Effect of Green Tea Extract on the Pharmacokinetics of Digoxin in Healthy Volunteers

[Speaker] Tae-Eun Kiim:1
[Co-author] Kwang-Hee Shin:2, Jeong-Eun Park:2, Jongmin Lee:3
1:Department of Clinical Pharmacology, Konkuk University Medical Center, Korea, 2:College of Pharmacy, Research Institute of Pharmaceutical Sciences, Kyungpook National University, Korea, 3:Department of Rehabilitation Medicine, Konkuk University School of Medicine, Korea

Previous in vitro studies have reported the inhibitory effect of green tea on p-glycoprotein. The aim of this study was to investigate the effect of green tea on the pharmacokinetics of digoxin which is a typical probe drug of p-glycoprotein in healthy volunteers.
At Day 1, all the subjects were orally administered 0.5 mg of digoxin. After a 14-day washout period, they were administered 0.5 mg of digoxin and 630 mg of green tea extract (GTX), concomitantly. Following the pretreatment of 630 mg of GTX from Day 16 through 28, the subjects were again concomitantly administered 0.5 mg of digoxin and 630 mg of GTX at Day 29. Blood samples for the pharmacokinetic assessments of digoxin were collected up to 8 hours after each dose. Pharmacokinetic parameters were estimated by non-compartmental analysis and compared by mixed effect model.
A total of 16 subjects were enrolled and 15 subjects completed the study. Compared to the single administration of digoxin alone (Day 1), the systemic exposure of digoxin was significantly reduced after the concomitant administration of GTX (Day 15): geometric mean ratio (GMR) and 90% confidence interval (CI) of AUClast was 0.69 (0.62-0.75) and those of Cmax was 0.72 (0.61-0.85). The concomitant administration of digoxin and extract following pretreatment of GTX (Day 29) also reduced the AUClast (GMR (90% CI): 0.67 (0.61-0.74)) and Cmax (GMR (90% CI): 0.74 (0.63-0.87)).
This study demonstrated that the co-administration of GTX reduces the systemic exposure of digoxin regardless of pretreatment of GTX.

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