Coagulation factor Xa and other antithrombin III-sensitive serine proteases (FXa/ATIII-sensitive proteases)

Coagulation factor Xa and other antithrombin III (ATIII)-sensitive serine proteases are essential enzymes within the human blood coagulation cascade. Factor Xa (FXa) occupies a central role as the primary component of the prothrombinase complex, which catalyzes the conversion of prothrombin to thrombin, the final effector of clot formation [1, 4]. ATIII is a circulating glycoprotein that functions as a natural anticoagulant by inhibiting the activity of several serine proteases, most notably thrombin (IIa) and FXa, but also factors IXa, XIa, and XIIa [2, 3]. Drugs targeting this system, such as unfractionated heparin and low-molecular-weight heparins (LMWHs), work by binding to ATIII and accelerating its inhibitory rate by up to 1,000-fold [3, 5]. This target group is clinically significant for the prevention and treatment of venous thromboembolism, pulmonary embolism, and arterial thrombosis in conditions like atrial fibrillation [4]. Direct oral anticoagulants (DOACs) also target Factor Xa specifically to prevent thrombus formation without the need for ATIII mediation [4]. Monitoring of these targets is often performed using the anti-Xa assay or activated partial thromboplastin time (aPTT) to ensure therapeutic efficacy and safety [3].

Other names

Factor XaStuart-Prower factorThrombinFactor IIaFactor IXaFactor XIaFactor XIIaSerine proteases of the coagulation cascade

Drugs targeting this group primarily act by potentiating the activity of antithrombin III (ATIII), a natural plasma inhibitor. Heparin and its derivatives bind to ATIII, inducing a conformational change that significantly accelerates its ability to neutralize Factor Xa, thrombin, and other serine proteases in the coagulation cascade. Direct Factor Xa inhibitors bind directly to the active site of Factor Xa without requiring ATIII as a cofactor.