DOACs target specific enzymes in the common pathway of coagulation cascade. (vs warfarin which attenuates thrombin generation by decreasing levels of factors 2, 7, 9, 10).
Dabigatran has high affinity for thrombin, inactivates fibrin-bound as well as unbound thrombin, preventing conversion of fibrinogen to fibrin.
Rivaroxaban, apixaban and edoxaban directly inhibits free and clot-bound factor Xa without requiring cofactors, and suppress synthesis of new plasma thrombin but has no effects on the activity of existing thrombin.
Nonspecific Reversal Agents:
- Activated charcoal
- For acute intoxication (dabigatran studies) within 1-2h after intake of drug
- Efficacy not tested in clinical practice
- Stimulates release of factor VIII and vWF from vascular endothelium
- One study (healthy volunteers), DDAVP infusion causes significant dose-dependent reduction in hirudin, induced prolongation of aPTT in vivo
- No clinical trials in bleeding patients on DTI
- PCCs (inactive)
- Inconsistent results
- PCCs (activated)
- Given at a dose of 50 or 100 IU/Kg reduces bleeding time in dabigatran-treated animal model
- Ex vivo study showed reversing impaired thrombin generation in healthy individuals treated with dabigatran
- Most reasonable alternative for reversing dabigatran (until recently) but weigh risk-benefit because of associated increased risk of thromboembolic complications
- no trial conducted to prove effect on reversal of dabigatran
- 4 case reports showed ineffective in dabigatran-induced bleeding in 3 patients
- Low plasma protein binding (35%), so dabigatran can be dialysed in case of overdose, life-threatening bleeding or before emergency surgical situation
- Difficulty with establishing access in bleeding patient
Summary of DOACs:
SPECIFIC REVERSAL AGENTS:
Idarucizumab is a humanized monoclonal Ab fragment (Fab) that binds free and thrombin-bound dabigatran. Kidneys eliminate idarucizumab-dabigatran complex. Idarucizumab binds to dabigatran with affinity 350x higher than binding affinity of dabigatran for thrombin.
Andexanet is a recombindnant modified human factor Xa decoy protein. It binds to Factor Xa inhibitors in their active site with high affinity. It binds and removes Factor Xa inhibitors. This is assessed by measurement of thrombin generation and anti-factor Xa activity.
Aripazine PER977 binds specifically to UFH and LMWH through noncovalent H bonding and charge-charge-interactions. It binds in a similar way to all 4 DOACs. This drug reverses anticoagulant activity in ex-vivo human studies through aPTT and anti-Xa analysis.
Idarucizumab and ANNEXA studies:
Tummala, Ramyashree et al. “Specific Antidotes Against Direct Oral Anticoagulants: A Comprehensive Review Of Clinical Trials Data”. International Journal of Cardiology 214 (2016): 292-298. Web.