Patients with atrial fibrillation taking Coumadin face numerous challenges. The first is simply keeping the prothrombin time (PT) or International Normalized Ratio (INR) in the therapeutic range, usually between 2 and 3. Initially, it can take weeks or even months to determine the proper dosing regimen. Then, the best-laid plans can be thrown off by seemingly innocuous dietary changes. And sometimes a very high or "supratherapeutic" INR can elevate risk of hemorrhage. When most surgeries or other invasive procedures are performed, the effects of warfarin must be allowed to wear off, or the possibility of bleeding complications skyrockets.