Novel Oral Anticoagulant Complications

Basics

Over last decade several novel oral anticoagulants (NOACs) have been developed:
- Direct thrombin inhibitors (Dabigatran)
- Factor Xa inhibitors (Apixaban, Edoxaban, Rivaroxaban)
Direct thrombin inhibitors inhibit both free and fibrin-bound thrombin as well as thrombin-induced platelet aggregation
Factor Xa inhibitors cause selective and reversible inhibition of factor Xa in both the intrinsic and extrinsic coagulation pathways
All four agents are metabolized through the liver and eliminated by the kidneys; dabigatran > edoxaban > rivaroxaban > apixaban
Commonly used for both prophylaxis and treatment of stroke, myocardial infarction, valvular disease, and venous thromboembolism
Measurement of anticoagulant effect is not routinely needed:
- Prothrombin time (PT)/International Normalization Ratio (INR) are of limited utility in measuring anticoagulant effect
- Best screening tests of anticoagulant effect in direct thrombin inhibitors are thrombin time (TT) and ecarin clotting time (ECT)
- Best screening test of anticoagulant effect in factor Xa inhibitors is chromogenic anti-FXa assays
Contraindications include any condition in which the risk of hemorrhage or adverse reaction outweighs clinical benefit
- Prior hypersensitivity
- Severe renal impairment
- Hepatic impairment
- Active or potential GI, intracerebral, or genitourinary bleeding

Bleeding incidence:
- Overall major bleeding events < warfarin
  - Less incidence of intracranial hemorrhage (ICH) than warfarin
  - Higher incidence of GI bleeding than warfarin
Thrombotic event:
- In patients who do not or cannot take prescribed NOACs are at risk for a thrombotic event

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