A practical approach to minimize the interaction of dietary vitamin K with warfarin

The many interactions between warfarin and other drugs and foods generate great challenges for clinicians and patients in maintaining stable anitcoagulation. Interactions due to variable vitamin K content of different dietary items influence the therapy of nearly all patients on warfarin. Unfortunately, there is no widely acceptable, patient-friendly strategy for managing such interactions. In this contribution, we propose a practical approach to managing this troublesome interaction, consisting of 'maintaining constant weekly dietary vitamin K intake scores'.

Twenty-three vitamin K-rich vegetables commonly seen in Taiwanese meals were identified and classified into seven score grades according to their relative vitamin K content per serving. The scores were based on published vitamin K content of different foods.

The vitamin K score was equivalent to 5 points for spinach and garland chrysanthemum per bowel, followed by (baby) bok choy, amaranth, arden lettuce (4 points); leaf mustard, edible rape, sweet potato leaf, bai cai and Chinese leek (3 points); and okra and Chinese celery (0·5 points). This classification can be used to guide patients in recording their weekly vitamin K scores with a view to maintaining it when on warfarin.

We suggest a novel approach to patient counselling on warfarin to maintain consistent dietary vitamin K intake and achieve a more stable anticoagulation response. A prospective randomized controlled trial to validate this pragmatic approach would be useful.