Exploratory and regulatory assessments on photosafety of new drug entities

Drug-induced phototoxicity is elicited after exposure of the skin and/or eyes to topically or systemically administered pharmaceutical substances, followed by exposure to sunlight. This undesirable side effect is one of the impediments in drug discovery and development, and substantial efforts have been made to avoid drug-induced phototoxic reactions. To evaluate the phototoxic potential of compounds, effective methodologies have been developed over the past few years, and screening strategies have also been proposed for predicting in vivo phototoxic reactions. European and American regulatory agencies have published guidelines for predicting and avoiding drug-induced phototoxicity in an early phase of drug discovery. The guidelines have indicated the requirements for assessing the photosafety of chemicals on the basis of their photochemical behaviors and have recommended some phototoxic assessment tools for aiding new drug development. A number of phototoxic screening systems have also been proposed on the basis of the pathogenesis of drug-induced phototoxicity, and some of them have already been applied to the phototoxic evaluation of new drug entities in drug discovery and development. The present review aims to summarize the current status of research tools, screening strategy and regulations for evaluating the photosafety of new drug candidates and to introduce our thoughts on the phototoxic risk assessments of compounds.