It is a vitamin K analog. Heparin binds to antithrombin III, causing it to bind more rapidly than normal with various clotting factors, thus inactivating them. Plasminogen is cleaved to plasmin by t-PA, and then hydrolyzes the clot. Recombinant t-PA is administered therapeutically to dissolve clots, such as during a heart attack. Because of antibody formation, streptokinase can only be used once in an individual.
Classic hemophilia is the most frequently encountered bleeding disorder.
Factor VIIIa is required to assist factor IXa in activating factor X to Xa, which then converts prothrombin to thrombin. Thrombin then converts fibrinogen to fibrin. Factor VIII resides on the X chromosome, and hence is an X-linked recessive disorder. About 1 in 10,000 males is born with the deficiency. Recombinant factor VIII is now available commercially.