Vitamin K1 supplementation to improve the stability of anticoagulation therapy with vitamin K antagonists: a dose-finding study

Background

Poor anticoagulant stability in patients using vitamin K antagonists is a risk factor for both bleeding and thrombosis. In previous studies supplementation with low dose vitamin K₁ was shown to improve the stability of anticoagulant control. We set up a study to confirm earlier reports and to determine the optimal daily dose of vitamin K₁ in preparation of a large study with clinical endpoints.

Design and Methods

Four hundred patients from two anticoagulation clinics starting with vitamin K antagonists, independently of a possible history of instable anticoagulation, were randomized to receive either placebo or 100, 150 or 200 μg of vitamin K₁ together with their treatment with vitamin K antagonists. The treatment was administered for 6 to 12 months. Anticoagulation stability, expressed as the percentage of time that the International Normalized Ratio was within the therapeutic range, was compared between the groups.

Results

After adjustment for age, sex, vitamin K antagonist used, anticoagulation clinic and interacting drugs as confounding factors the difference in percentage of time with the International Normalized Ratio within the therapeutic range between the placebo group and the vitamin K₁ groups was 2.1% (95% CI: ?3.2% – 7.4%) for the group taking 100 μg, 2.7% (95% CI: ?2.3% –7.6%) for the group taking 150 μg and 0.9% (95% CI: ?4.5% – 6.3%) for the group taking 200 μg vitamin K₁ group, in favor of the vitamin K₁ groups. The patients from both the 100 μg group and the 150 μg group had a 2-fold higher chance of reaching at least 85% of time with the International Normalized Ratio within the therapeutic range. There were no differences in thromboembolic or hemorrhagic complications between the groups.

Conclusions

In patients starting vitamin K antagonists, supplementation with low dose vitamin K₁ resulted in an improvement of time that anticoagulation was within the therapeutic range. Differences between doses were, however, small and the improvement is unlikely to be of clinical relevance. For future studies we recommend selecting only patients with instable anticoagulant control. (This study was registered at www.isrctn.org as ISRCTN37109430)