Which INR threshold must be reached before starting dabigatran after stopping warfarin?

• A. INR < 2
• B. INR < 3
• C. INR < 2.5
• D. INR < 1.5

Answer: (A)

When switching from warfarin to a direct oral anticoagulant like dabigatran, the key is avoiding overlap of anticoagulant effects. Warfarin’s activity is monitored by the INR, and you want that effect to have waned before starting the new drug. Starting dabigatran while warfarin is still exerting a strong effect increases the risk of bleeding from too much anticoagulation.

Therefore, the safest transition is to begin dabigatran once the INR has fallen back to a non-elevated, near-normal level, indicating that warfarin’s effect is no longer driving anticoagulation. If you start too soon, you risk excessive anticoagulation; if you wait too long, you risk a gap in protection. This approach balances safety (avoiding bleeding from overlapping effects) with timely anticoagulation coverage.