What is the onset timeframe for INR reduction after vitamin K administration?

What is the onset timeframe for INR reduction after vitamin K administration?

• A. ~24 hours
• B. Immediate
• C. 2-4 hours
• D. 48-72 hours

Answer: (A)

Vitamin K works by restoring the liver’s production of the vitamin K–dependent clotting factors II, VII, IX, and X. That synthesis takes time, so the INR doesn’t drop instantly after giving vitamin K. Even with faster IV administration, you typically start to see a meaningful reduction around 24 hours as new factors appear in circulation and restore coagulation balance. Shorter times like 2–4 hours are unlikely, and waiting 48–72 hours would be after the initial correction, not its onset. So, about 24 hours is the expected onset for INR reduction after vitamin K administration.

Vitamin K works by restoring the liver’s production of the vitamin K–dependent clotting factors II, VII, IX, and X. That synthesis takes time, so the INR doesn’t drop instantly after giving vitamin K. Even with faster IV administration, you typically start to see a meaningful reduction around 24 hours as new factors appear in circulation and restore coagulation balance. Shorter times like 2–4 hours are unlikely, and waiting 48–72 hours would be after the initial correction, not its onset. So, about 24 hours is the expected onset for INR reduction after vitamin K administration.