Relationship between particle packing and the physical stability of powder mixes.

The segregation tendency of powder mixes containing sugar-based direct compression tableting excipients with comparable particle size distributions and flow properties was studied under different vibration conditions. It was found that Tabfine and fine-particle pyridoxine hydrochloride mixes were virtually segregation-free, whereas segregation occurred in each of the other powder mixes containing Fast-flo, Dipac and Nu-tab. The segregation tendency of a specific powder mix following vibration was considered to be influenced by the packing of excipient particles in the powder bed. In general, the more densely packed the particles under given vibration conditions, the lower the segregation tendency. This was considered to be due to the tightly packed powder bed restricting individual particle movement and thereby reducing particle or ordered unit rearrangement.