Pharmacy Times
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Green leafy vegetables, which contain vitamin K, are well-known to cause fluctuationsin the international normalized ratio (INR) if eaten on an inconsistent basis. Otherfoods, such as oils, mayonnaise, and cashews, also contain vitamin K and can causevariations if consumed in large amounts. Patients and providers may be less likely toconsider beverages as the source of the problem, however, when the INR starts tofluctuate. Vegetable juice contains spinach, parsley, watercress, and lettuce juices, allof which are high in vitamin K. Supplements such as Boost, Ensure, Glucerna, and Slim-Fast contain 20 to 30 mcg of vitamin K per serving and can have a profound effect onthe INR if patients begin using these beverages and fail to mention it to their anticoagulationprovider.

Other drinks that have received attention in relation to warfarin therapy includegreen tea and cranberry juice. Green tea leaves are high in vitamin K, but the brewedtea has only a small amount. Cranberry juice was reported to cause an increase in theINR, possibly through an interaction with the CYP450 system, but a review of casereports did not substantiate this link.

Dr. Garrett is a clinical pharmacist practitioner at Cornerstone Health Carein High Point, NC.

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