ABSTRACT
This chapter discusses some of the issues surrounding solid-state characterization of the drug substance and its impact on stability and performance. The thermodynamically stable form could be verified during a stability study, but it is possible to have a metastable form remain completely unchanged for the duration of a normal drug substance stability study. The thermodynamic stability of the major polymorphs that have an impact on the drug substance in development should be assessed, if possible. The International Conference on Harmonization stability guideline indicates that conditions can be used if needed; hence, data from informal stability studies can be used to establish and justify the conditions. The type of stability studies conducted and the conditions under which they are conducted can be divided into two broad areas: Stress Studies: polymorph screening studies, informal stability studies and formal Stability Studies: accelerated testing, long-term testing.
