively. Steady-state dosing of clopidogrel 75 mg qd and dabigatran etexilate 150 mg bid (part 2) demonstrated minor effects on dabigatran pharmacokinetics (AUC_τ,ss ratio test/reference: 91.9%, 90% CI 78.7–107%) or its pharmacokinetic/pharmacodynamic relationships (activated partial thromboplastin time, ecarin clotting time, thrombin time). Similarly, clopidogrel bioavailability remained unchanged by chronic administration of dabigatran etexilate (part 3: ratio test/reference for AUC₀₋₂₄ was 103%; 90% CI 80.3–131%), as did its pharmacodynamic effects on the inhibition of platelet aggregation.

Conclusions

When given concomitantly, dabigatran etexilate and clopidogrel at clinically relevant doses did not appear to have significant effects on the pharmacokinetic and pharmacodynamic profiles of either agent.

Electronic supplementary material

The online version of this article (doi:10.1007/s00228-012-1304-8) contains supplementary material, which is available to authorized users.

Improving long-term ACS management: is there a role for the new antiplatelets?

Acute coronary syndrome (ACS) is a major health burden, resulting in increased hospital admissions and significant morbidity and mortality. Platelet activation, which leads to thrombin generation, is highly implicated in ACS, and antiplatelet agents represent the current standard of care. Established antiplatelet agents include acetylsalicylic acid (ASA), thienopyridines (clopidogrel, ticlopidine), and glycoprotein IIb/IIIa inhibitors. Recently, antiplatelet therapy for ACS has evolved to include more potent inhibitors (e.g., prasugrel, cangrelor, and ticagrelor). During the acute phase of an acute coronary event, both anticoagulation and dual antiplatelet therapy with aspirin and a thienopyridine are guideline recommended as first-line treatment. While anticoagulation is usually limited to the acute in-patient phase, dual antiplatelet therapy is recommended for 12 months. Despite the efficacy of antiplatelet agents in ACS, in many patients the residual risk of death from cardiac events, myocardial infarction, stroke, and refractory ischemia remains high. Dual therapy (i.e., ASA or clopidogrel plus a vitamin K antagonist [VKA]), and triple therapy (two antiplatelets plus a VKA) are associated with increases in bleeding complications. New oral anticoagulants that offer a novel mechanism of action may, when added to the current standard of care, provide a more comprehensive response to thrombin generation. In this review, we examine the pathology of ACS, investigate antiplatelet therapies and describe emerging anticoagulants that may be of benefit when used as combination therapy with antiplatelet agents for secondary prevention in ACS patients.

Antithrombotic therapy for stroke prevention in atrial fibrillation and mechanical heart valves

Cardioembolic strokes account for one-sixth of all strokes and are an important potentially preventable cause of morbidity and mortality. Vitamin K antagonists (e.g., warfarin) are effective for the prevention of cardioembolic stroke in patients with atrial fibrillation (AF) and in those with mechanical heart valves but because of their inherent limitations are underutilized and often suboptimally managed. Antiplatelet therapies have been the only alternatives to warfarin for stroke prevention in AF but although they are safer and more convenient they are much less efficacious. The advent of new oral anticoagulant drugs offers the potential to reduce the burden of cardioembolic stroke by providing access to effective, safe, and more convenient therapies. New oral anticoagulants have begun to replace warfarin for stroke prevention in some patients with AF, based on the favorable results of recently completed phase III randomized controlled trials, and provide for the first time an alternative to antiplatelet therapy for patients deemed unsuitable for warfarin. The promise of the new oral anticoagulants in patients with mechanical heart valves is currently being tested in a phase II trial. If efficacy and safety are demonstrated, the new oral anticoagulants will provide an alternative to warfarin for patients with mechanical heart valves and may also lead to increased use of mechanical valves for patients who would not have received them in the past because of the requirement for long term warfarin therapy.

Reversal of antithrombotic agents

Anticoagulants are the mainstay of therapy for thromboembolic diseases. In addition to the more traditional agents, new oral anticoagulants, including dabigatran etexilate, rivaroxaban, and apixaban, have been shown to be effective across several indications. Bleeding is a serious complication associated with any anticoagulant, but many of the traditional parenteral and new oral agents do not currently have specific antidotes. This review describes available and future options for the reversal of the effects of anticoagulants, in particular the new oral agents and discusses current management strategies for bleeding events in clinical practice.

New oral anticoagulants: a view from the laboratory

The new oral anticoagulants are rapidly replacing warfarin for several indications. In contrast to warfarin, which lowers the functional levels of all of the vitamin K-dependent clotting factors, the new agents target either factor Xa or thrombin. With targeted inhibition of coagulation, the new oral anticoagulants have pharmacological, biochemical, and clinical features distinct from those of warfarin. Focusing on laboratory perspectives, this article compares and contrasts the pharmacological and biochemical properties of the new oral anticoagulants with those of warfarin and uses this information to speculate on the underlying mechanisms responsible for the clinical features that differentiate the new agents from warfarin.

Melagatran, a direct thrombin inhibitor, but not edoxaban, a direct factor Xa inhibitor, nor heparin aggravates tissue factor-induced hypercoagulation in rats

There are concerns that some anticoagulants can paradoxically increase thrombogenesis under certain circumstances. We have shown that low-dose administration of a direct thrombin inhibitor, melagatran, significantly worsens the coagulation status induced by tissue factor injection in rats. We compared the effect of inhibition of thrombin and factor Xa for their potential to aggravate tissue factor-induced coagulation in rats. Hypercoagulation was induced by the injection of 2.8 U/kg tissue factor after administration of melagatran, heparin and edoxaban in rats. Blood samples were collected 10min after tissue factor injection. Platelet numbers, thrombin-antithrombin complex concentrations and plasma compound concentrations were measured. Though a high dose of melagatran (1mg/kg, i.v.) suppressed platelet consumption and thrombin-antithrombin complex generation induced by tissue factor, lower doses of melagatran (0.01, 0.03 and 0.1mg/kg, i.v.) significantly enhanced platelet consumption and thrombin-antithrombin complex generation. In addition, although melagatran (3mg/kg, i.v.) improved coagulation status when tissue factor was given 5min after the drug administration, and 2, 4 and 8h after melagatran dosing, it deteriorated coagulation status. These results were well explained by the plasma melagatran concentration. Low concentrations (15-234ng/ml) of melagatran aggravated coagulation status whereas it was mended by high concentrations (1190ng/ml or more) of the compound. In contrast, edoxaban and heparin did not show any exacerbation under these examination conditions. These results show that subtherapeutic concentrations of melagatran are associated with coagulation pathway activation, whereas factor Xa inhibition with edoxaban has a low risk of paradoxical hypercoagulation.

Healthcare burden associated with the post-thrombotic syndrome and potential impact of the new oral anticoagulants

Deep-vein thrombosis (DVT) can have a significant impact on a patient's life. In particular, the development of post-thrombotic syndrome as a long-term complication of DVT can have devastating consequences for the individual and impose a substantial economic burden on healthcare systems. Anticoagulants are the mainstay of DVT treatment; however, the current standard of care, a parenteral anticoagulant followed by a vitamin K antagonist, is associated with complex patient management, often resulting in suboptimal therapy. New, oral anticoagulants have been developed, and a direct thrombin inhibitor--dabigatran etexilate--and two direct Factor Xa inhibitors--rivaroxaban and apixaban--have completed and/or have ongoing phase III trials in the treatment of venous thromboembolism. These agents do not have the drawbacks of the vitamin K antagonists and hold promise for more effective treatment of DVT, possibly resulting in a reduction in the incidence of post-thrombotic syndrome.

Newer antithrombotic drugs

Thromboembolic disorders are one of the disorders for which we are still on the look out for a safe and efficient drug. Despite the widespread use of antithrombotic drugs for the prevention and treatment of arterial and venous thrombosis, thromboembolic diseases continue to be a major cause of death and disability worldwide. This shows our inefficiency in searching efficacious and safe antithrombotic drugs. We have reached the basic mechanism of thrombus formation and by interrupting various steps of this mechanism, we can prevent as well as treat thromboembolic disorders. In continuation of Aspirin, now, we are using Clopidogrel, Ticlopidine and GpIIb/IIIa inhibitors (Abciximab, Tirofiban and Eptifibatide). Warfarin is an old antithrombotic drug which is still being used; but due to various side effects and drug interactions, we are bound to use newer drugs. Newer antiplatelet drugs include Prasugrel, Ticagrelor and Cangrelor, whereas newer thrombin inhibitors are Ximelgatran and Dabigatran. Apixaban is also a newer entry in this category as factor Xa inhibitor. Idrabiotaparinux is an indirect inhibitor of Xa as it accelerates the activity of antithrombin. Moreover, researches and trials for better and safe drugs are ongoing.

Novos anticoagulantes para a profilaxia do tromboembolismo venoso em cirurgias ortopédicas de grande porte

Após cerca de 50 anos de experiência com a heparina e antagonistas da vitamina K (AVK), pesquisas e estudos com novos anticoagulantes vêm evoluindo de forma crescente nos últimos anos. Embora consagrados pelo uso, os anticoagulantes tradicionais têm limitações importantes em termos de controle laboratorial, complicações, efeitos colaterais, interações com medicamentos e dieta. A heparina não fracionada (HNF) tem interação com proteínas plasmáticas e parede vascular, pode desencadear trombocitopenia induzida pela heparina (TIH), só pode ser administrada por via parenteral, exige controle laboratorial pelo teste da tromboplastina parcial ativada (TTPa), pode provocar osteoporose e alopecia quando usada por períodos prolongados e sua produção tem origem biológica. A AVK tem a vantagem de poder ser ministrada por via oral, mas o controle (feito pela razão normatizada internacional) pode ser difícil em alguns casos, já que tem início de ação demorado, janela terapêutica estreita, interação com dieta e grande número de medicamentos, pode provocar necrose de pele em portadores de deficiência de antitrombina e de proteínas C e S, e pode induzir alterações fetais quando usada na gravidez. Na década de 1980, surgiram as heparinas de baixo peso molecular, que foram uma evolução da heparina não fracionada, pois apresentaram maior biodisponibilidade, dosagem por peso corporal, sem necessidade de controle laboratorial, administração por via subcutânea, menor risco de trombocitopenia induzida pela heparina, e eficácia e segurança similares à heparina não fracionada. Na última década surgiram, então, uma série de novos anticoagulantes no mercado, os quais têm apresentado resultados promissores em várias situações de profilaxia e tratamento do tromboembolismo venoso. Nesta revisão, são apresentados as novas heparinas de baixo peso molecular, as heparinas de ultrabaixo peso molecular, os pentassacarídeos, os novos inibidores diretos do fator Xa e inibidores do fator IIa.

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.

The evolving field of stroke prevention in patients with atrial fibrillation

Vitamin K antagonists have been the standard in stroke prophylaxis in patients with atrial fibrillation for decades, but several limitations make it difficult for patients to tolerate chronic anticoagulation treatment. New drugs are under evaluation in clinical trials, including direct thrombin inhibitors and factor Xa inhibitors. Antiplatelet agents such as clopidogrel and aspirin are alternatives to warfarin for stroke prevention but have proven less efficacious in trials. The only drug to have completed a Phase III trial successfully thus far is dabigatran. The 150-mg twice-a-day dose was superior to warfarin in efficacy and similar for major bleeding, whereas the 110-mg twice-a-day dose was noninferior for efficacy and reduced major bleeding. Both doses reduced intracranial hemorrhages substantially compared with warfarin. Dabigatran-assigned patients had a higher incidence of discontinuation due to gastrointestinal symptoms. Clinically apparent myocardial infarction rates were slightly higher in the dabigatran groups than the warfarin group. Dabigatran is the first agent to show superiority over warfarin for stroke prevention in atrial fibrillation, raising the standard for newer agents.

Alternatives to warfarin--the next generation of anticoagulants

Anticoagulation therapy plays an important role in the management of cardiovascular disease. Currently, oral anticoagulation therapy is reliant on vitamin K antagonists (VKA). In clinical practice, VKA present several limitations including a narrow therapeutic window and frequent drug and food interactions. Despite the clear clinical need for alternative anticoagulants it is only within the last decade that significant progress has been made. These new anticoagulants target specific factors in the hemostatic network and appear to overcome some of the difficulties seen with VKA. Many have now progressed to phase III clinical trials including patients with cardiovascular disease. This review aims to highlight the exciting progress that has been made in the development of these new anticoagulants. It will focus on the key agents that have demonstrated the most promise in clinical trials to date. This will include data on cardiovascular indications for anticoagulant therapy. Finally, the review aims to analyze the future prospects for these new agents. Several issues remain to be addressed for these agents to finally replace vitamin K antagonists as the mainstay of anticoagulant therapy.

[A new deal with new anticoagulants?]

The anticoagulant market has been very active recently with the development of new compounds including injectable anti-Xa such as fondaparinux, already available, and idraparinux, already replaced by its new biotynilateed form, and new oral drugs which can be divided into anti-IIa with dabigatran already available, and anti-Xa, such as the recently marketed rivaroxaban and apixaban still in the development stage. Others are coming forward. The competition is strong and the place for each drug remains to be determined. This review discusses these new anticoagulants in terms of efficacy and tolerance based on data in the literature. These recent reports mainly concern prophylaxis for orthopedic surgery but also consider treatment of deep venous thrombosis. The results of studies in heart patients have raised much curiosity since they will be determinant in the future use of innovating compounds, which could replace current oral anticoagulants. This will be upcoming but not yet for tomorrow.

New options with dabigatran etexilate in anticoagulant therapy

Thrombosis, the localized clotting of blood, occurs in both the arterial and venous circulation, and has a major impact on health outcomes. The primary etiology of myocardial infarctions, and approximately 80% of strokes, is acute arterial thrombosis. In combination this represents the most common cause of death in the Western world, while the third leading cause of cardiovascular-associated death is venous thromboembolism. An understanding of the pathogenic changes in the vessel wall and the blood that result in thrombosis is crucial for developing safer and more effective antithrombotic drugs. Dabigatran etexilate belongs to a new class of direct thrombin inhibitors. Following oral administration, dabigatran reaches peak plasma concentrations within 2 hours, shows linear pharmacokinetics, and a limited (but important) amount of direct drug interactions. Given once daily at 150 mg or 220 mg, it has proven to be competitive with enoxaparin in the prevention of venous thromboembolism after major orthopedic surgery, with a comparable safety profile. For stroke prevention in patients suffering from atrial fibrillation, dabigatran administered at a dose of 110 mg twice daily was associated with rates of stroke and systemic embolism that were similar to those associated with warfarin, as well as lower rates of hemorrhage. Dabigatran given at a dose of 150 mg twice daily, as compared with warfarin, was associated with lower rates of stroke and systemic embolism but similar rates of major hemorrhage. Oral bioavailability of dabigatran, together with a rapid onset and offset of action and predictable anticoagulation response, makes this newly available antithrombotic drug an attractive alternative to traditional anticoagulant therapies for numerous thrombosis-related indications.

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.

New antithrombotic drugs

Thrombosis, both venous and arterial, is a major cause of morbidity and mortality worldwide. Consequently, there is an ongoing search for new antithrombotic drugs, particularly novel antiplatelet agents and anticoagulants. A better understanding of the biochemical pathways involved in platelet activation and coagulation and of the links between these systems and the impact of thrombosis on inflammation has led to the identification of new targets for antithrombotic drugs. This paper focuses on these new targets and new antiplatelet drugs and anticoagulants and describes the major advances in the continuing search for more potent antithrombotic drugs that have limited effects on hemostasis.

[Perioperative venous thromboembolism prophylaxis: short review and recommendations]

The overall thromboembolic risk is the resultant of patient-related risk and surgical risk. The surgical risk is decreasing, especially with the introduction of new procedures (fast-track surgery). The value of prophylaxis has been firmly established. Mechanical prophylaxis is to be used as first-line prophylaxis when there is a risk of bleeding. Combining this with drugs increases the antithrombotic efficacy. However, the effectiveness of prophylaxis on pulmonary embolism and mortality has not been demonstrated. Renal function needs to be evaluated when low molecular weight heparins, fondaparinux, rivaroxaban or dabigatran are prescribed. An age of over 75 years and low body weight (<50 kg) have to be taken into account. There is a risk of spinal or epidural hematoma in patients receiving anticoagulants. Caution should be taken especially when administering the newer agents. Patients undergoing surgery that involves a moderate or high overall risk should receive prophylaxis until full mobilization. Patients who have undergone a total hip replacement, surgery for hip fracture, or major abdominal surgery should receive prophylaxis for about 5 weeks longer. The relevance of distal vein thromboses is debated. Surrogate venographic end-points should be gradually replaced by a combination of ultrasound and clinical criteria. The new antithrombotic agents will probably modify prevention in the years to come but currently there are very few long-term data for these products for which - it should be reminded - no antagonists are available.

[New oral anticoagulants: molecular characteristics, mechanisms of action, pharmacokinetics and pharmacodynamics]

The search for the ideal anticoagulant has been one of the most active research fields in medicine in the past few years. Anti-vitamin K replacement, particularly in the long term treatment of venous thromboembolism is a difficult objective to achieve due to the wide experience gathered in normal practice and low costs. But to improve the weak points of these drugs is an attractive challenge and would have a great health and social impact. It can be seen that the low molecular weight heparins, or even pentasaccharide, drugs that are already available on the market, although the have very predictable pharmacokinetics, their parenteral use, or their long half life, they are far from being ideal anticoagulants. Ximelagatran, a promising drug, a direct inhibitor of thrombin seemed to be a step forward, but the appearance of undesirable side effects led to its withdrawal. However, this line of investigation has remained open, as such that we now have data from clinical trials that back it up: the direct inhibition of thrombin and activated factor X. These two different mechanisms of action are showing promising results, in that the direct inhibitors of thrombin (dabigatran, hirudins...) are showing not to be inferior in efficacy and safety to enoxaparin in the primary prophylaxis of venous thromboembolism. Similarly, the activated factor X inhibitors (Rivaroxaban, Apixaban ) are also showing the same and in some cases, superior in its prevention. This review looks at the mechanisms of action of both pharmacological groups, their effects on haemostasis, and how they are reflected in coagulation times, their pharmacokinetics and pharmacodynamics. These new anticoagulants are nearer to the ideal anticoagulant and may, in the near future, change the panorama of anticoagulation, not only at health level, but also by achieving improved levels in the quality of life of the patients.

[Direct thrombin inhibitors: pharmacology and application in cardiovascular anesthesia]

The options for drug-controlled anticoagulation are becoming noticeably more manifold. In the area of anaesthesiology and intensive care, there are furthermore special disease patterns, such as heparin-induced thrombocytopenia (HIT) to be known, diagnosed and treated. This article gives a review of the substance groups of the direct thrombin inhibitors (DTI) as alternative anticoagulants for HIT in combination with cardiovascular diseases. For the administration of DTIs, experience and the correct dose are the keys to success and are the deciding factors for the two sides of haemostasis: thrombosis and haemorrhage.