Evaluation of chemical stability of St. John's wort commercial extract andsome preparations

Thermal and photostability of a commercial dried extract and capsules of St . John's wort (Hypericum perforatum L.) were evaluated under the ICH test c onditions. The extract was considered as drug substance and its preparation s as drug products. In addition, capsules of different colours correspondin g to different opaficient and pigment contents were also evaluated as prima ry package of drug product and the tests in the secondary pack were perform ed with amber containers, as well. A selective high-performance liquid chro matography (HPLC) for determination of stability of all the characteristic constituents, namely flavonols, hyperforins and hypericins, was carried out . Photostability testing showed all the constituents to be photosensitive i n the tested conditions. However, different opaficients and pigments presen t in the capsules influenced the stability of the different classes of cons tituents. Amber containers suggested as secondary packages influenced only in part the photostability of the investigated constituents. Long-term ther mal stability testing showed a very low (less than 4 months) hyperforins an d hypericins t(90), even if ascorbic and citric acids were added to the for mulation. From the results we have obtained it is clear that for St. John's wort preparations, a mere translation of the ICH guidelines to the field o f herbal products, as suggested by the WPHMP of the EMEA, cannot be accepte d. A revision and adaptation of the storage conditions should be elaborated . (C) 2001 Published by Elsevier Science B.V.