Background

There are nine species of Echinacea, a member of the daisy family. Three species, Echinacea angustifolia, Echinacea purpurea, and Echinacea pallida, are used for medicinal purposes. The most commonly studied is Echinacea purpurea, used for the prophylaxis and treatment of viral, bacterial, and fungal infections, particularly those of upper respiratory origin. Compelling evidence supporting its use in upper respiratory infections is lacking, however. Echinacea is also used as an immunostimulant after chemo- and radiation therapy, an adjunct in cancer treatment, and a topical promoter of wound healing.

Phytochemistry and pharmacology

Echinacea contains alkylamides, alkaloids, caffeic acid esters, polysaccharides, flavonoids, polyacetylenes, and essential oils. Pharmacological activity cannot be attributed to a single compound, although the lipophilic fraction, which contains the alkylamides (primarily the dodeca-2, 4, 8, 10-tetraenoic acid isobutylamides), polyacetylenes, and essential oil, appears to be more active than the hydrophilic fraction.

Echinacea has a number of immunomodulatory effects. In vitro, it activated immune cells, increased cytokine production, and inhibited hyaluronidase. In vivo, activated natural killer cells in humans and increased production of immunoglobulins G and M in rats.

Safety

Echinacea appears to have a low potential for toxicity and mutagenicity, and in a preliminary investigation, was not harmful during pregnanacy. It has been associated with allergic reactions, including one reported case of anaphylaxis. Therefore, echinacea should be used with caution in patients with asthma, atopy, or allergic rhinitis. Its immunomodulatory effects may diminish the effectiveness of immunosuppression in patients such as organ transplant recipients. Moreover, immunosuppression is possible if echinacea is taken long-term (> 8 weeks).

Although the pyrrolizidine alkaloids in echinacea lack the 1,2 unsaturated necrine ring system associated with hepatoxicity in other pyrrolizidine alkaloid-containing plants such as comfrey, concerns of potential hepatoxicity also have been raised.

The pharmacokinetics of echinacea have not been studied.

Preparations and dosage

Several preparations are available. The fresh ariel parts of the plant can be pressed to yield a juice that is stabilized with alcohol. The usual dosage is 6-9 ml of expressed plant juice or its equivalent as an extract per day. Preparations can also be made from plant root, and the usual dosage is 0.9 g of cut root several times daily.