Vitamin K for Improved Warfarin Anticoagulation Control
- Mahtani KR, Nunan D, Heneghan C.
- Cochrane Corner: Vitamin K for Improved Anticoagulation Control in Patients Receiving Warfarin. Heart 2015;Jul 1:[Epub ahead of print].
The following are five key points to remember from this Cochrane systematic review assessing the effects of concomitant low-dose oral vitamin K supplements to patients being initiated or maintained on warfarin therapy:
- Warfarin therapy, as measured by the international normalized ratio (INR), can be difficult to maintain in the target range. The time in target range (TTR) is a measure of the percentage of time that a patient’s INR is within his or her target range (e.g., 2.0-3.0), and correlates well with clinical outcomes such as bleeding and thromboembolic risk. Inconsistent dietary vitamin K intake is a leading cause of poor TTR for many warfarin-treated patients.
- Of the 4,031 references identified by their search strategy, only two randomized clinical trials involving 100 patients were assessed. Only one of these trials has been published in full manuscript format.
- The first study showed a significant improvement in the mean TTR for 70 participants who were randomized to receive 150 μg of vitamin K daily for 6 months or placebo. Mean TTR improved by 28 ± 20% for the vitamin K group versus 15 ± 20% for the placebo group. There were also fewer numbers of warfarin dose changes in the vitamin K group.
- The second study randomized 30 patients to either 175 μg of vitamin K daily or placebo for 6 months. This study found no difference in the number of dose changes during the follow-up period. However, this study was only published in abstract form.
- The authors note that the paucity of published data, few patients randomized, and the variability in vitamin K dosing should lead clinicians to interpret the results with caution. However, given the important clinical implications of an improved TTR, use of dietary vitamin K supplement may be considered for patients before switching from warfarin to a direct oral anticoagulant.
< Back to Listings