Safety and pharmacokinetics of purified soy isoflavones: single-dose administration to postmenopausal women
2002
Bloedon, LeAnne T. | Jeffcoat, A Robert | Lopaczynski, Wlodek | Schell, Michael J. | Black, Tracy M. | Dix, Kelly J. | Thomas, Brian F. | Albright, Craig | Busby, Marjorie G. | Crowell, James A. | Zeisel, Steven H.
Background: Soy isoflavones are being evaluated as chemopreventive agents for breast and other cancers. Objective: The objective was to perform safety and pharmacokinetic studies of purified unconjugated isoflavone preparations containing genistein, daidzein, and glycitein in postmenopausal women. Design: Twenty-four healthy postmenopausal women ingested a single dose of 1 of 2 purified (from soybeans) isoflavone preparations that delivered a genistein dose of 2, 4, 8, or 16 mg/kg body wt. These doses were higher than those previously administered to human females. Toxicity studies were performed 24 h and 3, 6, 14, and 30 d after isoflavone administration. Kinetic studies were performed during the first 24 h. Results: We observed a 7% decrease in systolic and diastolic blood pressure and a 32% decrease in the neutrophil count 24 h after treatment with formulation A. Isolated episodes of nausea, pedal edema, and breast tenderness were judged to be possibly related to the study treatment. The terminal plasma half-lives for free genistein, daidzein, and glycitein averaged 3.8, 7.7, and 3.4 h, respectively. The terminal pseudo half-lives for total genistein and total daidzein in plasma averaged 10.1 and 10.8 h, respectively. The estimated bioavailabilities of both total genistein and total daidzein from each of the 2 formulations were not significantly different. Conclusions: A single-dose administration of purified unconjugated isoflavones at amounts that exceed normal dietary intakes had minimal clinical toxicity in healthy postmenopausal women. The pharmacokinetic data suggest that chronic dosing at 12-24-h intervals would not lead to progressive accumulation of these isoflavones.
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