A specific antidote for reversal of
anticoagulation by direct and indirect
inhibitors of coagulation factor Xa
Lu G, Deguzman FR, Hollenbach SJ, et al.
Department of Biology, Portola Pharmaceuticals Inc., South San Francisco, California, USA
Nature Medicine, April 2013, Volume 19 No 4 pp446 - 451
Background
• Noval oral anticoagulants (factor Xa & IIa
inhibitors) widely used
• Higher incidence for (GI-)bleeding
• Until now no antidote for nOAC
• Management of bleeding difficult; Vitamin
K, tranexamin acid, FFP, rfVIIa, PCC not
effective
-> presentation of a recombinant agent
antagonizing factor Xa
-> proof of concept with in vitro & in vivo
investigations
A specific antidote for reversal of anticoagulation by direct and indirect inhibitors of coagulation factor Xa
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Recombinant Antidote (r-antidote)
• Truncated form of enzymatically inactive fXa
• Lacks GLA domain, catalytically inactive due to mutation in serine
residue
• Mature functional form, expressed in chinese hamster ovary
Aspects to prove:
• Specific binding to fXa?
• Reversal of anticoagulation?
• pro- or antithrombotic properties?
• Reduce loss of bleeding?
A specific antidote for reversal of anticoagulation by direct and indirect inhibitors of coagulation factor Xa
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r-Antidote: in vitro-essays
• Reversal of anticoagulation in human plasma:
• clotting assay & thrombin generation assay:
• high affinity for fXa-inhibitors
• Inhibitory activity dosedependently and completely
reversed by r-Antidote
• no pro- or anticoagulant activity
A specific antidote for reversal of anticoagulation by direct and indirect inhibitors of coagulation factor Xa
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In vivo rat model - reversal of anticoagulation
• Rapid normalisation of INR after r-antidote
infusion
• Reversal of anticoagulation correlates to
reduction of unbound fXa-inhibitor-fraction
A specific antidote for reversal of anticoagulation by direct and indirect inhibitors of coagulation factor Xa
Mouse model of blood loss (tail transection)
Treat-I: vehicle + vehicle + vehicle
Treat-II: vehicle + rivaroxaban + vehicle
Treat-III: ASA + vehicle + vehicle
Treat-IV: ASA + rivaroxaban + vehicle
Treat-V: ASA + rivaroxaban + r- Antidote
• ASS+Rivar.+r-antidote reduced blood loss by 85%
• After r-antidote rivaroxaban activity reduced by >80%
A specific antidote for reversal of anticoagulation by direct and indirect inhibitors of coagulation factor Xa
Rabbit model of blood loss (liver laceration model)
• Laceration of 2 liver lobes and blood loss collection over 15min after injection of
vehicle or rivaroxaban and r-antidote
• PT & aPTT increased 2.3x resp. 1.9x after rivaroxaban, blood loss 3.2x higher
• r-Antidote reduced blood loss by >85%, decreased anti-fXa activity by 98%
• Correlation of blood loss with reduction in anti-fXa-activity an free fXa-inhibiton
A specific antidote for reversal of anticoagulation by direct and indirect inhibitors of coagulation factor Xa
Reversal of ATIII-dependent fXa inhibitors by r-antidote
• r-antidote mimicking binding-site of fXa for ATIII
• Enoxaparin (LMWH) & Fondaparinux (pentasaccharide) indirect fXa inhibitor
(increase affinity of ATIII for fXa)
Enoxaparin
Fondaparinux
• anti-fXa activitiy of enoxaparin & fondaparinux dose-dependently reversed with
r-antidote
A specific antidote for reversal of anticoagulation by direct and indirect inhibitors of coagulation factor Xa
Reversal of ATIII-dependent fXa inhibitors by r-antidote
• Animal model (rat tail transection)
Enoxaparin
Treat-I: vehicle
Treat-II: Enoxaparin & vehicle
Treat-III Enoxaparin & r-antidote 2mg/h
Treat-IV: Enoxaparin & r-antidote 4mg/h
• Normalisation of hemostasis after
r-antidote administration
• Complete reversal of ATIII-dependent fXa
inhibition
Treat-I: vehicle
Treat-II: Fondaparinux & vehicle
Treat-III Fondaparinux & r-antidote
Treat-IV: fondaparinux & Protamine
A specific antidote for reversal of anticoagulation by direct and indirect inhibitors of coagulation factor Xa
Discussion
• r-antidote does not interfere with normal fXa function
• r-antidote with no anticoagulant or procoagulant activity
• Rapid onset of action & complete reversal of fXa-inhibitors activity
• Normalises hemostasis from anticoagulant drugs targeting fXa
• Universal antidote for direct & indirect fXa inhibition
Limitations
• Possible that used in vitro system are not sensitive enough
• Preclinical data based on animal model, difficulties to extrapolate to
humans
• unidentified interactions with other proteins
• immunogenicity
A specific antidote for reversal of anticoagulation by direct and indirect inhibitors of coagulation factor Xa
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Conclusion
• r-antidote capable to reverse nOAC-induced bleedings
• Rapid onset of action will have major impact in future daily practice
(bleeding management, surgical procedures)
• Increase safety of using fXa-inhibiting drugs.
• Phase II-study running
• Further studies (antidote IIa-inhibitor, unviversal fIIa & fXa-antidote) on
the way
A specific antidote for reversal of anticoagulation by direct and indirect inhibitors of coagulation factor Xa
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