Kudzu (Pueraria lobata) – Botany, Therapeutic Uses, Constituents, Pharmaco, Adverse Effects

Attempts have been made to enhance absorption of certain isoflavones by modifying the vehicle used for administration of purified substances. These approaches, which include use of phospholipid complexes or nanoparticles, tend to increase the extent of absorption and the isoflavone concentrations in various organs.

The most precise pharmacokinetic data on the chemical components of kudzu are obtained using chemically pure isoflavones. Plant extracts, such as those contained in consumer products, are less useful for such studies given the high degree of variation in the concentration of constituents among these preparations. This variability makes it difficult to know the amount of any particular chemical being administered. On the other hand, the use of pure chemicals makes it impossible to know whether other components of the extract influence the rate and extent of absorption, or the metabolism, of individual constituents. Because of this, results with pure compounds may not in all cases accurately reflect their pharmacokinetics when they are taken along with the other plant constituents, as is the case with commercial products. In one study a methanol extract was administered to mice, with body fluid measurements indicating the isoflavones were rapidly absorbed and subsequently eliminated to a large extent in urine and feces. Organ tissue analysis 24 hours after administration revealed these compounds were widely distributed throughout the body with the highest concentration in the liver. As none of these compounds was detected in the brain, it was concluded that puerarin, daidzin, and malonyl daidzin do not penetrate into the central nervous system, or are rapidly eliminated from this region of the body. Such data call into question whether isoflavone components of kudzu extracts directly affect the brain.

Qualitatively similar results were found when studying the absorption, distribution, metabolism, and elimination of puerarin when the purified compound was administered alone to rats. These experiments revealed that puerarin was absorbed into blood following oral administration, reaching its maximum serum concentration within approximately 40 minutes, declining thereafter. In this case the highest concentration of compound was found in the lungs, although some was detected in the brain as well.

The absorption in rats of a mixture of the kudzu aglycones daidzein, genistein, and glycitein has been compared with the absorption of daidzin, genistin, and glycitin, their corresponding glucosides. The results indicate that the oral bioavailability of these agents varies between 8% and 35%, with no consistent differences noted between the glycosides and the aglycones. These data indicate that these isoflavones appear in blood following oral administration, although the bioavailability is limited. The differences between the findings with the pure substance as compared to an extract highlights the difficulties associated with comparing the pharmacokinetic properties of an agent administered alone to when it is given as part of a compound mixture. Inasmuch as kudzu extract is most commonly taken by consumers, results with mixtures more accurately reflect what occurs with normal usage. Such data are inconclusive as to which, if any, of the kudzu isoflavones or their metabolites penetrate into the brain in sufficient quantities and for a sufficient period of time to have any clinically significant effect on central nervous system activity.