To date, only one study has evaluated the pharmacokinetics of the alkamides contained in the Echinacea products administered to humans (27). Subjects (n = 11) received a single oral 2.5-mL dose of the 60% ethanolic extract from E. angustifolia roots or placebo (60% ethanol). Six different alkamides were analyzed: (1) Undeca-2D/Z-ene-8,10-diynoic acid isobutylamides; (2) Dodeca-2D,4Z-diene-8,10-diynoic acid isobutylamide; (3) Dodeca-2E-ene-8,10-diynoic acid isobutylamide; (4) Dodeca-2E,4E,8Z,10E/ Z-tetraenoic acid isobutylamides; (5) Dodeca-2E,4E,8Z-trienoic acid isobutylamide; and (6) Dodeca-2E,4E-dienoic acid isobutylamide. The extract contained approx 2.5 mg of (4), and approx 0.5 mg of all other components. The Cmax and area under the curve (AUC) for (4) were approx 10-fold that achieved with each of the other components. Thus, despite a fivefold higher amount per dose, the 10-fold greater Cmax and AUC achieved with (4) suggest it exhibits a greater bioavailability than the other components.

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