Heparin, warfarin, and direct oral anticoagulants with their antidotes, lab monitoring, and bleeding precaution teaching points.
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- What is the mechanism of action of heparin?
- It binds antithrombin III and potentiates its action, inactivating thrombin and factor Xa.
- Which lab test is used to monitor unfractionated heparin therapy?
- aPTT (activated partial thromboplastin time).
- What is the typical therapeutic aPTT range for a patient on unfractionated heparin?
- About 1.5 to 2.5 times the normal control value.
- Heparin
- Protamine sulfate
- By what routes is unfractionated heparin typically administered?
- IV infusion or subcutaneous injection, never IM.
- What serious adverse reaction involves a drop in platelet count during heparin therapy?
- Heparin-induced thrombocytopenia (HIT).
- Name a commonly used low molecular weight heparin (LMWH).
- Enoxaparin.
- Does LMWH (enoxaparin) require routine aPTT monitoring like unfractionated heparin?
- No, it has a predictable dose response and is not routinely monitored.
- What is the mechanism of action of warfarin?
- It inhibits synthesis of vitamin K-dependent clotting factors II, VII, IX, and X.
- Which lab values are used to monitor warfarin therapy?
- PT (prothrombin time) and INR (international normalized ratio).
- What is the typical therapeutic INR range for a patient on warfarin for standard indications?
- 2.0 to 3.0.
- Warfarin
- Vitamin K (phytonadione)
- Besides vitamin K, what can be given for rapid reversal of severe warfarin-induced bleeding?
- Fresh frozen plasma or prothrombin complex concentrate.
- Why is heparin often used as a bridge when starting warfarin therapy?
- Warfarin takes several days to reach a therapeutic effect, so heparin provides immediate anticoagulation.
- Why should patients on warfarin keep their vitamin K intake consistent rather than avoid it entirely?
- Sudden changes in vitamin K intake alter warfarin's effectiveness and destabilize the INR.