ABSTRACT
The initial International Conference on Harmonization technical discussions, aimed at establishing the scientific principles to underwrite the guideline, quickly confirmed that photostability testing was a complex topic. The evaluation of photostability characteristics during the product’s actual period of use is addressed by the guideline. A systematic approach to photostability testing is recommended for both the drug substance and the drug product. In undertaking photostability studies, it is necessary to differentiate between those studies undertaken as part of the development phase and formal confirmatory studies. Turning now to the formulation, the guideline contains a decision tree covering the testing of drug product. Photostability is part of forced degradation testing carried out to show that the chosen packaging affords suitable protection to light. In evaluating the results of the photostability testing at each stage, the decision tree asks the question whether any observed changes are acceptable.
