Coagulation Factor Xa (FXa) (FXa)

Coagulation Factor Xa (FXa) is a critical serine protease in the blood coagulation cascade, serving as the convergence point for the intrinsic and extrinsic pathways [StatPearls: Heparin]. Its primary biological function is the conversion of prothrombin (Factor II) into thrombin (Factor IIa) within the prothrombinase complex, which is the rate-limiting step in clot formation [UniProt: P00742]. In pathological states, overactivity of FXa leads to excessive thrombin generation, contributing to the formation of arterial and venous thrombi [StatPearls: Factor Xa Inhibitors]. This can result in life-threatening conditions such as deep vein thrombosis, pulmonary embolism, and systemic embolism in patients with atrial fibrillation [StatPearls: Factor Xa Inhibitors]. Drugs that target FXa via antithrombin III, such as heparin and fondaparinux, act as indirect inhibitors by binding to the endogenous cofactor antithrombin III [PubMed: 12165030]. This binding induces a conformational change in antithrombin III that dramatically accelerates its natural inhibitory effect on FXa [PubMed: 12165030]. This mechanism is distinct from direct oral anticoagulants (DOACs) which bind directly to the active site of FXa without requiring a cofactor [StatPearls: Factor Xa Inhibitors]. Clinical management of these indirect inhibitors often requires monitoring of anti-Xa activity to ensure therapeutic efficacy while minimizing bleeding risks [StatPearls: Heparin].

Other names

Stuart-Prower factorFactor XThrombokinaseProthrombinase complex componentActivated Factor X

Indirect inhibition of Factor Xa through the potentiation of Antithrombin III (ATIII). These drugs bind to a specific pentasaccharide sequence on ATIII, inducing a conformational change in the reactive center loop of ATIII, which increases its affinity for and neutralization of Factor Xa by approximately 1,000-fold [StatPearls: Heparin, PubMed: 12165030].