Reversal of anticoagulants: an overview of current developments

New Anticoagulants for the Prevention and Treatment of Venous Thromboembolism

Anticoagulant drugs, like vitamin K antagonists and heparin, have been the mainstay for the treatment and prevention of venous thromboembolic disease for many years. Although effective if appropriately used, traditional anticoagulants have several limitations such as unpredictable pharmacologic and pharmacokinetic responses and various adverse effects including serious bleeding complications. New oral anticoagulants have recently emerged as an alternative because of their rapid onset/offset of action, predictable linear dose-response relationships and fewer drug interactions. However, they are still associated with problems such as bleeding, lack of reversal agents and standard laboratory monitoring. In an attempt to overcome these drawbacks, key steps of the hemostatic pathway are investigated as targets for anticoagulation. Here we reviewed the traditional and new anticoagulants with respect to their targets in the coagulation cascade, along with their therapeutic advantages and disadvantages. In addition, investigational anticoagulant drugs currently in the development stages were introduced.

Reversal of direct oral anticoagulants

Reversal agents for direct oral anticoagulants (DOACs), including factor X inhibitors and direct thrombin inhibitors, are a major concern in clinical practice. After DOACs were introduced and became widely used as an alternative for vitamin K antagonists in the management of venous thromboembolism and nonvalvular atrial fibrillation, the need for effective reversal agents has increased, particularly for life-threatening bleeding episodes related to DOACs or to reverse medication effects during urgent interventions. In the absence of specific reversal agents, prothrombin complex concentrate (PCC) and activated PCC are reasonable options to reverse bleeding associated with DOACs. However, high-quality clinical evidence is lacking. Idarucizumab is the only agent approved by the US Food and Drug Administration to reverse the effects of dabigatran; andexanet alfa and ciraparantag are also under evaluation as reversal agents for DOACs. This review summarizes the current evidence for nonspecific and specific reversal of DOACs.

Management of Severe Bleeding in Patients Treated with Direct Oral Anticoagulants

Background

The use of prothrombin complex concentrates and the role of plasma concentration of anticoagulants in the management of bleeding in patients treated with direct oral anticoagulants are still debated. Our aim was to describe management strategies and outcomes of severe bleeding events in patients treated with direct oral anticoagulants.

Methods

We performed a prospective cohort study of 732 patients treated with dabigatran, rivaroxaban, or apixaban hospitalized for severe bleeding, included prospectively in the registry from June 2013 to November 2015.

Results

Bleeding was gastrointestinal or intracranial in 37% (212 of 732) and 24% (141 of 732) of the cases, respectively. Creatinine clearance was lower than 60 ml/min in 61% (449 of 732) of the cases. The plasma concentration of direct oral anticoagulants was determined in 62% (452 of 732) of the cases and was lower than 50 ng/ml or higher than 400 ng/ml in 9.2% (41 of 452) and in 6.6% (30 of 452) of the cases, respectively. Activated or nonactivated prothrombin complex concentrates were administered in 38% of the cases (281 of 732). Mortality by day 30 was 14% (95% CI, 11 to 16).

Conclusions

Management of severe bleeding in patients treated with direct oral anticoagulants appears to be complex. The use of prothrombin complex concentrates differs depending on bleeding sites and direct oral anticoagulant plasma concentrations. Mortality differs according to bleeding sites and was similar to previous estimates.

Trauma patients on new oral anticoagulation agents have lower mortality than those on warfarin

BACKGROUND

Although anticoagulation with warfarin has been associated with increased risk of adverse outcomes after trauma, the effects of the new oral agents (NOA) such as dabigatran, apixaban, rivaroxaban are not yet well characterized.

METHODS

A retrospective review of a level 1 trauma center database identified all patients aged ≥ 50 admitted after trauma during a 24 month period starting September 2013. Demographics, including preadmission anticoagulation agents, injuries, hospital course and outcomes were abstracted from the electronic medical record.

RESULT

Over the 24-month period, 3,392 patients were admitted; 112 (3.3%) were anticoagulated with NOA and 373 (11.0%) with warfarin with a trend toward increasing utilization of the new agents compared with warfarin over that period. Although comparable in age, injury severity scores, and mechanism of injury, patients anticoagulated with warfarin had both a higher overall mortality (10.9%) compared with the NOA (6.25%) and the non-anticoagulated control (5.5%) groups (p < 0.001) as well as a higher trauma-related mortality (9.0%) versus NOA (2.8%) and control (3.7%) groups (p < 0.001). Patients on warfarin or NOA were admitted to intensive care unit or step down unit more frequently than control patients. (45.0% and 41.9% vs. 35.7% respectively; p < 0.001). The incidence of traumatic brain injury was similar among the three groups. Although it did not reach statistical significance, trauma-specific mortality in the traumatic brain injury subset was higher in the warfarin group (19.3%) than the NOA (16.7%) or control (10.9%) groups (p = 0.08). In a multivariable logistic regression, warfarin (odds ratio, 2.215; 95% confidence interval, 1.365-3.596; p = 0.001), but not the NOA (odds ratio, 0.871; 95% confidence interval, 0.258-2.939; p = 0.823), was an independent predictor for mortality.

CONCLUSIONS

Although the experience with the new oral anticoagulation agents is still limited, patients on these agents appear to have lower mortality after traumatic injury than patients on warfarin.

LEVEL OF EVIDENCE

Epidemiologic study, level III.

2017 consensus of the Asia Pacific Heart Rhythm Society on stroke prevention in atrial fibrillation

Atrial fibrillation (AF) is the most common sustained arrhythmia, causing a 2-fold increase in mortality and a 5-fold increase in stroke. The Asian population is rapidly aging, and in 2050, the estimated population with AF will reach 72 million, of whom 2.9 million may suffer from AF-associated stroke. Therefore, stroke prevention in AF is an urgent issue in Asia. Many innovative advances in the management of AF-associated stroke have emerged recently, including new scoring systems for predicting stroke and bleeding risks, the development of non-vitamin K antagonist oral anticoagulants (NOACs), knowledge of their special benefits in Asians, and new techniques. The Asia Pacific Heart Rhythm Society (APHRS) aimed to update the available information, and appointed the Practice Guideline sub-committee to write a consensus statement regarding stroke prevention in AF. The Practice Guidelines sub-committee members comprehensively reviewed updated information on stroke prevention in AF, emphasizing data on NOACs from the Asia Pacific region, and summarized them in this 2017 Consensus of the Asia Pacific Heart Rhythm Society on Stroke Prevention in AF. This consensus includes details of the updated recommendations, along with their background and rationale, focusing on data from the Asia Pacific region. We hope this consensus can be a practical tool for cardiologists, neurologists, geriatricians, and general practitioners in this region. We fully realize that there are gaps, unaddressed questions, and many areas of uncertainty and debate in the current knowledge of AF, and the physician׳s decision remains the most important factor in the management of AF.

Anticoagulant Reversal and Anesthetic Considerations

Bleeding complications are a common concern with the use of anticoagulant agents. In many situations, reversing of neutralizing their effects may be warranted. Prothrombin complex concentrate replaces coagulation factors lowered by warfarin, as does fresh frozen plasma, but in a more concentrated form. Protamine negates the effect of heparin and combines chemically with heparin molecules to form an inactive salt. It also partially reverses the effects of low-molecular-weight heparin. Recombinant activated factor VII is a nonspecific procoagulant that activates the extrinsic clotting pathway, resulting in thrombin generation, but does not directly neutralize the activity of any of the new oral anticoagulants.

Perioperative management of patients on direct oral anticoagulants

Direct oral anticoagulants (DOACs) have been licensed worldwide for several years for various indications. Each year, 10-15% of patients on oral anticoagulants will undergo an invasive procedure and expert groups have issued several guidelines on perioperative management in such situations. The perioperative guidelines have undergone numerous updates as clinical experience of emergency management has increased and perioperative studies including measurement of residual anticoagulant levels have been published. The high inter-patient variability of DOAC plasma levels has challenged the traditional recommendation that perioperative DOAC interruption should be based only on the elimination half-life of DOACs, especially before invasive procedures carrying a high risk of bleeding. Furthermore, recent publications have highlighted the potential danger of heparin bridging use when DOACs are stopped before an invasive procedure. As antidotes are progressively becoming available to manage severe bleeding or urgent procedures in patients on DOACs, accurate laboratory tests have become the standard to guide their administration and their actions need to be well understood by clinicians. This review aims to provide a systematic approach to managing patients on DOACs, based on recent updates of various perioperative guidance, and highlighting the advantages and limits of recommendations based on pharmacokinetic properties and laboratory tests.

Evaluation of the immunogenicity of the dabigatran reversal agent idarucizumab during Phase I studies

Aims

Idarucizumab, a humanized monoclonal anti‐dabigatran antibody fragment, is effective in emergency reversal of dabigatran anticoagulation. Pre‐existing and treatment‐emergent anti‐idarucizumab antibodies (antidrug antibodies; ADA) may affect the safety and efficacy of idarucizumab. This analysis characterized the pre‐existing and treatment‐emergent ADA and assessed their impact on the pharmacokinetics and pharmacodynamics (PK/PD) of idarucizumab.

Methods

Data were pooled from three Phase I, randomized, double‐blind idarucizumab studies in healthy Caucasian subjects; elderly, renally impaired subjects; and healthy Japanese subjects. In plasma sampled before and after idarucizumab dosing, ADA were detected and titrated using a validated electrochemiluminescence method. ADA epitope specificities were examined using idarucizumab and two structurally related molecules. Idarucizumab PK/PD data were compared for subjects with and without pre‐existing ADA.

Results

Pre‐existing ADA were found in 33 out of 283 individuals (11.7%), seven of whom had intermittent ADA. Titres of pre‐existing and treatment‐emergent ADA were low, estimated equivalent to <0.3% of circulating idarucizumab after a 5 g dose. Pre‐existing ADA had no impact on dose‐normalized idarucizumab maximum plasma levels and exposure and, although data were limited, no impact on the reversal of dabigatran‐induced anticoagulation by idarucizumab. Treatment‐emergent ADA were detected in 20 individuals (19 out of 224 treated [8.5%]; 1 out of 59 received placebo [1.7%]) and were transient in ten. The majority had specificity primarily toward the C‐terminus of idarucizumab. There were no adverse events indicative of immunogenic reactions.

Conclusion

Pre‐existing and treatment‐emergent ADA were present at extremely low levels relative to the idarucizumab dosage under evaluation. The PK/PD of idarucizumab appeared to be unaffected by the presence of pre‐existing ADA.

Reversal agents for use with direct and indirect anticoagulants

PURPOSE

The properties of three oral anticoagulant-specific reversal agents are reviewed, and guidance is presented to assist pharmacists in planning for the agents' introduction to the market.

SUMMARY

Idarucizumab, which received Food and Drug Administration approval in October 2015, is a humanized monoclonal antibody fragment that immediately neutralizes the anticoagulant effect of dabigatran, as evidenced by reduced unbound dabigatran concentrations and normalized coagulation tests. Preliminary Phase III trial results demonstrated a median maximum reversal of 100%, a median time to bleeding cessation of 11.4 hours, and normal intraoperative hemostasis in 92% of patients requiring anticoagulation reversal before an urgent procedure. Andexanet alfa is a factor Xa (FXa) decoy that binds to direct and indirect FXa inhibitors. In Phase III trials in healthy volunteers, andexanet alfa reduced anti-FXa activity by more than 90%, reduced the concentration of unbound direct FXa inhibitor, and inhibited thrombin generation. Ciraparantag is a reversal agent under development for reversal of anticoagulation with direct and indirect FXa inhibitors and certain factor IIa inhibitors; it exerts its effect through hydrogen bonding. Concerns for thromboembolic events directly related to administration of idarucizumab, andexanet alfa, or ciraparantag have not arisen. Pharmacists need to begin preparing for the introduction of these specific reversal agents through protocol development and provider education; in addition, pharmacy departments need to plan for procurement and storage. The specific reversal agents should be incorporated into antithrombotic stewardship or other clinical pharmacy programs for surveillance.

CONCLUSION

As agents that provide rapid reversal of direct oral anticoagulant activity become available, advance planning will help hospitals to optimize their use.

Current knowledge on assessing the effects of and managing bleeding and urgent procedures with direct oral anticoagulants

PURPOSE

Current knowledge on managing major bleeding events with available hemostatic agents, including their combined use with potential reversal agents, in patients taking direct oral anticoagulant (DOACs) is reviewed.

SUMMARY

Over the past five years, a new generation of oral agents, the DOACs, has emerged as commonly used anticoagulants for stroke prevention in non-valvular atrial fibrillation, and treatment or secondary prevention of venous thromboembolism. Management of a bleeding event in the setting of DOAC therapy should take into account the relative risks of bleeding and thrombosis, which will determine the degree of anticoagulant reversal required. In the setting of a major (critical) bleeding event associated with notable blood loss, management may include transfusions of blood products to sustain the function of organ systems, and the availability of specific reversal agents will provide additional options for bleeding management. Beyond withholding the DOAC and providing supportive management that addresses any factors contributing to the bleeding event, clinicians may desire to expedite the removal of any anticoagulation effects. In general, this is accomplished by either removing or neutralizing the anticoagulant or by independently establishing hemostasis.

CONCLUSION

With or without reversal agents, patients may require supportive management such as mechanical pressure, volume support, transfusions of blood products, and, depending on the situation, surgery to repair the bleeding source. Specific reversal agents are currently under development or have recently been approved for the urgent management of bleeding events or the facilitation of invasive procedures in patients receiving DOACs.

Recent advances in the understanding and management of atrial fibrillation: a focus on stroke prevention

Atrial fibrillation (AF) is associated with an increased risk of stroke compared with the general population. It is anticipated that by 2030 an estimated 14-17 million patients will be diagnosed with this most prevalent arrhythmia within the European Union. AF-related stroke confers a higher mortality and morbidity risk, and thus early detection and assessment for the initiation of effective stroke prevention with oral anticoagulation (OAC) is crucial. Recent guidelines point to the use of non-vitamin K antagonist OACs (NOACs) where appropriate in stroke prevention of patients with non-valvular AF. At present, there are four NOACS available, with no direct head-to-head comparisons to suggest the superiority of one drug over another. Simple and practical risk assessment tools have evolved over the years to facilitate stroke and bleeding risk assessment in busy clinics and wards to aid decision-making. At present, the CHA ₂DS ₂VASc (congestive heart failure, hypertension, age 65-74/>75, diabetes mellitus, stroke/transient ischemic attack/thromboembolism, vascular disease, female sex) score is recommended by many international guidelines as a simple and practical method of assessing stroke risk in such patients. Alongside this, use of the HAS BLED (hypertension systolic blood pressure >160 mmHg, abnormal liver/renal function [with creatinine ≥200 μmol/L], stroke, bleeding history or predisposition, labile international normalized ratio [range <60% of the time], elderly [>65], concomitant drugs/alcohol) score aims to identify patients at high risk of bleeding for more regular review and follow-up and draws attention to potentially reversible bleeding risk factors. The aim of this review article is to provide an overview of recent advances in the understanding and management of AF with a focus on stroke prevention.

Antiplatelet and Antithrombotic Therapy in Patients with Atrial Fibrillation Undergoing Coronary Stenting

Stroke prevention is the main priority in the management cascade of atrial fibrillation. Most patients require long-term oral anticoagulation (OAC) and may require percutaneous coronary intervention. Prevention of recurrent cardiac ischemia and stent thrombosis necessitate dual antiplatelet therapy (DAPT) for up to 12 months. Triple antithrombotic therapy with OAC plus DAPT of shortest feasible duration is warranted, followed by dual antithrombotic therapy of OAC and antiplatelet agent, and OAC alone after 12 months. Because of elevated risk of hemorrhagic complications, new-generation drug-eluting stents, lower-intensity OAC, radial access, and routine use of gastric protection with proton pump inhibitors are recommended.

Idarucizumab, a Specific Reversal Agent for Dabigatran: Mode of Action, Pharmacokinetics and Pharmacodynamics, and Safety and Efficacy in Phase 1 Subjects

The direct oral anticoagulants (DOACs) provide a number of clinical advantages over vitamin K antagonists for the treatment of thromboembolism, including improved efficacy and safety, as well as no need for regular monitoring of anticoagulant effect. However, as with all anticoagulants, bleeding complications may occur, and anticoagulant reversal may be required in specific clinical situations, such as in patients experiencing spontaneous or traumatic bleeds, or in anticoagulated patients requiring emergency surgery or other invasive procedures. Therefore, several reversal agents for the DOACs are in development. This includes the specific reversal agent idarucizumab, which has been approved by the U.S. Food and Drug Administration and the European Medicines Agency for use in patients treated with dabigatran when urgent reversal of its anticoagulant effects is needed. Idarucizumab is a humanized monoclonal antibody fragment that binds with high affinity to free and thrombin-bound dabigatran, resulting in an almost irreversibly bound idarucizumab-dabigatran complex and thereby neutralizing dabigatran's anticoagulant activity. The reversal of the anticoagulant effects of dabigatran by idarucizumab has been demonstrated in animal bleeding models, in healthy volunteers with a range of ages and renal function, and in anticoagulated patients. In the phase 1 trials, at doses of 2 g or greater, idarucizumab resulted in immediate and complete reversal of the dabigatran anticoagulant effects and was well tolerated. In the absence of dabigatran, idarucizumab showed no effect on coagulation parameters or thrombin formation. These findings provide initial evidence that idarucizumab could provide a safe and effective means of reversing anticoagulant activity in patients treated with dabigatran in need of emergency surgery or in emergency bleeding situations.

Idarucizumab and Factor Xa Reversal Agents: Role in Hospital Guidelines and Protocols

As expected with all antithrombotic agents, there is a risk of bleeding complications in patients receiving direct oral anticoagulants (DOACs) because of the DOAC itself, acute trauma, invasive procedures, or underlying comorbidities. For many bleeding events, a prudent course of action will be to withdraw the DOAC, then "wait and support" the patient, with the expectation that the bleeding event should resolve with time. Likewise, DOAC therapy may be interrupted ahead of a planned procedure, the stopping time being dependent on the agent involved and the patient's renal function. However, urgent reversal of anticoagulation is required in patients with serious or life-threatening bleeding or in those requiring urgent surgery or procedures. Novel specific reversal agents, either under development or recently approved, will need to be incorporated into local anticoagulation reversal protocols. For dabigatran-treated patients, idarucizumab recently has been approved for clinical use in cases of life-threatening or uncontrolled bleeding or when patients require emergency surgery or urgent procedures, both associated with a high risk of bleeding. As clinical experience with individual specific reversal agents grows, their roles in managing major bleeding events in DOAC-treated patients will become better defined. Future research, as well as ongoing use of idarucizumab, should help establish when it is appropriate to re-dose with idarucizumab, co-administer with prothrombin complex concentrates, or re-initiate DOAC after idarucizumab use. Ongoing trials should help identify the appropriate doses and expected durations of effect for andexanet alfa and ciraparantag, which are likely to vary depending on the individual oral anticoagulants.

Heparin-binding copolymer reverses effects of unfractionated heparin, enoxaparin, and fondaparinux in rats and mice

The parenteral anticoagulants may cause uncontrolled and life-threatening bleeding. Protamine, the only registered heparin antidote, is partially effective against low-molecular weight heparins, completely ineffective against fondaparinux and may cause unacceptable toxicity. Therefore, we aimed to develop a synthetic compound for safe and efficient neutralization of all parenteral anticoagulants. We synthesized pegylated PMAPTAC block copolymers, and then, we selected a lead heparin-binding copolymer (HBC). We assessed the effectiveness of HBC in the model of arterial thrombosis electrically induced in the carotid artery of rats by measuring thrombus weight, bleeding time, activated partial thromboplastin time, activated clotting time, and anti-factor Xa activity. The intravital tissue distribution, the cardiorespiratory, and organ toxicity were monitored. HBC diminished antithrombotic and anticoagulant effects of unfractionated heparin. Moreover, it stopped bleeding and completely reversed the enhancement of clotting times and anti-factor Xa activity caused by enoxaparin or fondaparinux. We observed slight pulmonary congestion and cell infiltration, but the cardiorespiratory parameters remained unchanged. We found a strong signal of fluorescently-labeled HBC in the urine, and a weaker in the liver and in the kidney. No signs of hepatic or nephrotoxicity were observed in the blood biochemistry or histopathologic examination. We developed a copolymer efficiently neutralizing effects of heparins in the living organism, which shows a very promising efficacy/safety profile and may help in the management of uncontrolled bleeding resulting from an anticoagulant injection. HBC could enable the safe replacement of unfractionated heparin with low-molecular weight heparins in patients undergoing cardiac surgery and complex vascular procedures.

Reversal of Anticoagulation and Management of Bleeding in Patients on Anticoagulants

Bleeding is the most common complication of all anticoagulants. Any bleeding patient on an anticoagulant should be risk-stratified based on hemodynamic instability, source of bleeding, and degree of blood loss. Although minor bleed may be managed with discontinuation of anticoagulant, major bleed may require transfusion of blood products and use of specific antidote. The residual effects of each anticoagulant may be monitored with distinct coagulation assay. Intravenous or oral vitamin K can reverse the effect of warfarin within 24 to 48 hours and is indicated for any bleeding, international normalized ratio of >10 or 4.5 to 10 in patients with other risk factors for bleeding. Fresh frozen plasma or prothrombin complex concentrate (PCC) may be necessary in major bleeding related to warfarin. Protamine sulfate reverses the effect of unfractionated heparin completely and of low-molecular-weight heparin (LMWH) partially. Idarucizumab has recently been approved in United States for dabigatran reversal, whereas andexanet alfa is expected to get approved in the near future for reversal of oral factor Xa inhibitors. The PCC may reverse the effect of rivaroxaban to some extent, but no data are available regarding reversal of apixaban and edoxaban. Aripazine has shown promising results to reverse the effects of LMWH, fondaparinux, and direct oral anticoagulants but is still in the developmental phase.

An update on the pharmaceutical management of thrombosis

INTRODUCTION

Anticoagulants such as heparins and vitamin K antagonists (VKA) are effective for thrombosis prevention and treatment, but are associated with the risk of bleeding and other limitations, spurring the search for improved drugs. Areas covered: to evaluate the newer anticoagulants, focusing on those tested in phase III clinical trials such as direct oral anticoagulants (DOACs), antisense oligonucleotides (ASO) and warfarin analogues. DOACs such as dabigatran, rivaroxaban, apixaban and edoxaban are licensed for stroke prevention in atrial fibrillation and treatment of venous thromboembolism, dabigatran, rivaroxaban and apixaban for postoperative thromboprophylaxis in patients undergoing elective hip or knee arthroplasty and rivaroxaban for secondary prevention of acute coronary syndromes. ASO interfering with Factor XI hepatic synthesis were effective and safe for thromboprophylaxis in elective knee arthroplasty. Expert opinion: DOACs have overcome some limitations of anticoagulants such as VKA, but are still associated with a risk of bleeding and they lack both standardized and widely available tests measuring their anticoagulant effect and a reversal agent, except for idarucizumab, specific for dabigatran, in case of major or life threatening bleeding or emergency surgery. Agents targeting Factor XI and possibly Factor XII may be ideal anticoagulants, as they can prevent thrombosis with low bleeding risk.

A Prospective, Randomized, Open-Label Study to Evaluate Two Management Strategies for Gastrointestinal Symptoms in Patients Newly on Treatment with Dabigatran

Introduction

In the pivotal RE-LY trial, dabigatran etexilate (DE) at the dose of 150-mg twice daily (BID), significantly reduced total stroke and ischemic stroke compared with warfarin in patients with non-valvular atrial fibrillation (NVAF), while the 110-mg BID dose had efficacy equivalent to warfarin, and major bleeds were significantly reduced. Both DE regimens were generally well tolerated; however, approximately 4% of the patients discontinued treatment with DE due to gastrointestinal (GI) discomfort.

Methods

Clinical trial NCT01493557 was a multicenter, randomized, active control, open-label study to assess the efficacy of two simple GI symptom (GIS) management strategies in DE-treated patients who developed GIS: (1) concurrent treatment with the proton pump inhibitor pantoprazole (DE-P), or (2) ingestion of DE after a meal (DE-M). Patients were initially randomized to either GIS management strategy. If the first did not resolve their GIS, patients had the option to “add on” the alternative strategy.

Results

A total of 1067 patients with NVAF received DE therapy BID for 3 months (United States, 150-mg or 75-mg; Canada, 150-mg or 110-mg). Of these, 117 (11%) patients reported GIS and were randomized to one of two GIS management strategies. At 4 weeks, a significantly higher rate of complete or partial effectiveness was observed in patients on DE-P than in those receiving DE-M, [50/58 (86.2%) versus 40/59 (67.8%), respectively; p = 0.0273]. Patients with ongoing GIS were asked to “add on” the alternate strategy for an additional 4 weeks. Overall, 92/117 (78.6%) of randomized patients experienced complete or partial effectiveness using either the initial strategy or a combination of the two strategies: DE-P, 47 (81.0%); and DE-M, 45 (76.3%, no significant difference) (by initial strategy).

Conclusion

The majority of patients enrolled either did not experience GIS at all, or their GIS resolved using either one individually, or a combination of the two strategies described.

Trial registration

http://www.ClinicalTrials.gov identifier: NCT01493557.

Electronic supplementary material

The online version of this article (doi:10.1007/s40119-016-0071-5) contains supplementary material, which is available to authorized users.

Pharmacology of Heparin and Related Drugs

Heparin has been recognized as a valuable anticoagulant and antithrombotic for several decades and is still widely used in clinical practice for a variety of indications. The anticoagulant activity of heparin is mainly attributable to the action of a specific pentasaccharide sequence that acts in concert with antithrombin, a plasma coagulation factor inhibitor. This observation has led to the development of synthetic heparin mimetics for clinical use. However, it is increasingly recognized that heparin has many other pharmacological properties, including but not limited to antiviral, anti-inflammatory, and antimetastatic actions. Many of these activities are independent of its anticoagulant activity, although the mechanisms of these other activities are currently less well defined. Nonetheless, heparin is being exploited for clinical uses beyond anticoagulation and developed for a wide range of clinical disorders. This article provides a "state of the art" review of our current understanding of the pharmacology of heparin and related drugs and an overview of the status of development of such drugs.

Pathogenesis, Diagnosis, and Treatment of Venous Thromboembolism in Older Adults

Older adults have a significantly greater risk of venous thromboembolism (VTE), including deep vein thrombosis and pulmonary embolism, than younger adults. The cause of this greater risk is thought to be multifactorial, including age-related changes in hemostatic factors and greater comorbid conditions and hospitalizations, but is not completely understood. Moreover, VTE remains underrecognized in older adults and may present atypically. Thus, a low index of clinical suspicion is essential when evaluating older adults with possible VTE. Despite this underrecognition in older adults, the diagnostic approach remains similar for all age groups and includes estimation of pretest probability, measurement of the D-dimer, and imaging. Antithrombotic agents are the mainstay of VTE treatment and, when used appropriately, substantially reduce VTE recurrence and complications. The approval of novel oral anticoagulants (NOACs), including dabigatran, rivaroxaban, apixaban, and edoxaban, provide clinicians with new therapeutic options. In some individuals, NOACs may offer advantages over warfarin, including fewer drug interactions, more-predictable anticoagulation, and lower risk of bleeding. Nevertheless, anticoagulation of VTE in older adults should always be performed cautiously, because age is a risk factor for bleeding complications. Identifying modifiable bleeding risk factors and balancing the risks of VTE recurrence with hemorrhage are important considerations when using anticoagulants in older adults.

Reversal agents for direct oral anticoagulants: A focused review

For several decades the vitamin K antagonist oral anticoagulants were the only outpatient therapy that existed to reduce the risk of stroke and thromboembolism. When the new direct oral anticoagulants were approved for use and addressed many of the issues associated with oral vitamin K antagonists, a new concern arose-the lack of rapid ability to reverse these agents. Physicians and patients were concerned that in cases of life-threatening bleeding or need for emergent surgery, an antidote to reverse the anticoagulation effect of these agents did not exist. Contemporary research has aimed to produce reversal agents that can be administered to safely neutralize the anticoagulant effect. In this focused review we describe the clinical development as well as mechanisms of action of three agents (idarucizumab, andexanet alpha, and ciraparantag). We review the pharmacokinetics, animal and human study data of these reversal agents and outline the evidence supporting their use. Although questions of safety and appropriate use remain, these reversal agents offer a significant step forward in the widespread use of direct oral anticoagulants and overall management of the anticoagulant effect.

Risk stratification, perioperative and periprocedural management of the patient receiving anticoagulant therapy

As a result of the aging US population and the subsequent increase in the prevalence of coronary disease and atrial fibrillation, therapeutic use of anticoagulants has increased. Perioperative and periprocedural management of anticoagulated patients has become routine for anesthesiologists, who frequently mediate communication between the prescribing physician and the surgeon and assess the risks of both thromboembolic complications and hemorrhage. Data from randomized clinical trials on perioperative management of antithrombotic therapy are lacking. Therefore, clinical judgment is typically needed regarding decisions to continue, discontinue, bridge, or resume anticoagulation and regarding the time points when these events should occur in the perioperative period. In this review, we will discuss the most commonly used anticoagulants used in outpatient settings and discuss their management in the perioperative period. Special considerations for regional anesthesia and interventional pain procedures will also be reviewed.

Four-factor prothrombin complex concentrate for life-threatening bleeds or emergent surgery: A retrospective evaluation

PURPOSE

Previous trials investigating usage of four-factor prothrombin complex concentrate (4F-PCC) excluded patients with various thrombotic risk factors. The objective of this study was to evaluate the safety and effectiveness of 4F-PCC in a real-world setting based on an institutional protocol that does not have strict exclusion criteria.

METHODS

This was a retrospective study of adult patients who received 4F-PCC. The primary outcome was a confirmed thromboembolism within 14 days after 4F-PCC administration. Secondary outcomes included international normalized ratio (INR) correction to <1.5 at first draw and incidence of INR rebound for patients undergoing reversal of warfarin and hemostatic effectiveness for patients experiencing a bleed.

RESULTS

Ninety-three patients received 4F-PCC. Sixty-three (67.7%) were reversed for bleeding and 30 (32.3%) for surgery. Eleven patients (11.8%) developed a thromboembolism within 14 days. The median (interquartile range) time to event was 5 (2-7) days. Significant risk factors were heparin-induced thrombocytopenia (P= .01) and major surgery within 14 days (P= .02), as well as the presence of >6 thrombotic risk factors (P= .01). For patients post-warfarin reversal, 45/63 (71.4%) achieved INR correction at first draw, 55/63 (87.3%) achieved INR correction within 24 hours, and 14/55 (25.5%) experienced INR rebound. Of these 14 patients, 8 (57.1%) did not receive concomitant vitamin K.

CONCLUSIONS

4F-PCC was associated with a notable thromboembolic risk. All patient-specific risk factors should be considered prior to administration. 4F-PCC remains a useful agent for warfarin reversal. Lack of concomitant vitamin K may contribute to INR rebound.

NOAC monitoring, reversal agents, and post-approval safety and effectiveness evaluation: A cardiac safety research consortium think tank

Four non-vitamin K antagonist oral anticoagulants (dabigatran, rivaroxaban, apixaban, and edoxaban) have been approved in the United States for treatment of atrial fibrillation (AF) and venous thromboembolic disease. They have been as or more effective than the prior standards of care, with less fatal or intracranial bleeding, fewer drug and dietary interactions, and greater patient convenience. Nonetheless, the absence of the ability for clinicians to assess compliance or washout with a simple laboratory test (or to adjust dosing with a similar assessment) and the absence of an antidote to rapidly stop major hemorrhage or to enhance safety in the setting of emergent or urgent surgery/procedures have been limitations to greater non-vitamin K antagonist oral anticoagulant usage and better thromboembolic prevention. Accordingly, a Cardiac Research Safety Consortium "think tank" meeting was held in February 2015 to address these concerns. This manuscript reports on the discussions held and the conclusions reached at that meeting.

Dabigatran approaching the realm of heparin-induced thrombocytopenia

Heparin-induced thrombocytopenia (HIT) is a serious, immune mediated complication of exposure to unfractionated or low-molecular-weight heparin. Though rare, it is a condition associated with high morbidity and mortality that requires immediate change to alternative anticoagulants for the prevention of life-threatening thrombosis. The direct thrombin inhibitors lepirudin and argatroban are currently licensed for the treatment of HIT. Dabigatran, a novel oral anticoagulant (NOAC) with a similar mechanism of action and effective use in other indications, has recently been proposed as another therapeutic option in cases of HIT. This review serves as an introduction to using dabigatran for this purpose, detailing the clinical aspects of its administration, evidence of its performance compared to other anticoagulants, and the preliminary reports of HIT successfully treated with dabigatran. As the literature on this develops, it will need to include clinical trials that directly evaluate dabigatran against the other NOACs and current treatment options.

Structure-guided residence time optimization of a dabigatran reversal agent

Novel oral anticoagulants are effective and safe alternatives to vitamin-K antagonists for anticoagulation therapy. However, anticoagulation therapy in general is associated with an elevated risk of bleeding. Idarucizumab is a reversal agent for the direct thrombin inhibitor, dabigatran etexilate (Pradaxa®) and is currently in Phase 3 studies. Here, we report data on the antibody fragment aDabi-Fab2, a putative backup molecule for idarucizumab. Although aDabi-Fab2 completely reversed effects of dabigatran in a rat model in vivo, we observed significantly reduced duration of action compared to idarucizumab. Rational protein engineering, based on the X-ray structure of aDabi-Fab2, led to the identification of mutant Y103W. The mutant had optimized shape complementarity to dabigatran while maintaining an energetically favored hydrogen bond. It displayed increased affinity for dabigatran, mainly driven by a slower off-rate. Interestingly, the increased residence time translated into longer duration of action in vivo. It was thus possible to further enhance the efficacy of aDabi-Fab2 based on rational design, giving it the potential to serve as a back-up candidate for idarucizumab.

Suboptimal Use of Oral Anticoagulants in Atrial Fibrillation: Has the Introduction of Direct Oral Anticoagulants Improved Prescribing Practices?

BACKGROUND AND OBJECTIVES

Atrial fibrillation (AF) and the associated risk of stroke are emerging epidemics throughout the world. Suboptimal use of oral anticoagulants for stroke prevention has been widely reported from observational studies. In recent years, direct oral anticoagulants (DOACs) have been introduced for thromboprophylaxis. We conducted a systematic literature review to evaluate current practices of anticoagulation in AF, pharmacologic features and adoption patterns of DOACs, their impacts on proportion of eligible patients with AF who receive oral anticoagulants, persisting challenges and future prospects for optimal anticoagulation.

LITERATURE SOURCE AND SELECTION CRITERIA

In conducting this review, we considered the results of relevant prospective and retrospective observational studies from real-world practice settings. PubMed (MEDLINE), Scopus (RIS), Google Scholar, EMBASE and Web of Science were used to source relevant literature. There were no date limitations, while language was limited to English. Selection was limited to articles from peer reviewed journals and related to our topic.

RESULTS

Most studies identified in this review indicated suboptimal use of anticoagulants is a persisting challenge despite the availability of DOACs. Underuse of oral anticoagulants is apparent particularly in patients with a high risk of stroke. DOAC adoption trends are quite variable, with slow integration into clinical practice reported in most countries; there has been limited impact to date on prescribing practice.

CONCLUSION

Available data from clinical practice suggest that suboptimal oral anticoagulant use in patients with AF and poor compliance with guidelines still remain commonplace despite transition to a new era of anticoagulation featuring DOACs.

Emergent Bleeding in Patients Receiving Direct Oral Anticoagulants

Direct oral anticoagulants (DOACs) offer clinical advantages over warfarin, such as minimal medication and food interactions and fixed dosing without the need for routine monitoring of coagulation status. As with all anticoagulants, bleeding, either spontaneous or provoked, is the most common complication. The long-term use of these drugs is increasing, and there is a crucial need for emergency medicine service professionals to understand the optimal management of associated bleeding. This review aims to describe the indications and pharmacokinetics of available DOACs; to discuss the risk of bleeding; to provide a treatment algorithm to manage DOAC-associated emergency bleeding; and to discuss future directions in bleeding management, including the role of specific reversal agents, such as the recently approved idarucizumab for reversal of the direct thrombin inhibitor dabigatran. Because air medical personnel are increasingly likely to encounter patients receiving DOACs, it is important that they have an understanding of how to manage patients with emergent bleeding.

Non-vitamin K antagonist oral anticoagulant reversal: hope is on the horizon

BACKGROUND

Non-vitamin K oral anticoagulants have become an attractive alternative to warfarin when patients require anticoagulation. Until recently, one of the biggest challenges to these agents was the lack of specific reversal of their anticoagulation when bleeding occurs or urgent/emergent procedures are required.

DATA SOURCES

This article is a narrative review of peer-reviewed publications with particular attention to authors that are experts in the field, society guidelines, and government publications.

CONCLUSIONS

Development of several drugs has led to agent-specific reversal. Idarucizumab has gained approval in the United States for reversal of dabigatran. Andexanet alfa has completed promising phase III trials for the reversal of factor Xa inhibitors. Aripazine (PER977) has shown promise as a universal reversal agent against non-vitamin K antagonist oral anticoagulants and heparin products.

New Direct Oral Anticoagulants (DOAC) and Their Use Today

The ideal anticoagulant is oral, has a wide therapeutic range, predictable pharmacokinetics and pharmacodynamics, a rapid onset of action, an available antidote, minimal side effects and minimal interactions with other drugs or food. With the development of the novel direct oral anticoagulants (DOAC), we now have an alternative to the traditional vitamin K antagonists (VKA) for the prevention and treatment of thrombosis. DOACs have limited monitoring requirements and very predictable pharmacokinetic profiles. They were shown to be non-inferior or superior to VKA in the prophylaxis or treatment of thromboembolic events. Particularly in terms of safety they were associated with less major bleeding, including intracranial bleeding, thus providing a superior benefit for the prevention of stroke in patients with atrial fibrillation. Despite these advantages, there are remaining limitations with DOACs: their dependence on renal and hepatic function for clearance and the lack of an approved reversal agent, whereas such antidotes are successively being made available. DOACs do not need regular monitoring to assess the treatment effect but, on the other hand, they interact with other drugs and interfere with functional coagulation assays. From a practical point of view, the properties of oral administration, simple dosing without monitoring, a short half-life allowing for the possibility of uncomplicated switching or bridging, and proven safety overwhelm the disadvantages, making them an attractive option for short- or long-term anticoagulation.

Edoxaban: A Comprehensive Review of the Pharmacology and Clinical Data for the Management of Atrial Fibrillation and Venous Thromboembolism

Historically, vitamin K antagonists have been the only class of oral anticoagulants available. Despite our experience with warfarin over the past 60 years, its use is associated with several pharmacokinetic and clinical disadvantages including unpredictable dosing, frequent monitoring, and delayed onset and offset. Edoxaban, an oral direct Xa inhibitor, may provide clinicians with an additional option in patients requiring chronic anticoagulation. This review examines the pharmacology and clinical data of edoxaban as a therapeutic alternative.

Emerging Tools for Stroke Prevention in Atrial Fibrillation

Ischaemic strokes resulting from atrial fibrillation (AF) constitute a devastating condition for patients and their carers with huge burden on health care systems. Prophylactic treatment against systemic embolization and ischaemic strokes is the cornerstone for the management of AF. Effective stroke prevention requires the use of the vitamin K antagonists or non-vitamin K oral anticoagulants (NOACs). This article summarises the latest developments in the field of stroke prevention in AF and aims to assist physicians with the choice of oral anticoagulant for patients with non-valvular AF with different risk factor profile.

Edoxaban for reducing the risk of stroke and systemic embolism in patients with non-valvular atrial fibrillation

INTRODUCTION

Oral anticoagulation is central to the management of patients with atrial fibrillation (AF) and at least one additional stroke risk factor. For decades, the vitamin K antagonists (e.g. warfarin) remained the only oral anticoagulant available for stroke prevention in AF. The non-vitamin K oral anticoagulants (NOACs) are now available, and these drugs include the direct thrombin inhibitors and factor Xa inhibitors. The latter class includes edoxaban, which has recently been approved for stroke prevention in AF by the United States Food and Drug Administration and the European Medicine Agency. In line with other NOACs, edoxaban avoids the many limitations of warfarin associated with variability of anticoagulation effect and multiple food and drug interactions.

AREAS COVERED

In this review, the currently available evidence on edoxaban in patients with non-valvular AF is discussed. The pharmacology, efficacy and safety, and current aspects of use of edoxaban in patients with non-valvular AF for stroke and thromboembolism prevention are reviewed.

EXPERT OPINION

Phase III trials on edoxaban for stroke prevention in non-valvular AF confirms non-inferiority of edoxaban compared to well-managed warfarin both in terms of efficacy and safety. Currently ongoing and future trials as well as real-world data are warranted to confirm its effectiveness and safety for chronic anticoagulation and improve evidence in other areas which are lacking evidence where NOAC use remains controversial.