USMLE Step 3 Drug MOA Practice Test 2026 – All-in-One Exam Prep

Fondaparinux is an anticoagulant that primarily functions by inhibiting factor Xa. Its mechanism involves a synthetic pentasaccharide structure that selectively binds to antithrombin III, causing a conformational change that enhances the activity of antithrombin. This activated antithrombin then effectively inhibits factor Xa through a catalytic process, leading to decreased thrombin generation and ultimately reducing the risk of thrombus formation.

In essence, while fondaparinux does rely on antithrombin III for its anticoagulant effect, its specific target is factor Xa, making it distinct from other anticoagulants that might directly inhibit thrombin or promote platelet aggregation. This targeted inhibition of factor Xa is what allows fondaparinux to provide effective anticoagulation with a lower risk of causing direct bleeding compared to other anticoagulants that might have broader effects on the coagulation cascade.