Although methods exist to readily determine the particle size distribution (PSD) of an active pharmaceutical ingredient (API)\nbefore its formulation into a final product, the primary challenge is to develop a method to determine the PSD of APIs in a finished\ntablet. To address the limitations of existing PSD methods, we used hot-stage microscopy to observe tablet disintegration during\ntemperature change and, thus, reveal the API particles in a tablet. Both mechanical and liquid disintegration were evaluated after we\nhad identified optimum milling time for mechanical disintegration and optimum volume of water for liquid disintegration. In each\ncase, hot-stage micrographs, taken before and after the API melting point, were compared with image analysis software to obtain\nthe PSDs. Then, the PSDs of the APIs from the disintegrated tablets were compared with the PSDs of raw APIs. Good agreement\nwas obtained, thereby confirming the robustness of our methodology. The availability of such a method equips pharmaceutical\nscientists with an in vitro assessment method that will more reliably determine the PSD of active substances in finished tablets.
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