[The importance of concomitant compounds in plant extracts]

Plant extracts are multi-composed mixtures that can be subdivided into main active substances and concomitant compounds. Concomitant compounds are called co-effectors because they can change the physicochemical properties of the main active substances and therefore influence the biopharmaceutical parameters, e.g. solubility and bioavailability. The composition and the properties of plant extracts depend on a multitude of different factors such as quality and degree of reduction of the plant, and the process of extraction and drying. Concomitant compounds affect the physical and chemical stability of plant extracts. The hygroscopicity also depends on the composition of the concomitant compounds. It is an important property for the further processing of the plant extract to solid dosage form, e.g. tablets. Solubility and dissolution rate can be influenced by the concomitant compounds. Both properties are important for the absorption of the active substances though in many cases the responsible substances and mechanisms are still unknown. Solubilisation by surface-active agents, formation of soluble drug-concomitant compound-associates and solid dispersion, in which the drug is finely dispersed or X-ray amorphous, are often responsible for the increased solubility. Improved wettability in the presence of the concomitant compounds results in better dissolution. Supersaturated solutions of the active substances are stabilized for months by inhibition of crystallization. Numerous examples are known for influencing the absorption by natural concomitant compounds. The absorption is enhanced by the increased amount of dissolved drug or by the alteration of membrane permeability. Adsorption or complex formation with the concomitant compounds decrease the absorption rate, in some cases also the extent of absorption.