Preclinical and Clinical Data for Factor Xa and "Universal" Reversal Agents

Methods to Correct Drug-Induced Coagulopathy in Bleeding Emergencies: A Comparative Review

OBJECTIVE

Anticoagulant and antiplatelet therapy have become increasingly popular. The goal of therapy is to prevent venous thromboembolism and platelet aggregation, respectively. Traditional anticoagulant and antiplatelet drugs are quickly being replaced with novel medications with more predictable pharmacokinetics. Unfortunately, these drugs carry the risk of uncontrolled hemorrhage because of drug-induced coagulopathy. Uncontrolled hemorrhage continues to be a major cause of preventable death: hemorrhage accounts for approximately 30% of trauma-related deaths, second to brain injury. Controlling hemorrhage while dealing with comorbidities remains a challenge to clinicians. There are many gaps in care and knowledge that contribute to the struggle of treating this patient population.

METHODS

This literature review is focused on the most effective ways to achieve hemostasis in a patient with drug-induced coagulopathy. The antiplatelet therapies aspirin, clopidogrel, ticlopidine, pasugrel, and ticagrelor are analyzed. Anticoagulant therapies are also reviewed, including warfarin, rivaroxaban, apixaban, edoxaban, and dabigatran. In addition, viscoelastic testing and platelet function assays are reviewed for their ability to monitor drug effectiveness and to accurately depict the patient's ability to clot. This review focuses on articles from the past 10 years. However, there are limitations to the 10-year restriction, including no new research posted within the 10-year timeline on particular subjects. The most recent article was then used where current literature did not exist (within 10 years).

RESULTS

Traditional anticoagulants have unpredictable pharmacokinetics and can be difficult to correct in bleeding emergencies. Vitamin K has been proven to reliably and effectively reverse the effect of vitamin K antagonists (VKAs) while having a lower anaphylactoid risk than frozen plasma. Prothrombin complex concentrates should be used when there is risk of loss of life or limb. Frozen plasma is not recommended as a first-line treatment for the reversal of VKAs. Novel anticoagulants have specific reversal agents such as idarucizumab for dabigatran and andexxa alfa for factor Xa (FXa) inhibitors. Although reliable, these drugs carry a large price tag. As with traditional anticoagulants, cheaper alternative therapies are available such as prothrombin complex concentrates. Finally, static coagulation testing works well for routine therapeutic drug monitoring but may not be appropriate during bleeding emergencies. Viscoelastic testing such as thromboelastography and rotational thromboelastometry depict in vivo hemostatic properties more accurately than static coagulation assays. Adding viscoelastic testing into resuscitation protocols may guide blood product usage more efficiently.

CONCLUSION

This review is intended to be used as a guide. The topics covered in this review should be used as a reference for treating the conditions described. This review article also covers laboratory testing and is meant as a guide for physicians on best practices. These findings illustrate recommended testing and reversal techniques based off evidence-based medicine and literature.

Restarting Oral Anticoagulation in Patients With Atrial Fibrillation After an Intracranial Hemorrhage

Atrial fibrillation is the most common sustained cardiac arrhythmia in the general population. In western countries with aging populations, atrial fibrillation poses a significant health concern, as it is associated with a high risk of thromboembolism, stroke, congestive heart failure, and myocardial infarction. Thrombi are generated in the left atrial appendage, and subsequent embolism into the cerebral circulation is a major cause of ischemic stroke. Therefore, patients have a lifetime risk of stroke, and those at high risk, defined as a CHA2DS2-VASc2 (congestive heart failure, hypertension, age >75 years, diabetes mellitus, stroke/transient ischemic attack/thromboembolism, vascular disease, age 65-74 yrs, sex category) ≥2, are usually placed on oral anticoagulants. Unfortunately, long-term anticoagulation poses bleeding risks, of which intracranial hemorrhage (ICH) is the most feared and deadly complication.In patients who survive an ICH, the question of oral anticoagulation resumption arises. It is a therapeutic dilemma in which clinicians must decide how to manage the risk of thromboembolism versus recurrent hemorrhage. Although there is a substantial amount of retrospective data on the topic of resumption of anticoagulation, there are, at this time, no randomized controlled trials addressing the issue. We therefore sought to address ICH risk and management, summarize high quality existing evidence on restarting oral anticoagulation, and suggest an approach to clinical decision-making.

The Interactions of Nintedanib and Oral Anticoagulants-Molecular Mechanisms and Clinical Implications

Nintedanib is a synthetic orally active tyrosine kinase inhibitor, whose main action is to inhibit the receptors of the platelet-derived growth factor, fibroblast growth factor and vascular endothelial growth factor families. The drug also affects other kinases, including Src, Flt-3, LCK, LYN. Nintedanib is used in the treatment of idiopathic pulmonary fibrosis, chronic fibrosing interstitial lung diseases and lung cancer. The mechanism of action suggests that nintedanib should be considered one of the potential agents for inhibiting and revising the fibrosis process related to COVID-19 infections. Due to the known induction of coagulation pathways during COVID-19 infections, possible interaction between nintedanib and anticoagulant seems to be an extremely important issue. In theory, nintedanib could increase the bleeding risk, thrombosis and lead to thrombocytopenia. The data from clinical trials on the concomitant use of nintedanib and antithrombotic agents is very limited as this patient group was within the standard exclusion criteria. Nintedanib is an important therapeutic option, despite its interaction with anticoagulants. If anticoagulant therapy is necessary, the more effective and safer option is the concomitant administration of DOACs and nintedanib, especially when drug-monitored therapy will be used in patients at high risk of bleeding complications.

NOACs: an emerging class of oral anticoagulants-a review article

Background

NOACs, commonly known as novel oral anticoagulants, are the non-vitamin K antagonist oral anticoagulants which are relatively newer in the market. It has displaced vitamin K antagonists, notably warfarin, for many indications. These agents are dabigatran, rivaroxaban, apixaban, and edoxaban.

Main body

The drugs are licenced to prevent stroke and also systemic embolism in patients on treatment for atrial fibrillation and prevent venous thromboembolism. Rivaroxaban and apixaban are approved for prophylaxis of thrombus following surgical hip or knee arthroplasty. The recent surveys reveal that use of NOACs has steeply increased due to its safety profile and convenience to use. Also, the studies have shown that NOACs have lesser bleeding complications and associated mortality in contrast to traditional anticoagulants. The upcoming years are known to be NOACs’ age due to the significant findings in this area.

Conclusion

Therefore, a basic understanding on these drugs is highly recommended to provide a better service to the patients. This article aims to provide quick and brief information on the novel class of drugs. It equips an overview of NOAC and deals with the following areas: (i) pharmacology, (ii) laboratory methods, (iii) peri-operative management, (iv) advantages, (v) challenges, and (vi) future.

Comparing Safety and Efficacy of Dabigatran and Factor Xa Inhibitors for Stroke Prevention in Hemophiliacs with Non-Valvular Atrial Fibrillation

BACKGROUND

Atrial fibrillation, a progressively rising global health problem, is also rising in Hemophiliacs due to an increase in life expectancy in them. While treating Hemophiliacs with AF, deciding eligibility, choosing the anticoagulant based on risk-benefit ratio are tough decisions for physicians to make. This review paper aims to explore and compare existing studies, reviews and consensus papers to assess the safety of different Novel Oral Anticoagulants (NOACS) in this population.

METHODS

Thorough literature search was conducted on Pubmed using Atrial Fibrillation, Hemophilia A, Oral anticoagulants, stroke prevention, Dabigatran, factor Xa inhibitors as keywords separately and in combinations. Papers in English language only from the past 5 years were selected for review. After removing duplicate results, 80 papers were selected and after applying different exclusion criteria and according to relevance, 40 papers were finalized for review.

RESULTS

The keywords AF, Stroke prevention, oral anticoagulants, Hemophilia a, Factor Xa inhibitors and Dabigatran gave 24899, 13619, 8964, 3503, 2850, 2799 results, respectively. Combination keywords also showed some papers and out of short-listed 80 relevant papers 35 were finalized. Reviewing and analyzing these papers revealed no clinical trials in hemophiliacs with AF in the past 5 years and 5 clinical trials comparing NOACs with Warfarin in general population. Rest were systematic reviews, consensus papers and meta-analyses on management in this group. A few compared these drugs for AF in the general population but not specifically in Hemophiliacs and others. consensus papers developed suggestions for management and showed that NOACs are superior to Warfarin but need individual evaluation in Hemophiliacs with AF.

CONCLUSIONS

Patients with Hemophilia can also have thrombo-embolism despite their bleeding tendency and NOACs are a better option in them because of less need for monitoring, no food interactions and fewer drug interactions. This comparative review emphasized the need for more work to develop proper guidelines for thrombo-prophylaxis management in this specific group.

Andexanet alfa for reversal of factor Xa inhibitor-associated anticoagulation

Background:

Review of clinical data on andexanet alfa for the reversal of factor Xa (FXa) inhibitor associated anticoagulation.

Data sources:

In the present review, we identified articles via PubMed using the combined keywords andexanet alfa, apixaban, enoxaparin, edoxaban, and rivaroxaban. Additional online searches via PubMed, Google Scholar, and Lexicomp were conducted for both prescribing and cost information. Portola Pharmaceuticals was contacted for information used for United States Food and Drug Administration approval of andexanet alfa.

Study selection and data extraction:

English-language clinical trials and reviews published between January 2008 and April 2019 were included for review. Bibliographies of selected articles were reviewed manually for relevant publications, focusing on reversal strategies for apixaban, enoxaparin, edoxaban, or rivaroxaban associated anticoagulation using andexanet alfa. Review articles were excluded.

Data synthesis:

The safety and tolerability of andexanet alfa were evaluated in one phase I, two phase II, and one phase III clinical trials. The use of andexanet alfa for reversing FXa inhibitor-associated anticoagulation were evaluated in the phase III ANNEXA-4 study.

Conclusions:

Studies evaluating laboratory parameters for coagulation show that andexanet alfa rapidly neutralizes the anticoagulant effects of apixaban, enoxaparin, edoxaban, and rivaroxaban. Clinical studies show that andexanet alfa improves markers related to coagulation, and reverses major bleeding in healthy volunteers and patients with life-threatening bleeding. Interruption of anticoagulation may result in thromboembolic and ischemic events. The use of andexanet alfa requires close monitoring for signs and symptoms of thromboembolic events, ischemic events, and cardiac arrest. Furthermore, anticoagulation should be resumed following the administration of andexanet alfa as soon as medically appropriate.

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.

Direct-Acting Oral Anticoagulants and Their Reversal Agents-An Update

Background: Over the last ten years, a new class of drugs, known as the direct-acting oral anticoagulants (DOACs), have emerged at the forefront of anticoagulation therapy. Like the older generation anticoagulants, DOACs require specific reversal agents in cases of life-threatening bleeding or the need for high-risk surgery. Methods: Published literature was searched, and information extracted to provide an update on DOACS and their reversal agents. Results: The DOACs include the direct thrombin inhibitor—dabigatran, and the factor Xa inhibitors—rivaroxaban, apixaban, edoxaban, and betrixaban. These DOACs all have a rapid onset of action and each has a predictable therapeutic response requiring no monitoring, unlike the older anticoagulants, such as warfarin. Two reversal agents have been approved within the last five years: idarucizumab for the reversal of dabigatran, and andexanet alfa for the reversal of rivaroxaban and apixaban. Additionally, ciraparantag, a potential “universal” reversal agent, is currently under clinical development. Conclusions: A new generation of anticoagulants, the DOACs, and their reversal agents, are gaining prominence in clinical practice, having demonstrated superior efficacy and safety profiles. They are poised to replace traditional anticoagulants including warfarin.

Approaches to prevent bleeding associated with anticoagulants: current status and recent developments

Anticoagulants are widely used for the prophylaxis and treatment of cardiovascular disorders and to prevent blood clotting during surgeries. However, the major limitation associated with anticoagulant therapy is bleeding; all the current anticoagulants do have a bleeding risk. The propensity to bleed is much higher among the elderly population and patients with renal insufficiency. Therefore, there is an utmost and urgent clinical need for a highly efficient, nontoxic antidote with excellent anticoagulant reversal activity. This will significantly improve the safety of anticoagulation therapy. This review summarizes the current options and approaches to reverse anticoagulation activity of clinically used anticoagulants. We start with an introduction to thrombosis and then summarize the details of current clinically available anticoagulants and their mechanisms of action and limitations. This is followed by current practices in anticoagulant neutralization including the details of the only clinically approved unfractionated heparin antidote, protamine; recent advances in the development of antidotes against heparin-based drugs; and direct oral anticoagulants (DOACs).

Betrixaban (Bevyxxa): A Direct-Acting Oral Anticoagulant Factor Xa Inhibitor

Betrixaban (Bevyxxa): a direct-acting oral anti-coagulant factor Xa inhibitor.

Reversing factor Xa inhibitors - clinical utility of andexanet alfa

Approximately half of patients started on an oral anticoagulant in the USA now receive one of the newer direct oral anticoagulants (DOACs). Although there is an approved reversal agent for the direct thrombin inhibitor dabigatran, a specific reversal agent for the anti-factor Xa (FXa) DOACs has yet to be licensed. Unlike the strategy to reverse the only oral direct thrombin inhibitor with idarucizumab, which is a humanized monoclonal antibody fragment, a different approach is necessary to design a single agent that can reverse multiple anti-FXa medications. Andexanet alfa is a FXa decoy designed to reverse all anticoagulants that act through this part of the coagulation cascade including anti-FXa DOACs, such as apixaban, edoxaban and rivaroxaban, and indirect FXa inhibitors such as low-molecular-weight heparins. This narrative reviews the development of andexanet alfa and explores its basic science, pharmacokinetics/pharmacodynamics, animal models, and human studies.

Exploring indications for the Use of direct oral anticoagulants and the associated risks of major bleeding

Thrombosis is a leading cause of morbidity and mortality in the United States. Arterial and venous thromboses are implicated in the pathogenesis of major disorders, including myocardial infarction, ischemic stroke, and venous thromboembolism. Over the past decade, direct oral anticoagulants (DOACs) (eg, direct thrombin inhibitor and factor Xa [FXa] inhibitors) have been adopted as alternatives to warfarin due to their clinical advantages and efficacy for the treatment of thrombosis. As with all anticoagulants, treatment with DOACs is associated with a risk of major bleeding, including life-threatening gastrointestinal bleeds and intracranial hemorrhages (ICHs). In turn, the burden of bleeding associated with DOAC treatment is itself associated with substantial healthcare costs that are amplified by an increased risk of thromboembolic events and mortality following major bleeding events, especially in patients with ICHs. Given the rapid adoption of the DOACs and projected usage in the large patient population affected by thromboembolic conditions, clinicians are increasingly likely to encounter patients with major bleeding events due to DOAC therapy. Unlike warfarin, effective strategies to manage these bleeds are limited. There is an unmet need for reversal agents for use in the management of patients who receive FXa inhibitors and experience life-threatening bleeding or need emergency surgery. Andexanet alfa and ciraparantag are being evaluated as potential antidotes for both direct and indirect FXa inhibitors.

Emerging Role of Direct Oral Anticoagulants in the Management of Heparin-Induced Thrombocytopenia

Heparin-induced thrombocytopenia (HIT) and heparin-induced thrombocytopenia with thrombosis (HITT) are rare but potentially limb- and life-threatening complications of heparin therapy. Continuation of heparin or low-molecular-weight heparin is contraindicated due to platelet activation in the presence of (heparin-dependent) HIT antibodies. Primary treatment options currently include argatroban, fondaparinux, or bivalirudin. However, the parenteral administration routes and interference of argatroban with traditional coagulation markers complicate management. The goal of this review is to assess the viability of direct oral anticoagulants as an alternative treatment option in patients with HIT/HITT. Their use in HIT/HITT is reasonable, given absent cross-reactivity preformed with HIT antibodies. Furthermore, their rapid onset of action and induction of effective anticoagulation provide a favorable basis for their use in this condition. Herein, we summarize 3 studies and 8 case reports comprising 56 patients in whom direct oral anticoagulants were used in the treatment of HIT/HITT.

Bleeding with direct oral anticoagulants vs warfarin: clinical experience

The risk of bleeding in the setting of anticoagulant therapy continues to be re-evaluated following the introduction of a new generation of direct oral anticoagulants (DOACs). Interruption of DOAC therapy and supportive care may be sufficient for the management of patients who present with mild or moderate bleeding, but in those with life-threatening bleeding, a specific reversal agent is desirable. We review the phase 3 clinical studies of dabigatran, rivaroxaban, apixaban, and edoxaban in patients with nonvalvular atrial fibrillation, in the context of bleeding risk and management.