What is the mechanism of action of apixaban?

• A. Direct thrombin inhibitors
• B. Direct factor Xa inhibitors
• C. Platelet aggregation inhibitors
• D. Vitamin K antagonists

Answer: (B)

Apixaban works by directly inhibiting Factor Xa. It binds to the active site of Factor Xa, blocking its ability to convert prothrombin to thrombin. With less thrombin produced, the formation of fibrin and the propagation of clots are reduced. This sets it apart from drugs that inhibit thrombin itself, from vitamin K antagonists that reduce production of vitamin K–dependent clotting factors, and from antiplatelet drugs that interfere with platelet function. So the mechanism is direct inhibition of Factor Xa, not inhibition of thrombin, not vitamin K–dependent factor synthesis, and not platelets.