New Anticoagulants for Atrial Fibrillation

Surfing the Blood Coagulation Cascade: Insight into the Vital Factor Xa

Factor Xa (FXa) plays a key role in haemostasis, it is a central part of the blood coagulation cascade which catalyzes the production of thrombin and leads to clot formation and wound closure. Therefore, FXa is an attractive target for the development of new anticoagulant agents. In this review, we will first describe the molecular features of this fundamental protein in order to understand its mechanism of action, an essential background for the design of novel inhibitors by means of synthetic organic chemistry or using peptides obtained from recombinant methodologies. Then, we will review the current state of the synthesis of novel direct FXa inhibitors along with their mechanisms of action. Finally, approved reversal agents that aid in maintaining blood haemostasis by using these commercial drugs will also be discussed.

Comparative Effectiveness and Safety of Rivaroxaban in Adults With Nonvalvular Atrial Fibrillation

BACKGROUND

All evidence regarding benefits and harms of rivaroxaban for stroke prevention has not been appraised yet.

STUDY QUESTION

What are the comparative effectiveness and safety of rivaroxaban in adults with nonvalvular atrial fibrillation?

DATA SOURCES

Randomized controlled trials (RCTs), meta-analyses, and observational studies were identified in several databases in October 2018.

STUDY DESIGN

Rapid review with evidence appraisal using the Grading of Recommendations Assessment, Development and Evaluation working group approach.

RESULTS

Two direct RCTs (23,021 patients) suggest that rivaroxaban is noninferior to warfarin in the prevention of stroke and systemic embolism (pooled relative risk [RR] 0.73, 95% confidence interval [CI], 0.43-1.24), reduces risk of hemorrhagic stroke (RR 0.59, 95% CI, 0.38-0.92), fatal bleeding (RR 0.49, 95% CI, 0.31-0.76), and cardiac arrest (RR 0.45, 95% CI, 0.25-0.82, 2 RCTs), but increases risk of major gastrointestinal bleeding (RR 1.46, 95% CI, 1.19-1.78). In observational studies, rivaroxaban is associated with lower risk of ischemic stroke (RR 0.87, 95% CI, 0.77-0.99, 222,750 patients), acute myocardial infarction (RR 0.61, 95% CI, 0.48-0.78, 73,739 patients), and intracranial hemorrhage (RR 0.64, 95% CI, 0.45-0.92, 197,506 patients) but higher risk of gastrointestinal bleeding (RR 1.30, 95% CI, 1.19-1.42, 188,968 patients) and higher risk of mortality when compared with warfarin in European studies (RR 1.19, 103,270 patients in the UK; RR 2.02, 22,358 patients in Denmark) but lower risk of mortality in Taiwan (RR 0.58, 40,000 patients). Network meta-analyses and observational studies suggest that rivaroxaban is associated with higher risk of bleeding when compared with apixaban (RR 2.14, 72,586 patients), dabigatran (RR 1.24, 67,102 patients), and edoxaban (RR 1.32, 71,683 patients).

CONCLUSIONS

Research on the long-term comparative effectiveness, safety, and effects on quality of life between rivaroxaban and other novel oral anticoagulants is urgently needed.

Practical use of dabigatran etexilate for stroke prevention in atrial fibrillation

Atrial fibrillation (AF) is associated with an increased risk of thromboembolism, and is the most prevalent factor for cardioembolic stroke. Vitamin K antagonists (VKAs) have been the standard of care for stroke prevention in patients with AF since the early 1990s. They are very effective for the prevention of cardioembolic stroke, but are limited by factors such as drug-drug interactions, food interactions, slow onset and offset of action, haemorrhage and need for routine anticoagulation monitoring to maintain a therapeutic international normalised ratio (INR). Multiple new oral anticoagulants have been developed as potential replacements for VKAs for stroke prevention in AF. Most are small synthetic molecules that target thrombin (e.g. dabigatran etexilate) or factor Xa (e.g. rivaroxaban, apixaban, edoxaban, betrixaban, YM150). These drugs have predictable pharmacokinetics that allow fixed dosing without routine laboratory monitoring. Dabigatran etexilate, the first of these new oral anticoagulants to be approved by the United States Food and Drug Administration and the European Medicines Agency for stroke prevention in patients with non-valvular AF, represents an effective and safe alternative to VKAs. Under the auspices of the Regional Anticoagulation Working Group, a multidisciplinary group of experts in thrombosis and haemostasis from Central and Eastern Europe, an expert panel with expertise in AF convened to discuss practical, clinically important issues related to the long-term use of dabigatran for stroke prevention in non-valvular AF. The practical information reviewed in this article will help clinicians make appropriate use of this new therapeutic option in daily clinical practice.

Direct thrombin and factor Xa inhibition for stroke prevention in patients with atrial fibrillation

Nonvalvular atrial fibrillation (AF) is the most common clinically significant cardiac arrhythmia occurring in patients in the United States. The primary clinical consequence of AF is an increase in the risk and severity of strokes. Treatment guidelines recommend anticoagulation therapy for most patients with AF. One risk-stratification scheme, the CHADS2 index, is simple and widely used to determine the management of patients with AF in regard to stroke prevention. However, new schemes, such as CHA2DS2-VASc, further refine risk stratification to identify patients who would obtain a net clinical benefit from a particular management strategy, thus improving the quality of management. For patients with AF for whom oral anticoagulation (OAC) is advisable, vitamin K antagonist (VKA) therapy is well established and effective. However, OAC with VKAs presents challenges to prescribers and patients in maintaining therapeutic efficacy. Novel OACs may offer alternatives to VKAs. Dabigatran etexilate, a direct thrombin inhibitor, was approved by the US Food and Drug Administration (FDA) in 2010 for reducing the risk of stroke and systemic embolism in patients with nonvalvular AF. The activated factor X (factor Xa) inhibitor rivaroxaban was recently approved by the FDA both for prophylaxis of deep vein thrombosis, which may lead to pulmonary embolism in patients undergoing knee or hip arthroplasty, and for reducing the risk of stroke and systemic embolism in patients with nonvalvular AF. Apixaban, another factor Xa inhibitor, was recently shown to be effective for stroke prevention in patients with nonvalvular AF. This article reviews clinical considerations regarding new agents that may offer alternatives to VKA therapy for the prevention of stroke in patients with AF.

A new era of oral anticoagulation in atrial fibrillation: implications in clinical practice

For > 50 years, vitamin K antagonists were the only available oral drugs for the prevention of thromboembolism in patients with atrial fibrillation. Recently, new oral anticoagulants (the direct thrombin inhibitor dabigatran and the direct activated factor X (factor Xa) inhibitors rivaroxaban and apixaban) have completed phase 3 clinical trials for the same indications. The direct factor Xa inhibitor apixaban was approved by the US Food and Drug Administration in December 2012. In this article, we provide a comprehensive assessment of the safety and efficacy of the new oral anticoagulants. We focus primarily on the balance between thromboembolic and hemorrhagic risk and the implications of such risks in clinical practice. Bleeding and thromboembolic risk estimation tools and their roles in the correct utilization of new oral anticoagulation are also discussed.

Novel 2-aminobenzamides as potential orally active antithrombotic agents

In an effort to develop potent antithrombotic agents, a series of novel 2-aminobenzamide derivatives were synthesized and screened for their in vivo antithrombotic activity. Among the 23 compounds tested, compound (8g) showed the most promising antithrombotic activity, which was comparable with clinically used aspirin or warfarin, but at variance with these standard drugs, 8g did not exhibit the increased bleeding time, suggesting its potential as a novel antithrombotic agent.

Knee length versus thigh length graduated compression stockings for prevention of deep vein thrombosis in postoperative surgical patients

BACKGROUND

Graduated compression stockings (GCS) are a valuable means of thromboprophylaxis in hospitalised postoperative surgical patients. But it is still unclear whether knee length graduated compression stockings (KL) or thigh length (TL) stockings are more effective.

OBJECTIVES

The aim of this review was to systematically analyse the randomised, controlled trials that have evaluated the effectiveness of KL versus TL GCS as a thromboprophylaxis tool in hospitalised patients undergoing various types of surgery.

SEARCH METHODS

The Cochrane Peripheral Vascular Diseases Group Trials Search Co-ordinator searched the Specialised Register (last searched February 2012) and CENTRAL (2012, Issue 1). The authors searched MEDLINE and EMBASE (until 27 February 2012) and they also searched the reference lists of relevant articles to identify additional trials.

SELECTION CRITERIA

Randomised controlled trials published in any language on KL versus TL GCS used as a thromboprophylaxis tool in hospitalised patients of any age and either gender.

DATA COLLECTION AND ANALYSIS

Data extraction was undertaken independently by two review authors using data extraction sheets and confirmed by the third review author.

MAIN RESULTS

Three studies, with a combined total of 496 patients, matched the inclusion criteria for this review. All three included studies evaluated the role of KL and TL in thromboprophylaxis among a group of postoperative patients. These studies showed no significant difference in the ability of the two modalities of leg compression to reduce the incidence of deep vein thrombosis in postoperative patients. In both the fixed-effect model (odds ratio (OR) 1.55, 95% confidence interval (CI) 0.78 to 3.07, P = 0.21) and random-effects model (OR 1.32, 95% CI 0.43 to 4.06, P = 0.63) KL graduated compression stockings were as effective as TL stockings in thromboprophylaxis. However, there was significant heterogeneity (Tau(2) = 0.50; Chi(2) = 4.12, df = 2 (P = 0.13); I(2) = 51%) among trials. Results of this review may be considered weak because there was significant heterogeneity among included trials resulting from inadequate randomisation techniques, allocation concealment, power calculations and the absence of intention-to-treat analysis.

AUTHORS' CONCLUSIONS

This review found that there is insufficient high quality evidence to determine whether or not KL and TL GCS differ in their effectiveness in terms of reducing the incidence of deep vein thrombosis (DVT) in hospitalised patients.  A major multicentre RCT is required to address this issue. In the meantime, the decision on which type of stocking to use in clinical practice is likely to be influenced by factors such as patient compliance, ease of use and cost implications.

Current therapies in ischemic stroke. Part A. Recent developments in acute stroke treatment and in stroke prevention

Stroke is the third leading cause of death with an increasing prevalence. In previous years many important achievements and new therapeutic strategies have been established. This article provides an overview on recent developments and is an update to the article of Green et al. that was published in 2004. As this article is a comprehensive review we divided it in two parts. In this Part A of our review, recent developments in acute stroke treatment and in stroke prevention are described. In Part B we will reflect on neuroprotection.

Anticoagulation management in clinical practice: preventing stroke in patients with atrial fibrillation

Atrial fibrillation (AF) is a major and widely recognized risk factor for cardioembolic stroke. Prophylactic therapy for the prevention of stroke in patients with AF is often achieved through oral anticoagulation, specifically with warfarin, which has been used for this purpose for more than 50 years. Although warfarin therapy is effective when implemented appropriately, it is often underutilized and requires consistent monitoring to ensure both safety in avoiding bleeding and efficacy in preventing strokes. Because the burden of AF-related stroke continues to rise, healthcare professionals need to understand the strengths and limitations of current and emerging treatment options. This review outlines current practices for managing the risk of stroke with anticoagulation in patients with AF, and discusses how new oral anticoagulants may affect clinical practice.

Role of emerging antithrombotic therapy in the prevention of cardioembolic complications in patients with atrial fibrillation

Atrial fibrillation (AF) is the most common sustained cardiac arrhythmia and is an independent risk factor of potentially catastrophic cardioembolic strokes. AF patients are categorized into high-, intermediate-, and low-risk for thromboembolic complications using the CHADS(2) or CHA(2)DS(2)-VASc scoring system. Oral anticoagulation using warfarin has been the standard therapy for stroke prevention in intermediate- to high-risk AF patients. However, warfarin use has been limited by several factors such as narrow therapeutic windows, drug-drug and drug-food interactions, and hemorrhagic complications. Rigorous research evaluated dual antiplatelet therapy of clopidogrel and aspirin (acetylsalicylic acid) as a potential alternative to warfarin in the ACTIVE W trial. Dual antiplatelet therapy of clopidogrel and aspirin was found to be inferior to warfarin in preventing stroke and systemic embolism with increased bleeding risk. Other extensive research has led to the development of new antithrombotic agents. Recently, dabigatran etexilate 150 mg twice daily, a direct thrombin inhibitor, was approved by the US FDA for stroke prevention in patients with non-valvular AF after it was found to be superior to warfarin in preventing thromboembolic events and associated with less bleeding in the RE-LY trial. It was also cost effective when compared with warfarin. Dabigatran can be considered in high-risk AF patients who are unable or unwilling to comply with the frequent laboratory and clinic visits that are required when receiving treatment with warfarin. Factor Xa inhibitors are another class of new anticoagulants that have been developed. Oral rivaroxaban was non-inferior to warfarin in thromboprophylaxis and with similar bleeding in the ROCKET-AF trial (HR 0.88; p = 0.117). Apixaban, another factor Xa inhibitor, was superior to aspirin in reducing stroke and systemic embolism in patients with AF in the AVERROES trial (HR 0.45; p < 0.001). The results of the ARISTOTLE trial, which is evaluating apixaban against warfarin in ∼18 000 patients with AF, are expected to be available later this year. Edoxaban, another oral factor Xa inhibitor, is currently being evaluated against warfarin in the ENGAGE AF-TIMI 48 trial in ∼20 000 patients with AF. With these new developments, there is a necessity for the clinical practitioner to become familiar with these new and upcoming therapies and guidelines. This review provides an overview of the available data regarding the clinical usefulness of these agents.

Structure and property based design of factor Xa inhibitors: pyrrolidin-2-ones with aminoindane and phenylpyrrolidine P4 motifs

The rational design, syntheses and evaluation of potent sulfonamidopyrrolidin-2-one-based factor Xa inhibitors incorporating aminoindane and phenylpyrrolidine P4 motifs are described. These series delivered highly potent anticoagulant compounds with excellent oral pharmacokinetic profiles; however, significant time dependant P450 inhibition was an issue for the aminoindane series, but this was not observed with the phenylpyrrolidine motif, which produced candidate quality molecules with potential for once-daily oral dosing in humans.

Dabigatran etexilate: a possible replacement for heparinoids and vitamin K antagonists?

Dabigatran etexilate is the first oral anticoagulant to be approved in the United States in decades. It works directly by inhibiting clot-bound and free factor IIa (ie, thrombin) and indirectly by inhibiting platelet aggregation induced by thrombin. It is approved in the United States for stroke prophylaxis in nonvalvular atrial fibrillation. There is evidence to suggest that it is also effective for the treatment of acute venous thromboembolism and venous thromboembolism prophylaxis after knee and hip replacement surgery. Dabigatran etexilate therapy does not require laboratory monitoring, an advantage over warfarin. Unlike the earlier direct thrombin inhibitor, ximelagatran, it has demonstrated no potential for serious hepatotoxicity. It is also subject to a much lower degree of interpatient variability in dose response, has no diet-drug interactions, and has fewer clinically significant drug-drug interactions compared with warfarin. Dabigatran etexilate appears to be a valuable addition to our anticoagulant armamentarium.

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.