Long-term pharmacokinetics of an extract of isoflavones from red clover (Trifolium pratense)

J Altern Complement Med. 2002 Apr;8(2):135-42. doi: 10.1089/107555302317371424.


Objectives: To study the pharmacokinetics of isoflavones from red clover (Trifolium pratense) after long-term administration as a once-daily dietary supplementary.

Design: Fourteen (14) subjects who had been consuming a low-isoflavone diet for 2 weeks were given an oral dose of two isoflavone tablets (approximately 80 mg of total isoflavones) daily for 2 weeks and appeared for a study day at 9:00 AM after an overnight fast on the day that they were to receive the last dose. Plasma samples were collected for a 48-hour period after the last dose. Plasma isoflavones were assayed by high-performance liquid chromatography (HPLC).

Results: Trough plasma levels were significantly higher for daidzein and genistein after long-term dosing than levels taken prior to the commencement of the study and plasma levels of isoflavones after long-term dosing were in the range previously reported in populations that consume an isoflavone-rich diet. The plasma half-lives observed after long-term administration were, in most cases, consistent with once-daily administration.

Conclusions: Isoflavones have pharmacokinetic characteristics that suggest that once-daily administration is adequate when they are administered long-term as dietary supplements.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Chromatography, High Pressure Liquid
  • Dietary Supplements
  • Dose-Response Relationship, Drug
  • Female
  • Genistein / pharmacokinetics
  • Humans
  • Isoflavones / blood
  • Isoflavones / pharmacokinetics*
  • Isoflavones / therapeutic use
  • Male
  • Middle Aged
  • Plant Extracts / blood
  • Plant Extracts / pharmacokinetics*
  • Plant Extracts / therapeutic use
  • Time Factors
  • Trifolium*


  • Isoflavones
  • Plant Extracts
  • formononetin
  • daidzein
  • Genistein
  • biochanin A