Results of five randomized studies on the immunomodulatory activity of preparations of Echinacea

This article describes and discusses five placebo-controlled randomized studies investigating the immunomodulatory activity of preparations containing extracts of Echinacea in healthy volunteers. A total of 134 (18 female and 116 male) healthy volunteers between 18 and 40 years of age were studied. Two studies tested intravenous homeopathic complex preparations containing Echinacea angustifolia D1 (study 1) and D4 (study 5). Two studies (2 and 3a) tested oral alcoholic extracts of roots of E. purpurea, one study an extract of E. pallida roots (study 3b), and one study an extract of E. purpurea herb (study 4). Test and placebo preparations were applied for four (study 5) or five (studies 1-4) consecutive days. The primary outcome measure for immunomodulatory activity was the relative phagocytic activity of polymorphonuclear neutrophil granulocytes (PNG), measured in studies 1 and 2 with a microscopic method and in studies 3, 4, and 5 with two different cytometric methods. The secondary outcome measure was the number of leukocytes in peripheral venous blood. Safety was assessed by a screening program of blood and other objective parameters as well as by documentation of all subjective side effects. In studies 1 and 2 the phagocytic activity of PNG was significantly enhanced compared with placebo [maximal stimulation 22.7% (95% confidence interval 17.5-27.9%) and 54.0% (8.4-99.6%), respectively], while in the other studies no significant effects were observed. Analysis of intragroup differences revealed significant changes in phagocytic activity during the observation periods in five test and three control groups. Leukocyte number was not influenced significantly in any study. Side effects due to the test preparations could not be detected. Our studies provide evidence for immunomodulatory activity of the homeopathic combination tested in study 1 and the E. purpureae radix extract tested in study 2. The negative results of the other three studies are difficult to interpret due to the different methods for measuring phagocytosis, the relevant changes in phagocytic activity within most placebo and treatment groups during the observation period, and the small sample sizes. Future studies should be performed on patients rather than healthy volunteers and use standardized or chemically defined monopreparations of Echinacea.