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Last reviewed dd mmm yyyy. Last edited dd mmm yyyy

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Low molecular weight heparin (LMWH) is now accepted as a safe and effective antithrombotic agent for use in a range of venous and arterial clotting disorders.

In contrast to unfractionated heparin, which has a molecular weight in the range 3000-30000, LMWH has a mean molecular weight of 5000. LMWH primarily results in inhibition of factor Xa with relative sparing of thrombin.

  • unfractionated heparin acts on both thrombin and factor Xa about equally, whereas low molecular weight heparin is more active against factor Xa
  • LMWH allows patients with uncomplicated deep vein thrombosis to be treated in the community, thus saving an average of 4 or 5 days of admission per patient
  • LMWH has been shown to be more effective than vitamin K antagonists (almost all being warfarin) in preventing deep vein thrombosis after major orthopaedic surgery, with no significant difference in rates of bleeding

The advantages of LMWH compared to unfractionated heparin include:

  • equal or improved antithrombotic activity
  • reduced incidence of bleeding
  • improved pharmacokinetics
  • no need for coagulation monitoring
  • no need for dose adjustments
  • lower incidence of thrombocytopenia
  • can be administered by the patient at home


  1. BMJ. 2006 Jan 28;332(7535):215-9.

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