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A simple formula for predicting the warfarin dose in atrial fibrillation: development, external validation, and model
Anunya Ujjin1,2, Natnicha Pongbangli3, Wanwarang Wongcharoen4
1Division of Medicine, Neurological Institute of Thailand, Bangkok, Thailand.
Thrombosis Journal
|October 10, 2025
Summary
A new, simple warfarin dosing formula using age, weight, and creatinine levels helps prevent overdosing in high-risk patients. This practical tool aids clinicians in safely managing warfarin therapy, especially for those with atrial fibrillation.
Area of Science:
- Pharmacology
- Clinical Medicine
- Drug Dosing
Background:
- Warfarin dosing is highly individualized.
- Existing prediction formulas are often complex and impractical for routine clinical use.
Purpose of the Study:
- To identify predictors of warfarin maintenance dosage.
- To develop a simplified warfarin dosing formula.
- To identify high-risk atrial fibrillation patients prone to bleeding without pharmacogenetic data.
Main Methods:
- Retrospective cohort study (2011-2021).
- Development of a first-order equation for warfarin dose prediction.
- Validation in separate training and testing cohorts with target INR of 2.0-3.0.
Main Results:
- A formula was developed: 3 + (0.02 × body weight) - (0.02 × age) - (0.4 × serum creatinine).
- The formula identified increased overdose risk in patients with low body weight, advanced age, or reduced eGFR.
- Validation cohort results confirmed the formula's performance.
Conclusions:
- A straightforward warfarin dosing formula incorporating age, body weight, and serum creatinine effectively reduces overdose risk.
- This formula is particularly beneficial for managing high-risk patient populations, including those with atrial fibrillation.
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