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Effects of Ginkgo Biloba Extract on Pharmacokinetics and Pharmacodynamics of Tolbutamide and Midazolam in Healthy Volunteers

From the Departments of Pharmacokinetics and Pharmacodynamics, Center of Excellence Program in the 21st Century (Dr Uchida, Ms Maruyama, Dr Ohmori, Dr Oki, Dr S. Yamada) and Division of Drug Evaluation and Informatics (Dr H. Yamada), School of Pharmaceutical Sciences, University of Shizuoka, Shizuoka, Japan; Department of Clinical Pharmacology & Therapeutics, Hamamatsu University School of Medicine, Hamamatsu, Japan (Dr Li, Dr Watanabe); National Institute of Health and Nutrition, Tokyo, Japan (Dr Umegaki); and Department of Clinical Pharmacology & Therapeutics, School of Medicine, Oita University, Oita, Japan (Dr Ohashi).

This study was undertaken to clarify the influence of repeated oral administration of Ginkgo biloba extract (GBE) on CYP2C9 and CYP3A4. CYP2C9 probe (tolbutamide, 125 mg) and CYP3A4 probe (midazolam, 8 mg) were orally administered to 10 male healthy volunteers before and after GBE intake (360 mg/d) for 28 days, and they received 75 g glucose after the dosing of tolbutamide. Plasma drug concentrations and blood glucose levels were measured. The area under concentration versus time curve (AUC_0-) for tolbutamide after GBE intake was slightly but significantly (16%) lower than that before GBE intake. Concomitantly, GBE tended to attenuate AUC_0-2 of blood glucose-lowering effect of tolbutamide. AUC_0- for midazolam was significantly (25%) increased by GBE intake and oral clearance was significantly (26%) decreased. Thus, it is suggested that the combination of GBE and drugs should be cautious in terms of the potential interactions, especially in elderly patients or patients treated with drugs exerting relatively narrow therapeutic windows.

Key Words: Ginkgo biloba extract • CYP2C9 • CYP3A4 • pharmacokinetic interaction

Address for reprints: Shizuo Yamada, PhD, Departments of Pharmacokinetics and Pharmacodynamics and Center of Excellence Program in the 21st Century, School of Pharmaceutical Sciences, University of Shizuoka, 52-1 Yada, Suruga-ku, Shizuoka, 422-8526; e-mail: yamada{at}ys7.u-shizuoka-ken.ac.jp.

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