Warfarin should be avoided or monitored closely when co-administered with which of the following?

• A. Monitor INR closely when used together
• B. Avoid when possible; monitor INR closely
• C. No monitoring needed
• D. Switch to another anticoagulant

Answer: (B)

Warfarin has a very narrow therapeutic window and is influenced by many drug interactions that can raise or lower INR, risking bleeding or thrombosis. The Beers Criteria recommends avoiding combinations that interact strongly whenever possible. When a necessary co-medication must be used, INR should be monitored closely and the warfarin dose adjusted to keep the INR in the target range. This approach minimizes harm while still providing effective anticoagulation. The other options fall short because simply monitoring INR without trying to avoid the interaction increases risk, no monitoring is unsafe, and switching to another anticoagulant isn’t always feasible or the default course.