Warfarin Institute of America

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FEVERFEW INTERACTIONS WITH WARFARIN

Botanical Name: Tanacetum parthenium

  Feverfew is an herbal medicine most commonly used for migraine prophylaxis.¹ It has also been used in the treatment of fever and rheumatoid arthritis. Feverfew’s mechanism of action includes inhibition of platelet activity and aggregation, inhibition of serotonin release and inhibition of prostaglandin synthesis.⁴ Feverfew’s antiplatelet effects are mediated by actions on platelet sulphydryl groups and inhibition of thromboxane B2.^2,3 This antiplatelet action could potentiate the effects of warfarin. Warfarin inhibits the production of vitamin K dependent clotting factors. This helps to prevent the formation of clots. Antiplatelet activity also decreases clot formation via a mechanism distinct from that of warfarin. While there is no clinical data documenting an interaction between feverfew and warfarin, feverfew’s antiplatelet activity is well established and could theoretically increase the risk of a significant bleeding episode if it is added to a warfarin regimen. Prothrombin time (PT/INR) is used to monitor warfarin therapy. However, prothrombin time does not measure antiplatelet activity. This means that the first sign of a problem could be bleeding. Patients should be educated about the possible interaction between the two medications and caution should be used when taking the two products simultaneously.

References:

1. Miller LG. Herbal Medicinals: Selected Clinical Considerations Focusing on Known or Potential Drug-Herb Interactions. Archives of Internal Medicine. 1998;158(20):2200-11.
2. Sumner J, Salan U, Knight DW, Hoult JR. Inhibition of 5-Lipoxygenase and Cyclo-oxygenase in Leukocytes by Feverfew. Involvement of Sesquiterpene Lactones and Other Components. Biochemical Pharmacology. 1992;43(11):2313-20.
3. Heptinstall S, Groenewegen WA, Spangenberg P, Loesche W. Extracts of Feverfew May Inhibit Platelet Behaviour Via Neutralization of Sulphydryl Groups. Journal of Pharmacy & Pharmacology. 1987;39(6):459-65.
4. Heck AM, DeWitt BA, Lukes AL. Potential interactions between alternative therapies and warfarin. Am J Health-Syst Pharm. 2000;57:1221-30.

© 2003 Shawna Lucero Used by permission

An editorial about the lack of concern for manufacturers of these products and their interactions with other medications.

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Last updated November 7, 2004