The influence of film coating on pellet properties

There are numerous reasons for which film coatings are applied to pellet formulations; for example, controlled release, taste masking, and improved stability. The aim of this paper was to study the influence of pellet shape on the deposition of film coatings in a fluid-bed process by monitoring the pellet shape as a function of the film thickness formed. Eight pellet batches were used, of which four were spherical visually, and the other batches can be described as ovoids, dumbbells, long dumbbells, and cylinders. The average coat thickness of the pellets assessed by cross-section measurements did not appear to be influenced by the initial shape of the pellets. The fluid-bed process, however, had an impact especially for those pellets that had an aspect ratio greater than 1.5. The change in the pellet shape during film coating could only be monitored effectively employing a three-dimensional shape factor. Significant changes in shape occurred at the beginning of the coating process up to approximately the first 15 min, after which the shape remained constant.