Investigations on the Photo-Transformation of Retinol Acetate

Taking into account the advanced photosensitivity of some pharmaceutical substances, there are several special requirements for their use, storage and even their assay in pharmaceutical formulations. Despite numerous attempts made in order to characterize the intrinsic photo-transformation tendency of drugs, the problem is far to be solved satisfactorily. In this paper a model study is performed in the concrete case of retinol acetate (vitamin A), a compound with well-known photosensitivity, using a photochemical reactor of original conception. In the case of vitamin A, a single dominant photochemical process seems to be takes place, as suggested by HPLC UV-spectroscopy and chemometric processing of spectrophotometric data. An adequate interpretation of kinetic data allows to define and determine a rate constant suitable to express the intrinsic photo-instability, irrespective of some experimental factors such as initial concentration, the nature of solvent etc. The processing technique we have been used is suitable even in the case when the spectroscopic behavior of reaction product is unknown. The described strategy is based on the monomolecular pathway supposition, successfully tested in the case of vitamin A.