[Evaluation of Photostability of Small Molecular Compounds with Solid-state UV Spectra].

It is crucial to evaluate the photostability of drugs. However, it requires a longer period of time to evaluate the photodegradation of compounds because extended light exposure to the compound is required to detect photodegradation products with the help of the commonly utilized technique of chromatography. Therefore, a simple and easy approach to estimate the photostability of the compound is required particularly for the initial screening of the drug candidates. It was reported in our previous manuscript that, focusing on ultraviolet-visible (UV/vis) spectrometry, the area under the spectrum curve in the ultraviolet-A (UVA) range (AUSCUVA) are closely related to the photodegradation of indomethacin polymorphs. In this study, the solid-state UV/vis absorption spectra of compound A polymorphs, indomethacin complexes and some small molecule compounds were determined and analyzed to check the applicability of this method. AUSCUVA are closely related to the photodegradation of compound A polymorphs as well as indomethacin. On the contrary, no close relation was observed between AUSCUVA of indomethacin complexes and their photodegradation. Additionally, the result indicated that the differences in their solid-state UV/vis absorption spectra were observed between photosensitive and photostable compounds. Photosensitive compounds show absorption in UVA range, while photostable compounds exhibit less absorption. In conclusion, the solid-state UV/vis absorption spectra of small molecular compounds might provide the key information on the photosensitivity.

A New Method for Classification of Salts and Cocrystals Using Solid-State UV Spectrophotometry.

Salt and cocrystal formulations are widely used as techniques to improve physicochemical properties of compounds. Some spectrometric techniques to distinguish cocrystals from salts have been reported; however, it has not been possible to adapt these formulations with many compounds, because of limitations, high difficulty, and exceptions. Therefore, we focused on the possibility of UV spectrometry, which had not been reported as a classification technique for salts and cocrystals. The integration values of solid-state UV/visible (Vis) spectra of indomethacin salts were larger than those of physical mixtures of indomethacin and counter molecules, while that of indomethacin cocrystal was not large compared with that of the physical mixture. From these results, differences between a salt and a cocrystal were observed in their solid-state UV/Vis absorption spectra for indomethacin complexes. Therefore, it is suggested that solid-state UV/Vis absorption spectra can be used as a new technique to classify salts and cocrystals.

Utility of Solid-State UV/Vis Spectra on the Evaluation of Photostability of Indomethacin Crystals.

Evaluating the stability of drugs over ranges of various environmental conditions is necessary to ensure the quality of the drug throughout the shelf life. In this study, we used indomethacin, which is well known as a photosensitive drug, and evaluated the photostability of prepared crystals. HPLC analysis revealed that all the indomethacin crystals were degraded by light exposure. However, the indomethacin crystals involving solvates had different degrees of photodegradation and different solid-state UV/Vis spectra. The value of the absorption integral in the UVA range related closely to the photodegradation of indomethacin crystals involving solvates. Therefore, it is easy to compare the photosensitivity among the crystals without actual analytical data, by use of a suitable analytical method and using light exposure samples. Moreover, it is possible to predict the value of photodegradation ratio from the solid-state UV/Vis spectra of indomethacin crystals. Therefore, this method may provide key information for selecting the most appropriate crystal form of photosensitive drugs.