Coagulation - Heparin - low molecular weight

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Coagulation

Therapy related coagulopathies

Heparin - low molecular weight

Reviewer: Jeremy Parsons, M.D. (see Reviewers page)
Revised: 13 June 2012, last major update June 2012
Copyright: (c) 2002-2012, PathologyOutlines.com, Inc.

General
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● 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

Clinical features
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● 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

Monitoring
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● 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

Diagrams
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Function of LMWH

Additional references
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● Clin Lab Med 2009;29:283

End of Coagulation > Therapy related coagulopathies > Heparin - low molecular weight

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