Comparison of alkamide pharmacokinetics between equivalent liquid and tablet echinacea preparations

Abstract

The traditional liquid preparations of echinacea suffer poor compliance due to the strong, characteristic tingling sensation associated with the alkamides. Tablet preparations are a dose form which offers much better compliance, but there have been concerns that alkamides from these are not as well absorbed. To investigate this concern, the relative oral bioavailability of alkamides from two different echinacea formulations (liquid and tablet) were compared in a small two way crossover study in humans (n=3) and their pharmacokinetics parameters compared. The liquid preparation was a mixture of Echinacea purpurea L. (Moench) root (300mg/mL) and Echinacea angustifolia DC. root (200mg/mL) extracted in 60% ethanol. The tablet preparation was also a mixture of Echinacea purpurea root (675mg/tablet) and Echinacea angustifolia root (600mg/tablet) but was prepared from the dried ethanolic extracts of the two Echinacea species. 9 mL of the liquid, containing 9.1mg of the tetraene alkamide, was diluted to 25 mL with water and then swallowed immediately. 3 tablets, containing 7.8mg of the tetraene alkamide were swallowed with 25 mL of water. Alkamides were rapidly absorbed and measurable in plasma from both preparations. No significant differences in the tetraene alkamide pharmacokinetic parameters for T1/2, AUCt-lin and Cmax in the two different preparations were found. Tmax increased from 20 minutes with the liquid to 30 minutes with the tablet which is not unexpected as the tablet required time for disintegration before absorption could occur. By swallowing the liquid product immediately, the normal method of dosing for this product, any buccal absorption should have been minimised. These results suggest that there is no significant difference in the bioavailability of alkamides from liquid and tablet echinacea formulations and that both any alkamide loss due to digestive processes and the absorption site is similar in both preparations.