[Current status of low molecular weight heparin]

Low molecular weight heparins, discovered in 1976, are obtained from standard heparin by chemical or enzyme depolymerisation. Lowering of the molecular weight of polysaccharide chains has enabled dissociation of anti-IIa activity, associated with the risk of hemorrhage, from anti-Xa activity which forms the basis of anti-thrombotic activity. The anti-Xa/anti-IIa ratio varies according to low molecular weight heparin preparations from 2.5 to 10, while it is invariably 1 for standard heparin. Pharmacokinetics and a bioavailability of the order of 100 percent are undeniable advantages which distance them even farther from standard heparin. Clinical trials have provided validation as prophylaxis in general surgery and orthopedic surgery without laboratory surveillance apart from platelets, with the technique of use being very easy for nursing staff. Various trials concerned with the curative treatment of deep devnous thrombosis have shown that low molecular weight heparins are equally effective as non-fractionated heparin with, apparently, less hemorrhagic complications. However the lack of homogeneity of units, despite the international standard, requires prescribers to comply with the dosages and laboratory monitoring (anti-Xa activity) indicated by different manufacturers, which forms a barrier to their use.