In medicine, low molecular weight heparin (LMWH) is a class of medication used as an anticoagulant in diseases that feature thrombosis, as well as for prophylaxis in situations that lead to a high risk of thrombosis. more...
Heparin is a naturally-occurring polysaccharide that inhibits coagulation, the process whereby thrombosis occurs. In nature, heparin consists of molecular chains of varying lengths, or molecular weights. Heparin derived from natural sources (including intestine) can be administered therapeutically to prevent thrombosis (see anticoagulation). However, the effects of natural, or unfractionated, heparin can be difficult to predict. After a standard dose of unfractionated heparin, coagulation parameters must be monitored very closely to prevent over- or under-anticoagulation.
Low molecular weight heparin, in contrast, consists of only short chains of polysaccharide, obtained by the deaminative hydrolysis of unfractionated heparin. Nitrous acid selectively cleaves the glycosidic bonds of the heparin with formation of di, tetra, hexa and higher saccharides terminated with 2,5-anhydro-D-mannose (AM) residues as reducing terminal groups. Having a lower average molecular weight means that a given dose of LMWH will be absorbed more predictably, leading to overall more predictable anticoagulation. It is also more selective for factor Xa and has less effect on thrombin.
Its differences with unfractioned heparin are:
- Average molecular weight: heparin is about 20000 Da and LMWH is about 3000 Da
- No need for monitoring of the APTT coagulation parameter
- Possibly a smaller risk of bleeding
- Smaller risk of osteoporosis in long-time use
- Smaller risk of heparin-induced thrombocytopenia, a feared side-effect of heparin.
Because it can be given subcutaneously and does not require aPTT monitoring, LMWH permits outpatient treatment of conditions such as deep vein thrombosis or pulmonary embolism that previously mandated inpatient hospitalization for unfractionated heparin administration
The use of LMWH needs to be monitored closely in patients at extremes of weight or in patients with renal dysfunction. An anti-factor Xa activity may be useful for monitoring anticoagulation. Given its renal clearance, LMWH may not be feasible in patients who have end stage renal disease.
Makes of LMWHs include:
- Bemiparin (Zibor®)
- Dalteparin (Fragmin®)
- Enoxaparin (Clexane® and Lovenox®)
- Nadroparin (Fraxiparin® and Fraxodi®)
- Tinzaparin (Innohep®)
- Several others
- Weitz JI. Low-molecular-weight heparins. N Engl J Med 1997;337:688-98. PMID 9278467.
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