Effects of echinacea supplementation on alkylamide pharmacokinetics

Echinacea preparations are widely used for the prevention and treatment of colds and flu. Studies have shown that alkylamides are present in plasma after oral dosing with echinacea preparations [1,2]. It is well known that continued use of certain drugs can result in changes to their clearance rate and hence their pharmacokinetic profiles and therapeutic effects. Pharmacokinetic data such as this does not exist for the prophylactic use of echinacea. In this study, the effects of supplementation with echinacea on alkylamide bioavailability and pharmacokinetics were examined before and after prophylactic use of echinacea. Six healthy volunteers aged 24 to 66 years with a body mass index ranging from 22.7 to 24.6 participated in the study. They consumed 2 echinacea tablets twice a day for 14 days. On days 0 and 15, participants consumed 4 echinacea tablets (a total of 17.67mg of alkylamides). Blood samples were taken at 0, 30, 90, 120, 180, 240 and 360 minutes post dose and alkylamide levels were determined as previously described [1]. There was no evidence for either the induction or inhibition of alkylamide metabolism as evidenced by consistent elimination half life data. There was a trend towards more rapid alkylamide absorption and achievement of a higher Cmax before the prophylactic use of echinacea but these changes were not statistically significant and there was no difference to the extent of absorption (AUC). Plasma ratios of the tetraene alkylamides were also examined. These were similar to those found in the tablets used in the study and were not altered after prophylactic use of echinacea. In conclusion, prophylactic use of echinacea for 2 weeks does not appear to alter the pharmacokinetics of the alkylamides in echinacea.