ABSTRACT
The Q1B guidance laid a framework for consistency within the industry around photostability testing. Importantly, the document specifies light sources, study types to be conducted (forced stress and confirmatory), the presentation of samples, and the importance of having proper control over the light-dose delivered. Arguably the most important section of the document is the decision flow chart for the photostability testing of drug products. The flow chart provides a stepwise approach to evaluating and mitigating the effects of photostability on drug products and, in doing so, clearly indicates the burden of protection required by pharmaceutical applicants in regulatory submissions. Some of the shortcomings that have been noted in the document are around definition of what constitutes an “acceptable change” during photostability testing, disagreements in the community over light sources recommended, and that the guidance leaves out any mention of the implications of photostability on product administration. Baertschi produced an excellent practical interpretation of the guideline shortly after its publication that provides many useful suggestions for satisfying Q1B requirements ( 3 ).
