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:
- crystal structure (polymorphism);
- crystallinity (unintended crystallization of an amorphous state);
- hydration state;
- flowability (powder).
These characteristics alter the bio-availability of the drug as well as its therapeutic effects. Also problems during processing can be the consequence of improper storage. Finally, changes in the chemical and physical properties of a drug affect its stability, and thus its shelf-life. Thermal analysis provides first information about the behavior of a pharmaceutical substance in specific temperature and humidity conditions.
How Does Temperature and Humidity Influence the Pharmaceutical Substance? Thermal Analysis Gives the Answers
A thermogravimetric measurement exhibits the behavior of the sample under temperature effect. The combination of this method with the Kinetics Neo software allows for determination of the kinetics of the decomposition reaction of a substance. The results can be used to predict the stability during long-time isotherms, i.e., the shelf life with regard to thermal stability. Moreover, connecting a humidity generator to a thermogravimetric balance enables to gather information about the hygroscopy and stability of the sample in a humid atmosphere. This is possible by using STA devices, combining the advantages of a thermobalance and a true DSC (Differential Scanning Calorimeter).