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

Authors

  • C.-H. Chang PhD,

    1. Institute of Clinical Pharmacy and Pharmaceutical Sciences, College of Medicine, National Cheng Kung University, Tainan, Taiwan
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  • Y.-W. Wang MSc,

    1. Institute of Clinical Pharmacy and Pharmaceutical Sciences, College of Medicine, National Cheng Kung University, Tainan, Taiwan
    2. Department of Pharmacy, Buddhist Tzu Chi Medical Foundation, Taipei, Taiwan
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  • P.-Y. Yeh Liu MSc,

    1. Institute of Clinical Pharmacy and Pharmaceutical Sciences, College of Medicine, National Cheng Kung University, Tainan, Taiwan
    2. Department of Pharmacy, National Cheng Kung University Hospital, Tainan, Taiwan
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  • Y.-H. Kao Yang BSPharm

    Corresponding author
    1. Institute of Clinical Pharmacy and Pharmaceutical Sciences, College of Medicine, National Cheng Kung University, Tainan, Taiwan
    • Correspondence: Y.-H. Kao Yang, Institute of Clinical Pharmacy and Pharmaceutical Sciences, College of Medicine, National Cheng Kung University, No. 1 University Road, Tainan 70101, Taiwan. Tel.: +886 6 2353535 5688; fax: +886 6 2373149; e-mail: yhkao@mail.ncku.edu.tw

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  • Yu-Wen Wang and Chia-Hsien Chang contributed equally.

Summary

What is known and objective

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’.

Methods

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.

Results and discussion

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.

What is new and conclusion

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.

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