In managing warfarin for an older adult with a prosthetic heart valve, under what condition should warfarin be discontinued immediately?

Warfarin is an anticoagulant commonly used in patients with prosthetic heart valves to prevent thromboembolic events. It works by inhibiting vitamin K-dependent clotting factors, which requires careful monitoring of the International Normalized Ratio (INR).

When the INR increases to significantly high levels, particularly to 8 or above, the risk of serious bleeding increases substantially. This is a critical threshold because an INR at this level indicates that the blood is too thin, making it unsafe for the patient. Therefore, immediate discontinuation of warfarin is warranted to prevent potential severe complications such as hemorrhage.

In contrast, while an INR of 4 is elevated and would necessitate monitoring and possibly some management, it does not warrant an immediate discontinuation of warfarin unless there are additional risk factors. A headache, in general, is not an indication for stopping warfarin unless it is associated with other concerning symptoms indicating a potential bleed. Similarly, starting a new medication may require careful consideration of interactions and may lead to adjustments in warfarin dosing rather than an outright cessation.