Journal of Thrombosis and Haemostasis, 12: 1425–1427
DOI: 10.1111/jth.12667
COMMENTARY
Prothrombin complex concentrate for non-vitamin K oral anticoagulant reversal: good enough for now? M. MAKRIS*† *Department of Cardiovascular Science, University of Sheffield; and †Sheffield Haemophilia and Thrombosis Centre, Royal Hallamshire Hospital, Sheffield, UK
To cite this article: Makris M. Prothrombin complex concentrate for non-vitamin K oral anticoagulant reversal: good enough for now? J Thromb Haemost 2014; 12: 1425–7. See also Levi M, Moore KT, Castillejos CF, Kubitza D, Berkowitz SD, Goldhaber SZ, Raghoebar M, Patel MR, Weitz JI, Levy JH. Comparison of three-factor and four-factor prothrombin complex concentrates regarding reversal of the anticoagulant effects of rivaroxaban in healthy volunteers. This issue, pp 1428–36.
Vitamin K antagonists have been the main oral anticoagulants in use worldwide for > 50 years. They are highly effect in preventing recurrence of venous thromboembolism and thrombotic stroke in patients with atrial fibrillation [1,2]. Despite this high degree of efficacy, they have a number of limitations, including the need for regular monitoring and significant interactions with multiple medications, and are associated with bleeding complications. The overall risk of bleeding in patients receiving warfarin has been reported to be 3.0% annually for serious bleeding and 0.6% for fatal bleeding [3]. The recent introduction of three new oral non-vitamin K direct-acting anticoagulants (NOACs) is transforming the landscape of thrombosis management, and patients are now changing from vitamin K antagonists to the NOACs. NOACs are taken at a fixed dose once or twice daily without the need for monitoring. Dabigatran inhibits thrombin, whereas rivaroxaban and apixaban are factor Xa inhibitors [4]. In a meta-analysis that compared NOACs with warfarin in the treatment of acute symptomatic venous thromboembolism, NOACs were as effective as warfarin and were associated with a significantly lower risk of bleeding complications [5]. The main adverse effect of all anticoagulants is bleeding, and hematologists are frequently consulted on how to optimally reverse their effect in an emergency, either Correspondence: Mike Makris, Sheffield Haemophilia and Thrombosis Centre, Royal Hallamshire Hospital, Glossop Road, Sheffield S10 2JF, UK. Tel.: +44 114 2712760; fax: +44 114 2756126. E-mail: [email protected] Received 31 May 2014 Manuscript handled by: S. Kitchen Final decision: F. R. Rosendaal, 10 July 2014 © 2014 International Society on Thrombosis and Haemostasis
because of major bleeding or because of urgent surgery that cannot be delayed. Despite the fact that the reversal of the effect of oral vitamin K antagonists may appear to be straightforward, with vitamin K and replacement of the deficient clotting factors with prothrombin complex concentrates (PCCs), several issues remain. For example, there is debate as to whether three-factor PCCs (which contain no FVII) are as effective as four-factor PCCs, which contain FII, FVII, FIX, and FX [6]. Furthermore, despite the widespread use of PCCs for warfarin reversal in Europe for decades, these products were only recently licensed in the USA [7]. Proving efficacy and safety to the US regulators was a difficult task. One of the main concerns with the use of NOACs is the lack of a specific antidote [8]. Fortunately, severe bleeding complications requiring emergency reversal are rare, and the relatively short half-life of NOACs in patients without renal impairment means that waiting and providing supportive care are often sufficient [8]. The lack of a specific antidote for commonly used anticoagulants is not a new issue, as it is not possible to completely reverse the anticoagulant effect of low molecular weight heparin even with protamine, but this has not held back their international adoption in clinical practice [9]. Currently, there are no specific NOAC antidotes, and several guidelines recommend the off-label use of activated PCC (aPCC) and non-activated PCCs for reversal of the anticoagulant effect [8,10,11]. A large number of publications have reported the effect of activated and non-activated PCCs on NOAC reversal in vitro, ex vivo, and in several animal models [12]. Unfortunately, the experimental conditions, animal species and type of model vary enormously, and it is not possible to compare directly the different results. The literature on in vitro and animal studies of PCCs for NOAC reversal has been reviewed recently, and the main conclusion is that they are at least partially effective [12]. For reversal of the
1426 M. Makris
effects of rivaroxaban and apixaban, PCCs are effective and are preferred over aPCC – the main reason for the preference for non-activated PCCs being the perceived reduced thrombogenicity in comparison with aPCC. For reversal of the effect of dabigatran, the results for PCCs and aPCC are less clear. In a recent study, van Ryn et al. [13] compared five activated and non-activated PCCs in the rat tail-bleeding model. Whereas both activated and non-activated PCCs were able to correct the bleeding time and increase the endogenous thrombin potential, only the activated product reduced the lag time. The corrections were seen at low dabigatran levels, but at high anticoagulant doses none of the concentrates was effective. Whereas many centers recommend a PCC for dabigatran reversal, primarily because this is the only product stocked at their hospital, some feel that aPCC is superior, despite its higher perceived thrombogenicity. Several case reports and case series on the use of nonspecific reversal agents in patients with NOAC-related bleeding have been published, but clinicians must be careful in interpreting these, owing to publication bias. Papers describing successful outcomes are more likely to be published, but the good outcome could relate to patient selection. Individuals who are more likely to do well are those with non-intracranial bleeding, those without renal impairment, and those who present some time after taking their last dose of NOAC. A recent article described the real-life risk of bleeding and its management in a large cohort of patients taking rivaroxaban [14]. Beyer-Westendorf et al. [14] set up a prospective registry of patients starting NOACs in Dresden, Germany, and analyzed the data for the 1776 patients in the study who were receiving rivaroxaban. A total of 1072 bleeding episodes in 762 patients were reported, and 66 of these were classified as major according to the ISTH definition [15]. The annual rate of major bleeding was 3.4% (95% confidence interval 2.6–4.4). Interestingly, despite the presence of major bleeding, 62.1% of patients were managed conservatively, whereas the rest required surgical or interventional treatment, primarily endoscopic treatment for gastrointestinal bleeding. Only six (9.1%) of the patients with major bleeding received non-activated PCCs, and none received recombinant FVIIa (rFVIIa) or aPCC. PCCs were effective in controlling bleeding in five of the six patients, and two died, one from sepsis and one from intracerebral bleeding [14]. In the current issue of the journal, Levi et al. [16] compare a three-factor PCC and a four-factor PCC in reversing the coagulopathy associated with supratherapeutic rivaroxaban levels achieved following administration of the drug to healthy volunteers at twice the licensed treatment dose. The three-factor PCC was at least as good as the four-factor PCC in correcting the suppressed thrombin generation. The four-factor PCC, which contains FVII, was better at reducing the prothrombin time, which is not surprising in view of the sensitivity of this test to
FVII, but the clinical implication of this is questionable. The correction of the thrombin generation is likely to be a better indicator of the bleeding diathesis. Although the Levi study was performed with a single FXa-inhibiting NOAC and two PCCs, it is reasonable to expect that this will be a class effect, but the effect of other PCCs should be confirmed by appropriate experimentation. The efficacy of the PCC in this study cannot, however, be extrapolated to dabigatran, which inhibits thrombin. Although PCCs are the main non-specific drugs recommended for NOAC reversal at present, within the next 3– 5 years we can expect there to be licensed specific antidotes for both the thrombin-inhibiting and FXainhibiting NOACs. Early data suggested that reversal of the effect of dabigatran is possible with a humanized antibody fragment against the drug (aDabi-Fab) [17] or with trypsinized mutated (S195A) thrombin [18]. Complete FXa reversal was demonstrated in vitro and in an animal model with a modified FXa molecule that is catalytically inactive, owing to deletion of the GLA domain and activation peptide and a mutation in the active site [19]. These specific antidotes are effective in vitro and in animal models, but their use has not been reported in NOAC-related active bleeding in humans. Trials under these conditions are challenging, owing to the rarity of bleeding with these new drugs and the difficulty in recruiting such individuals in clinical trials during an active bleeding episode. Although the future of NOAC reversal is likely to involve these new specific antidotes, for now it appears that PCCs are reasonable alternatives. Disclosure of Conflict of Interests The author has acted as consultant to Bayer, CSL Behring, and NovoNordisk. He took part in an Advisory Panel organized by BPL, and gave lectures for Baxter, Bayer, Biogen Idec, Biotest, Octapharma, Pfizer, and SOBI. He has received travel support from Baxter and Bayer. References 1 Hutten BA, Prins MH. Duration of treatment with vitamin K antagonists in symptomatic venous thromboembolism. Cochrane Database Syst Rev 2006: CD001367. 2 Andersen LV, Vestergaard P, Deichgraeber P, Lindholt JS, Mortensen LS, Frost L. Warfarin for the prevention of systemic embolism in patients with non-valvular atrial fibrillation: a metaanalysis. Heart 2008; 98: 1607–13. 3 Landfeld CS, Beyh RJ. Anticoagulant-related bleeding: clinical epidemiology, prediction, and prevention. Am J Med 1993; 95: 315–28. 4 Schulman S, Crowther MA. How I treat with anticoagulants in 2012: new and old anticoagulants, and when and how to switch. Blood 2012; 119: 3016–23. 5 van der Hulle T, Kooiman J, den Dexter PL, Dekkers OM, Klok FA, Huisman MV. Effectiveness and safety of novel oral anticoagulants as compared with vitamin K antagonists in the treat-
© 2014 International Society on Thrombosis and Haemostasis
PCC for NOAC reversal 1427
6
7
8
9
10
11 12
13
ment of acute symptomatic venous thromboembolism: a systematic review and meta-analysis. J Thromb Haemost 2014; 12: 320– 8. Makris M, van Veen JJ. Three or four factor prothrombin complex concentrate for emergency anticoagulation reversal? Blood Transfusion 2011; 9: 117–19. Sarode R, Milling TJ, Refaai MA, Mandione A, Schneider A, Durn BL, Goldstein JN. Efficacy and safety of a 4-factor prothrombin complex concentrate in patients on vitamin K antagonists presenting with major bleeding: a randomised, plasma controlled, phase IIIb study. Circulation 2013; 128: 1234–43. Makris M, van Veen JJ, Tait CR, Mumford AD, Laffan M. Guideline on the management of bleeding in patients on antithrombotic agents. Br J Haematol 2013; 160: 35–46. van Veen JJ, Maclean RM, Hampton KK, Laidlaw S, Kitchen S, Toth P, Makris M. Protamine reversal of low molecular weight heparin: clinically effective? Blood Coagul Fibrinolysis 2011; 22: 565–70. Kaatz S, Kouides PA, Garcia DA, Spyropoulos AC, Crowther M, Douketis JD, Chan AK, James A, Moll S, Ortel TL, van Cott EM, Ansell J. Guidance on the emergent reversal of oral thrombin and factor Xa inhibitors. Am J Hematol 2012; 87(Suppl. 1): S141–5. Kaatz S, Crowther M. Reversal of target specific oral anticoagulants. J Thromb Thrombolysis 2013; 36: 195–202. Dickneite G, Hoffman M. Reversing the new oral anticoagulants with prothrombin complex concentrates (PCCs): what is the evidence? Thromb Haemost 2014; 111: 189–98. van Ryn J, Schurer J, Kink-Elband M, Clemens A. Reversal of Dabigatran-induced bleeding by coagulation factor concentrates
© 2014 International Society on Thrombosis and Haemostasis
14
15
16
17
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19
in a rat-tail bleeding model and lack of effect on assays of coagulation. Anesthesiology 2014; 120: 1429–40. Beyer-Westerndorf J, Forster K, Pannach S, Ebertz F, Gelbricht V, Thieme C, Michalski F, Kohler C, Werth S, Sahin K, Tittl L, Hansel U, Weiss N. Rates, management, and outcome of bleeding complications during rivaroxaban therapy in daily care – results from the Dresden NOAC registry. Blood 2014; 124: 955–62. Schulman S, Kieron C. Definition of major bleeding in clinical investigations of antihemostatic medicinal products in non-surgical patients. J Thromb Haemost 2005; 3: 692–4. Levi M, Moore KT, Castillejos CF, Kubitza D, Berkowitz SD, Goldhaber SZ, Raghoebar M, Patel MR, Weitz JI, Levy JH. Comparison of three- and four-factor prothrombin complex concentrates on the anticoagulant effects of rivaroxaban in healthy volunteers. J Thromb Haemost 2014; 12: 1428–36. Schiele F, van Ryn J, Canada K, Newsome C, Sepulveda E, Park J, Nar H, Litzenburger T. A specific antidote for dabigatran: functional and structural characterisation. Blood 2013; 121: 3554–62. Sheffield WP, Lambourne MD, Eltringham-Smith LJ, Bhakta V, Arnold DM, Crowther MA. S195A thrombin reduces the anticoagulant effects of dabigatran in vitro and in vivo. J Thromb Haemost 2014; 12: 1110–15. Lu G, DeGuzman FR, Hollenbach SJ, Karbarz MJ, Abe K, Lee G, Luan P, Hutchaleelaha A, Inagaki M, Conley PB, Phillips DR, Sinha U. A specific antidote for reversal of anticoagulation by direct and indirect inhibitors of coagulation factor Xa. Nat Med 2013; 19: 446–53.
DOI: 10.1111/jth.12667
COMMENTARY
Prothrombin complex concentrate for non-vitamin K oral anticoagulant reversal: good enough for now? M. MAKRIS*† *Department of Cardiovascular Science, University of Sheffield; and †Sheffield Haemophilia and Thrombosis Centre, Royal Hallamshire Hospital, Sheffield, UK
To cite this article: Makris M. Prothrombin complex concentrate for non-vitamin K oral anticoagulant reversal: good enough for now? J Thromb Haemost 2014; 12: 1425–7. See also Levi M, Moore KT, Castillejos CF, Kubitza D, Berkowitz SD, Goldhaber SZ, Raghoebar M, Patel MR, Weitz JI, Levy JH. Comparison of three-factor and four-factor prothrombin complex concentrates regarding reversal of the anticoagulant effects of rivaroxaban in healthy volunteers. This issue, pp 1428–36.
Vitamin K antagonists have been the main oral anticoagulants in use worldwide for > 50 years. They are highly effect in preventing recurrence of venous thromboembolism and thrombotic stroke in patients with atrial fibrillation [1,2]. Despite this high degree of efficacy, they have a number of limitations, including the need for regular monitoring and significant interactions with multiple medications, and are associated with bleeding complications. The overall risk of bleeding in patients receiving warfarin has been reported to be 3.0% annually for serious bleeding and 0.6% for fatal bleeding [3]. The recent introduction of three new oral non-vitamin K direct-acting anticoagulants (NOACs) is transforming the landscape of thrombosis management, and patients are now changing from vitamin K antagonists to the NOACs. NOACs are taken at a fixed dose once or twice daily without the need for monitoring. Dabigatran inhibits thrombin, whereas rivaroxaban and apixaban are factor Xa inhibitors [4]. In a meta-analysis that compared NOACs with warfarin in the treatment of acute symptomatic venous thromboembolism, NOACs were as effective as warfarin and were associated with a significantly lower risk of bleeding complications [5]. The main adverse effect of all anticoagulants is bleeding, and hematologists are frequently consulted on how to optimally reverse their effect in an emergency, either Correspondence: Mike Makris, Sheffield Haemophilia and Thrombosis Centre, Royal Hallamshire Hospital, Glossop Road, Sheffield S10 2JF, UK. Tel.: +44 114 2712760; fax: +44 114 2756126. E-mail: [email protected] Received 31 May 2014 Manuscript handled by: S. Kitchen Final decision: F. R. Rosendaal, 10 July 2014 © 2014 International Society on Thrombosis and Haemostasis
because of major bleeding or because of urgent surgery that cannot be delayed. Despite the fact that the reversal of the effect of oral vitamin K antagonists may appear to be straightforward, with vitamin K and replacement of the deficient clotting factors with prothrombin complex concentrates (PCCs), several issues remain. For example, there is debate as to whether three-factor PCCs (which contain no FVII) are as effective as four-factor PCCs, which contain FII, FVII, FIX, and FX [6]. Furthermore, despite the widespread use of PCCs for warfarin reversal in Europe for decades, these products were only recently licensed in the USA [7]. Proving efficacy and safety to the US regulators was a difficult task. One of the main concerns with the use of NOACs is the lack of a specific antidote [8]. Fortunately, severe bleeding complications requiring emergency reversal are rare, and the relatively short half-life of NOACs in patients without renal impairment means that waiting and providing supportive care are often sufficient [8]. The lack of a specific antidote for commonly used anticoagulants is not a new issue, as it is not possible to completely reverse the anticoagulant effect of low molecular weight heparin even with protamine, but this has not held back their international adoption in clinical practice [9]. Currently, there are no specific NOAC antidotes, and several guidelines recommend the off-label use of activated PCC (aPCC) and non-activated PCCs for reversal of the anticoagulant effect [8,10,11]. A large number of publications have reported the effect of activated and non-activated PCCs on NOAC reversal in vitro, ex vivo, and in several animal models [12]. Unfortunately, the experimental conditions, animal species and type of model vary enormously, and it is not possible to compare directly the different results. The literature on in vitro and animal studies of PCCs for NOAC reversal has been reviewed recently, and the main conclusion is that they are at least partially effective [12]. For reversal of the
1426 M. Makris
effects of rivaroxaban and apixaban, PCCs are effective and are preferred over aPCC – the main reason for the preference for non-activated PCCs being the perceived reduced thrombogenicity in comparison with aPCC. For reversal of the effect of dabigatran, the results for PCCs and aPCC are less clear. In a recent study, van Ryn et al. [13] compared five activated and non-activated PCCs in the rat tail-bleeding model. Whereas both activated and non-activated PCCs were able to correct the bleeding time and increase the endogenous thrombin potential, only the activated product reduced the lag time. The corrections were seen at low dabigatran levels, but at high anticoagulant doses none of the concentrates was effective. Whereas many centers recommend a PCC for dabigatran reversal, primarily because this is the only product stocked at their hospital, some feel that aPCC is superior, despite its higher perceived thrombogenicity. Several case reports and case series on the use of nonspecific reversal agents in patients with NOAC-related bleeding have been published, but clinicians must be careful in interpreting these, owing to publication bias. Papers describing successful outcomes are more likely to be published, but the good outcome could relate to patient selection. Individuals who are more likely to do well are those with non-intracranial bleeding, those without renal impairment, and those who present some time after taking their last dose of NOAC. A recent article described the real-life risk of bleeding and its management in a large cohort of patients taking rivaroxaban [14]. Beyer-Westendorf et al. [14] set up a prospective registry of patients starting NOACs in Dresden, Germany, and analyzed the data for the 1776 patients in the study who were receiving rivaroxaban. A total of 1072 bleeding episodes in 762 patients were reported, and 66 of these were classified as major according to the ISTH definition [15]. The annual rate of major bleeding was 3.4% (95% confidence interval 2.6–4.4). Interestingly, despite the presence of major bleeding, 62.1% of patients were managed conservatively, whereas the rest required surgical or interventional treatment, primarily endoscopic treatment for gastrointestinal bleeding. Only six (9.1%) of the patients with major bleeding received non-activated PCCs, and none received recombinant FVIIa (rFVIIa) or aPCC. PCCs were effective in controlling bleeding in five of the six patients, and two died, one from sepsis and one from intracerebral bleeding [14]. In the current issue of the journal, Levi et al. [16] compare a three-factor PCC and a four-factor PCC in reversing the coagulopathy associated with supratherapeutic rivaroxaban levels achieved following administration of the drug to healthy volunteers at twice the licensed treatment dose. The three-factor PCC was at least as good as the four-factor PCC in correcting the suppressed thrombin generation. The four-factor PCC, which contains FVII, was better at reducing the prothrombin time, which is not surprising in view of the sensitivity of this test to
FVII, but the clinical implication of this is questionable. The correction of the thrombin generation is likely to be a better indicator of the bleeding diathesis. Although the Levi study was performed with a single FXa-inhibiting NOAC and two PCCs, it is reasonable to expect that this will be a class effect, but the effect of other PCCs should be confirmed by appropriate experimentation. The efficacy of the PCC in this study cannot, however, be extrapolated to dabigatran, which inhibits thrombin. Although PCCs are the main non-specific drugs recommended for NOAC reversal at present, within the next 3– 5 years we can expect there to be licensed specific antidotes for both the thrombin-inhibiting and FXainhibiting NOACs. Early data suggested that reversal of the effect of dabigatran is possible with a humanized antibody fragment against the drug (aDabi-Fab) [17] or with trypsinized mutated (S195A) thrombin [18]. Complete FXa reversal was demonstrated in vitro and in an animal model with a modified FXa molecule that is catalytically inactive, owing to deletion of the GLA domain and activation peptide and a mutation in the active site [19]. These specific antidotes are effective in vitro and in animal models, but their use has not been reported in NOAC-related active bleeding in humans. Trials under these conditions are challenging, owing to the rarity of bleeding with these new drugs and the difficulty in recruiting such individuals in clinical trials during an active bleeding episode. Although the future of NOAC reversal is likely to involve these new specific antidotes, for now it appears that PCCs are reasonable alternatives. Disclosure of Conflict of Interests The author has acted as consultant to Bayer, CSL Behring, and NovoNordisk. He took part in an Advisory Panel organized by BPL, and gave lectures for Baxter, Bayer, Biogen Idec, Biotest, Octapharma, Pfizer, and SOBI. He has received travel support from Baxter and Bayer. References 1 Hutten BA, Prins MH. Duration of treatment with vitamin K antagonists in symptomatic venous thromboembolism. Cochrane Database Syst Rev 2006: CD001367. 2 Andersen LV, Vestergaard P, Deichgraeber P, Lindholt JS, Mortensen LS, Frost L. Warfarin for the prevention of systemic embolism in patients with non-valvular atrial fibrillation: a metaanalysis. Heart 2008; 98: 1607–13. 3 Landfeld CS, Beyh RJ. Anticoagulant-related bleeding: clinical epidemiology, prediction, and prevention. Am J Med 1993; 95: 315–28. 4 Schulman S, Crowther MA. How I treat with anticoagulants in 2012: new and old anticoagulants, and when and how to switch. Blood 2012; 119: 3016–23. 5 van der Hulle T, Kooiman J, den Dexter PL, Dekkers OM, Klok FA, Huisman MV. Effectiveness and safety of novel oral anticoagulants as compared with vitamin K antagonists in the treat-
© 2014 International Society on Thrombosis and Haemostasis
PCC for NOAC reversal 1427
6
7
8
9
10
11 12
13
ment of acute symptomatic venous thromboembolism: a systematic review and meta-analysis. J Thromb Haemost 2014; 12: 320– 8. Makris M, van Veen JJ. Three or four factor prothrombin complex concentrate for emergency anticoagulation reversal? Blood Transfusion 2011; 9: 117–19. Sarode R, Milling TJ, Refaai MA, Mandione A, Schneider A, Durn BL, Goldstein JN. Efficacy and safety of a 4-factor prothrombin complex concentrate in patients on vitamin K antagonists presenting with major bleeding: a randomised, plasma controlled, phase IIIb study. Circulation 2013; 128: 1234–43. Makris M, van Veen JJ, Tait CR, Mumford AD, Laffan M. Guideline on the management of bleeding in patients on antithrombotic agents. Br J Haematol 2013; 160: 35–46. van Veen JJ, Maclean RM, Hampton KK, Laidlaw S, Kitchen S, Toth P, Makris M. Protamine reversal of low molecular weight heparin: clinically effective? Blood Coagul Fibrinolysis 2011; 22: 565–70. Kaatz S, Kouides PA, Garcia DA, Spyropoulos AC, Crowther M, Douketis JD, Chan AK, James A, Moll S, Ortel TL, van Cott EM, Ansell J. Guidance on the emergent reversal of oral thrombin and factor Xa inhibitors. Am J Hematol 2012; 87(Suppl. 1): S141–5. Kaatz S, Crowther M. Reversal of target specific oral anticoagulants. J Thromb Thrombolysis 2013; 36: 195–202. Dickneite G, Hoffman M. Reversing the new oral anticoagulants with prothrombin complex concentrates (PCCs): what is the evidence? Thromb Haemost 2014; 111: 189–98. van Ryn J, Schurer J, Kink-Elband M, Clemens A. Reversal of Dabigatran-induced bleeding by coagulation factor concentrates
© 2014 International Society on Thrombosis and Haemostasis
14
15
16
17
18
19
in a rat-tail bleeding model and lack of effect on assays of coagulation. Anesthesiology 2014; 120: 1429–40. Beyer-Westerndorf J, Forster K, Pannach S, Ebertz F, Gelbricht V, Thieme C, Michalski F, Kohler C, Werth S, Sahin K, Tittl L, Hansel U, Weiss N. Rates, management, and outcome of bleeding complications during rivaroxaban therapy in daily care – results from the Dresden NOAC registry. Blood 2014; 124: 955–62. Schulman S, Kieron C. Definition of major bleeding in clinical investigations of antihemostatic medicinal products in non-surgical patients. J Thromb Haemost 2005; 3: 692–4. Levi M, Moore KT, Castillejos CF, Kubitza D, Berkowitz SD, Goldhaber SZ, Raghoebar M, Patel MR, Weitz JI, Levy JH. Comparison of three- and four-factor prothrombin complex concentrates on the anticoagulant effects of rivaroxaban in healthy volunteers. J Thromb Haemost 2014; 12: 1428–36. Schiele F, van Ryn J, Canada K, Newsome C, Sepulveda E, Park J, Nar H, Litzenburger T. A specific antidote for dabigatran: functional and structural characterisation. Blood 2013; 121: 3554–62. Sheffield WP, Lambourne MD, Eltringham-Smith LJ, Bhakta V, Arnold DM, Crowther MA. S195A thrombin reduces the anticoagulant effects of dabigatran in vitro and in vivo. J Thromb Haemost 2014; 12: 1110–15. Lu G, DeGuzman FR, Hollenbach SJ, Karbarz MJ, Abe K, Lee G, Luan P, Hutchaleelaha A, Inagaki M, Conley PB, Phillips DR, Sinha U. A specific antidote for reversal of anticoagulation by direct and indirect inhibitors of coagulation factor Xa. Nat Med 2013; 19: 446–53.
