Low Molecular Weight Heparins (LMWH)

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Key Points

  • Low Molecular Weight Heparins (LMWH)
    • Drug Names
      • Enoxaparin
      • Dalteparin
      • Fondaparinux
        • not technically part of the LMWH class, its mechanism of action is the same
    • Mechanism
      • Binds to and activates antithrombin III
        • Primarily inhibits factor Xa
        • Chemical structure of the complex causes LMWH to act selectively on factor Xa, not thrombin (in contrast to unfractionated heparin)
      • Does not require routine lab monitoring
        • Less monitoring makes LMWH preferred as an outpatient medication
        • Administered subcutaneously with longer half-life (2-4 hours) than unfractionated heparin (1-2 hours)
        • Better bioavailability than unfractionated heparin; renally excreted
    • Clinical Use
      • Anticoagulation
        • Pregnancy
          • First-line drug for anticoagulation in pregnancy due to ease of use
          • Heparins do not cross the placenta (low risk of teratogenicity and fetal hemorrhage)
        • Clot prevention
          • e.g. DVT/PE prophylaxis in hospitalized patients, cancer patients, outpatients at risk of DVT/PE
        • Less commonly used for acute coronary syndrome (ACS)
          • Less commonly used here than IV unfractionated heparin due to slower onset
        • In general:
          • IV unfractionated heparin is acute, rapid-acting anticoagulant for hospital use only (needs monitoring)
          • In contrast, subcutaneous LMWH is slower-acting, easier to use in outpatient setting (no monitoring needed)
    • Adverse Effects
      • Bleeding
        • Obvious side effect seen with all anticoagulants
      • Lower risk of heparin-induced-thrombocytopenia
    • Reversal
      • More difficult to reverse than unfractionated heparin, as protamine sulfate has less effect