- crystal structure (polymorphism);
- crystallinity (unintended crystallization of an amorphous state);
- hydration state;
- flowability (powder).
Temperature, humidity and light may have great influence on the quality, stability and efficacy of drug substances and products, so that knowledge of the adequate storage conditions is essential to ensure safety of the patient. Stability studies on storage conditions for drugs and drug products are given in the guidelines of ICH (International Council for Harmonization of Technical Requirements for Pharmaceuticals for Human Use) and WHO (World Health Organization). This testing involves long-time studies of several months. It highlights potential irreversible transformations of the drug due to fluctuation of temperature and/or humidity, concerning its: