Low molecular weight heparin
Several chemical processes have been applied to unfractionated heparin (UFH) to reduce the size of the sulfated polysaccharide molecules. The low molecular weight heparins (LMWH) currently available in Australia are dalteparin and enoxaparin. These LMWH contain variable proportions of polysaccharides, which cannot bind simultaneously to thrombin and antithrombin and thus selectively inhibit factor Xa activity. They have similar clinical properties, but are not biologically identical. Their doses and units vary, and care is required when prescribing. The LMWH are cleared more slowly than UFH and have a prolonged action. Danaparoid is a low molecular weight heparinoid, and is a more selective inhibitor of factor Xa than LMWH.
The incidence of haemorrhagic adverse effects is similar for UFH and LMWH. Although protamine only partially reverses the effect of LMWH, it does appear to reduce bleeding. Monitoring factor Xa levels is not generally required, but may be necessary in high-risk patients such as those with renal impairment, or if overdose is suggested by bleeding.
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