Clinical use of echinacea

INTRODUCTION

Echinacea species are commonly referred to as coneflowers, a group of native American wildflowers from the daisy family (Asteraceae/Compositae) (picture 1) [1]. Echinacea is indigenous to North America and was used by Native Americans in the Great Plains. Samples of echinacea have been found in archeological digs from the 1600s, thought to be the location of Lakota Sioux Indian village sites [2]. Native Americans were noted to use echinacea both topically and systemically for ailments such as burns, snakebites, pain, cough, and sore throat [3].

At present, echinacea is mainly used for treating and preventing uncomplicated upper respiratory tract infections such as the common cold [4]. Retail sales for echinacea in the United States in 2004 were estimated to be 155 million dollars [5]. The National Health Interview Survey found that echinacea was the most common natural product in 2002, used by 7.6 percent of American adults [6]. In Germany, more than 2 million physicians' prescriptions for echinacea are filled each year [7].

Various echinacea species including Echinacea purpurea, E. angustifolia, and E. pallida have been touted as "immune stimulants" by a number of investigators [7]. Medicinal preparations of root and above-ground parts of echinacea species have been the subject of in vitro, animal, and human studies to evaluate their possible mechanism(s), safety, and efficacy.

MECHANISM OF ACTION

Echinacea products contain a variety of bioactive ingredients including echinacosides, caffeic acids, alkylamides, polysaccharides, and glycoproteins [8]. Though several echinacea products are standardized to the amount of echinacosides, there is no general consensus on the active component(s) of echinacea responsible for its purported medicinal properties.

In vitro, echinacea causes macrophage activation and the release of tumor necrosis factor, interleukin 1, interleukin 6, and interferon [9-11]. Echinacea has been noted to have antiviral activity against influenza, herpes, and poliovirus. Phenolic compounds present in echinacea demonstrate antioxidant activity [12]. It has also been reported to have antiinflammatory activity through inhibition of lipoxygenase and cyclooxygenase [13], and is able to stimulate the anterior pituitary-adrenal cortex.