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

Dabigatran anticoagulation and Stanford type A aortic dissection: lethal coincidence: Case report with literature review

BACKGROUND

Novel oral anticoagulants are now encountered in patients needing emergency surgery. Knowledge and treatment options are limited.

METHODS AND RESULT

We present the case of a 76-year-old patient who suffered from an acute Stanford type A aortic dissection, needing emergency surgical aortic repair. He was anticoagulated with dabigatran due to past atrial fibrillation. Despite haemodiafiltration, surgical revision and massive transfusion of packed red blood cells, fresh frozen plasma, platelets, coagulation factors, and recombinant factor VIIa, the patient died from intractable bleeding with sustained therapeutic levels of dabigatran.

CONCLUSION

After reviewing the literature, we summarize the limited treatment options and show possible approaches for patients treated with dabigatran needing emergency surgery.

A mouse bleeding model to study oral anticoagulants

New oral anticoagulants to reduce the incidence of thrombosis have recently become available. When compared to the existing therapy, warfarin, these novel agents have similar efficacy with a reduced risk of spontaneous bleeding. However, these novel agents have been associated with significant, even fatal, bleeding following trauma. Reversal agents are being developed that bind and neutralize these oral anticoagulants. However, these are not yet available. Another strategy is to increase thrombin generation by administration of "bypassing" agents such as prothrombin complex concentrates or factor VIIa. Several animal models have been used to model the hemostatic defect induced by the thrombin inhibitor dabigatran. A rat tail injury model, a rabbit cuticle bleeding model, and a rabbit kidney laceration model have all been reported to show increased bleeding, but with supratherapeutic doses of dabigatran. A mouse tail transection model has been reported to reflect increased bleeding at peak therapeutic dabigatran levels. We found that the Whinna saphenous vein hemostasis model reliably reflects a hemostatic defect at therapeutic levels of dabigatran. This model can potentially reflect the effects of reversal or bypassing agents.

Translational insights into traumatic brain injury occurring during dabigatran or warfarin anticoagulation

To date, only limited data are available on the effects of pretreatment with novel oral anticoagulants in the event of traumatic brain injury (TBI). We determined intracerebral hemorrhage volume and functional outcome in a standardized TBI model in mice treated with warfarin or dabigatran. Additionally, we investigated whether excess concentrations of dabigatran could increase bleeding and whether this was preventable by using prothrombin complex concentrate (PCC). C57 mice were treated orally with warfarin or dabigatran; sham-treated mice served as controls. Effective anticoagulation was verified by measurement of international normalized ratio and diluted thrombin time, and TBI was induced by controlled cortical impact (CCI). Twenty-four hours after CCI, intracerebral hemorrhage volume was larger in warfarin-pretreated mice than in controls (10.1 ± 4.9 vs 4.1 ± 1.7 μL; analysis of variance post hoc P=0.001), but no difference was found between controls and dabigatran-pretreated mice (5.3 ± 1.5 μL). PCC applied 30 minutes after CCI did not reliably reduce intracerebral hemorrhage induced by excess dabigatran concentration compared with saline (10.4 ± 11.2 vs 8.7 ± 7.1 μL). Our data suggest pathophysiological differences in TBI occurring during warfarin and dabigatran anticoagulation. The reduced hemorrhage formation under dabigatran therapy could present a safety advantage compared with warfarin. An excess dabigatran concentration, however, can increase hemorrhage.

[Perioperative management of new oral anticoagulants]

New oral anticoagulants do represent a major step forward as compared to low molecular weight heparins and vitamin K antagonists. Several issues deserve attention regarding their perioperative management. Three (and very soon four or five) active molecules are available on the market, adding to the major intra- and inter-individual variability, to the high number of drug-drug interactions, and to the interferences of renal function and many other parameters. New tests are available including the diluted thrombin time for dabigatran and a specific anti-Xa test for rivaroxaban and apixaban. No antidote is approved yet. Scheduled surgery: the safest suggestion is to mimic the perioperative management of vitamin K antagonist, with a 5-day interruption and low molecular weight heparin bridging whenever necessary. Emergency procedures: several suggestions issued from the Groupe d'Intérêt en Hémostase Péri-opératoire are proposed.

The role of prothrombin complex concentrates in reversal of target specific anticoagulants

Over the past several years a new era for patients requiring anticoagulation has arrived. The approval of new target specific oral anticoagulants offers practitioners several advantages over traditionally used vitamin K antagonist agents including predictable pharmacokinetics, rapid onset of action, comparable efficacy and safety, all without the need for routine monitoring. Despite these benefits, hemorrhagic complicates are inevitable with any anticoagulation treatment. One of the major disadvantages of the new oral anticoagulants is lack of specific antidotes or reversal agents for patients with serious bleeding or need for urgent surgery. As use of the new target specific oral anticoagulants continues to increase, practitioners will need to understand both the pharmacodynamics and pharmacokinetic properties of the agents, as well as, the available literature with use of non-specific therapies to reverse anticoagulation. Four factor prothrombin complex concentrates have been available for several years in Europe, and recently became available in the United States with approval of Kcentra. These products have shown efficacy in reversing anticoagulation from vitamin K antagonists, however their usefulness with the new target specific oral anticoagulants is poorly understood. This article will review the properties of dabigatran, rivaroxaban and apixaban, as well as the limited literature available on the effectiveness of prothrombin complex concentrates in reversal of their anticoagulant effects. Additional studies are needed to more accurately define the role of prothrombin complex concentrates in patients with life threatening bleeding or who require emergent surgery, as current data is both limited and conflicting.

Reversal of target-specific oral anticoagulants

The target-specific oral anticoagulants represent the first new oral anti-thrombotic therapy in over 50 years and have the potential to make therapy easier and hence more accessible to many patients. Like any new therapy, the potential benefits must be weighed against the potential challenges and one of the most concerning aspects of the new target-specific oral anticoagulants is the lack of a proven method to reverse their effect. Unlike the vitamin K antagonist, i.e. warfarin, there is no specific antidote for these medications. This paper will review the limited data on the use of non-specific therapies to reverse anticoagulation for the new agents. We hope to prepare clinicians who are faced with a patient who has serious bleeding or needs emergent surgery while taking dabigatran, rivaroxaban or apixaban.

Prothrombin complex concentrates and a specific antidote to dabigatran are effective ex-vivo in reversing the effects of dabigatran in an anticoagulation/liver trauma experimental model

Introduction

New oral anticoagulants are effective alternatives to warfarin. However, no specific reversal agents are available for life-threatening bleeding or emergency surgery. Using a porcine model of trauma, this study assessed the ability of prothrombin complex concentrate (PCC), activated PCC (aPCC), recombinant FVIIa (rFVIIa) and a specific antidote to dabigatran (aDabi-Fab) to reverse the anticoagulant effects of dabigatran.

Methods

Dabigatran etexilate (DE) was given orally for 3 days (30 mg/kg bid) and intravenously on day 4 to achieve consistent, supratherapeutic concentrations of dabigatran. Blood samples were collected at baseline, after oral DE, after intravenous dabigatran, and 60 minutes post-injury. PCC (30 and 60 U/kg), aPCC (30 and 60 U/kg), rFVIIa (90 and 180 μg/kg) and antidote (60 and 120 mg/kg) were added to blood samples ex-vivo. Coagulation was assessed by thromboelastometry, global coagulation assays and diluted thrombin time.

Results

Plasma concentrations of dabigatran were 380 ± 106 ng/ml and 1423 ± 432 ng/ml after oral and intravenous administration, respectively, and all coagulation parameters were affected by dabigatran. Both PCCs and aDabi-Fab, but not rFVIIa, reversed the effects of dabigatran on thromboelastometry parameters and prothrombin time. In contrast, aPTT was only normalised by aDabi-Fab. Plasma concentration (activity) of dabigatran remained elevated after PCC and rFVIIa therapy, but was not measureable after aDabi-Fab.

Conclusion

In conclusion, PCC and aPCC were effective in reducing the anticoagulant effects of dabigatran under different conditions, while aDabi-Fab fully corrected all coagulation measures and decreased the plasma concentration of dabigatran below the limit of detection. No significant effects were observed with rFVIIa.

Perioperative management of target-specific oral anticoagulants

Target-specific oral anticoagulants (TSOACs), which offer rapid onset and more predictable pharmacokinetics/dynamics compared with vitamin K antagonists, are rapidly growing in number and approved indications. At least 1 in 10 Americans receiving outpatient anticoagulant therapy requires interruption of anticoagulation for an invasive procedure annually, and management of these new agents in the perioperative setting is made challenging by difficulty measuring anticoagulant effect and the lack of effective reversal. Surgical planning must account for individual patient risks for bleeding and thrombosis, the type of procedure, and expected drug clearance. Based upon these considerations, a perioperative plan encompassing timing of TSOAC cessation and resumption, as well as bridging therapy, if needed, can be developed. Perioperative strategies remain largely predicated on extrapolations from pharmacokinetics and expert opinion, though a growing body of literature is providing greater guidance in this important area.

The acute management of haemorrhage, surgery and overdose in patients receiving dabigatran

Dabigatran is an oral direct thrombin inhibitor (DTI) licensed for stroke prevention in atrial fibrillation and likely to be soon approved in Europe for treatment of venous thrombosis. Predictable pharmacokinetics and a reduced risk of intracranial haemorrhage do not negate the potential risk of haemorrhage. Unlike warfarin, there is no reversal agent and measurement of the anticoagulant effect is not 'routine'. The prothrombin time/international normalised ratio response to dabigatran is inconsistent and should not be measured when assessing a patient who is bleeding or needs emergency surgery. The activated partial thromboplastin time (APTT) provides a qualitative measurement of the anticoagulant effect of dabigatran. Knowledge of the time of last dose is important for interpretation of the APTT. Commercially available DTI assays provide a quantitative measurement of active dabigatran concentration in the plasma. If a patient receiving dabigatran presents with bleeding: omit/delay next dose of dabigatran; measure APTT and thrombin time (consider DTI assay if available); administer activated charcoal, with sorbitol, if within 2 h of dabigatran ingestion; give tranexamic acid (1 g intravenously if significant bleeding); maintain renal perfusion and urine output to aid dabigatran excretion. Dabigatran exhibits low protein binding and may be removed by dialysis. Supportive care should form the mainstay of treatment. If bleeding is life/limb threatening, consider an additional haemostatic agent. There is currently no evidence to support the choice of one haemostatic agent (FEIBA, recombinant factor VIIa, prothrombin complex concentrates) over another. Choice will depend on access to and experience with available haemostatic agent(s).

Prothrombin complex concentrate

Each month, subscribers to The Formulary Monograph Service receive 5 to 6 well-documented monographs on drugs that are newly released or are in late phase 3 trials. The monographs are targeted to Pharmacy & Therapeutics Committees. Subscribers also receive monthly 1-page summary monographs on agents that are useful for agendas and pharmacy/nursing in-services. A comprehensive target drug utilization evaluation/medication use evaluation (DUE/MUE) is also provided each month. With a subscription, the monographs are sent in print and are also available on-line. Monographs can be customized to meet the needs of a facility. A drug class review is now published monthly with The Formulary Monograph Service. Through the cooperation of The Formulary, Hospital Pharmacy publishes selected reviews in this column. For more information about The Formulary Monograph Service, call The Formulary at 800-322-4349. The December 2013 monograph topics are vortioxetine, mechlorethamine gel, brimonidine tartrate topical gel, obinutuzumab, and miltefosine. The DUE/MUE is on vortioxetine.

Non-vitamin K antagonist oral anticoagulants in cardiovascular disease management: evidence and unanswered questions

WHAT IS KNOWN AND OBJECTIVE

Anticoagulation is important in the management of cardiovascular disorders; however, traditional anticoagulants such as heparins and vitamin K antagonists (VKAs) have limitations, including parenteral administration with the former and the need for coagulation monitoring and dose adjustments with the latter. Three non-VKA oral anticoagulants (OACs), dabigatran, rivaroxaban and apixaban, are available for the prevention of stroke in patients with atrial fibrillation (AF) and may change clinical practice. This article reviews current knowledge and important unanswered questions on the use of these agents in patients with cardiovascular disease.

METHODS

A literature search was performed using PubMed and the search terms dabigatran, rivaroxaban, apixaban, AF and acute coronary syndrome (ACS). Peer-reviewed, published clinical trials, review articles, relevant treatment guidelines and prescribing information documents were identified and reviewed for relevance.

RESULTS AND DISCUSSION

Dabigatran is an oral direct thrombin inhibitor; rivaroxaban and apixaban are oral direct Factor Xa inhibitors. These agents have a quicker onset and offset of action, more predictable pharmacokinetic and pharmacodynamic profiles, and fewer drug-drug interactions than VKAs, allowing use of fixed doses. For the prevention of stroke in patients with AF, the non-VKA OACs were either non-inferior or superior to warfarin with similar or improved bleeding profiles, particularly with respect to reductions in intracranial haemorrhage. In patients with ACS receiving dual antiplatelet therapy, the addition of rivaroxaban significantly reduced the rate of death from cardiovascular causes, myocardial infarction or stroke without increasing fatal bleeding, but led to higher rates of major bleeding. Dose reductions with non-VKA OACs are mandated in certain circumstances in patients with AF, such as moderate renal impairment. Contraindications include creatinine clearance <15 mL/min (<30 mL/min for dabigatran in Europe and Canada) and moderate or severe hepatic impairment, but patients can be transitioned to other anticoagulants if appropriate. It is unknown which non-VKA OAC is optimal for stroke prevention in patients with AF, although factors such as co-medications (e.g. dabigatran may be preferred if a patient is taking a co-medication that is a strong cytochrome P450 3A4 inhibitor) and renal function (rivaroxaban and apixaban depend less on renal clearance than dabigatran) will be important for individual patients. Addition of rivaroxaban to antiplatelet therapy for prevention of recurrent events in patients with recent ACS is approved in Europe for patients at the highest risk (with elevated cardiac biomarkers) and must take into account the increased risk of major bleeding. Although routine coagulation monitoring is not required, an understanding of which assays are appropriate for each non-VKA OAC and how they are affected is important. In a bleeding emergency, non-specific prohaemostatic agents are suggested to reverse the action of the non-VKA OACs, but more clinical data are needed.

WHAT IS NEW AND CONCLUSION

Non-VKA OACs provide similar or improved efficacy and, on current evidence, improved safety. They provide greater convenience, compared with traditional anticoagulants for the prevention of stroke in patients with AF. Rivaroxaban may be of benefit to selected high-risk patients with ACS. Selection of the most appropriate non-VKA OAC will depend on individual patient factors.

Hip arthroplasty fatality related to dabigatran induced gastrointestinal haemorrhage

We report a fatality due to massive gastrointestinal haemorrhage in a patient receiving prophylactic dabigatran etexilate following a total hip replacement. A 79-year-old woman was commenced on dabigatran for venous thromboembolic prophylaxis following a total hip replacement. She presented again four days after surgery with haematemesis and hypotension but her coagulopathy could not be corrected, leading to her death. This case highlights the lack of reversal agent for dabigatran etexilate that resulted in this fatal complication.

Dabigatran, intracranial hemorrhage, and the neurosurgeon

Dabigatran etexilate (Pradaxa) is a novel oral anticoagulant that has gained FDA approval for the prevention of ischemic stroke and systemic embolism in patients with nonvalvular atrial fibrillation. In randomized trials, the incidence of hemorrhagic events has been demonstrated to be lower in patients treated with dabigatran compared with the traditional anticoagulant warfarin. However, dabigatran does not have reliable laboratory tests to measure levels of anticoagulation and there is no pharmacological antidote. These drawbacks are challenging in the setting of intracerebral hemorrhage. In this article, the authors provide background information on dabigatran, review the existing anecdotal experiences with treating intracerebral hemorrhage related to dabigatran therapy, present a case study of intracranial hemorrhage in a patient being treated with dabigatran, and suggest clinical management strategies. The development of reversal agents is urgently needed given the growing number of patients treated with this medication.

Treatment with novel oral anticoagulants: indications, efficacy and risks

PURPOSE OF REVIEW

To summarize data relevant to novel oral anticoagulants (nOACs), mainly apixaban, dabigatran and rivaroxaban, as alternatives to vitamin K antagonists (VKAs).

RECENT FINDINGS

RE-LY was the first contemporaneous study to compare a nOAC, dabigatran, with dose-adjusted warfarin, for prevention of stroke and systemic embolism in atrial fibrillation. Since then multiple studies have compared nOACs to warfarin for acute (RE-COVER, RECOVER-II, EINSTEIN-DVT and EINSTEIN-PE) and extended treatment of venous thromboembolism (VTE) (AMPLIFY-EXT, RE-MEDY and RE-SONATE). Additional studies have examined stroke prevention in atrial fibrillation (ARISTOTLE and ROCKET-AF). We do not examine, in depth, use of nOACs in coronary artery disease.

SUMMARY

nOACs are an acceptable alternative to VKAs in certain situations - these are at least as effective as warfarin for secondary prevention of VTE and for prevention of stroke and systemic embolism in patients with atrial fibrillation. These compare favorably with warfarin with respect to their rate of fatal and major bleeding. However, special attention should be given when using these drugs in certain patient populations, in particular in patients with renal insufficiency, those receiving additional antithrombotic therapy, those with questionable compliance, patients of child bearing potential and those with a high risk of gastrointestinal bleeding.

Consensus Recommendations for Preventing and Managing Bleeding Complications Associated with Novel Oral Anticoagulants in Singapore

Introduction: Novel oral anticoagulants (NOACs) have at least equivalent efficacy compared to standard anticoagulants with similar bleeding risk. Optimal management strategies for bleeding complications associated with NOACs are currently unestablished. Materials and Methods: A working group comprising haematologists and vascular medicine specialists representing the major institutions in Singapore was convened to produce this consensus recommendation. A Medline and EMBASE search was conducted for articles related to the 3 available NOACs (dabigatran, rivaroxaban, apixaban), bleeding and its management. Additional information was obtained from the product monographs and bibliographic search of articles identified. Results: The NOACs still has substantial interactions with a number of drugs for which concomitant administration should best be avoided. As they are renally excreted, albeit to different degrees, NOACs should not be prescribed to patients with creatinine clearance of <30 mLs/min. Meticulous consideration of risk versus benefits should be exercised before starting a patient on a NOAC. In patients presenting with bleeding, risk stratification of the severity of bleeding as well as identification of the source of bleeding should be performed. In life-threatening bleeds, recombinant activated factor VIIa and prothrombin complex may be considered although their effectiveness is currently unsupported by firm clinical evidence. The NOACs have varying effect on the prothrombin time and activated partial thromboplastin time which has to be interpreted with caution. Routine monitoring of drug level is not usually required. Conclusion: NOACs are an important advancement in antithrombotic management and careful patient selection and monitoring will permit optimisation of their potential and limit bleeding events. Key words: Conversion, Drug interactions, Monitoring, Perioperative, Procoagulant agents

Reversal of apixaban induced alterations in hemostasis by different coagulation factor concentrates: significance of studies in vitro with circulating human blood

Apixaban is a new oral anticoagulant with a specific inhibitory action on FXa. No information is available on the reversal of the antihemostatic action of apixaban in experimental or clinical settings. We have evaluated the effectiveness of different factor concentrates at reversing modifications of hemostatic mechanisms induced by moderately elevated concentrations of apixaban (200 ng/ml) added in vitro to blood from healthy donors (n = 10). Effects on thrombin generation (TG) and thromboelastometry (TEM) parameters were assessed. Modifications in platelet adhesive, aggregating and procoagulant activities were evaluated in studies with blood circulating through damaged vascular surfaces, at a shear rate of 600 s(-1). The potential of prothrombin complex concentrates (PCCs; 50 IU/kg), activated prothrombin complex concentrates (aPCCs; 75 IU/kg), or activated recombinant factor VII (rFVIIa; 270 μg/kg), at reversing the antihemostatic actions of apixaban, were investigated. Apixaban interfered with TG kinetics. Delayed lag phase, prolonged time to peak and reduced peak values, were improved by the different concentrates, though modifications in TG patterns were diversely affected depending on the activating reagents. Apixaban significantly prolonged clotting times (CTs) in TEM studies. Prolongations in CTs were corrected by the different concentrates with variable efficacies (rFVIIa≥aPCC>PCC). Apixaban significantly reduced fibrin and platelet interactions with damaged vascular surfaces in perfusion studies (p<0.05 and p<0.01, respectively). Impairments in fibrin formation were normalized by the different concentrates. Only rFVIIa significantly restored levels of platelet deposition. Alterations in hemostasis induced by apixaban were variably compensated by the different factor concentrates investigated. However, effects of these concentrates were not homogeneous in all the tests, with PCCs showing more efficacy in TG, and rFVIIa being more effective on TEM and perfusion studies. Our results indicate that rFVIIa, PCCs and aPCCs have the potential to restore platelet and fibrin components of the hemostasis previously altered by apixaban.

European Heart Rhythm Association Practical Guide on the use of new oral anticoagulants in patients with non-valvular atrial fibrillation

New 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 will 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 listed 15 topics of concrete clinical scenarios and formulated as practical answers as possible based on available evidence. The 15 topics are: (1) Practical start-up and follow-up scheme for patients on NOACs; (2) How to measure the anticoagulant effect of NOACs; (3) Drug-drug interactions and pharmacokinetics of NOACs; (4) Switching between anticoagulant regimens; (5) Ensuring compliance of NOAC intake; (6) How to deal with dosing errors; (7) Patients with chronic kidney disease; (8) What to do if there is a (suspected) overdose without bleeding, or a clotting test is indicating a risk of bleeding? (9) Management of bleeding complications; (10) Patients undergoing a planned surgical intervention or ablation; (11) Patients undergoing an urgent surgical intervention; (12) Patients with AF and coronary artery disease; (13) Cardioversion in a NOAC-treated patient; (14) Patients presenting with acute stroke while on NOACs; (15) NOACs vs. VKAs in AF patients with a malignancy. Since new information is becoming available at a rapid pace, an EHRA Web site with the latest updated information accompanies this text (www.NOACforAF.eu).

Pathology consultation on monitoring direct thrombin inhibitors and overcoming their effects in bleeding patients

OBJECTIVES

Direct thrombin inhibitors (DTIs), a relatively new class of anticoagulants, present several challenges regarding monitoring of their anticoagulant effects and overcoming bleeding associated with their use. The aim of this article is to (1) briefly present the pharmacologic properties of currently available DTIs, (2) discuss approaches to laboratory assessment of these drugs, and (3) review management of bleeding associated with their use.

METHODS

Published literature on DTIs, including clinical trials, case reports, and experimental animal models, was reviewed. The primary authors also reviewed their first-hand experiences with DTI anticoagulation.

RESULTS

Based on the literature review and the practical experiences of the authors, suggestions for the monitoring of DTIs and algorithmic approaches for the management of DTI-associated bleeding were developed.

CONCLUSIONS

Routine coagulation assays (eg, the prothrombin time) show a relatively poor correlation with the degree of anticoagulation and DTI drug concentrations. Newer assays, such as the ecarin clotting time and dilute thrombin time, may be more useful in assessing DTI anticoagulation, but these assays are not yet widely available. Low-grade DTI-associated bleeds are best managed with cessation of the drug and supportive care, while higher-grade and/or life-threatening bleeds may best be reversed by active drug removal (eg, via the administration of activated charcoal or hemodialysis). At present there is little evidence to suggest that transfusion products such as factor concentrates or thawed plasma are of any particular benefit in DTI reversal; however, these products may play a supportive role in the management of bleeding.

Reversing the new oral anticoagulants with prothrombin complex concentrates (PCCs): what is the evidence?

Newer oral anticoagulants offer several advantages over traditional agents (e.g. warfarin), but they are still associated with a bleeding risk and currently there is no validated reversal treatment for them. While there is little support for the use of fresh frozen plasma, and limited data available on the effects of activated recombinant factor VII, preclinical data suggest that prothrombin complex concentrates (PCCs) may have potential in this setting. PCCs are currently used to successfully reverse warfarin-induced anticoagulation; however, clinical evidence for their use with new oral anticoagulants is lacking, with most of the available data coming from preclinical animal studies. Furthermore, there appears to be variation in the ability of different PCCs to reverse the coagulopathy induced by the new anticoagulants, and a lack of correlation between the reversal of laboratory test results and the reversal of anticoagulant-induced bleeding. Although there have been encouraging results, care must be taken in generalising findings from animal models and nonbleeding human subjects to the situation in bleeding patients. Ultimately, more evidence supporting anticoagulation reversal for new anticoagulants is needed, particularly regarding the treatment of bleeding in human patients in a clinical setting. According to the current evidence, use of PCCs may be considered a reasonable approach in dire clinical situations; however, a consensus has not yet been reached regarding PCC use or dosing, due to lack of clinical data.

Clinical use of new oral anticoagulant drugs: dabigatran and rivaroxaban

Orally active small molecules that selectively and specifically inhibit coagulation serine proteases have been developed for clinical use. For some patients these oral direct inhibitors (ODIs) offer substantial benefits over oral vitamin K antagonists (VKA). However, for the majority of patients with good anticoagulant control with VKAs the advantages of the ODIs are primarily convenience and few drug interactions. The drugs are prescribed at fixed dose without the need for monitoring or dose adjustment in the majority of patients and the rapid onset of anticoagulation and short half-life make initiation and interruption of anticoagulation considerably easier than with VKAs. As yet, specific antidotes to ODIs are not available for clinical use but these are in development as rapid reversal agents. As with all anticoagulants produced so far, there is a correlation between intensity of anticoagulation and bleeding. Consequently, the need to consider the balance of benefit and risk in each individual patient is no less important than with VKA therapy. Dabigatran and rivaroxaban have been chosen for this review as examples of a thrombin inhibitor and an inhibitor of factor Xa respectively. The clinical application of these drugs is the focus of the review.

Dabigatran and kidney disease: a bad combination

Dabigatran is an oral direct thrombin inhibitor widely used to prevent and treat various thromboembolic complications. An advantage of this agent over other anticoagulants is that routine laboratory monitoring and related dose adjustments are considered unnecessary. A major disadvantage is the absence of a reliable means of reversing its anticoagulant effect. After U.S. Food and Drug Administration approval, recently emerged data suggest a higher bleeding risk with dabigatran, especially in the elderly. Clinicians are thus faced with caring for patients with serious bleeding events without readily available tests to measure drug levels or the anticoagulant effects of dabigatran and without effective antidotes to rapidly reverse the anticoagulant effect. On the basis of dabigatran's pharmacokinetic profile, hemodialysis and continuous renal replacement therapy have been used to remove dabigatran with the hope, still unproven, that this would rapidly reverse the anticoagulant effect and reduce bleeding in patients with normal and those with reduced kidney function. However, the best clinical approach to the patient with serious bleeding is not known, and the risks of placing a hemodialysis catheter in an anticoagulated patient can be substantial. This article reviews this issue, addressing clinical indications, drug pharmacokinetics, clinical and laboratory monitoring tests, and dialytic and nondialytic approaches to reduce bleeding in dabigatran-treated patients.

The new oral anticoagulants: practical management for patients attending for endoscopic procedures

Guidelines published by the British Society of Gastroenterology have standardised the care of patients attending for endoscopy procedures, taking aspirin, clopidogrel and warfarin. Two new oral anticoagulant drugs, Rivaroxaban and Dabigatran, are licensed and National Institute of Clinical Excellence (NICE) approved for use in the UK. Unlike warfarin, these drugs do not require regular monitoring, and are at least as effective in preventing stroke in non-valvular atrial fibrillation. As such, they are likely to become popular among patients and clinicians alike. This paper summarises the practical management of patients taking these drugs attending for endoscopic procedures.

Clinical review: Clinical management of new oral anticoagulants: a structured review with emphasis on the reversal of bleeding complications

New oral anticoagulants, including dabigatran, rivaroxaban, and apixaban, have been recently approved for primary and secondary prophylaxis of thromboembolic conditions. However, there is no clear strategy for managing and reversing their anticoagulant effects. We aimed to summarize the available evidence for clinical management and reversal of bleeding associated with new oral anticoagulants. Using a systematic review approach, we aimed to identify studies describing reversal strategies for dabigatran, rivaroxaban, and apixaban. The search was conducted using Medline, EMBASE, HealthSTAR, and grey literature. We included laboratory and human studies. We included 23 studies reported in 37 out of 106 potentially relevant references. Four studies were conducted in humans and the rest were in vitro and in vivo studies. The majority of the studies evaluated the use of prothrombinase complex concentrate (PCC), either activated or inactivated, and recombinant activated factor VII (rFVIIa). Other interventions were also identified. Laboratory studies suggest that hemostatic parameters and bleeding might be partially or completely corrected by PCC for rivaroxaban better than dabigatran. Studies in humans suggest that PCC might reverse the effects of rivaroxaban better than dabigatran assessed by hemostatic tests. We were not able to locate studies evaluating the clinical efficacy of these agents. The best available evidence suggests that PCC (activated or inactivated) might be the best option for reversing new anticoagulants. Evidence for rFVIIa is less compelling. There might be differences in the efficacy of reversing agents for different anticoagulants. Studies assessing the clinical efficacy of these reversal agents are urgently needed.

The role of the laboratory in treatment with new oral anticoagulants

Orally active small molecules that selectively and specifically inhibit coagulation serine proteases have been developed for clinical use. Dabigatran etexilate, rivaroxaban and apixaban are given at fixed doses and do not require monitoring. In most circumstances, these drugs have predictable bioavailability, pharmacokinetic effects, and pharmacodynamic effects. However, there will be clinical circumstances when assessment of the anticoagulant effect of these drugs will be required. The effect of these drugs on laboratory tests has been determined in vitro by spiking normal samples with a known concentration of active compound, or ex vivo by using plasma samples from volunteers and patients. Data on the sensitivity of different reagents are now available, and so guidance as to the effect and interpretation of a test result is now possible. Laboratories should be aware of the sensitivity of their own assays to each drug. This may be achieved by using appropriate calibrated plasma samples.

A specific antidote for dabigatran: functional and structural characterization

We present an antidote for dabigatran that effectively reverses its anticoagulative effect in human plasma in vitro and in rats in vivo. The antidote shares structural features with thrombin in the mode of binding but has no activity in coagulation tests.

Novel oral anticoagulants for stroke prevention in patients with atrial fibrillation: dawn of a new era

Atrial fibrillation (AF) is an important cause of ischemic stroke and is the underlying cause of > 20% of all strokes, with increasing age being a risk factor. Until recently, warfarin was the only available oral anticoagulant used to decrease this risk in patients with AF. However, there are several disadvantages of warfarin use, such as the requirement for monitoring the international normalized ratio, its wide range of drug-food interactions, and its narrow therapeutic index. Thus, there has been a strong impetus for the development of newer oral anticoagulants with predictable pharmacokinetics that obviate the need for monitoring the international normalized ratio. The US Food and Drug Administration has approved a direct thrombin inhibitor (dabigatran) and 2 factor Xa inhibitors (rivaroxaban and apixaban) for stroke prevention in patients with nonvalvular AF. There are several other new oral anticoagulant agents on the horizon, including the factor Xa inhibitor edoxaban. This review article discusses the pharmacological properties, clinical trial data, and practical issues associated with the use of these novel oral anticoagulants.

The acute management of haemorrhage, surgery and overdose in patients receiving dabigatran

Dabigatran is an oral direct thrombin inhibitor (DTI) licensed for stroke prevention in atrial fibrillation and likely to be soon approved in Europe for treatment of venous thrombosis. Predictable pharmacokinetics and a reduced risk of intracranial haemorrhage do not negate the potential risk of haemorrhage. Unlike warfarin, there is no reversal agent and measurement of the anticoagulant effect is not 'routine'. The prothrombin time/international normalised ratio response to dabigatran is inconsistent and should not be measured when assessing a patient who is bleeding or needs emergency surgery. The activated partial thromboplastin time (APTT) provides a qualitative measurement of the anticoagulant effect of dabigatran. Knowledge of the time of last dose is important for interpretation of the APTT. Commercially available DTI assays provide a quantitative measurement of active dabigatran concentration in the plasma. If a patient receiving dabigatran presents with bleeding: omit/delay next dose of dabigatran; measure APTT and thrombin time (consider DTI assay if available); administer activated charcoal, with sorbitol, if within 2 h of dabigatran ingestion; give tranexamic acid (1 g intravenously if significant bleeding); maintain renal perfusion and urine output to aid dabigatran excretion. Dabigatran exhibits low protein binding and may be removed by dialysis. Supportive care should form the mainstay of treatment. If bleeding is life/limb threatening, consider an additional haemostatic agent. There is currently no evidence to support the choice of one haemostatic agent (FEIBA, recombinant factor VIIa, prothrombin complex concentrates) over another. Choice will depend on access to and experience with available haemostatic agent(s).

The old and new: PCCs, VIIa, and long-lasting clotting factors for hemophilia and other bleeding disorders

What is the correct use of established clotting factors, prothrombin complex concentrates (PCCs), and activated factor VII in bleeding complications of trauma, surgery, and old and new oral anticoagulants? How will new clotting factors, specifically the long-acting factors, change the hemostatic management of coagulation deficiency disorders? From bench to bedside, comparative coagulation studies and clinical trials of modified clotting factors are providing insights to help guide hemostatic management of congenital and acquired bleeding disorders. Comparative thrombin-generation studies and preclinical and clinical trials suggest that PCCs and fresh-frozen plasma are effective in reversing the anticoagulant effects of warfarin, yet there are few data to guide reversal of the new oral anticoagulants dabigatran and rivaroxaban. Although coagulation studies support the use of PCCs to reverse new oral anticoagulants, correlation with clinical response is variable and clinical trials in bleeding patients are needed. For congenital bleeding disorders, exciting new technologies are emerging from the bench. Data from clinical trials of molecularly modified coagulation factors with extended half-lives suggest the possibility of fewer infusions, reduced bleeds, and better quality of life in persons with hemophilia. Preclinical studies of other novel prohemostatic approaches for hemophilia and other congenital coagulation disorders include RNA interference silencing of antithrombin, monoclonal anti-tissue factor pathway inhibitor (anti-antibody, anti-tissue factor pathway inhibitor) aptamer, bispecific anti-IXa/X antibody, and fucoidans. Understanding the comparative coagulation studies of established prohemostatic agents, the pharmacokinetics of new long-acting clotting factors, and their correlation with bleeding outcomes will provide opportunities to optimize the hemostatic management of both congenital and acquired hemostatic disorders.