How long does it typically take for the effects of vitamin K1 on INR to be noted after administration?

The effects of vitamin K1 (phylloquinone) on the International Normalized Ratio (INR) are generally observed within a specific timeframe because vitamin K is crucial for synthesizing clotting factors that rely on it for activation. After administration of vitamin K1 to reverse the anticoagulant effects of vitamin K antagonists like warfarin, it typically takes approximately 24 hours to see a significant effect reflected in INR values.

This time frame is due to the half-lives of the vitamin K-dependent clotting factors affected by anticoagulant therapy. Factors II (prothrombin), VII, IX, and X all require vitamin K for their synthesis and can take some time to regenerate once vitamin K is available. Because these clotting factors need to be translated in the liver and then released into circulation, it supports the reason why the INR changes are noted after about 24 hours post-administration of vitamin K1.

While earlier changes might occur, particularly with factors that have shorter half-lives such as VII, the more complete reversal that reflects in INR typically takes a full day to materialize.