Which medication requires INR monitoring and frequent dose adjustments?

• A. Heparin.
• B. Warfarin.
• C. Enoxaparin.
• D. Acetaminophen.

Answer: (B)

INR monitoring is essential for warfarin because its effect on blood clotting sits in a very narrow range and varies a lot between individuals and over time. The INR reflects how long the blood takes to clot, and doses must be adjusted based on this value to keep anticoagulation effective but not excessive. Diet, other medications, illness, and genetics can all change warfarin’s effect, so frequent dose tweaks are necessary, especially when starting therapy or when factors change. The other options don’t rely on INR for routine monitoring: heparin is guided by aPTT (and sometimes anti-Xa), enoxaparin is typically not monitored with INR, and acetaminophen does not anticoagulate.