Petasins in the treatment of allergic diseases: results of preclinical and clinical studies.

Plant extracts are causing an increased interest in the treatment of many chronic diseases, including asthma and other allergic diseases. Several laboratories characterized petasins (petasin, isopetasin, and neopetasin) isolated from extracts of butterbur (Petasites hybridus) as pharmacologically active components, which inhibit leukotriene synthesis in leukocytes. The molecular mechanisms by which petasins abrogate inflammatory effector cell functions have, at least partially, been identified. In vitro studies revealed that petasins may have several intracellular targets and this may depend on the stereoisomer used. In an open clinical trial in patients suffering from allergic rhinitis, a reduction of leukotriene and histamine levels in nasal fluids was associated with the butterbur extract administration. To better evaluate the clinical value in this particular allergic disease, the clinical efficacy of the drug was compared with an established antihistamine treatment scheme in a double-blind study; no significant difference was observed between the two treatment groups. In this article, we critically review recently published work and summarize the current stage in the pharmacological characterization of butterbur extracts.