The purpose of this study is to determine whether vitamin K supplementation will improve anticoagulation control in patients on hemodialysis taking warfarin for atrial fibrillation. Patients who participate will receive vitamin K1 three times a week on dialysis days for a period of four months. INR levels collected during this period will be compared to the four month period prior to receiving the vitamin K1 to determine if vitamin K improves the standard deviation of INRs and time in therapeutic range.

Patients on hemodialysis with atrial fibrillation are at increased risk of stroke. These patients often take warfarin to reduce this risk. Warfarin is a drug that is used to prevent clots in the bloodstream. The dose of warfarin varies from person to person, and its effect is measured using a blood test called the international normalized ratio (INR). In most patients with atrial fibrillation the goal is to keep the INR between 2 and 3. Patients on hemodialysis often have unstable INR levels. Vitamin K supplementation has been shown to improve INR control in patients on warfarin but has not yet been studied in hemodialysis patients.

In this study, patients on hemodialysis receiving warfarin for atrial fibrillation will receive vitamin K 400 mcg orally three times a week on dialysis days for 4 months. INR levels in the four months before and the four months while receiving vitamin K will be reviewed.

The primary end point will look at INR stability and be measured by calculating the standard deviation of INR values before and after receiving vitamin K. The goal of this study is to determine whether vitamin K supplementation improves INR control in patients on hemodialysis taking warfarin for atrial fibrillation.

Inclusion Criteria:

• greater than 18 years of age
• Receiving in-house hemodialysis for at least 6 months
• Previously diagnosed with atrial fibrillation
• On warfarin for at least 6 months with a target INR of 2-3

Exclusion Criteria:

• are unable to provide informed consent
• have a mechanical heart valve
• are receiving supplements containing vitamin K
• have a known hypersensitivity to vitamin K

When the study is complete aggregate data of the study will be published and shared. Individual participant data that may identify participants will not be shared. If a participant requests information on his/her individual participant data, it will be provided to the requesting participant.