Which of the following describes the action of apixaban, edoxaban, and rivaroxaban?

• A. Direct factor Xa inhibitor
• B. Direct thrombin inhibitor
• C. Vitamin K antagonist
• D. Platelet aggregation inhibitor

Answer: (A)

They are direct inhibitors of factor Xa in the coagulation cascade. By binding to factor Xa, these drugs prevent the conversion of prothrombin (factor II) to thrombin (factor IIa), which reduces thrombin generation and the formation of fibrin clots. This mechanism distinguishes them from direct thrombin inhibitors (which block thrombin itself), vitamin K antagonists (which impair synthesis of several vitamin K–dependent factors rather than directly inhibiting an enzyme), and platelet aggregation inhibitors (which prevent platelets from clumping together rather than interfering with the coagulation cascade).