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Warfarin

An oral anticoagulant that inhibits vitamin K-dependent clotting factors

Definition

Warfarin (Coumadin) is an oral anticoagulant that inhibits the production of vitamin K-dependent clotting factors (II, VII, IX, X) and proteins C and S. It is used for atrial fibrillation, DVT/PE treatment and prevention, and mechanical heart valves.

Monitoring

  • Test: PT/INR
  • Therapeutic INR: 2.0 to 3.0 for most indications (afib, DVT, PE)
  • Therapeutic INR: 2.5 to 3.5 for mechanical mitral valve
  • INR greater than 5: High bleeding risk, may require vitamin K

Antidote

Vitamin K (phytonadione). For severe bleeding: also fresh frozen plasma (FFP) or prothrombin complex concentrate (PCC/Kcentra).

Drug Interactions (Many)

  • Increase INR (bleeding risk): Antibiotics (cipro, bactrim), amiodarone, fluconazole, NSAIDs, acetaminophen (chronic).
  • Decrease INR (clotting risk): Vitamin K, rifampin, carbamazepine, St. John's wort.

Dietary Considerations

Maintain CONSISTENT vitamin K intake. Do NOT eliminate green leafy vegetables; consume same amount daily. Avoid cranberry juice (increases effect).

Nursing Considerations

  • Monitor INR regularly.
  • Assess for bleeding: nosebleeds, gums, stool, urine, bruising.
  • Teach bleeding precautions: soft toothbrush, electric razor, avoid aspirin/NSAIDs.
  • Use medic alert identification.
  • Teratogenic: contraindicated in pregnancy (use heparin or LMWH).

NCLEX Relevance

Vitamin K antidote, consistent diet, and bleeding precautions are highly tested.