Pathophysiology: Factor V is an essential component in the blood coagulation cascade. Factor V is synthesized in the liver and possibly in megakaryocytes. Factor V circulates in an inactive form. During coagulation, factor V is converted to the active cofactor, factor Va, via limited proteolysis by the serine protease a-thrombin. Factor Va and activated factor Xa form the prothrombinase complex. The prothrombinase complex is responsible for the rapid conversion of the zymogen prothrombin to the active serine protease a-thrombin. Thrombin cleaves fibrinogen to form fibrin, leading to the ultimate step in coagulation, the formation of a fibrin clot. Treatment : treatment: Heparin: This anticoagulant medication works more quickly than warfarin does. It can be administered directly into a vein (intravenously) or under the skin (subcutaneously) Warfarin (Coumadin, Jantoven):This anticoagulant comes in pill form, so it's easier to take than heparin. Warfarin may cause birth defects, so it isn't usually recommended during pregnancy, especially the first trimester. Bleeding is the most common side effect of warfarin. Introduction : Factor V Leiden thrombophilia is a genetic disorder of blood clotting. Factor V Leiden is a variant (mutated form) of human factor V that causes an increase in blood clotting (hypercoagulability).