Morphological evaluation of low-dose midazolam granules by laser Raman microscopy

Raman analysis has higher sensitivity for the detection of active pharmaceutical ingredients (APIs) than additives; thus, it is expected to be used for the evaluation of low-content preparations. The purpose of this study was to clarify the usefulness of granule morphology assessment using Raman analysis in the development of low-content formulations. In this study, midazolam was used as a model drug to prepare granules as a low-content formulation. Raman images were used to visualize the distribution of ingredients on the surface of the granules, determine the particle size of midazolam bound to the granules, and investigate the types of excipient components to which midazolam is bound. It was suggested that midazolam particles of a certain size were difficult to bind to excipients and had particularly low adhesion to mannitol. It was revealed that this phenomenon caused the segregation of the content of midazolam particles in the granules. Therefore, to obtain granules with good content uniformity, it was considered necessary to control the particle size of the API and select an additive that does not differ in adhesiveness to the main drug. Additionally, the findings obtained by morphological observation could be clarified by the quantitative evaluation of additives using Raman.