Factor Xa
Also known as: activated factor X, FXa, Stuart–Prower factor (activated)
The clotting enzyme at the junction of the two arms of the coagulation cascade, which converts prothrombin into thrombin. Apixaban, rivaroxaban and edoxaban block it directly, preventing clots in atrial fibrillation and venous thromboembolism without the monitoring warfarin needs.
- Kind
- protein
- Also called
- activated factor X, FXa, Stuart–Prower factor (activated)
- Where it is found
- Circulating in plasma as inactive factor X; activated on the surface of platelets and damaged endothelium at the site of injury.
What it does
Coagulation proceeds as a chain of enzyme activations that all converge on factor X. Once activated to factor Xa, it assembles with factor Va on the surface of platelets to form the prothrombinase complex, which generates thrombin, and thrombin then converts fibrinogen into the fibrin mesh of a clot and amplifies its own production. Each molecule of Xa yields many molecules of thrombin, so blocking Xa is an efficient way to reduce clotting. Direct oral anticoagulants bind the active site of Xa reversibly, take effect within hours, and have predictable dosing that does not require INR checks, although kidney function, body weight and interacting drugs (strong inhibitors or inducers of CYP3A4 and P-glycoprotein) affect their levels. Low-molecular-weight heparins such as enoxaparin inhibit Xa indirectly through antithrombin. Andexanet alfa is a specific reversal agent; bleeding is the shared main risk of every drug in this pathway, and it multiplies when they are combined with antiplatelets or NSAIDs.
Role in the body
Conversion of prothrombin to thrombin, the amplifying step of the coagulation cascade.