Therapy related coagulopathies
Heparin - low molecular weight

Topic Completed: 1 June 2012

Revised: 4 January 2019, last major update June 2012

Copyright: (c) 2002-2016,, Inc.

PubMed Search: Heparin [title] AND low molecular weight[title]

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Cite this page: Parsons J. Heparin - low molecular weight . website. Accessed June 4th, 2020.
Definition / general
  • Can be used instead of standard heparin for many patients, with similar efficacy and safety
  • Produced by breaking heparin into shorter polysaccharide chains
  • Molecular weight is approximately 5,000 daltons
Diagrams / tables

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Function of LMWH

Clinical features
  • Less likely to bind to acute phase reactant proteins, platelets, platelet factor 4, macrophages and other sites, due to its shorter length
  • Has more predictable anticoagulant effect than standard heparin, less need for laboratory monitoring, lower incident of heparin induced thrombocytopenia, greater bioavailability
  • Longer half life than standard heparin (4 vs. 1.5 hours), which is prolonged in renal failure
  • Inhibits factor Xa by 2 to 4x more than factor IIa, so does not substantially prolong PT and PTT
  • Unlike regular heparin, does not as readily inhibit thrombin or factor IXa (this also contributes to a lower number of bleeding side effects)
  • Typically do not monitor except for periodic platelet counts
  • Indications for monitoring include pregnancy, renal failure, obesity, prolonged use, infants and children, patients at high risk for bleeding / thrombosis
  • Monitor by measuring anti-factor Xa activity, drawn 4 hours after injection
  • Typical therapeutic range is 0.6 to 1.0 U/ml for twice a day dosing, higher for once a day dosing, 1.0 to 2.0 U/ml for prophylactic dosing
  • Effects are reversed with protamine sulfate
Additional references
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