Heparin Leo Mechanism of Action

Heparin is a naturally occurring anticoagulant which prevents the coagulation of blood in vivo and in vitro. Following administration of full therapeutic doses of heparin the whole blood clotting time, the thrombin time and the one-stage prothrombin time are prolonged. The prolongation of clotting time is proportional to the dose administered. Whereas with therapeutic doses, the bleeding time is usually unaffected. In most cases the clotting time is not measurably affected by low doses of heparin.
Heparin acts at multiple sites in the normal coagulation system. Small amounts of heparin in combination with antithrombin III (heparin cofactor) can prevent the development of a hypercoagulable state by inactivating activated Factor X, preventing the conversion of prothrombin to thrombin (the principle of low dose prophylaxis). Once a hypercoagulable state exists, larger amounts of heparin in combination with antithrombin III can inhibit the coagulation process by inactivating thrombin and earlier clotting intermediates, thus preventing the conversion of fibrinogen to fibrin (the principle of full dose therapy). Heparin also prevents the formation of a stable fibrin clot by inhibiting the activation of the fibrin stabilizing factor.
Heparin does not have fibrinolytic activity; therefore, it will not lyse existing clots.
Menstruation and pregnancy are not contraindications to heparin therapy. Heparin does not cross the placenta or appear in breast milk.
In addition to the anticoagulant properties, heparin also has some lipaemia clearing effect, which may be utilized in the treatment and prevention of atherosclerosis and fat embolism.