Potentiation of Warfarin Anticoagulation by Topical Herbal Oil: A Case Report
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Abstract
Warfarin is an effective oral anticoagulant for stroke prevention in atrial fibrillation and for the treatment of thromboembolic disorders. Despite its established effectiveness, warfarin has a narrow therapeutic window and is prone to drug, food, and herbal product interactions. Although interactions with oral drugs are well documented, data on interactions with topical agents remain scarce. This case report describes two instances of markedly elevated international normalised ratio (INR) associated with the use of a topical herbal oil. Two female patients on warfarin therapy presented to Hospital Kuala Lumpur with significantly elevated INR (> 10) following the topical application of “Herbal Oil Y”. Both patients were receiving warfarin to prevent stroke due to atrial fibrillation. The first patient, a 31-year-old woman, had initiated warfarin one week before admission. The second patient, a 69-year-old woman, had been taking warfarin for five years. Both patients denied recent dietary changes, over-the-counter medications, or oral herbal supplements. However, they reported applying Herbal Oil Y a day before admission. Warfarin induced over-anticoagulation was treated with intravenous vitamin K or prothrombin complex concentrate. Both patients were discharged in stable condition after close ward monitoring. These cases suggest a possible interaction between topically applied Herbal Oil Y and warfarin, likely due to the systemic absorption of active herbal constituents. Patients receiving warfarin therapy should be counselled on the potential risks associated with concomitant herbal product use, including topical preparations, to minimise adverse events.
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