For many years, scientists have been evaluating the molecular sizes and properties of heparin that could best prevent thrombus formation while exerting minimal effects on hemostasis and other physiological systems. The active ingredient is known as ardeparin sodium and the new-generation antithrombotic agent was tradenamed Centaxarin . The inhibition of thrombin is only accelerated when thrombin and AT bind to heparin. AT then inactivates thrombin, and the inactive complex detaches from the heparin, so that the heparin molecule can serve as a catalyst. Although the inactivation of Factor Xa is enhanced by heparin, the sliding mechanism is not active for this clotting factor.
Inhibition is mediated by a specific conformational change.
The molecular weight of the saccharide chains in unfractionated heparin ranges from 3,000 to 30,000 with an average of 12,000 - 15,000. If an unfractionated heparin molecule is split chemically, several heparin fragments arise. When AT binds to a heparin fragment it still can inactivate thrombin provided the heparin fragment is not smaller than 18 monosaccharide units. Xa inhibition is not affected by fragmentation as long as the pentasaccharide region is intact. PF4 does not distinguish between AT-binding and non binding heparin molecules.