Low molecular weight heparin


  • Class of anticoagulant medications.
  • Defined as heparin salts having an average molecular weight of less than 8000 Dalton
  • LMWHs inhibit the coagulation process through binding to antithrombin which in turn inhibits activated factor X.[1]
  • LMWH therapy is monitored by the anti-factor Xa assay (measures anti-factor Xa activity).
    • Cannot be acceptably measured using the partial thromboplastin time (PTT) or activated clotting time (ACT) tests.


LMWHAverage molecular weightRatio anti-Xa/anti-IIa activity
Enoxaparin (Lovenox)45003.9

Clinical Differences from Unfractionated heparin

  • Less frequent subcutaneous dosing
  • Once or twice daily subcutaneous injection for treatment of venous thromboembolism and in unstable angina instead of intravenous infusion of high dose heparin.
  • No need for monitoring of the aPTT coagulation parameter as required for high dose heparin.[2]
  • Possibly a smaller risk of bleeding
  • Smaller risk of osteoporosis in long-term use.
  • Smaller risk of heparin-induced thrombocytopenia, a potential side effect of heparin.
  • The anticoagulant effects of heparin are typically reversible with protamine sulfate, while protamine's effect on LMWH is limited.


See Also


  1. Garcia DA, Baglin TP, Weitz JI, et al. (2012). "Parenteral anticoagulants: Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines"
  2. http://chestjournal.chestpubs.org/content/119/1_suppl/64S.full
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