Characterization of mannitol granules and powder: A comparative study using two flowability testers

In the manufacture of tablets, especially in direct tableting processes, the flowability of excipient powders and formulated powders is one of the most important characteristics. In the past two decades, orally disintegrating tablets (ODTs) have been prepared as popular solid dosage forms for elderly patients. Many types of mannitol granules have been developed and marketed as new pharmaceutical excipients for ODTs, owing to the solubility and palatability of mannitol. Characterizing the flow behaviors of these mannitol granules is essential to their use. The flowability of mannitol excipients was the focus of the present study. A fine crystalline mannitol powder, eight commercial types of mannitol granules and four types of mannitol mixture granules were evaluated. Two flowability testers were used for comparing and analyzing the samples' flowabilities. A variety of methodologies were used: an assessment using Carr's index, a shear test and a dynamic flow test. Mannitol powder showed the lowest Carr's index, meaning the lowest flowability. Spherical mannitol granules showed the lowest angle of internal friction in the shear test and extremely low basic flow energy in the dynamic flow test. Larger granules showed relatively high values for Carr's index, but also a relatively high total flow energy.