Tranexamic acid is a synthetic derivative of lysine used as an antifibrinolytic in the treatment and prevention of major bleeding. It targets plasminogen in blood vessels where these clots occur. The clotting process consists of two pathways, intrinsic and extrinsic, which converge to create stable fibrin which traps platelets and forms a hemostatic plug. The intrinsic pathway is activated by trauma inside the vasculature system, when there is exposed endothelial collagen. Endothelial collagen only becomes exposed when there is damage. The pathway starts with plasma kallikrein activating factor XII. The activated factor XIIa activates factor XI. Factor IX is then activated by factor XIa. Thrombin activates factor VIII and a Calicum-phospholipid-XIIa-VIIIa complex forms. This complex then activates factor X, the merging point of the two pathways. The extrinsic pathway is activated when external trauma causes blood to escape the vasculature system. Activation occurs through tissue factor released by endothelial cells after external damage. The tissue factor is a cellular receptor for factor VII. In the presence of calcium, the active site transitions and a TF-VIIa complex is formed. This complex aids in activation of factors IX and X. Factor V is activated by thrombin in the presence of calcium, then the activated factor Xa, in the presence of phospholipid, calcium and factor Va can convert prothrombin to thrombin. The extrinsic pathway occurs first, producing a small amount of thrombin, which then acts as a positive feedback on several components to increase the thrombin production. Thrombin converts fibrinogen to a loose, unstable fibrin and also activates factor XIII. Factors XIIIa strengthens the fibrin-fibrin and forms a stable, mesh fibrin which is essential for clot formation. The blood clot can be broken down by the enzyme plasmin. Plasmin is formed from plasminogen by tissue plasminogen activator. Tranexamic acid competitively and reversibly inhibits the activation of plasminogen via binding at several distinct sites, including four or five low-affinity sites and one high-affinity site. Plasmin is unable to be formed form plasminogen, and therefore, dissolution of the fibrin clot is prevented. Adverse effects such as seizures, headaches, backache, abdominal pain, nausea, vomiting, diarrhea, fatigue, pulmonary embolism, deep vein thrombosis, anaphylaxis, impaired color vision, and other visual disturbances can occur from the use of Tranexamic acid.

Tranexamic Acid Pathway (New) References