Fondaparinux sodium is an antithrombin-dependent factor Xa inhibitor. IC50 & Target: Factor Xa^[1] In Vitro: Fondaparinux sodium is the first agent of a new class of anticoagulants that selectively target factor Xa. For Fondaparinux, its IC₅₀ values (anti-Xa IU/ml) are 0.59±0.05 for activated monocytes (ac-M) and 0.17±0.03 for monocyte-derived microparticles (MMPs)^[2]. In Vivo: Fondaparinux sodium has a linear, dose-dependent pharmacokinetic profile, which provides a highly predictable response. Fondaparinux sodium is 100% bioavailable, has a rapid onset of action, and has a half-life of 14 to 16 hours, allowing for sustained antithrombotic activity over a 24-hour period. The drug does not affect prothrombin time or activated partial thromboplastin time, nor does it affect platelet function or aggregation^[1].