Multivitamins and Warfarin

Publication Date: 
Tue, 11/08/2011

Vitamin K has been used for many years to counter the affects over anticoagulation. In more routine settings a recent study has shown that over the counter use of vitamin K in multi-vitamin form has varying affects on patients taking warfarin.

A small study population showed a significant impact of a vitamin K containing multi-vitamin in a select sub-group. A 25 micrograms vitamin K multiple vitamin for four weeks resulted in the following outcomes. Group 1 experienced a decline in INR values by an average of 0.51 and required a 5.3% increase in dosage adjustment. Group 2 did not experience a significant change resulting a need for warfarin adjustment.

The author's concluded, "vitamin K -containing multivitamins reduce INR in patients with low vitamin K(1) status. Our study suggests that vitamin K-depleted patients are sensitive to even small changes in vitamin K(1) intake."1

While the bleeding risk is diminished with INR values below 2.0, the rate of thromboembolism increases .The full efficacy of anticoagulation is seen only at an international normalized ratio (INR) of 2.0 and above. The proportion of patients who had a severe or fatal stroke did not differ significantly between those with an admission INR of 1.5 to 1.9 and those with an INR of less than 1.5.

More frequent testing of INR results in catching declining therapeutic INR values sooner. This strategy has the potential to prevent products as common as multi-vitamins from increasing the stroke in higher risk patients.

  1. Kurnik D, et al. Over-the-counter vitamin K1-containing multivitamin supplements disrupt warfarin anticoagulation in vitamin K1-depleted patients. Thromb Haemost, November 1, 2004; 92(5): 1018-24.