Potential Interactions Between Alternative Therapies and Warfarin

Amy M. Heck, Beth A. Dewitt, and Anita L. Lukes

Disclosures

Am J Health Syst Pharm. 2000;57(13) 

In This Article

Abstract and Introduction

Abstract

Potential and documented interactions between alternative therapy agents and warfarin are discussed.

An estimated one third of adults in the United States use alternative therapies, including herbs. A major safety concern is potential interactions of alternative medicine products with prescription medications. This issue is especially important with respect to drugs with narrow therapeutic indexes, such as warfarin. Herbal products that may potentially increase the risk of bleeding or potentiate the effects of warfarin therapy include angelica root, arnica flower, anise, asafoetida, bogbean, borage seed oil, bromelain, capsicum, celery, chamomile, clove, fenugreek, feverfew, garlic, ginger, ginkgo, horse chestnut, licorice root, lovage root, meadowsweet, onion, parsley, passionflower herb, poplar, quassia, red clover, rue, sweet clover, turmeric, and willow bark. Products that have been associated with documented reports of potential interactions with warfarin include Coenzyme Q10 , danshen, devil's claw, dong quai, ginseng, green tea, papain, and vitamin E. Interpretation of the available information on herb- warfarin interactions is difficult because nearly all of it is based on in vitro data, animal studies, or individual case reports. More study is needed to confirm and assess the clinical significance of these potential interactions.

There is evidence that a wide range of alternative therapy products have the potential to interact with warfarin. Pharmacists and other health care professionals should question all patients about use of alternative therapies and report documented interactions to FDA's MedWatch program.

Introduction

Alternative medicine therapies have become increasingly popular, and it has been estimated that one third of all Americans use herbal products.[1] In 1997, herbal medicine sales increased nearly 59%, reaching an estimated total of $3.24 billion.[1,2] Despite widespread use of alternative therapies, scientific data about their safety and efficacy are lacking in most cases. This makes it very difficult for pharmacists to advise patients appropriately about safe concomitant use of alternative therapies and prescription medications. New information about therapeutic efficacy, adverse effects, and potential drug interactions of alternative therapies is frequently reported in the medical literature. Therefore, it is important for pharmacists to have current knowledge in order to remain a reliable source of drug information for patients and other health care professionals.

One particular safety concern is potential interactions of alternative medicine products with prescription medications. This issue is especially important with respect to drugs with narrow therapeutic indexes, such as warfarin. More food and drug interactions have been reported for warfarin than for any other prescription medication.[3,4] Multiple pathways exist for interference with warfarin, and interactions may lead to either hemorrhage or thrombotic episodes by increasing or reducing this agent's effect. Therefore, close monitoring of therapy and knowledge of potential interactions of herbs with warfarin are extremely important.

This article discusses potential and documented herb-warfarin interactions.

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