Low Molecular Weight Heparins

Low molecular weight heparins (LMWH) are modern anticoagulation drugs. Compared with other drugs of this group, LMWH have specific advantages and disadvantages that should be the issue of this article.


Low molecular weight heparins are produced by various chemical processes (usually depolymerization) of heparin. They block the coagulation cascade, which is a complex process that leads to formation of blood clots. The coagulation cascade consists of a series of proteins (clotting factors) that help to activate each other. Low molecular weight heparins interfere with this cascade by blocking the factor number ten (factor X).

The most widely used low molecular weight heparins include nadroparin, enoxaparin, bemiparin and dalteparin.


As already mentioned, low molecular weight heparins are used against blood clotting. In reduced dose, they are used in prevention of deep vein thrombosis and pulmonary embolism. In higher doses, they are effective in therapy of the both mentioned conditions. LMWH may be administered for a limited period of time in the therapy of superficial phlebitis and it is also applied to patients with atrial fibrillation as prevention of ischemic stroke. Nowadays, preventive doses of LMWH are usually applied to all hospitalized patients with higher risk of blood clotting and patients after surgical procedures (especially orthopedic).


Low molecular weight heparins are usually administered by subcutaneous injection. The application is easy, most often under the skin of the abdomen or thighs. Some medication may sting for a while, but it goes away quickly. During long-term administration, bruises can occur at the site of application. This is due to the local anticoagulant effect.


Low molecular weight heparins have a number of advantages. Their effect starts relatively quickly and lasts for limited time - between 12 to 24 hours, depending on the preparation. This means that LMWH are great in situation when we desire instant and short-term effect. Thanks to their attributes, LMWH may be used in patients before surgical interventions.


The effect of low molecular weight heparins can be tested evaluated from a venous blood sample as the level of serum factor anti-Xa. The blood sample should be taken in approximately 3 hours after administration of the low molecular weight heparin.


The main disadvantage is the need to regularly apply the injection. Cautious approach is needed in patients with acute or chronic renal failure. The doses of LMWH should be reduced and the effectiveness monitored by anti-Xa. When a bleeding complication occurs, we have no antidote, which could counter the effect of LMWH. In some patients, temporary decrease of platelet numbers was observed during usage of LMWH.


Jiri Stefanek, MD  Author of texts: Jiri Stefanek, MD
 Contact: jiri.stefanek@seznam.cz
 Sources: basic text sources