Evaluation of chemical stability of St. John's wort commercial extract and some 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 conditions. The extract was considered as drug substance and its preparations as drug products. In addition, capsules of different colours corresponding to different opaficient and pigment contents were also evaluated as primary package of drug product and the tests in the secondary pack were performed with amber containers, as well. A selective high-performance liquid chromatography (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 in the tested conditions. However, different opaficients and pigments present in the capsules influenced the stability of the different classes of constituents. Amber containers suggested as secondary packages influenced only in part the photostability of the investigated constituents. Long-term thermal stability testing showed a very low (less than 4 months) hyperforins and hypericins t(90), even if ascorbic and citric acids were added to the formulation. 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 of herbal products, as suggested by the WPHMP of the EMEA, cannot be accepted. A revision and adaptation of the storage conditions should be elaborated.