Heparin, a glycosaminoglycan, is produced by mast cells and is present on the endothelial surface of blood vessels. After binding to antithrombin, for which it contains a special pentasaccharide sequence, the inhibitory action of antithrombin to activated clotting factors II and X is strongly enhanced. In this way the formation of fibrin from fibrinogen is inhibited. Traditionally heparin is administered in an un-fractionated form (UH) derived from pork or beef sources. Today, more and more low-molecular-weight fractions of heparin (LMWH) are used (e.g. nadroparin).

In comparison to UH, LMWH inhibits factor IIa relatively less and factor Xa relatively more. The clinical relevance hereof is questionable. The advantage of LMWH to UH is a better biological availability and a more predictable clinical response. This makes subcutaneous administration possible, without the necessity of laboratory control with the APTT, as is the case with UH.

LMWH Heparin has a very direct onset of action. It is applied as prophylaxis and therapy against arterial and venous thrombosis. Heparin must be administered parenterally, because it is degraded in the intestinum. The major side effect of heparin is bleeding. Discontinuation of intravenously administered heparin will stop the anticoagulant effect after 2-4 hours. After subcutaneous administration the effect can last much longer. If necessary, protamine sulphate can be used to reverse heparin action, which is less active however against LMWH. Another side effect of heparin is osteoporosis and thrombocytopenia (a rare, but potentially severe life threatening complication with paradoxal thrombosis).


Heparin is a co-factor of 


The primary action of heparin is 




The monitoring of the extent of coagulation by unfractionated heparin is typically done by….