Unsuspected source of vitamin K in patients treated with anticoagulants: a case report

The administration of warfarin requires careful attention. The concurrent intake of drugs can either enhance or compete with its anticoagulant effect. Less frequently encountered are the effects from vitamin K added to food, intake of foods with naturally occurring high levels of vitamin K and diets deficient in vitamin K. We report a case in which loss of anticoagulant control was caused by a dietary supplement taken during a weight reducing diet by a patient who was receiving warfarin following a pulmonary embolus. A review of the literature reveals several similar cases. Amounts of vitamin K in food supplements and in foods with large amounts of naturally occurring vitamin K are tabulated along with suggestions for surveillance of patients taking anticoagulants.