Reversal of dabigatran anticoagulation by prothrombin complex concentrate (Beriplex P/N) in a rabbit model

Prothrombin Complex Concentrate Is Effective in Treating the Anticoagulant Effects of Dabigatran in a Porcine Polytrauma Model

Background

In the event of trauma, emergency reversal of anticoagulation therapy may be required. However, no specific reversal agents are routinely available for the direct oral anticoagulants such as dabigatran. The authors investigated four-factor prothrombin complex concentrate (PCC) for treating dabigatran-induced anticoagulation in a porcine polytrauma model.

Methods

Dabigatran etexilate was given orally for 3 days and intravenously on day 4 to 32 pigs. Animals were randomized 1:1:1:1 to PCC (25, 50, or 100 U/kg) or saline. Study medication was administered 12 min after bilateral femur fractures and blunt liver injury. The primary endpoint was blood loss at 300 min.

Results

The mean plasma concentration of dabigatran was 487 ± 161 ng/ml after intravenous administration. Blood loss was 3,855 ± 258 ml in controls and 3,588 ± 241 ml in the PCC25 group. In the PCC50 and PCC100 groups, blood loss was significantly lower: 1,749 ± 47 ml and 1,692 ± 97 ml, respectively. PCC50 and PCC100 effectively reduced dabigatran’s effects on coagulation parameters, whereas control and (to a lesser extent) PCC25 animals developed severe coagulopathy. Sustained increases in endogenous thrombin potential occurred with PCC50 and PCC100.

Conclusion

Four-factor PCC (50 or 100 U/kg) is effective in reducing blood loss in dabigatran-anticoagulated pigs, but higher doses may induce a procoagulant state.

Four-factor prothrombin complex concentrate reverses apixaban-associated bleeding in a rabbit model of acute hemorrhage

BACKGROUND

Apixaban is a direct factor Xa inhibitor approved for the treatment and prevention of thromboembolic disease. There is a lack of data regarding its reversal in cases of acute bleeding or prior to emergency surgery that needs addressing.

OBJECTIVES

This study assessed whether a four-factor prothrombin complex concentrate (4F-PCC; Beriplex(®) /Kcentra(®) , CSL Behring) can effectively reverse apixaban-associated bleeding in an in vivo rabbit model and evaluated the correlations between in vivo hemostasis and in vitro coagulation parameters.

METHODS

For dose-finding purposes, anesthetized rabbits were treated with a single intravenous dose of apixaban (800-1600 μg kg(-1) ) and, following a standardized kidney incision, volume of blood loss and time to hemostasis were measured. In a subsequent study phase, anesthetized rabbits were treated with apixaban 1200 μg kg(-1) followed by 4F-PCC (6.25-100 IU kg(-1) ), and the effects on the same bleeding parameters were assessed. In parallel, coagulation parameters were monitored.

RESULTS

Dose-dependent increases in time to hemostasis and total blood loss were observed post apixaban administration. Preincision treatment with 4F-PCC resulted in a statistically significant reversal in bleeding time (all doses) and volume (doses ≥ 12.5 IU kg(-1) ). Of the coagulation parameters measured, thrombin generation initiated using the RD reagent (phospholipids only) was the most sensitive to in vivo measures of 4F-PCC's hemostatic efficacy, although some correlations were also observed for prothrombin time and whole blood clotting time.

CONCLUSIONS

In this rabbit model of acute hemorrhage, 4F-PCC showed potential for reversing the bleeding effects of apixaban. Clinical data in apixaban-treated patients are needed to confirm these results.

Managing target-specific oral anticoagulant associated bleeding including an update on pharmacological reversal agents

Target-specific oral anticoagulants (TSOACs) dabigatran, rivaroxaban and apixaban are approved for the prevention and treatment of thromboembolism in several clinical settings. Bleeding is the major complication of anticoagulant therapy, including TSOACs, and anticoagulant reversal strategies are highly desired for the management of anticoagulant-associated major bleeding in addition to maximum supportive care and procedural/surgical intervention. Unlike VKAs for which vitamin K and coagulation factor replacement with prothrombin complex concentrate (PCC) can restore hemostasis, there are no clinically available agents proven to reverse TSOAC anticoagulant effect and ameliorate TSOAC-related major bleeding. This narrative review critically evaluates the evidence for TSOAC reversal using non-specific reversal agents PCC, activated PCC (APCC) and recombinant activated factor VII (rVIIa) which have been assessed primarily using in vitro experiments, animal models and healthy human volunteers. Aripazine is a novel agent undergoing clinical development for non-specific anticoagulant reversal, including TSOACs. Data are presented regarding specific reversal agents idarucizumab (dabigatran) and andexanet alfa (oral factor Xa inhibitors) currently being evaluated in clinical trials. A practical approach to management of patients with TSOAC-associated bleeding is also provided. There is an urgent need for clinical studies that evaluate the efficacy and safety of reversal strategies for TSOAC-related major bleeding with assessment of clinical outcomes such as bleeding and mortality.

Perioperatively acquired disorders of coagulation

Purpose of review

To provide an overview of acquired coagulopathies that can occur in various perioperative clinical settings. Also described are coagulation disturbances linked to antithrombotic medications and currently available strategies to reverse their antithrombotic effects in situations of severe hemorrhage.

Recent findings

Recent studies highlight the link between low fibrinogen and decreased fibrin polymerization in the development of acquired coagulopathy. Particularly, fibrin(ogen) deficits are observable after cardiopulmonary bypass in cardiac surgery, on arrival at the emergency room in trauma patients, and with ongoing bleeding after child birth. Regarding antithrombotic therapy, although new oral anticoagulants offer the possibility of efficacy and relative safety compared with vitamin K antagonists, reversal of their anticoagulant effect with nonspecific agents, including prothrombin complex concentrate, has provided conflicting results. Specific antidotes, currently being developed, are not yet licensed for clinical use, but initial results are promising.

Summary

Targeted hemostatic therapy aims to correct coagulopathies in specific clinical settings, and reduce the need for allogeneic transfusions, thus preventing massive transfusion and its deleterious outcomes. Although there are specific guidelines for reversing anticoagulation in patients treated with antiplatelet agents or warfarin, there is currently little evidence to advocate comprehensive recommendations to treat drug-induced coagulopathy associated with new oral anticoagulants.

Case Report: Apixaban-Associated Gluteal Artery Extravasation Reversed With PCC3 Without FFP

Apixaban, an oral factor Xa inhibitor, has no commercially available assay to measure its activity and no specific antidote. To date, recommendations for managing bleeding associated with apixaban are based on studies with animal models and healthy volunteers (who do not have identified thrombogenic risk factors) and expert opinion. No clinical experience has been published in the literature. Ideally, apixaban would be reversed sufficiently to stop a perilous bleed without producing more thrombogenic risk than the patients' underlying risk factors. Three-factor prothrombin complex concentrate (PCC3) is the least thrombogenic among the suggested reversal agents. Fresh frozen plasma (FFP) is sometimes recommended to add to PCC3, but it adds considerable volume. We describe successful management of an active left gluteal arterial extravasation due to trauma and associated apixaban, in a patient with aortic stenosis and atrial fibrillation, by administration of PCC3 alone, without the added volume of FFP.

Dabigatran-Associated Intracranial Hemorrhage: Literature Review and Institutional Experience

Dabigatran etexilate is an oral direct thrombin inhibitor approved for prevention of stroke and systemic embolization in patients with nonvalvular atrial fibrillation and for the treatment of venous thromboembolism. Although dabigatran has a favorable safety profile, predictable pharmacokinetics, fewer drug interactions than warfarin, and does not require monitoring, clinical data regarding dabigatran reversal are limited. In addition, currently available laboratory assays allow measurement of the presence, but not extent, of dabigatran-associated anticoagulation. Patient age, renal function, weight, concurrent drug therapy, adherence, and concomitant disease states can affect dabigatran's efficacy and safety. Management of dabigatran-related intracranial hemorrhage must be approached on a case-by-case basis and include assessment of degree of anticoagulation, severity of hemorrhage, renal function, timing of last dabigatran dose, and risk of thromboembolic events. Initial management includes dabigatran discontinuation and general supportive measures. Oral activated charcoal should be administered in those who ingested dabigatran within 2 hours. Four-factor prothrombin complex concentrates (4PCCs), activated PCC, or recombinant activated factor VII use may be reasonable but is not evidence based. Reserve fresh frozen plasma for patients with dilutional coagulopathy. If readily available, hemodialysis should be considered, particularly in patients with advanced kidney injury or excessive risk of thromboembolic events. More clinical studies are needed to determine a standardized approach to treating dabigatran-associated intracranial hemorrhage. Institutional protocol development will facilitate safe, efficacious, and timely use of the limited management options.

Risk of Fatal Bleeding in Episodes of Major Bleeding with New Oral Anticoagulants and Vitamin K Antagonists: A Systematic Review and Meta-Analysis

BACKGROUND

The reversibility of new/novel oral anticoagulants (NOAC) is not well understood, whereas the reversal strategies for bleeding associated with vitamin k antagonists (VKA), such as warfarin, is well established. It is unknown whether outcomes are different between bleeds occurring with NOAC compared to VKA use.

OBJECTIVES

This systematic review and meta-analysis of randomized controlled trials determines the relative odds of fatal bleeding given that a patient suffered a major bleed while on NOAC versus VKA therapy.

SEARCH METHODS

Data on major and fatal bleeding events was sought from randomized controlled trials of NOAC agents compared to VKAs.

MAIN RESULTS

20 trials were included in the meta-analysis. From which, 4056 first-time, major bleeding events were reported and included in the primary analysis. The summary odds ratio for the conditional odds of fatal bleeding given that a major bleeding event occurred was 0.65 [0.52, 0.81] favoring the NOAC agents (p = 0.0001). The reduced odds of fatal bleeding with NOACs was not demonstrated after controlling for bleeding location. Given that an intracranial bleeding event occurred, the summary odds ratio for the conditional odds of fatal bleeding was 0.96 [0.70, 1.32]. For extracranial bleeding events, the summary odds ratio was also statistically insignificant at 0.945 [0.66, 1.35]. AUTHOR’S CONCLUSIONS: The odds ratio calculated in this meta-analysis showed a reduced odds of death in major bleeding associated with NOAC use. This risk reduction was due to a disproportionate amount of intracranial bleeding in the VKA arms. For any given bleeding site, there was no evidence of a significant difference in fatal outcomes from bleeds associated with NOAC versus VKA use.

PROTOCOL REGISTRATION

Protocol registered on PROSPERO under CRD42014013294.

Reversal of the novel oral anticoagulants dabigatran, rivoraxaban, and apixaban

PURPOSE OF REVIEW

We summarize the available data related to reversing the anticoagulant effect of the oral direct thrombin and factor Xa inhibitors and provide our opinion on treating patients presenting with severe and life-threatening hemorrhage related to these agents.

RECENT FINDINGS

No specific antidotes are currently available for the oral direct thrombin and factor Xa inhibitors but two promising agents are under investigation in phase 3 trials. No data are available on reversing these agents in bleeding patients. Activated charcoal may be effective in reducing factor Xa inhibitor absorption up to 6 h after ingestion. Animal models suggest that unactivated 4-factor prothrombin complex concentrate may be an effective reversal agent. Recent data in warfarin-treated patients suggest that 4-factor prothrombin complex concentrate may provide more rapid and effective hemostasis than fresh frozen plasma.

SUMMARY

In the absence of evidence in bleeding patients, animal models and ex-vivo studies suggest administration of coagulant factors in the form of hemostatic agents may be of benefit in reversing the effect of direct thrombin and factor Xa inhibitors. Specific reversal agents and clinical data in patients with hemorrhage remain an unmet need.

Updated European Heart Rhythm Association Practical Guide on the use of non-vitamin K antagonist anticoagulants in patients with non-valvular atrial fibrillation

The current manuscript is an update of the original Practical Guide, published in June 2013[Heidbuchel H, Verhamme P, Alings M, Antz M, Hacke W, Oldgren J, et al. European Heart Rhythm Association Practical Guide on the use of new oral anticoagulants in patients with non-valvular atrial fibrillation. Europace 2013;15:625-51; Heidbuchel H, Verhamme P, Alings M, Antz M, Hacke W, Oldgren J, et al. EHRA practical guide on the use of new oral anticoagulants in patients with non-valvular atrial fibrillation: executive summary. Eur Heart J 2013;34:2094-106]. Non-vitamin K antagonist oral anticoagulants (NOACs) are an alternative for vitamin K antagonists (VKAs) to prevent stroke in patients with non-valvular atrial fibrillation (AF). Both physicians and patients have to learn how to use these drugs effectively and safely in clinical practice. Many unresolved questions on how to optimally use these drugs in specific clinical situations remain. The European Heart Rhythm Association set out to coordinate a unified way of informing physicians on the use of the different NOACs. A writing group defined what needs to be considered as 'non-valvular AF' and listed 15 topics of concrete clinical scenarios for which practical answers were formulated, based on available evidence. The 15 topics are (i) practical start-up and follow-up scheme for patients on NOACs; (ii) how to measure the anticoagulant effect of NOACs; (iii) drug-drug interactions and pharmacokinetics of NOACs; (iv) switching between anticoagulant regimens; (v) ensuring adherence of NOAC intake; (vi) how to deal with dosing errors; (vii) patients with chronic kidney disease; (viii) what to do if there is a (suspected) overdose without bleeding, or a clotting test is indicating a risk of bleeding?; (xi) management of bleeding complications; (x) patients undergoing a planned surgical intervention or ablation; (xi) patients undergoing an urgent surgical intervention; (xii) patients with AF and coronary artery disease; (xiii) cardioversion in a NOAC-treated patient; (xiv) patients presenting with acute stroke while on NOACs; and (xv) NOACs vs. VKAs in AF patients with a malignancy. Additional information and downloads of the text and anticoagulation cards in >16 languages can be found on an European Heart Rhythm Association web site (www.NOACforAF.eu).

Direct oral anticoagulants: new drugs and new concepts

Direct oral anticoagulants (DOACs) are approved for multiple thromboembolic disorders and provide advantages over existing agents. As with all anticoagulants, management protocols for the eventuality of bleeding are important. Randomized phase III studies generally show that DOACs have a similar risk of clinically relevant bleeding compared with standard anticoagulants, with reductions in major bleeding in some cases. This may be particularly important in patients with atrial fibrillation, for whom the rate of intracranial hemorrhage was approximately halved with DOACs compared with warfarin. Conversely, the risk of gastrointestinal bleeding may be increased. Specific patient characteristics, such as renal impairment, comedications, and particular aspects of each drug, including the proportion eliminated by the kidneys, must be taken into account when assessing the risk of bleeding. Although routine coagulation monitoring of DOACs is not required, it may be useful under some circumstances. Of the traditional clotting assays, a sensitive and calibrated prothrombin time may be useful for detecting the presence or absence of clinically relevant factor Xa inhibitor concentrations (rivaroxaban or apixaban), but specific anti-factor Xa assays can measure drug levels quantitatively. For dabigatran, the results of an activated partial thromboplastin time test may exclude a clinically relevant pharmacodynamic effect, but a calibrated dilute thrombin time assay can be used for quantification of drug levels. In the event of mild or moderate bleeding, normal hemostatic support measures are recommended. For life-threatening bleeding, use of nonspecific prohemostatic agents may be considered, although clinical evidence is scarce. Specific antidotes are in development.

Monitoring the Effects and Antidotes of the Non-vitamin K Oral Anticoagulants

In the last decade, we have witnessed the emergence of the oral non-vitamin K oral anticoagulants (NOACs), which have numerous advantages compared with the vitamin K antagonists, particularly their lack of need for monitoring; as a result their use is increasing. Nonetheless, the NOACs face two major challenges: the need for reliable laboratory assays to assess their anticoagulation effect, and the lack of approved antidotes to reverse their action. This article provides an overview of monitoring the anticoagulant effect of NOACs and their potential specific antidotes in development.

Bleeding Risk, Management and Outcome in Patients Receiving Non-VKA Oral Anticoagulants (NOACs)

Modern direct-acting anticoagulants are rapidly replacing vitamin K antagonists (VKA) in the management of millions of patients worldwide who require anticoagulation. These drugs include agents that inhibit activated factor X (FXa) (such as apixaban and rivaroxaban) or thrombin (such as dabigatran), and are collectively known today as non-VKA oral anticoagulants (NOACs). Since bleeding is the most common and most dangerous side effect of long-term anticoagulation, and because NOACs have very different mechanisms of action and pharmacokinetics compared with VKA, physicians are naturally concerned about the lack of experience regarding frequency, management and outcome of NOAC-associated bleeding in daily care. This review appraises trial and registry (or "real-world") data pertaining to bleeding complications in patients taking NOACs and VKA and provides practical recommendations for the management of acute bleeding situations.

Practical management of bleeding in patients receiving non-vitamin K antagonist oral anticoagulants

Non-vitamin K antagonist oral anticoagulants (NOACs) are increasingly used in the prevention and treatment of venous thromboembolism and in the prevention of stroke in patients with non-valvular atrial fibrillation. In phase III clinical trials and meta-analyses, the NOACs were at least as effective as vitamin K antagonists (VKAs) and were associated with a similar or lower incidence of major bleeding, including consistent and significant decreases in intracranial bleeding, although with an increase in gastrointestinal bleeding for some agents compared with VKAs. Subsequent real-world evidence supports these outcomes. Despite this, physicians have concerns about serious bleeding or emergencies because there are no specific reversal agents for the NOACs. However, in clinical trials, patients receiving NOACs generally had similar or better outcomes after these events than those taking VKAs. As with any bleeding, anticoagulant-related bleeding should first be stratified according to severity and location; risk can be minimised by ongoing assessment. Management protocols for NOAC-related bleeding are similar to those for VKAs but should take into account the pharmacological profile of the specific drug. Because of their short half-lives, NOAC-related mild bleeding can often be controlled by temporarily withholding treatment. More severe bleeding requires standard escalating haemodynamic support measures, and non-specific reversal agents can be considered in life-threatening situations, based on limited clinical data. Specific and rapid reversal agents are not currently available for any oral anticoagulant and restoration of coagulation may not necessarily lead to better outcomes. Nevertheless, specific NOAC reversal agents are in development and show promise in healthy volunteers.

Antidotes for novel oral anticoagulants: current status and future potential

The direct thrombin inhibitor dabigatran and the anti-Xa agents rivaroxaban, edoxaban, and apixaban are a new generation of oral anticoagulants. Their advantage over the vitamin K antagonists is the lack of the need for monitoring and dose adjustment. Their main disadvantage is currently the absence of a specific reversal agent. Dabigatran's, unlike the anti-Xa agents, absorption can be reduced by activated charcoal if administered shortly after ingestion and it can be removed from the blood with hemodialysis. Prothrombin complex concentrate, activated prothrombin complex concentrate, and recombinant factor VIIa all show some activity in reversing the anticoagulant effect of these drugs but this is based on ex vivo, animal, and volunteer studies. It is unclear, which, if any, of these drugs is the most suitable for emergency reversal. Three novel molecules (idarucizumab, andexanet, and PER977) may provide the most effective and safest way of reversal. These agents are currently in premarketing studies.

Direct oral anticoagulants: key considerations for use to prevent stroke in patients with nonvalvular atrial fibrillation

Atrial fibrillation (AF) is the most common cardiac arrhythmia worldwide. Strokes that occur as a complication of AF are usually more severe and associated with a higher disability or morbidity and mortality rate compared with non-AF-related strokes. The risk of stroke in AF is dependent on several risk factors; AF itself acts as an independent risk factor for stroke. The combination of effective anticoagulation therapy, risk stratification (based on stroke risk scores, such as CHADS₂ and CHA₂DS₂-VASc), and recommendations provided by guidelines is essential for decreasing the risk of stroke in patients with AF. Although effective in preventing the occurrence of stroke, vitamin K antagonists (VKAs; eg, warfarin) are associated with several limitations. Therefore, direct oral anticoagulants, such as apixaban, dabigatran etexilate, edoxaban, and rivaroxaban, have emerged as an alternative to the VKAs for stroke prevention in patients with nonvalvular AF. Compared with the VKAs, these agents have more favorable pharmacological characteristics and, unlike the VKAs, they are given at fixed doses without the need for routine coagulation monitoring. It remains important that physicians use these direct oral anticoagulants responsibly to ensure optimal safety and effectiveness. This article provides an overview of the existing data on the direct oral anticoagulants, focusing on management protocols for aiding physicians to optimize anticoagulant therapy in patients with nonvalvular AF, particularly in special patient populations (eg, those with renal impairment) and other specific clinical situations.

Design and rationale for RE-VERSE AD: A phase 3 study of idarucizumab, a specific reversal agent for dabigatran

Idarucizumab, a Fab fragment directed against dabigatran, produced rapid and complete reversal of the anticoagulation effect of dabigatran in animals and in healthy volunteers. The Study of the REVERSal Effects of Idarucizumab in Patients on Active Dabigatran (RE-VERSE AD™) is a global phase 3 prospective cohort study aimed at investigating idarucizumab in dabigatran-treated patients who present with uncontrollable or life-threatening bleeding, and in those requiring urgent surgery or intervention. We describe the rationale for, and design of the trial (clinicaltrials.gov NCT02104947).

Novel Oral Anticoagulants: Efficacy, Laboratory Measurement, and Approaches to Emergent Reversal

Warfarin, the most commonly used of the vitamin K antagonists, has been a mainstay of oral anticoagulation for decades. However, its usage is limited by morbidity and mortality secondary to bleeding as well as a cumbersome therapeutic monitoring process. In the past several years, a number of competing novel oral anticoagulants (NOACs) have been developed, each of which aspires to match or exceed warfarin's effectiveness while mitigating bleeding risk and eliminating therapeutic monitoring requirements. At present, 1 oral direct thrombin inhibitor and 2 direct factor Xa inhibitors are approved by the US Food and Drug Administration. Here, we compare the clinical efficacy and safety profiles of these new drugs. In addition, we discuss various laboratory assays that may be useful to measure these drugs in certain clinical circumstances. Finally, we discuss emerging strategies to reverse these agents in an emergency. The purpose of this article is to provide a framework for practicing pathologists to advise clinicians on NOAC laboratory measurement and management of NOAC-associated bleeding.

Updates in the perioperative and emergency management of non-vitamin K antagonist oral anticoagulants

Perioperative management of patients treated with the non-vitamin K antagonist oral anticoagulants is an ongoing challenge. Due to the lack of good clinical studies involving adequate monitoring and reversal therapies, management requires knowledge and understanding of pharmacokinetics, renal function, drug interactions, and evaluation of the surgical bleeding risk. Consideration of the benefit of reversal of anticoagulation is important and, for some low risk bleeding procedures, it may be in the patient's interest to continue anticoagulation. In case of major intra-operative bleeding in patients likely to have therapeutic or supra-therapeutic levels of anticoagulation, specific reversal agents/antidotes would be of value but are currently lacking. As a consequence, a multimodal approach should be taken which includes the administration of 25 to 50 U/kg 4-factor prothrombin complex concentrates or 30 to 50 U/kg activated prothrombin complex concentrate (FEIBA®) in some life-threatening situations. Finally, further studies are needed to clarify the ideal therapeutic intervention.

Emergency reversal of dabigatran for emergency surgery

An 80-year-old woman had the anticoagulant effect of dabigatran etexilate reversed using factor eight inhibitor bypassing activity (FEIBA) in order to facilitate emergency surgery for an incarcerated femoral hernia. She had atrial fibrillation was taking the anticoagulant for stroke prevention. That afternoon her international normalised ratio (INR) was 1.3 and activated partial thromboplastin time ratio (APPTr) was 2.17, having taken dabigatran that morning. 3000 units of FEIBA and 10 mg of vitamin K were administered and she was taken to theatre for emergency surgery. Surgery was successful, total blood loss was less than 100 mL and there were no complications. The following morning she had an INR of 1.1 and APPTr of 1.49. She made an uneventful postoperative recovery and was discharged home. There is a limited evidence base guiding practice in the clinical scenario described. The only controlled studies available are animal experiments.

Use of 4-factor prothrombin complex concentrate in the treatment of a gastrointestinal hemorrhage complicated by dabigatran

Target-specific oral anticoagulants (TSOACs) provide patients and healthcare providers with an alternative to vitamin K antagonists (VKA). The TSOACs are of similar or superior efficacy to warfarin, but unlike VKAs, there are no approved ‘antidotes’ for rapid reversal of life-threatening bleeding on therapy. We report here the case of an 83-year-old gentleman, who presented to the emergency department with severe gastrointestinal hemorrhage and coagulopathy (hemoglobin: 5.3 g/dL and INR: 2.2) while on the direct thrombin inhibitor dabigatran. His coagulopathy reversed rapidly after administration of 4-factor prothrombin complex concentrate (4 F-PCC), and after initial administration of 2 units of packed red blood cells, no further product transfusions were required. He was discharged 4 days later without further complications.

Emergency reversal of anticoagulation: novel agents

Historically, oral anticoagulation involved the administration of vitamin K antagonists, such as warfarin. However, because of the need for frequent monitoring and the desire for safer anticoagulants, several novel oral anticoagulants have been developed. These newer agents include the factor Xa inhibitors (eg, rivaroxaban, apixaban, edoxaban), along with the direct thrombin inhibitors (eg, dabigatran). This manuscript provides a brief overview of their uses and mechanisms of action, along with a review of currently available evidence for reversal strategies when life-threatening bleeding occurs.

New oral anticoagulants: a practical guide on prescription, laboratory testing and peri-procedural/bleeding management. Australasian Society of Thrombosis and Haemostasis

New oral anticoagulants (NOAC) are becoming available as alternatives to warfarin to prevent systemic embolism in patients with non-valvular atrial fibrillation and for the treatment and prevention of venous thromboembolism. An in-depth understanding of their pharmacology is invaluable for appropriate prescription and optimal management of patients receiving these drugs should unexpected complications (such as bleeding) occur, or the patient requires urgent surgery. The Australasian Society of Thrombosis and Haemostasis has set out to inform physicians on the use of the different NOAC based on current available evidence focusing on: (i) selection of the most suitable patient groups to receive NOAC, (ii) laboratory measurements of NOAC in appropriate circumstances and (iii) management of patients taking NOAC in the perioperative period, and strategies to manage bleeding complications or 'reverse' the anticoagulant effects for urgent invasive procedures.

Global assays and the management of oral anticoagulation

Coagulation tests range from global or overall tests to assays specific to individual clotting factors and their inhibitors. Whether a particular test is influenced by an oral anticoagulant depends on the principle of the test and the type of oral anticoagulant. Knowledge on coagulation tests applicable in monitoring status and reversal of oral anticoagulation is a prerequisite when studying potential reversal agents or when managing anticoagulation in a clinical setting. Specialty tests based on the measurement of residual activated factor X (Xa) or thrombin activity, e.g., are highly effective for determining the concentration of the new generation direct factor Xa- and thrombin inhibitors, but these tests are unsuitable for the assessment of anticoagulation reversal by non-specific prohemostatic agents like prothrombin complex concentrate (PCC) and recombinant factor VIIa (FVIIa). Global coagulation assays, in this respect, seem more appropriate. This review evaluates the current status on the applicability of the global coagulation assays PT, APTT, thrombin generation and thromboelastography in the management of oral anticoagulation by vitamin K antagonists and the direct factor Xa and thrombin inhibitors. Although all global tests are influenced by both types of anticoagulants, not all tests are useful for monitoring anticoagulation and reversal thereof. Many (pre)analytical conditions are of influence on the assay readout, including the oral anticoagulant itself, the concentration of assay reagents and the presence of other elements like platelets and blood cells. Assay standardization, therefore, remains an issue of importance.

Effective Reversal of Edoxaban-associated Bleeding with Four-factor Prothrombin Complex Concentrate in a Rabbit Model of Acute Hemorrhage

Background:

Edoxaban is an oral, selective direct factor Xa inhibitor approved in Japan for venous thromboembolism prevention after orthopedic surgery. Data are lacking regarding reversal strategies for edoxaban; this study assessed whether four-factor prothrombin complex concentrate (Beriplex®/Kcentra®; CSL Behring GmbH, Marburg, Germany) can effectively reverse its effects on hemostasis using a previously described rabbit model.

Methods:

The study comprised assessments of thrombin generation in vitro, pharmacokinetic parameters, and edoxaban reversal in vivo. In a blinded in vivo stage, a standardized kidney incision was performed in animals (n = 11 per group) randomized to receive vehicle + saline, edoxaban (1,200 μg/kg) + saline, or edoxaban (1,200 μg/kg) + four-factor prothrombin complex concentrate (50 IU/kg). Animals were monitored for treatment impact on hemostasis and coagulation parameters. Data are median (range). Statistical tests were adjusted for multiple testing.

Results:

Edoxaban administration increased blood loss (30 [2 to 44] ml) and time to hemostasis (23 [8.5 to 30.0] min) compared with the control group (3 [1 to 8] ml and 3 [2.0 to 5.0] min, respectively). Biomarkers of coagulation (prothrombin time, activated partial thromboplastin time, whole blood clotting time) and thrombin generation parameters (e.g., peak thrombin, endogenous thrombin potential, lag time) were also affected by edoxaban. Administration of four-factor prothrombin complex concentrate significantly reduced time to hemostasis (to 8 [6.5 to 14.0] min, observed P < 0.0001) and total blood loss (to 9 [4 to 22] ml, observed P = 0.0050) compared with the edoxaban + saline group. Of the biomarkers tested, prothrombin time, whole blood clotting time, and endogenous thrombin potential correlated best with clinical parameters.

Conclusion:

In a rabbit model of hemostasis, four-factor prothrombin complex concentrate administration significantly decreased edoxaban-associated hemorrhage.

Reversal of Dabigatran Effects in Models of Thrombin Generation and Hemostasis by Factor VIIa and Prothrombin Complex Concentrate

Background:

The oral thrombin inhibitor dabigatran has the drawbacks that it does not have a validated antidote. Data from animal studies and plasma coagulation assays suggest that prothrombin complex concentrate (PCC) or recombinant factor VIIa (FVIIa) might reverse dabigatran anticoagulation.

Methods:

Cellular elements make a significant contribution to hemostasis. Our goals were to (1) test the hypothesis that both FVIIa and a 4-factor PCC improve parameters of thrombin generation in the presence of dabigatran in a cell-based model; and (2) determine whether results in a cell-based model correlate with hemostasis in vivo.

Results:

PCC reversed dabigatran effects on the rate, peak, and total amount of thrombin but did not shorten the lag (n = 6 experiments in triplicate). By contrast, FVIIa shortened the lag, increased the rate and peak, but did not improve total thrombin (n = 6). Effects of PCC were seen at both therapeutic and markedly supratherapeutic dabigatran levels, whereas beneficial effects of FVIIa decreased as the dabigatran level increased. The PCC effect was reproduced by adding prothrombin, factor X, and factor IX. At therapeutic dabigatran levels, both PCC and FVIIa normalized hemostasis time in a mouse saphenous vein bleeding model.

Conclusions:

A cell-based model reflects the effects on thrombin generation of clinically relevant levels of FVIIa and PCC in the presence of dabigatran. Enhancing the rate of thrombin generation and peak thrombin level appear to correlate best with hemostasis in vivo. The ineffectiveness of FVIIa at supratherapeutic dabigatran levels may explain conflicting reports of its efficacy in dabigatran reversal.

What is the role of hemodialysis for dabigatran-associated major bleeding?

A 70-year-old male with a history of atrial fibrillation who is being anticoagulated with dabigatran etexilate presents to the emergency room with melena. He reports taking his most recent dose of dabigatran more than 2 hours ago. On examination, he is hypotensive and tachycardic, and he continues to have melanotic stools. Laboratory testing reveals a calculated creatinine clearance of 15 mL/min, a prothrombin time of 16.5 seconds (reference range: 11.8-15.2 seconds), an international normalized ratio of 1.2 (reference range: 0.9-1.2), and an activated partial thromboplastin time of 50 seconds (reference range: 22.2-33.0 seconds). You are asked by the emergency medicine physician whether hemodialysis should be considered to decrease the patient's plasma dabigatran level.

Reversing targeted oral anticoagulants

Dabigatran, rivaroxaban, and apixaban are orally active anticoagulants that are approved in many countries. Dabigatran inhibits thrombin, whereas rivaroxaban and apixaban are factor Xa inhibitors. In clinical trials, these novel oral anticoagulants were at least as effective as warfarin for preventing stroke in patients with atrial fibrillation, but with a lower rate of serious bleeding. However, the lack of true antidotes for these agents has caused concern when patients suffer life-threatening bleeding or trauma or require emergent invasive procedures. True antidotes are under development for all of these agents. In the meantime, activated and nonactivated prothrombin complex concentrates have been used as reversal agents. Factor VIIa may also be effective for reversal of the factor Xa inhibitors. Reversal of novel oral anticoagulants by these hemostatic agents has not been studied in bleeding human patients, so their true efficacy and appropriate dosing are not known.

Clinical Applications of 4-Factor Prothrombin Complex Concentrate: A Practical Pathologist's Perspective

A 4-factor prothrombin complex concentrate (4F-PCC), containing therapeutic doses of vitamin K–dependent coagulation factors, was recently licensed in the United States for reversal of vitamin K antagonist therapy. However, given the emergence of several oral anticoagulants for which there are no specific reversal agents, and the existence of many other complex bleeding disorders, it is likely that clinicians will seek to use 4F-PCCs for any number of off-label indications. Thus, the goal of this review is to explore practical issues regarding 4F-PCC, with an emphasis on issues relevant to blood bankers and pathologists. Specifically, our aims are to (1) examine the role of 4F-PCC in vitamin K antagonist reversal, (2) review its potential use in the treatment of hemorrhage due to novel oral anticoagulants, and (3) explore potential uses in liver disease, trauma-associated bleeding, and rare coagulopathies. Safety and other practical considerations of 4F-PCCs will also be discussed.

Management of hemorrhage with the target-specific oral anticoagulants

The target-specific oral anticoagulants have recently been introduced as alternatives to warfarin for both prophylactic and therapeutic indications. Although their efficacy and side-effect profiles have been favorable, there is significant concern about management of hemorrhage with these agents as there is no direct reversal agent available. It is important for clinicians to be aware of these agents and the issues that surround them. Most of the management of hemorrhage is based on expert opinion and case reviews. Given the potentially catastrophic consequences of acute hemorrhage while patients are on anticoagulation, specific treatments are needed. Some methods that have been described include activated charcoal, hemodialysis, prohemostatic agents, and transfusions. Target-specific therapies have been shown to be effective in early studies in animal models; however, the effects in humans are still under investigation. More investigation is needed on the management of bleeding complications from target-specific oral anticoagulants.

Management of the bleeding patient receiving new oral anticoagulants: a role for prothrombin complex concentrates

Ease of dosing and simplicity of monitoring make new oral anticoagulants an attractive therapy in a growing range of clinical conditions. However, newer oral anticoagulants interact with the coagulation cascade in different ways than traditional warfarin therapy. Replacement of clotting factors will not reverse the effects of dabigatran, rivaroxaban, or apixaban. Currently, antidotes for these drugs are not widely available. Fortunately, withholding the anticoagulant and dialysis are freqnently effective treatments, particularly with rivaroxaban and dabigatran. Emergent bleeding, however, requires utilization of Prothrombin Complex Concentrates (PCCs). PCCs, in addition to recombinant factor VIIa, are used to activate the clotting system to reverse the effects of the new oral anticoagulants. In cases of refractory or emergent bleeding, the recommended factor concentrate in our protocols differs between the new oral anticoagulants. In patients taking dabigatran, we administer an activated PCC (aPCC) [FELBA] due to reported benefit in human in vitro studies. Based on human clinical trial evidence, the 4-factor PCC (Kcentra) is suggested for patients with refractory rivaroxaban- or apixaban-associated hemorrhage. If bleeding continues, recombinant factor VIIa may be employed. With all of these new procoagulant agents, the risk of thrombosis associated with administration of factor concentrates must be weighed against the relative risk of hemorrhage.

Reversal of dabigatran-induced bleeding by coagulation factor concentrates in a rat-tail bleeding model and lack of effect on assays of coagulation

BACKGROUND

Dabigatran is a potent oral anticoagulant. Like any anticoagulant, there is an increased risk of bleeding associated with its use, and reversal may be needed in cases of severe bleeding.

METHODS

In this study, six coagulation factor concentrates (CFCs) were tested for their ability to reduce bleeding induced by oral dabigatran etexilate (30 mg/kg) in a rat-tail bleeding model (n = 5 to 8 per group): three-factor (Profilnine [Grifols Biologicals Inc., Los Angeles, CA] and Bebulin [Baxter BioScience, Westlake Village, CA]) and four-factor prothrombin complex concentrates (Beriplex [CSL Behring, Marburg, Germany] and Octaplex [Octapharma AG, Lachen, Switzerland]), activated prothrombin complex concentrate (Factor Eight Inhibitor Bypassing Activity; Baxter AG, Vienna, Austria), and recombinant factor VIIa (NovoSeven; NovoNordisk, Bagsværd, Denmark). The effect of CFCs on prolongation of coagulation assays was measured. Thrombin generation after administration of each CFC was compared in vitro using human plasma (n = 5) spiked with dabigatran in concentrations corresponding to median peak (200 ng/ml) and supratherapeutic values (600 and 1,000 ng/ml).

RESULTS

Dabigatran resulted in an approximately three-fold increase in bleeding time, consistent with supratherapeutic dabigatran plasma levels. Beriplex (35 and 50 IU/kg), Octaplex (40 IU/kg), Profilnine (50 IU/kg), Bebulin (60 IU/kg), Factor Eight Inhibitor Bypassing Activity (100 U/kg), and NovoSeven (500 μg/kg) significantly decreased this prolonged bleeding time over 30 min (P < 0.001). The coagulation assays were prolonged three- to eight-fold over baseline (P = 0.01). None of the CFCs produced a consistent change in these assays that was predictive of reduced bleeding. Thrombin generation reversal was dependent on the concentration of dabigatran and each CFC; normalization occurred at the lower concentration of dabigatran with most CFCs, but not at higher concentrations.

CONCLUSIONS

In this animal model, bleeding induced by high doses of dabigatran can be reduced by CFCs. However, routine coagulation assays do not predict this effect.

New oral anticoagulants: clinical indications, monitoring and treatment of acute bleeding complications

New oral anticoagulants like the direct thrombin inhibitor, dabigatran (Pradaxa®), and factor Xa-inhibitors, rivaroxaban (Xarelto®) and apixaban (Eliquis®) are available for prophylaxis and treatment of thromboembolic disease. They are emerging alternatives to warfarin and provide equal or better clinical outcome together with reduced need for routine monitoring. Methods for measuring drug concentrations are available, although a correlation between plasma drug concentrations and the risk of bleeding has not been firmly established. Standard laboratory measures like prothrombin time and activated partial thromboplastin time are not sensitive enough to detect thrombin or factor Xa inhibition provided by new oral anticoagulants. Thus, these standard tests may only be used as a crude estimation of the actual anticoagulation status. Further challenges regarding patients receiving new oral anticoagulants who presents with major bleeding or need for emergency surgery pose a unique problem. No established agents are clinically available to reverse the anticoagulant effect, although preclinical data report prothrombin complex concentrate as more efficient than fresh frozen plasma or other prohaemostatic agents. This review summaries current knowledge on approved new oral anticoagulants and discusses clinical aspects of monitoring, with particular focus on the management of the bleeding patient.

Reversal of target-specific oral anticoagulants

Target-specific oral anticoagulants (TSOACs) provide safe and effective anticoagulation for the prevention and treatment of thrombosis in a variety of clinical settings by interfering with the activity of thrombin (dabigatran) or factor Xa (rivaroxaban, apixaban, edoxaban, betrixaban). Although TSOACs have practical advantages over vitamin K antagonists (VKAs), there are currently no antidotes to reverse their anticoagulant effect. Herein we summarize the available evidence for TSOAC reversal using nonspecific and specific reversal agents. We discuss important limitations of existing evidence, which is derived from studies in human volunteers, animal models and in vitro experiments. Studies evaluating the safety and efficacy of reversal agents on clinical outcomes such as bleeding and mortality in patients with TSOAC-associated bleeding are needed.