This study will examine how the herbal remedy ginkgo biloba may affect the body's elimination
of other medicines. Many people take ginkgo biloba to improve memory, mental alertness and
overall feeling of well being. Since this product is considered a food supplement and not a
drug, it is not subject to the rigorous pre-market testing required for prescription and
over-the-counter (OTC) drugs. As a result, information has not been collected on possible
interactions between ginkgo biloba and other medications. This study will look at how ginkgo
biloba affects the elimination of phenytoin-a medication used to treat patients with
seizures.
Normal healthy volunteers 21 years of age or older may be eligible for this 40-day study.
Candidates will provide a medical history and undergo a physical examination and routine
blood tests. Women of childbearing age must use a reliable form of birth control other than
oral contraceptives ("the pill").
For at least 2 weeks before the study and throughout its duration, study participants may not
have any of the following: 1) medications that can affect platelet function (e.g., aspirin,
Motrin, Advil, Nuprin, ibuprofen, etc.); 2) alcoholic beverages; 3) grapefruit and grapefruit
juice; and 4) all medications except those given by study personnel.
On day 1 of the study, subjects take one 500-mg dose of phenytoin at 8:00 A.M.. On an empty
stomach. (Subjects fast the night before taking the phenytoin and are allowed to eat
breakfast 2 hours after the dose). Blood samples are drawn just before dosing and again at
0.5, 1, 1.5, 2, 4, 6, 8, 10, 12, 24, 32, 48, 72 and 96 hours after the dose. Blood drawn on
this first study day is collected through a catheter (small plastic tube) placed in a vein to
avoid multiple needlesticks. After the 12-hour sample is collected, the subject goes home and
then returns to the clinic for the remaining blood draws, which are taken by direct
needlestick.
When the blood sampling is completed, subjects begin ginkgo therapy. The NIH Clinical Center
provides participants a supply of 60-mg capsules of ginkgo to take twice a day (at 8 A.M. and
8 P.M..) for 4 weeks. At the end of the 4 weeks, subjects are given a second dose of
phenytoin as described above and repeat the blood sampling procedure. Subjects continue
taking ginkgo during this second phenytoin study.
Phase:
Phase 1
Details
Lead Sponsor:
National Institutes of Health Clinical Center (CC)