Medicine & USMLE

Low Molecular Weight Heparins (Enoxaparin, Fondaparinux, Dalteparin)

Hematology Drugs
  1. Dabigatran / Argatroban
  2. Factor Xa Inhibitors (Rivaroxaban, Apixaban)
  3. Heparin
  4. Low Molecular Weight Heparins (Enoxaparin, Fondaparinux, Dalteparin)
  5. Warfarin
  6. Aspirin
  7. GPIIb/IIIa Inhibitors (Abciximab, Tirofiban, Eptifibatide)
  8. Clopidogrel
  9. Alteplase / tPA
  10. Iron
  11. Filgrastim
  12. Epoetin Alfa


Low molecular weight heparins are a heparin derivative that include the drugs enoxaparin, fondaparinux, and dalteparin. They are used to prevent blood clots, especially in post-surgery patients who are at an increased risk of DVTs due to limited mobility. Low molecular weight heparins are considered safer than normal or unfractionated heparin, although potential side effects include a lowered platelet count or thrombocytopenia as well as bleeding.

Key Points

  • Drug Names
    • Enoxaparin (Lovenox)
    • Dalteparin (Fragmin)
    • Fondaparinux (Atrixta)
    • Mechanism
      • A heparin derivative that has a similar anticoagulation effect but a much lower risk of bleeding
        • LMWHs inactivate Factor Xa, but unlike heparin, they are less likely to inactivate thrombin (Factor II)
      • PTT monitoring is not required; steady therapeutic levels are reached at recommended doses
    • Clinical Use
      • Prevent clot formation
        • Prevent clots post-surgery to avoid complications like DVT and PE
        • Administered subcutaneously 1-2x daily, comes in a pre-filled syringe
          • Mild redness or bruising at the injection site is normal
    • Administration
      • Administered subcutaneously in the abdomen, at least 2 inches away from umbilicus
      • Comes in a prefilled syringe, air bubble should not be expelled before administration
      • Pinch skin and insert needle at a 90 degree angle
      • Do not rub the injection site following administration
    • Side Effects and Adverse Reactions
      • Bleeding
        • Much lower risk than unfractionated heparin
        • Monitor CBC levels to look out for occult bleeding
      • Thrombocytopenia
        • Low platelet count can result from heparin-induced thrombocytopenia, which is a autoimmune destruction of platelets caused by LMWH administration
        • Less common than with unfractionated heparin
        • Monitor CBC levels
    • Antidote
      • Protamine Sulfate