2. Warfarin (10 mg + 10 mg vitamin K orally) with collection of plasma over 96 hours. Plasma collection times are at 0, 3, 6, 12, 24, 36, 48, 72 and 96 hours after dosing. The INR will be checked at 48 hours. If the INR is >1.7, 5 mg of vitamin K will be administered by mouth daily until the INR is 1.2.