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Warfarin Dose Adjustment Calculator

Adjust weekly warfarin dose by INR — based on common evidence-based maintenance protocols.

Protocol: Adjust weekly dose by 5–20% based on INR deviation from goal. Hold dose for INR ≥5.

About Warfarin Adjustment

Warfarin requires individualized dosing because of its narrow therapeutic index and high inter-patient variability driven by genetics (CYP2C9, VKORC1), diet (vitamin K intake), drug interactions, and acute illness. The common practical rule is: adjust weekly dose by a percentage, not by single tablets, and recheck INR in 1–2 weeks.

Typical Adjustment Tables (target 2-3)

  • INR < 1.5 — increase weekly dose 10–20%; recheck in 1 week
  • INR 1.5–1.9 — increase weekly dose 5–10%; recheck in 2 weeks
  • INR 2.0–3.0 — no change; recheck in 4 weeks
  • INR 3.1–3.9 — decrease weekly dose 5–10%
  • INR 4.0–4.9 — hold 1 dose, decrease weekly 10%
  • INR ≥ 5.0 (no bleeding) — hold 1–2 doses, consider oral vitamin K 1–2.5 mg if INR ≥ 9
  • Major bleeding — hold warfarin, give vitamin K 5–10 mg IV + 4-factor PCC

Disclaimer

This calculator provides general adjustment guidance based on common clinical protocols. Patient-specific factors, bleeding status, drug interactions, and clinical judgment may override these recommendations. Always confirm with your anticoagulation service.