Novel factor Xa inhibitors for prevention and treatment of thromboembolic diseases

Complete investigations (autopsy, toxicology, and histology) in a death due to apixaban overdose

The dead body of a 54-year-old man was found at home by his partner. He was off work due to depression. A letter with suicidal intention was present on the scene. He was known to be a heavy drinker, and near the body, an empty bottle of whisky was found. In addition, 2 empty blisters of Eliquis (apixaban) 5 mg, corresponding to 40 tablets, were identified. Apixaban is an oral anticoagulant, acting as a factor Xa inhibitor. Autopsy findings were mostly unremarkable, except numerous bruises and some superficial self-inflected wounds. Histology showed hematomas of calyces and renal pelvis and in the liver, several areas of perivenular haemorrhagic necrosis. Others organs were congestive. Femoral venous blood alcohol was 0.11 g/L. In femoral venous blood, a toxic concentration of apixaban was measured at 1184 ng/mL using LC-MS/MS. Other drugs found at therapeutic concentrations included diazepam (99 ng/mL), nordiazepam (171 ng/mL), flecainide (447 ng/mL), and mianserine (65 ng/mL). Using liquid chromatography coupled to high-resolution mass spectrometry, 2 metabolites were identified, O-desmethyl-apixaban (61.8% of the apixaban response) and hydroxyl-apixaban (4.5% of the apixaban response). Long-term therapy was confirmed by a concentration of 10390 pg/mg in pubic hair.

Efficacy and Safety of Oral Anticoagulants in Older Adult Patients With Atrial Fibrillation: Pairwise and Network Meta-Analyses

OBJECTIVE

To evaluate the efficacy and safety of oral anticoagulants for older adult patients with atrial fibrillation (AF).

DESIGN

Pairwise and network meta-analyses.

SETTING AND PARTICIPANTS

Patients with AF aged ≥75 years.

METHODS

PubMed, Embase, and the Cochrane library were searched for published randomized controlled trials and adjusted observational studies evaluating the use of a non-vitamin K antagonist oral anticoagulants (NOACs), vitamin K antagonist, or antiplatelet drug for the prevention of stroke. The primary efficacy and safety outcomes were the composite of stroke and systemic embolism (SSE) and major bleedings.

RESULTS

This study included 38 studies enrolling 1,022,908 older adult patients with AF. Results from pairwise meta-analyses showed that NOACs were superior to warfarin for all outcomes, except that dabigatran increased the risk of gastrointestinal (GI) bleedings. Aspirin was associated with a higher risk of SSE and ischemic stroke than warfarin or NOACs. Results of network meta-analyses indicated that apixaban significantly reduced the risk of SSE, major bleedings, and GI bleedings than warfarin, rivaroxaban, and dabigatran. Apixaban, edoxaban, rivaroxaban, and dabigatran reduced the risk of ischemic stroke and intracranial bleeding compared to warfarin. Dabigatran showed lower risk of all-cause mortality than warfarin and of intracranial bleeding than rivaroxaban.

CONCLUSIONS AND IMPLICATIONS

NOACs are of at least equal efficacy, or even superior to warfarin. The safety profile of individual NOAC agents was significantly different, as apixaban performs better than the other oral anticoagulants in reducing major bleeding and GI bleeding, whereas dabigatran increased the risk of GI bleeding.

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.

Subacute administration of Astaxanthin inhibits vitamin K-dependent clotting factors in rats

This study investigated the effect of Astaxanthin (ASTX) on levels and activities of the clotting factors in control rats. Untreated or ASTX-treated rats (10 mg/kg, dissolved in DMSO) were used in this study. ASTX treatment was conducted for 10 days daily. ASTX significantly decreased the platelet count and prolonged values of prothrombin and activated partial thromboplastin time (PT and aPTT, respectively). Besides, it significantly reduced serum levels of vitamin K and the plasma activities and hepatic expression of vitamin K-dependent factors (FII, FVII, FIX, and FX) without altering the activities or levels of all other clotting factors nor plasma levels of fibrinogen or von Willebrand Factor. These effects were associated with a reduction in serum and fecal levels of cholesterol and triglycerides and lower serum levels of LDL-c. In conclusion, ASTX exerts an in vivo hypocoagulant effects mediated by the inhibition of vitamin K-dependent factors. PRACTICAL APPLICATIONS: The findings presented here are the first that show the ability of Astaxanthin (ASTX) to inhibit coagulation in rats by suppressing the circulatory levels of Vitamin K and decrease the synthesis and release of all Vitamin-K dependent factor (FII, FVII, FIX, and FX). Since some synthetic anti-coagulants had side effects, these findings may illustrate ASTX as a natural anti-coagulant with fewer side effects that require further investigation in more clinical trials. Besides, awareness should be established for those individuals with some bleeding disorders who are being treated with ASTX for other beneficial effects.

Novel assay based on diluted prothrombin time reflects anticoagulant effects of direct oral factor Xa inhibitors: Results of multicenter study in Japan

BACKGROUND

Direct oral anticoagulants targeting factor Xa (DXaIs) are administered as prophylaxis for various venothrombotic diseases without routine monitoring required. However, assessment of their anticoagulant effects is necessary to prevent severe events, including major bleeding and/or refractory thrombosis.

OBJECTIVES

We examined the correlation of ratio of inhibited thrombin generation (RITG), determined using a novel assay based on dilute prothrombin time (dPT), with coagulant markers and laboratory test results to show drug effects. In addition, RITG usefulness as a confirmation test for DXaI therapy was investigated.

METHODS

Citrated plasma samples were obtained from patients treated with rivaroxaban (n = 882), apixaban (n = 1214), or edoxaban (n = 820) at 4 different institutions in Japan. Laboratory tests, including prothrombin time (PT), activated partial thromboplastin time (APTT), D-dimer, and plasma concentrations of DXaIs, were conducted, with drug concentrations divided into peak and trough groups, within and after 5 h of administration.

RESULTS

In each DXaI group, RITG was positively correlated with PT, APTT, and drug concentration, and negatively with D-dimer. RITG fluctuation during the peak and trough periods reflected the anticoagulant activity characteristic of each DXaI, which was different from blood concentration fluctuations. RITG showed a significant decrease in cases with thrombosis, while that was increased in those with hemorrhage.

CONCLUSION

We developed RITG, a novel measurement method based on dPT. RITG represents residual coagulation ability in plasma samples, and is useful for assessment of bleeding and thrombotic tendencies in DXaI patients. RITG can be utilized to confirm the effectiveness of oral anticoagulation therapy with DXaI agents.

The hypocoagulant effect of Crataegus aronia in rats entails vitamin K-dependent and vitamin K-independent effects

This study investigated the effect of the aqueous extract of Crataegus aronia on blood coagulation in rats. Rats (200 ± 10 g,) were divided into two groups (6 rats/each) of control or C. aronia-treated rats which treated with the vehicle or the extract (200 mg/kg) for 21 days. With normal liver structure, serum levels of ALT, AST and ɣ-GT, platelet count, and plasma levels of vWF, values of PT and aPTT were significantly increased in C. aronia-treated rats. Also, it lowered serum levels of vitamin K (VK) and plasma activities of FII, FV, FVII, FVIII, FIX, FX, and FXI and downregulated hepatic levels of the VK-dependent factors (FII, FVII, FIX, and FX). In addition, C. aronia reduced fecal levels of triglycerides and cholesterol and serum levels triglycerides, cholesterol, LDL-c, and vLDL-c. In conclusion, with the hypocoagulant effect of C. aronia activity involves VK-dependent and non-vitamin K-dependent factors. PRACTICAL APPLICATIONS: In this study, we are reporting for the first time an in vivo hypocoagulant effect of C. aronia in rats. Such effect involved both VK-dependent and independent factors. However, the decrease in the activity and expression of VK-dependent factors was associated with reduced fecal levels of TGs and CHOL and serum levels of TGs, CHOL, LDL-c, and vLDL-c. These data suggest a possible impairment in the VK absorption, transport, or hepatic uptake. These data encourage further pharmacological, translational, and clinical studies to isolate the active ingredients to investigate them at the human level.

Assessing Coagulation by Rotational Thromboelastometry (ROTEM) in Rivaroxaban-Anticoagulated Blood Using Hemostatic Agents

Introduction

The use of direct oral anticoagulants (DOACs) such as rivaroxaban (Xarelto) is increasingly common. However, therapies for reversing anticoagulation in the event of hemorrhage are limited. This study investigates the ability of hemostatic agents to improve the coagulation of rivaroxaban-anticoagulated blood, as measured by rotational thromboelastometry (ROTEM).

Hypothesis/Problem

If a chitosan-based hemostatic agent (Celox), which works independently of the clotting cascade, is applied to rivaroxaban-anticoagulated blood, it should improve coagulation by decreasing clotting time (CT), decreasing clot formation time (CFT), and increasing maximum clot firmness (MCF). If a kaolin-based hemostatic agent (QuikClot Combat Gauze), which works primarily by augmenting the clotting cascade upstream of factor Xa (FXa), is applied to rivaroxaban-anticoagulated blood, it will not be effective at improving coagulation.

Methods

Patients (age >18 years; non-pregnant) on rivaroxaban, presenting to the emergency department (ED) at two large, university-based medical centers, were recruited. Subjects (n=8) had blood drawn and analyzed using ROTEM with and without the presence of a kaolin-based and a chitosan-based hemostatic agent. The percentage of patients whose ROTEM parameters responded to the hemostatic agent and percent changes in coagulation parameters were calculated.

Results

Data points analyzed included: CT, CFT, and MCF. Of the samples treated with a kaolin-based hemostatic agent, seven (87.5%) showed reductions in CT, eight (100.0%) showed reductions in CFT, and six (75.0%) showed increases in MCF. The average percent change in CT, CFT, and MCF for all patients was 32.5% (Standard Deviation [SD]: 286; Range:-75.3 to 740.7%); -66.0% (SD:14.4; Range: -91.4 to -44.1%); and 4.70% (SD: 6.10; Range: -4.8 to 15.1%), respectively. The corresponding median percent changes were -68.1%, -64.0%, and 5.2%. Of samples treated with a chitosan-based agent, six (75.0%) showed reductions in CT, three (37.5%) showed reductions in CFT, and five (62.5%) showed increases in MCF. The average percent changes for CT, CFT, and MCF for all patients were 165.0% (SD: 629; Range:-96.9 to 1718.5%); 139.0% (SD: 174; Range: -83.3 to 348.0%); and -8.38% (SD: 32.7; Range:-88.7 to 10.4%), respectively. The corresponding median percent changes were -53.7%, 141.8%, and 3.0%.

Conclusions

Rotational thromboelastometry detects changes in coagulation parameters caused by hemostatics applied to rivaroxaban-anticoagulated blood. These changes trended in the direction towards improved coagulability, suggesting that kaolin-based and chitosan-based hemostatics may be effective at improving coagulation in these patients.

BarJ, DavidA, KhaderT, MulcareM, TedeschiC. Assessing coagulation by rotational thromboelastometry (ROTEM) in rivaroxaban-anticoagulated blood using hemostatic agents. Prehosp Disaster Med. 2017;32(5):580–587.

Synthesis and in Vitro and in Vivo Anticoagulant and Antiplatelet Activities of Amidino- and Non-Amidinobenzamides

Three amidino- and ten non-amidinobenzamides were synthesized as 3-aminobenzoic acid scaffold-based anticoagulant and antiplatelet compounds. The anticoagulant activities of thirteen synthesized compounds 1-13, and 2b and 3b as prodrugs were preliminary evaluated by screening the prolongation of activated partial thromboplastin time (aPTT) and prothrombin time (PT) in vitro. From the aPTT results obtained, two amidinobenzamides, N-(3'-amidinophenyl)-3-(thiophen-2''-ylcarbonylamino) benzamide (1, 33.2 ± 0.7 s) and N-(4'-amidinophenyl)-3-(thiophen-2''-ylcarbonylamino) benzamide (2, 43.5 ± 0.6 s) were selected to investigate the further anticoagulant and antiplatelet activities. The aPTT results of 1 (33.2 ± 0.7 s) and 2 (43.5 ± 0.6 s) were compared with heparin (62.5 ± 0.8 s) in vitro at 30 μM. We investigated the effect of 1 and 2 on blood anticoagulant activity (ex vivo) and on tail bleeding time (in vivo) on mice. A tail cutting/bleeding time assay revealed that both 1 and 2 prolonged bleeding time in mice at a dose of 24.1 g/mouse and above. Compounds 1 and 2 dose-dependently inhibited thrombin-catalyzed fibrin polymerization and platelet aggregation. In addition, 1 and 2 were evaluated on the inhibitory activities of thrombin and FXa as well as the generation of thrombin and FXa in human umbilical vein endothelial cells (HUVECs). Collectively, 1 and 2 possess some antiplatelet and anticoagulant activities and offer a basis for development of a novel antithrombotic product.

New Insights into the Pros and Cons of the Clinical Use of Vitamin K Antagonists (VKAs) Versus Direct Oral Anticoagulants (DOACs)

Vitamin K-antagonists (VKA) are the most widely used anticoagulant drugs to treat patients at risk of arterial and venous thrombosis for the past 50 years. Due to unfavorable pharmacokinetics VKA have a small therapeutic window, require frequent monitoring, and are susceptible to drug and nutritional interactions. Additionally, the effect of VKA is not limited to coagulation, but affects all vitamin K-dependent proteins. As a consequence, VKA have detrimental side effects by enhancing medial and intimal calcification. These limitations stimulated the development of alternative anticoagulant drugs, resulting in direct oral anticoagulant (DOAC) drugs, which specifically target coagulation factor Xa and thrombin. DOACs also display non-hemostatic vascular effects via protease-activated receptors (PARs). As atherosclerosis is characterized by a hypercoagulable state indicating the involvement of activated coagulation factors in the genesis of atherosclerosis, anticoagulation could have beneficial effects on atherosclerosis. Additionally, accumulating evidence demonstrates vascular benefit from high vitamin K intake. This review gives an update on oral anticoagulant treatment on the vasculature with a special focus on calcification and vitamin K interaction.

Synthesis of 3,4-diaminobenzoyl derivatives as factor Xa inhibitors

The coagulation factor Xa (FXa) plays a central role in the blood coagulation cascade. Recent studies have shown that FXa is a particularly attractive target for the development of oral antithrombotic agents. In view of the excellent pharmaceutical properties of 1,2-phenylenediamine-based FXa inhibitors and the reported structure-activity relationship (SAR) analysis of FXa inhibitors, we designed and synthesized a series of 3,4-diaminobenzoyl-based FXa inhibitors. Intensive SAR studies on this new series led to the discovery of 3,4-dimethoxyl substituted compound 7b. 7b is a highly potent, selective, direct FXa inhibitor with excellent in vivo antithrombotic activity.

The pharmacokinetics of edoxaban for the prevention and treatment of venous thromboembolism

INTRODUCTION

Thromboembolic diseases will become the most important contributors to mortality and morbidity for modern societies. Current antithrombotic strategies using heparins or vitamin K antagonists are inconvenient, with limitations and inherent side effects. A series of new oral anticoagulants with powerful and reliable antithrombotic actions have been developed in the last decade.

AREAS COVERED

Edoxaban is a direct and specific inhibitor of activated factor X, delivered orally. This article reviews literature from PubMed and articles referenced within. The text explores the pharmacological aspects of its antithrombotic action. Pharmacokinetics, metabolism and drug interactions are examined. The review places the results of recent clinical trials that have evaluated the antithrombotic potential of edoxaban versus standard antithrombotic therapies in the prophylaxis and treatment of venous thromboembolism into perspective. The possible relationship between the pharmacokinetic profile of edoxaban and the favorable results in clinical trials is discussed.

EXPERT OPINION

Edoxaban is perceived as a major advance, compared to vitamin K antagonists, in the prevention and treatment of thromboembolic disease given its favorable efficacy, safety, pharmacokinetic profile and renal clearance. The results of ongoing large international trials exploring the prevention of thrombotic complications in patients in different clinical settings should ensure the approval of edoxaban to treat new indications.

The discovery of rivaroxaban: translating preclinical assessments into clinical practice

Direct oral anticoagulants that target a single coagulation factor (such as factor Xa or thrombin) have been developed in recent years in an attempt to address some of the limitations of traditional anticoagulants. Rivaroxaban is an oral, direct factor Xa inhibitor that inhibits free and clot-bound factor Xa and factor Xa in the prothrombinase complex. Preclinical studies demonstrated a potent anticoagulant effect of rivaroxaban in plasma as well as the ability of this agent to prevent and treat venous and arterial thrombosis in animal models. These studies led to an extensive phase I clinical development program that investigated the pharmacological properties of rivaroxaban in humans. In these studies, rivaroxaban was shown to exhibit predictable pharmacokinetics and pharmacodynamics and to have no clinically relevant interactions with many commonly prescribed co-medications. The pharmacodynamic effects of rivaroxaban (for example, inhibition of factor Xa and prolongation of prothrombin time) were closely correlated with rivaroxaban concentrations in plasma. The encouraging findings from preclinical and early clinical studies were expanded upon in large, randomized phase III studies, which demonstrated the clinical efficacy and safety of rivaroxaban in a broad spectrum of patients. This article provides an overview of the discovery and development of rivaroxaban, describing the pharmacodynamic profile established in preclinical studies and the optimal translation to clinical studies in healthy subjects and patient populations.

Prevention of stroke and systemic embolism with rivaroxaban compared with warfarin in Chinese patients with atrial fibrillation

This study assessed the effects and safety of rivaroxaban versus warfarin in Chinese patients with atrial fibrillation. In this double-blind clinical trial, a total of 353 consecutive patients with atrial fibrillation who were at risk of stroke or systemic embolism were enrolled to receive either rivaroxaban or warfarin. The primary effect endpoint occurred in five patients in the rivaroxaban group (2.29% per year) and in seven patients in the warfarin group (2.91% per year) (hazard ratio with warfarin, 0.76, 95% CI, 0.64-0.91; p = 0.03). Major and non-major clinically relevant bleeding occurred in 38 patients (14.3% per year) in the rivaroxaban group and in 36 patients (13.7% per year) in the warfarin group (hazard ratio rivaroxaban versus warfarin, 1.07; 95% CI, 0.93-1.14; p = 0.39). Adverse events were similar between these two arms (p > 0.05). In conclusion, oral administration of rivaroxaban reduced the risk of stroke or systemic embolism without significantly increasing the safety concern.

Rivaroxaban: a novel oral anticoagulant for the prevention and treatment of several thrombosis-mediated conditions

The development of rivaroxaban (XARELTO®) is an important new medical advance in the field of oral anticoagulation. Thrombosis-mediated conditions constitute a major burden for patients, healthcare systems, and society. For more than 60 years, the prevention and treatment of these conditions have been dominated by oral vitamin K antagonists (such as warfarin) and the injectable heparins. Thrombosis can lead to several conditions, including deep vein thrombosis, pulmonary embolism, myocardial infarction, stroke, and/or death. Prevention and treatment of thrombosis with an effective, convenient-to-use oral anticoagulant with a favorable safety profile is critical, especially in an aging society in which the risk of thrombosis, and the potential for bleeding complications, is increasing. Rivaroxaban acts to prevent and treat thrombosis by potently inhibiting coagulation Factor Xa in the blood. Factor Xa converts prothrombin to thrombin, which initiates the formation of blood clots by converting fibrinogen to clot-forming fibrin and leads to platelet activation. After a large and novel clinical development program in over 75,000 patients to date, rivaroxaban has received approval for multiple indications in the United States, European Union, and other countries worldwide to prevent and treat several thrombosis-mediated conditions. This review will highlight some of the unique aspects of the rivaroxaban development program.

Practical management of anticoagulants in family medicine after orthopedic surgery

In order to prevent postoperative venous thromboembolism, prophylactic anticoagulant therapy is routinely administered to hospitalized patients after total hip arthroplasty (THA) and total knee arthroplasty (TKA). However, after hospital discharge, anticoagulant therapy is primarily managed by a primary care physician (PCP). The agents traditionally used for this purpose are associated with certain limitations that affect anticoagulation management. The new, fixed-dose oral anticoagulants have predictable pharmacokinetic and pharmacodynamic profiles, no requirement for coagulation monitoring, and a low propensity for food and drug interactions. As a result, they have the potential to simplify and improve postoperative outcomes in patients who have undergone THA or TKA and allow for simpler management of anticoagulation in these patients. This article examines the clinical evidence for benefits of the new oral anticoagulants, discusses caveats regarding their appropriate use, and provides some guidance regarding bleeding management with these agents.

Pharmacokinetic evaluation of rivaroxaban for the treatment of acute coronary syndromes

INTRODUCTION

Arterial and venous thrombotic states, including myocardial infarction (MI), stroke and deep vein thrombosis with subsequent pulmonary embolism, are a significant cause of cardiovascular mortality and morbidity. Factor Xa (FXa) plays a pivotal role in thrombus formation. Its inhibition following acute coronary syndromes (ACS) blocks amplification of thrombin generation and subsequent clot formation, resulting in a risk reduction in recurrent MI, stroke and death. For this reason, a predictable form of oral anticoagulation continues to be an ongoing need. Rivaroxaban , the first oral FXa inhibitor, acts by direct inhibition of FXa and does not require an antithrombin cofactor for its activity.

AREAS COVERED

This paper describes the pharmacokinetics (PK) of low-dose rivaroxaban tested in patients with ACS. Age, gender, renal function and body weight have no clinically significant effects on the PK of the drug in treatment of ACS. Caution should be maintained during co-administration of strong CYP3A4 inducers and inhibitors. Among patients with moderate and severe hepatic impairment and in those with associated coagulopathies, rivaroxaban however is contraindicated.

EXPERT OPINION

The mortality benefit with low-dose rivaroxaban in ACS patients was first demonstrated in ATLAS ACS2 TIMI-51 trial. With its rapid oral bioavailability, predictable PK, low drug-drug interaction and no need for monitoring, the use of low-dose rivaroxaban in addition to dual antiplatelet therapy offers an appealing new option in improving outcomes following ACS in the modern era of novel oral FXa inhibitors.

New anticoagulants - promising and failed developments

New direct and indirect acting factor Xa (FXa) and thrombin inhibitors are being developed to overcome the downsides of the conventional anticoagulants - unfractionated and low molecular weight heparins and vitamin K antagonists. Ximelagatran and idraparinux failed to demonstrate an acceptable safety profile. Rivaroxaban and dabigatran are approved for the post-operative prevention of thromboembolic complications after elective hip or knee replacement surgery; dabigatran is approved for the prevention of embolism in patients with atrial fibrillation in an increasing number of countries. Several novel indirect antithrombin-dependent anticoagulants as well as antithrombin-independent oral direct FXa and thrombin inhibitors are investigated in multiple indications for the prophylaxis and treatment of venous thromboembolism and the prophylaxis of arterial thrombotic disorders. Quality-adjusted life years costs and incremental cost-effectiveness ratios are relatively high at present, but may decrease after approval of more new anticoagulants for additional indications.

Venous thrombosis in children: an emerging issue

More and more cases of venous thrombosis are diagnosed in children thanks to newer imaging modalities. Central venous catheters have become commonplace in the care of critically ill children and have contributed to the increased rate of thrombotic events. Lastly, children who develop life-threatening or chronic medical conditions are surviving longer because of advanced medical therapies; these intensive therapies can be complicated by events such as thrombosis. Over the last 10 years, specific guidelines for treating thrombosis in children have become available. Nevertheless, in many situations anticoagulant treatment is specially tailored to each individual patient's needs. Some new antithrombotic drugs which have undergone clinical testing in adults might be beneficial to paediatric patients with thromboembolic disorders; unfortunately, clinical data and reports on the use of these drugs in children, when available, are extremely limited. The aim of this review is to provide physicians with enough background information to be able to manage thrombosis in children. First, by helping them detect a thrombotic event in a child. Upon confirmation of the diagnosis, the physician will request the appropriate tests and will choose the best treatment on the basis of the guidelines and recommendations. Moreover, the paediatrician will have the information he or she needs to identify which children are at highest risk of acute thrombotic events and relevant long-term sequelae and, therefore, to decide on the appropriate prophylactic or pharmacologic strategy. Lastly, we would like to provide the paediatrician with information on future drugs with regard to the treatment and prophylaxis of thrombosis.

Oral rivaroxaban after symptomatic venous thromboembolism: the continued treatment study (EINSTEIN-extension study)

Over recent years, research on anticoagulant drugs has been guided by the requirement for convenient administration and a wide therapeutic window to allow fixed dosing without the need for coagulation monitoring. Rivaroxaban is the first of a new class of anticoagulant drugs, the direct, selective inhibitors of Factor Xa. The EINSTEIN-extension study compared rivaroxaban with placebo in patients who completed their standard treatment course after venous thromboembolism (VTE), in whom there was equipoise with respect to the need for continued anticoagulation. After 6-12 months of treatment, rivaroxaban significantly reduced the risk of recurrent VTE at the cost of a moderate increase in bleeding complications. Overall, these results suggest that rivaroxaban can be a valid alternative to warfarin for patients requiring long-term secondary prevention of VTE. However, additional data are needed for special populations including the elderly, patients with cancer, renally impaired patients and morbidly obese patients, all of whom were scarcely represented in this trial.

Evaluation of the efficacy and safety of rivaroxaban using a computer model for blood coagulation

Rivaroxaban is an oral, direct Factor Xa inhibitor approved in the European Union and several other countries for the prevention of venous thromboembolism in adult patients undergoing elective hip or knee replacement surgery and is in advanced clinical development for the treatment of thromboembolic disorders. Its mechanism of action is antithrombin independent and differs from that of other anticoagulants, such as warfarin (a vitamin K antagonist), enoxaparin (an indirect thrombin/Factor Xa inhibitor) and dabigatran (a direct thrombin inhibitor). A blood coagulation computer model has been developed, based on several published models and preclinical and clinical data. Unlike previous models, the current model takes into account both the intrinsic and extrinsic pathways of the coagulation cascade, and possesses some unique features, including a blood flow component and a portfolio of drug action mechanisms. This study aimed to use the model to compare the mechanism of action of rivaroxaban with that of warfarin, and to evaluate the efficacy and safety of different rivaroxaban doses with other anticoagulants included in the model. Rather than reproducing known standard clinical measurements, such as the prothrombin time and activated partial thromboplastin time clotting tests, the anticoagulant benchmarking was based on a simulation of physiologically plausible clotting scenarios. Compared with warfarin, rivaroxaban showed a favourable sensitivity for tissue factor concentration inducing clotting, and a steep concentration–effect relationship, rapidly flattening towards higher inhibitor concentrations, both suggesting a broad therapeutic window. The predicted dosing window is highly accordant with the final dose recommendation based upon extensive clinical studies.

[New oral anticoagulants from the perspective of trauma surgery]

Heparins and vitamin K antagonists have been the cornerstones of anticoagulation therapy for several decades. While these compounds have proven to be effective at inhibiting the coagulation process, they have inherent limitations. This has spurred efforts to develop therapies that will overcome these drawbacks while matching the efficacy of the conventional anticoagulants. Significant advances have been made in the development of more specific treatments targeting factor Xa or thrombin and providing more predictable anticoagulant responses. They also offer the convenience of oral administration with fixed dose regimens not requiring routine monitoring which may have an impact on compliance. The factor Xa inhibitor rivaroxaban and the thrombin inhibitor dabigatran etexilate have become available for prevention of venous thromboembolism after elective hip and knee replacement surgery and registration of the factor Xa inhibitor apixaban is expected to occur soon. Furthermore, first clinical evidence has become available for all of these compounds in patients requiring long-term anticoagulation. It is to be expected that these results will lead to improvements in prevention of stroke in patients with atrial fibrillation and in treatment of venous thromboembolism.

Quantification of apixaban's therapeutic utility in prevention of venous thromboembolism: selection of phase III trial dose

A model-based approach was used to integrate data from a phase II study in order to provide a quantitative rationale for selecting the apixaban dosage regimen for a phase III trial. The exposure-response models demonstrated that an increase in daily steady-state area under the plasma concentration-vs.-time curve (AUC(ss)) of 1 microg x h/ml would increase the odds ratio for major bleeding by 0.118 and decrease the odds ratio for venous thromboembolism (VTE) by 0.0499. The therapeutic utility index (TUI) was used to integrate the efficacy and safety predictions to quantify apixaban's efficacy/safety balance as a function of AUC(ss). Of the apixaban dosage regimens tested in phase II, the 2.5 mg twice-daily (b.i.d.) dosage regimen had the highest TUI (86.2%). This was also higher than the TUI for either 30 mg b.i.d. enoxaparin (82.5%) or for warfarin (71.8%). Subjects with moderate renal impairment are expected to have a 43% increase in apixaban exposure; however, apixaban's TUI suggests that dose adjustment is not needed in these subjects with renal impairment.

New aspects on treatment modalities for thromboembolic episodes

Venous thromboembolism (VTE) has been treated with a glycosaminoglycan, followed by a vitamin K antagonist during the past 60 years. During the past two decades the glycosaminoglycans have undergone refinement, allowing for simplification of care for these patients, but parenteral administration is still required. Therefore, the current completion of phase III trials with selective, predictable and orally available anticoagulants with rapid onset brings promise for a change in paradigm in the treatment of VTE in the next few years. Whereas these efforts will lead to further simplification of the therapy there are also trials conducted to advance the treatment by rapid resolution of the thromboembolism in order to improve long-term outcome. Catheter-directed thrombolysis, perhaps also with thrombus fragmentation and stent insertion, if demonstrated to be successful for the reduction of the postthrombotic syndrome, will only be an alternative for a minority of patients due to the complexity, risks and cost of therapy. This treatment increases the complexity at the same time as new drug regimens offer simplicity. This review focuses on the novel therapies for VTE although the new anticoagulants will also play a major role in the management of arterial disease, which will be briefly presented.

Discovery of a tetrahydropyrimidin-2(1H)-one derivative (TAK-442) as a potent, selective, and orally active factor Xa inhibitor

Coagulation enzyme factor Xa (FXa) is a particularly promising target for the development of new anticoagulant agents. We previously reported the imidazo[1,5-c]imidazol-3-one derivative 1 as a potent and orally active FXa inhibitor. However, it was found that 1 predominantly undergoes hydrolysis upon incubation with human liver microsomes, and the human specific metabolic pathway made it difficult to predict the human pharmacokinetics. To address this issue, our synthetic efforts were focused on modification of the imidazo[1,5-c]imidazol-3-one moiety of the active metabolite 3a, derived from 1, which resulted in the discovery of the tetrahydropyrimidin-2(1H)-one derivative 5k as a highly potent and selective FXa inhibitor. Compound 5k showed no detectable amide bond cleavage in human liver microsomes, exhibited a good pharmacokinetic profile in monkeys, and had a potent antithrombotic efficacy in a rabbit model without prolongation of bleeding time. Compound 5k is currently under clinical development with the code name TAK-442.

Safety, pharmacokinetics and pharmacodynamics of single/multiple doses of the oral, direct Factor Xa inhibitor rivaroxaban in healthy Chinese subjects

AIMS

To investigate the safety, pharmacokinetics and pharmacodynamics of rivaroxaban, an oral, direct Factor Xa (FXa) inhibitor, in healthy, male Chinese subjects.

METHODS

Two randomized, single-blind, placebo-controlled, dose-escalation studies were conducted in healthy Chinese men aged 18-45 years. In the single-dose study, subjects received single, oral doses of rivaroxaban 2.5, 5, 10, 20 and 40 mg. In the multiple-dose study, oral rivaroxaban was administered in doses of 5, 10, 20 and 30 mg twice daily for 6 days.

RESULTS

Rivaroxaban, in single and multiple doses up to 60 mg, was well tolerated. Rapid absorption was observed in both studies (time to C(max) 1.25-2.5 h). In the multiple-dose study, rivaroxaban exposure increased dose-proportionally after the first dose and at steady state (for the 5-20-mg doses). The half-life of rivaroxaban was up to 7.9 h in the single-dose study. Maximal inhibition of FXa activity was achieved within 1-3 h of dosing in the single-dose study [at 20 mg FXa inhibition as a median percentage change from baseline, 45.92; 95% confidence interval (CI) 44.64, 50.70] and 2-3 h after administration at steady state in the multiple-dose study (at 20 mg median FXa inhibition as a median percentage change from baseline, 60.25; 95% CI 56.16, 63.05), in line with maximum rivaroxaban plasma concentrations.

CONCLUSIONS

Rivaroxaban demonstrated predictable pharmacokinetics and pharmacodynamics in healthy Chinese subjects, in line with findings observed previously in White subjects. This suggests that fixed doses of rivaroxaban may be administered to all patients, regardless of their ethnic origin.

New anticoagulants and regional anesthesia

PURPOSE OF REVIEW

The use of pharmacological thromboprophylaxis in the perioperative period may conflict with regional anesthetic techniques in which maintaining hemostatic integrity is essential. Recently, new anticoagulants have been developed with more efficacy and a better safety profile. This article reviews the basis for the actual recommendations and the current status and management of these new drugs.

RECENT FINDINGS

Recent studies have outlined that the risk of epidural hematoma after neuraxial anesthesia may be higher than estimated. Therefore, it is imperative to follow the published recommendations. The use of new anticoagulant drugs may take into account the pharmacological profile of each one to safely perform regional anesthesia, mainly the time to reach peak plasma level and half-life.

SUMMARY

When new anticoagulant drugs are used for thromboprophylaxis in orthopedic surgery, the performance of neuraxial anesthetic techniques should be based on their pharmacology. If a peripheral blockade is chosen, these recommendations should be followed when a block is performed in a noncompressible area.

New pharmacotherapy for stroke prevention in atrial fibrillation: update 2010

Atrial fibrillation (AF) is the most commonly encountered arrhythmia in clinical practice and is associated with substantial morbidity and mortality. Its prevalence increases with age, affecting about 1% of patients aged <60 years and almost 10% of patients >80 years. AF is associated with a fivefold increasing risk of embolism or stroke with absolute risk ranging from less than 1% to 20% per year, depending on patient age and the presence of clinical risk factors including congestive heart failure, systemic hypertension, diabetes mellitus and prior history of cardioembolic events. Vitamin K antagonists (VKAs) and acetyl salicylic acid are currently the only licensed antithrombotic therapies for stroke prevention in patients with AF. Anticoagulants are very effective for stroke prevention in patients with AF, overall a 64% relative risk reduction. Nonetheless, approximately 50% of patients with AF who have an indication for VKA receive anticoagulant therapy, of which only 50% maintain adequate therapeutic ranges. Furthermore, 50% will discontinue VKAs within 3 to 5 years regardless of appropriate international normalized ratio control. Underutilization of VKAs is related, in part, to their numerous limitations and difficulty in maintaining adequate therapeutic control, prompting the development of new antithrombotic strategies that are equally effective and safer, and easier to manage than VKAs. This review focuses on new antithrombotic therapies for stroke prevention in patients with AF.