Need for Additional, Specific Information in Studies with Echinacea

It was with great interest that I read the June 2000 publication titled “Ineffectiveness of Echinacea for Prevention of Experimental Rhinovirus Colds” (7). Unlike other recently published trials examining the efficacy of echinacea for cold treatment (4, 6), this trial found no significant effect of a 300-mg dose of an echinacea product containing 0.16% cichoric (chicoric) acid and negligible amounts of alkamides and echinacoside, compared to a placebo. This study was unique in that it involved patients inoculated with rhinovirus. Unfortunately, this trial failed to report the echinacea species used, the plant parts used, the formulation, and the method of extraction. We are told a dose of 300 mg was administered, but the reader is left to question whether this is a liquid formulation or a dried extract. If an extract, is it an aqueous or alcoholic extract? The German Commission E has approved the aerial parts of the Echinacea purpurea plant, manufactured as a fresh-pressed juice in 22% ethanol by volume, as a preservative (e.g., Echinacin and Echinaguard) and the roots of the E. pallida plant, manufactured as a water-alcohol extract, for clinical use (2). The root of E. purpurea and the root of E. angustifolia were not approved, due to a lack of clinical trials (2). It is true that recent trials have used a variety of different species and formulations; this information is generally provided in Materials and Methods and helps to discern which types of preparations are most likely to be clinically effective. In the study of Brinkeborn et al., a dried ethanolic extract of E. purpurea (95% herb, 5% root) was shown to significantly reduce cold symptoms compared to placebo, while a root preparation of E. purpurea did not (4). These findings seem to coincide with the German Commission E's recommendation.

Chemical constituents among echinacea species include the lipophilic fractions (e.g., alkamides and polyacetylenes), water-soluble polysaccharides, caffeoyl conjugates (e.g., echinacoside, cichoric acid, and caffeic acid), and flavonoids (3). The alkamides, polysaccharides, and chicoric acid are most often recognized for their immune-modulating effects (8). The concentration of these constituents depends on the species, the plant parts used, and the method of extraction. In the trial reported in June, the percent of cichoric acid is stated and the relative lack of alkamides is addressed, but the presence of polysaccharides is unknown. If the preparation was prepared by alcohol extraction, it is likely that the concentration of polysaccharides would have been lower. Merely knowing the concentration of cichoric acid does not provide sufficient information. Cichoric acid is present in both the above- and the below-ground parts of E. purpurea as well as other species (3). If this was a root preparation of E. purpurea, similar to the one studied by Brinkeborn et al., the observed lack of effectiveness might not be surprising. To date, the evidence for the effectiveness of echinacea for cold treatment appears promising (1, 5). Future studies should provide a detailed description of the herb being used and the method of preparation. This, in turn, will allow future research to focus on those preparations that appear most promising.