Structure of the active pharmaceutical ingredient bismuth subsalicylate

Structure determination of pharmaceutical compounds is invaluable for drug development but remains challenging for those that form as small crystals with defects. Bismuth subsalicylate, among the most commercially significant bismuth compounds, is an active ingredient in over-the-counter medications such as Pepto-Bismol, used to treat dyspepsia and H. pylori infections. Despite its century-long history, the structure of bismuth subsalicylate is still under debate. Here we show that advanced electron microscopy techniques, namely three-dimensional electron diffraction and scanning transmission electron microscopy, can give insight into the structure of active pharmaceutical ingredients that are difficult to characterize using conventional methods due to their small size or intricate structural features. Hierarchical clustering analysis of three-dimensional electron diffraction data from ordered crystals of bismuth subsalicylate revealed a layered structure. A detailed investigation using high-resolution scanning transmission electron microscopy showed variations in the stacking of layers, the presence of which has likely hindered structure solution by other means. Together, these modern electron crystallography techniques provide a toolbox for structure determination of active pharmaceutical ingredients and drug discovery, demonstrated by this study of bismuth subsalicylate. Pepto-Bismol has been used to treat gastrointestinal disorders for over a century, yet the structure of its active ingredient is still under debate. Here, the authors apply electron crystallography to unveil the structure of bismuth subsalicylate.

Automated summary

In this study, advanced electron microscopy techniques were used to determine the structure of bismuth subsalicylate, a commercially significant compound in over-the-counter medications. The results showed that these techniques provide valuable insights into the structure of active pharmaceutical ingredients that are difficult to characterize using conventional methods.