Should warfarin and Ginkgo biloba be taken together?: responses from community pharmacists and health food store personnel to an interaction query

• Published in: Canadian pharmacists journal Vol. 135; no. 10; p. 30
• Main Authors: Melnyk, Paul S, Shevchuk, Yvonne M, Sue, Millie
• Format: Journal Article
• Language: English
• Published: Ottawa SAGE PUBLICATIONS, INC 01.12.2002
• Subjects: Anticoagulants; Drugs; Herbal medicine; Physiological aspects
• ISSN: 1715-1635; 1913-701X

Extracts from the leaves of the Ginkgo tree have become popular for the treatment of dementia and many other indications. Ginkgolide B is a component of Ginkgo that inhibits platelet activating factor by displacing it from binding sites.(8) Platelet activating factor is involved in platelet aggregation, free radical production and increased microvascular permeability.(9) The antagonism of platelet activating factor is thought to give Ginkgo antiplatelet activities and a propensity to interact with warfarin.(8)(10) Case reports of spontaneous bleeding in association with the use of Ginkgo(8)(11)(12)(13) have led authors to advise that the combination be used either with caution,(14)(15) or not at all.(2)(10)(16) Commonly used references also indicate that there is a potential for bleeding as a result of this drug-herb interaction.(17)(18) An unpublished case describes a probable interaction involving a 61-year-old female patient who started taking Ginkgo biloba while on warfarin (personal communication, Bill Wilson, Health Canada 2000). In two weeks, the patient's international normalized ratio (INR) more than tripled. When Ginkgo was discontinued, the INR returned to pretreatment values. This study was a comparative evaluation of responses by pharmacists and health food store personnel to a drug information question. A scenario involving the potential use of warfarin and Ginkgo biloba was developed. During a two-week study period, a pharmacy student investigator (MS) telephoned every pharmacy and health food store in the city of Saskatoon. The pharmacy telephone numbers were obtained from the 1998 provincial registry. The health food store phone numbers were acquired from the 1998-1999 Saskatoon telephone directory (yellow pages). Telephone calls were made from the student investigator's home to prevent recognition of DSIS personnel and telephone number. The stores were contacted from Monday to Friday between 1000 and 1630 hours. The investigator asked the person who answered the telephone exactly the same question: "My mother is taking warfarin. Is it okay for her to take Ginkgo?" No attempt was made to ascertain the training or position of the individual answering the telephone. Further information was not provided by the investigator unless prompted by the staff member who answered the telephone. The investigator would respond to the staff member's questions by using the following information: The caller's mother is 65-years-old and has been taking warfarin for an unknown length of time because of a previous clot in her leg. Her mother has learned from an unknown source that Ginkgo biloba is used to improve memory. Neither the caller nor her mother have used the herb; the person wants to know if it would be safe for her mother to begin using the herb. She does not know her mother's other medications or how often her mother has blood tests performed. The person does not patronize the store and does not know where her mother purchases, or plans to purchase, her medications or herbal products. The family has recently moved from another city. The results of this study are discouraging for patients who seek advice on herbal medicines. Thirty-three and 60% of responses from pharmacists and health food store personnel, respectively, were considered to be unacceptable, very unacceptable or neutral. Some health food store personnel and pharmacists readily recommended use of the combination of Ginkgo and warfarin without knowledge of the potential problem and, apparently, without referring to reliable resources. This poor judgement suggests that these individuals are not well trained in the area of herbal medicine, or the stores in which they work do not have adequate references. For the responses that were considered neutral in acceptability, the investigator was referred to pharmacists or physicians for further information. It is not known whether 'real' patients would ever have received appropriate advice from these referrals. Stores that sell products containing Ginkgo biloba should be expected to provide sufficient and accurate information to allow patients to make informed decisions regarding the use of such products.