Clinical Resources
Warfarin Dose Adjustment Guide
INR-Based Warfarin Dose Titration and Management
mg/week
Clinical Pearls
- Pharmacology: Warfarin inhibits vitamin K epoxide reductase (VKORC1), reducing synthesis of factors II, VII, IX, and X. Full anticoagulant effect takes 5–7 days due to the long half-life of factor II (~60 h).
- Factors affecting INR: Dietary vitamin K intake (green leafy vegetables), drug interactions (amiodarone, antibiotics, azole antifungals, NSAIDs), liver disease, acute illness, alcohol use, thyroid status, and genetic polymorphisms (CYP2C9, VKORC1).
- Time in Therapeutic Range (TTR): Target TTR ≥65–70% for optimal efficacy and safety. TTR <60% is associated with increased stroke and bleeding risk. Consider switching to a DOAC if TTR remains poor despite adherence.
- SAMe-TT₂R₂ Score: Predicts likelihood of achieving good TTR on warfarin. Score >2 suggests the patient may do better on a DOAC. Components: Sex (female +1), Age <60 (+1), Medical history (+1), Treatment interactions (+1), Tobacco use (+2), Race non-Caucasian (+2).
- Dose adjustments should generally be made in 5–20% increments. Large dose changes risk overcorrection. Always consider adherence and recent dietary/medication changes before adjusting.
References
- Holbrook A, Schulman S, Witt DM, et al. Evidence-Based Management of Anticoagulant Therapy: Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: ACCP Guidelines. Chest. 2012;141(2 Suppl):e576S–e600S.
- January CT, Wann LS, Alpert JS, et al. 2014 AHA/ACC/HRS Guideline for the Management of Patients With Atrial Fibrillation. Circulation. 2014;130(23):e199–e267.
- Ansell J, Hirsh J, Hylek E, Jacobson A, Crowther M, Palareti G. Pharmacology and Management of the Vitamin K Antagonists: ACCP Evidence-Based Clinical Practice Guidelines (8th Edition). Blood. 2012;120(Suppl):SCI-37.