Low molecular weight heparins: Are they superior to unfractionated heparins to prevent and to treat deep vein thrombosis?

In many countries, low molecular weight heparins (LMWHs) have replaced unfr actionated heparin (UH) for prevention and treatment of venous thromboembol ism. The present paper reviews the possible advantages of LMWHs over UH. In spite of their lower molecular weight distribution, LMWHs are functionally more heterogeneous than UH. Their anti-Xa/anti-IIa ratio varies significan tly, and the injection of the same dose generates different anti-Xa activit ies and activated partial thromboplastin time (APTT) prolongations. Their p harmacodynamic properties account for their more convenient use in comparis on with UH; however, there is a risk of accumulation in case of renal insuf ficiency. Even if they are less anticoagulant on the basis of the APTT prol ongation, they are not less prohemorrhagic than UH. LMWHs are probably less immunogenic and probably induce less osteoporosis. Several meta-analyses p ublished between 1992 and 1999 indicate that LMWHs are as efficient as UH i n preventing postoperative deep vein thrombosis (DVT) in general surgery an d more efficient than UH in preventing DVT in orthopedic surgery and treati ng established DVT. (C) 2000 Elsevier Science Ltd. All rights reserved.