Coagulation factors IXa, XIa, XIIa and plasmin (FIXa, FXIa, FXIIa, and Plasmin)

Coagulation factors IXa, XIa, XIIa, and plasmin are a group of serine proteases that collectively regulate the balance between blood clot formation and dissolution (DrugBank). Factors IXa, XIa, and XIIa are integral to the intrinsic pathway of the coagulation cascade; their sequential activation leads to the generation of thrombin and the subsequent formation of a fibrin clot (UniProt). Plasmin, the active form of plasminogen, is the primary enzyme of the fibrinolytic system, responsible for degrading fibrin polymers into soluble fragments to maintain vascular patency (StatPearls). This ensemble of enzymes is the primary therapeutic target for broad-spectrum serine protease inhibitors such as aprotinin, which is used to reduce perioperative blood loss and the need for blood transfusions in cardiac surgery (PubMed). By inhibiting both the pro-coagulant intrinsic pathway and the pro-fibrinolytic activity of plasmin, these agents help maintain clot stability and modulate the systemic inflammatory response (NIH). However, targeting these factors carries significant risks, including severe anaphylactic reactions and potential renal impairment (FDA). Monitoring of therapy is typically performed using the activated partial thromboplastin time (aPTT) and markers of fibrinolysis such as D-dimer (StatPearls).

Other names

Christmas factor (IXa)Plasma thromboplastin antecedent (XIa)Hageman factor (XIIa)Fibrinolysin (Plasmin)Intrinsic pathway and fibrinolytic serine proteases

Serine protease inhibition