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1. Warfarin is adjusted to increase INR to 2.0-3.0 (target 2.5) in AF.

2. Initial dose is usually 5.0 mg/day, and this is often decreased to 2.5 mg/day.

3. Warfarin is a vitamin K antagonist that prevents activation of Factors II, VII, IX, and X.

4. After starting warfarin, Factor VII is the most rapidly decreasing procoagulant, but protein C (an anticoagulant) also decreases rapidly-so you may rarely see an initial net procoagulant effect.

5. This may occur until the slower-clearing Factor II decreases enough to result in a net anticoagulant state.

6. This usually takes - 4 days. This potential problem is addressed by commencing heparin-bridging therapy (within 8 hours), and keeping patients on heparin for at least 4 days.

7. Monitor the INR more frequently if the diet is changed or the patient is put on an antibiotic that might kill the gut flora required for proper vitamin K absorption which can result in raised INR.


1. Wilkinson, I. (2017). Oxford handbook of clinical medicine. Oxford: Oxford University Press.
2. Hannaman, R. A., Bullock, L., Hatchell, C. A., & Yoffe, M. (2016). Internal medicine review core curriculum, 2017-2018. CO Springs, CO: MedStudy.
3. Image: no reference available.

Ⓒ A. Manickam 2018

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