Andexanet Alfa: Reversal agent for FXa Inhibitors

Transcription

1 Andexanet Alfa: Reversal agent for FXa Inhibitors Grace Gilmore, Prof Ross Baker, Dr Jim Tiao, Dr Quintin Hughes, Dr Jasmine Tay, Scott McGregor WA Centre for Thrombosis and Haemostasis, Murdoch University, Murdoch, Western Australia. Perth Blood Institute, Nedlands, Western Australia

2 Introduction The main point of the oral Xa inhibitors was: No monitoring. More predictable pharmacokinetics No food interactions Therefore: No reversal agent

3 Introduction Clinical trials v real life Bleeds Urgent surgery Available products PCC Charcoal dialysis

4 Andexanet Alpha Modified recombinant protein derived from human FX Approx 41kDa Lacks a membrane-binding ƴ-carboxyglutamic acid (GLA) domain Is not catalytically active due to a serine alanine residue mutation in the protease catalytic triad. Binds to FXa inhibitor in their active site 1:1 Stoichiometry

5 Andexanet Alfa AMSRJ Spring2014 Volume1,Number11

6 Aim and Method Aim Determine the effect of Andexanet Alfa on routine clotting tests. Methods PT, aptt, TCT and DRVVT were performed using Siemens reagents on the Sysmex CS 5100 Coagulation Analyser. Anti FXa assay was performed using the STAGO kit.

7 Time (seconds) Results Adding Andexanet alfa to normal plasma PT aptt TCT Concentration of Andexanet Alfa (μg/ml)

8 Chromogenic Anti-Xa Activity Assay (% of Baseline) Results Drug reversal 100% ~ 300ng/ml ~85-90% Rivaroxaban Apixaban Andexanet alfa concentration (μg/ml)

9 Lupus Anticoagulant Detection a challenge due to: Antibody heterogeneity Reagent and analyser variability Differing interpretation strategies Mixing studies Not definite Multiple factor deficiency due to VKA are corrected, There is usually no underlying factor deficiency with FXa inhibitors.

10 Lupus Anticoagulant Testing Lupus-anticoagulant testing at NOAC trough levels Ratzinger et al Coagulation and Fibrinolysis 2016 Frequent False positive results of lupus anticoagulant tests in plasma of patients receiving the new oral anticoagulants and enoxaparin Martinuzz et al. IJLH 2014 Interactions between rivaroxaban and antiphospholipid antibodies in thrombotic antiphospholipid syndrome Arachchillage et al. JTH 2015 Effects of the oral, direct factor Xa inhibitor apixaban on routine coagulation assays and anti FXa assays Hillarp et al. JTH 2014

11 Time (Seconds) Lupus anticoagulant FXa Inhibitor Concentration (ng/ml) Rivaroxaban Apixaban Rivaroxaban + Phospholipids Apixaban + Phospholipids

12 Time (Seconds) Lupus Anticoagulant Andexanet alfa Concentration (μg/ml ) Minimal phospholipids Excess phospholipids

13 Normalised drvvt Ratio Normalised drvvt Ratio Influence of rivaroxaban, apixaban and andexanet alfa on normalised drvvt ratios Andexanet Alfa Concentration (μg/ml ) Direct FXa Inhibitor Concentration (ng/ml) Apixaban Rivaroxaban Andexanet alfa Figure 5. Influence of rivaroxaban, apixaban and andexanet alfa on normalised drvvt ratios (normal phospholipid:excess phospholipid ratio) using drug diluted in commercial normal plasma.

14 Results Sample FXa Inhibitor Level ng/ml Baseline drvvt Ratio R R R A A A

15 Results Sample FXa Inhibitor level ng/ml Baseline DRVVT Ratio R R R A A A

16 Summary Andexanet alfa prolongs aptt in a concentration-dependent manner in-vitro, with negligible effects on PT or TCT Andexanet alfa (250μg/mL) neutralises rivaroxaban and apixaban by ~85-90%, based on anti-xa assays Rivaroxaban induces a false-positive LA test via drvvt in a concentration-dependent manner. Andexanet alfa corrects this without affecting the true interpretation in LA-positive patients. Apixaban and andexanet alfa proportionately prolong the drvvt with and without phospholipid, so the LA ratio and interpretation remains unaffected

17 Acknowledgments Thanks To: Portola Pharmaceuticals Prof Ross Baker Scott McGregor Dr Quintin Hughes Dr Jim Tiao Dr Jasmine Tay Rene Mamode