LOW-MOLECULAR-WEIGHT HEPARINS FOR THE TREATMENT OF DEEP-VEIN THROMBOSIS

The pharmacologic characteristics of low-molecular-weight (LMW) hepari ns and unfractionated heparin are reviewed, and clinical trials compar ing LMW heparins with unfractionated heparin for the initial treatment of deep-vein thrombosis (DVT) are described. LMW heparins are derived from native heparin and range in mass from 3000 to 8000 daltons. All LMW heparins contain the antithrombin III-specific pentasaccharide uni t found on unfractionated heparin. LMW heparins are stronger inhibitor s of factor Xa than unfractionated heparin, but their mechanism of act ion, like that of unfractionated heparin, is predominantly the inhibit ion of thrombin. The efficacy of LMW heparins in the prophylaxis of DV T is not correlated with activated partial thromboplastin time (APTT); monitoring of APTT or anti-factor Xa may not be necessary. Compared w ith unfractionated heparin, LMW heparins have a lower affinity for hep arin cofactor II, platelet factor 4, von Willebrand factor, and vascul ar epithelium. Subcutaneously administered LMW heparins are more bioav ailable than s.c. unfractionated heparin. In clinical trials in patien ts with DVT, LMW heparins (dalteparin, enoxaparin, nadroparin, and tin zaparin) have resulted in venography scores similar to those obtained with unfractionated heparin. Frequencies of recurrent thromboembolism and bleeding complications were also similar. Dalteparin and logiparin were effective when administered in single daily subcutaneous doses; this could lead to lower treatment costs. Additional studies are neede d to compare LMW heparins and unfractionated heparin with respect to e fficacy, bleeding complications, mortality, and cost. LMW heparins may be valuable alternatives to unfractionated heparin for the treatment of DVT.