enoxaparin & fondparinux

     A critical pentasaccharide sequence inheparin molecules is required for their binding to ATIII and for promoting the change in conformation of ATIII. In unfractionated heparin, which has a molecular size distribution of 5,000 to 30,000 d, with the majority of chains containing ≥ 18 saccharide units and LMWHs (CLEXANE), produced by chemical or enzymatic depolymerization of unfractionated heparin to yield molecular species that range from 1,000 to 10,000 d,only approximately 30% of the molecules present in heparin preparations contain the ATIII-binding sequence. The remainder is composed of polyanionic chains that may bind nonspecifically, through electrostatic interactions, to a large number of other plasma proteins. This phenomenon possibly accounts for some of the  undesirable side effects of LMWH like HIT.  well-defined pentasaccharides constitutes more potent, more selective, and consequently safer drugs.  fondaparinux (ARIXTRA) is a synthetic pentasaccharide that selectively inhibits factor Xa.

          Enoxaparin( clexane) is a low molecular weight heparin marketed as Lovenox or Clexane.it binds to and accelerates the activity of antithrombin III. By activating antithrombin III, enoxaparin preferentially potentiates the inhibition of coagulation factors Xa and IIa. The anticoagulant effect of enoxaparin can be directly correlated to its ability to inhibit factor Xa. Factor Xa catalyzes the conversion of prothrombin to thrombin, so enoxaparin’s inhibition of this process results in decreased thrombin and ultimately the prevention of fibrin clot formation.Enoxaparin does not affect the international normalized ratio (INR), prothrombin time (PT) or activated partial thromboplastin time (aPTT). anti factorXa is used to monitor its acitivity.