Photodegradation and photosensitization in pharmaceutical products: Assessing drug phototoxicity
Toxic reactants are a common result of the interaction of sunlight with pharmaceutical agents transported in the blood system or applied topically. Over the past decade there has been a considerable amount of research toward understanding both the unimolecular deactivation pathway of photoexcited pharmaceutical products and their photosensitizing capability in the presence of biological substrates. This work summarizes recent developments in the study of the photodegradation mechanism of ketoprofen, fenofibric acid, and tiaprofenic acid. An analysis of excited-state electronic energy levels, the type of intermediates formed following excitation, and transient intermediate lifetimes is presented. The analysis involves both parent drugs and their major photoproducts. Phototoxicity, usually the result of adverse photochemical reactions following direct photoexcitation of the drugs, is shown to be strongly related to the photoexcitation of photoproducts when high radiation dose conditions prevail. The photoproducts are the species directly involved in photosensitizing reactions.