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:

  1. 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.
  2. 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.
  3. 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.
  4. 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.
  5. 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.

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