ABSTRACT
As indicated in the previous chapters, the shelf-life of a drug product is estimated based on stability data collected from long-term stability studies. These long-term stability studies are usually conducted under certain assumptions about controlled design factors such as storage conditions (e.g., temperature and humidity) and package types. These assumptions include, but are not limited to: (a) the drug product is expected to degrade linearly over time, (b) the drug is stored under ambient storage conditions such as 25◦C and 60% relative humidity, and (c) the components and composition remain unchanged. Once these assumptions are met, an optimal design is selected to achieve the best precision for estimating the drug shelf-life. In practice, these assumptions may not be met, especially when: (a) there are postapproval changes in components and composition, site, batch size (scale-up or scale-down), or manufacturing equipment and processes, and (b) the drug product is shipped to foreign markets or different regions. In this case regulatory agencies may require additional stability data to be collected to support the changes.
