Medicine & USMLE


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


Heparin is an anticoagulant or blood thinner, meaning its purpose is to prevent blood clots. This is useful in preventing blood clots from forming to cause DVTs, pulmonary embolisms, heart attacks, or strokes. However, heparin is a high alert medication because of its high risk of bleeding. Heparin requires regular lab draws to monitor PTT levels, which should be between 1.5 to 2 times the patient’s baseline. If the PTT level is more than double the baseline, do not give the heparin and alert the provider. Heparin is also known to cause heparin-induced thrombocytopenia, or low platelet levels, so keep an eye on that lab value as well. Finally, the antidote of heparin is protamine, which is given via IV in cases where the effects of heparin need to be reversed.

Key Points

  • Mechanism
    • Anticoagulant
      • Inhibits clot formation by binding with antithrombin III to inactivate thrombin and inhibit the conversion of fibrinogen to fibrin
      • Prolongs clotting time
    • Measure PTT to monitor effectiveness of heparin therapy
      • Therapeutic PTT level for patients on heparin is 1.5-2x the baseline levels (usually 46-70 seconds)
      • Dosing is usually based on the patient’s weight
    • Clinical Use
      • Prevent clot formation
        • Note that heparin does not break up existing clots, instead it prevents clots from getting bigger and new clots from forming
        • Prevent clots that could lead to thrombotic events like heart attack, stroke, pulmonary embolism, or DVT
        • Prevent clotting during open heart surgery
        • Used to flush central lines
        • IV heparin may be ordered and administered concurrently in the first few days a patient takes warfarin, since warfarin takes several days to have a therapeutic effect (usually around 5 days). This is referred to as a “heparin bridge”.
      • Disseminated intravascular coagulation (DIC)
    • Side Effects and Adverse Reactions
      • Bleeding
        • Heparin is a high alert medication meaning dosage and administration mistakes can cause significant harm to the patient.
          • IV heparin must always be administered through a programmable pump, never by gravity alone
          • IV heparin requires a second nurse witness for initiation, rate change, and when each new bag of heparin is hung. Check hospital protocol for details.
      • Heparin-Induced Thrombocytopenia (HIT)
        • Acute drop in platelet count caused by heparin administration, and a resulting autoimmune response that destroys platelets
        • Stop heparin immediately and consult provider (usually treated with argatroban)
    • Antidote
      • Protamine (Sulfate)
        • Given via IV to reverse the effects of heparin