What is the most appropriate reason for advising a patient to take warfarin at the same time each day around 6pm?

• A. To prevent interactions with afternoon meals
• B. To ensure a consistent effect on INR if taken the following morning
• C. To maximise absorption of warfarin
• D. To avoid morning drowsiness from other meds

Answer: (B)

Consistent timing of warfarin dosing helps keep the anticoagulant effect predictable. Warfarin works in a way that the INR (which reflects clotting tendency) changes gradually as vitamin K–dependent clotting factors are produced and degraded, and those factors have relatively long half-lives. Because the morning INR you measure will largely reflect the dose taken the previous evening, taking warfarin at the same time each day (around 6pm) minimizes day-to-day fluctuations in drug exposure. This makes INR results more reliable and dosing easier to adjust. It isn’t mainly about maximizing absorption or avoiding drowsiness, and meals can influence vitamin K intake more than the timing of the dose itself.