Warfarin
Brand names: Coumadin, Jantoven
Class: 🩸 Anticoagulants & Antiplatelets
The NP-board angle on warfarin is the indication you cannot replace with a DOAC — mechanical heart valves. It inhibits vitamin K epoxide reductase, depleting factors II, VII, IX, X and proteins C and S. Indications also include atrial fibrillation, VTE treatment and prevention, and antiphospholipid syndrome (where DOACs failed in trials). INR goal is 2–3 for AFib and VTE, 2.5–3.5 for mechanical mitral valve. Initial overlap with heparin or LMWH is required because protein C falls fastest, producing a transient hypercoagulable state (warfarin-induced skin necrosis). Reverse with vitamin K, FFP, or 4-factor PCC depending on urgency. Counsel on consistent vitamin K intake, drug interactions (antibiotics, amiodarone, NSAIDs), and bleeding precautions.
✅ Indications
A-fib, mechanical heart valves (only approved option), VTE treatment/prevention, antiphospholipid syndrome.
⚙️ Mechanism of Action
Vitamin K epoxide reductase inhibitor — ↓ factors II, VII, IX, X + proteins C, S.
📏 Dosing
Start 5 mg daily; adjust per INR. Target INR 2–3 (most) or 2.5–3.5 (mechanical mitral valve).
🚫 Contraindications
Active bleeding, pregnancy (teratogenic — warfarin embryopathy), severe HTN (uncontrolled).
⚠️ Adverse Effects
Bleeding, skin necrosis (early, protein C deficiency), warfarin embryopathy, purple toe syndrome.
🔬 Monitoring
INR weekly initially, then stable pts q4 weeks minimum.
💎 Board Pearls
- 🥬 Keep vitamin K intake CONSISTENT (not avoid). Sudden ↑ greens → ↓ INR; sudden ↓ → ↑ INR.
- ⚡ Reversal: vitamin K (mild), FFP or 4-factor PCC (emergent major bleed).
- 🫀 ONLY oral anticoagulant approved for mechanical heart valves (no DOACs).
- 💊 Countless drug interactions — always check before adding a med.
Practice Questions
You are reviewing the chart of a 68-year-old woman with a mechanical mitral valve prosthesis implanted two years ago for rheumatic mitral stenosis. She asks whether she can switch from her current warfarin regimen to apixaban for convenience. Which is the most appropriate response?
Related Drugs in This Class
- Apixaban — Eliquis
- Rivaroxaban — Xarelto
- Aspirin — Bayer, Ecotrin
- Clopidogrel — Plavix
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