Non-Uniformity of Pellets Coating, Effect on the Dose Release Profile and How to Improve the Coating Process by Reducing the Electrostatic Charging of the Pellets

M. Marucci, A. Holmgren, H. Carlsson, A. Jarke, M. Johansson and C. von Corswant

Abstract
The aim of this work was to study the effect of several process parameters used during pellets coating in two wurster fluid beds of different scales on: a) the uniformity of pellets coating, and b) the presence of an initial burst in the release profile caused by the existence of a significant fraction of pellets having a very thin film coating. The pellets used in this work presented high insulating properties. The pellets were coated with extended release films made mainly of ethyl cellulose and it was shown that larger pellets had a thicker coating. The choice of the process parameters had a large effect on the amount of pellets that were subtracted from the coating process due to the buildup of electrostatic charges on the pellets. Using not too high fluidizing air flows, pellets of larger size, a smaller pellets load and humidified air to fluidize the pellets resulted in more uniform coatings and, consequently, in more favorable release profiles that did not present or presented a reduced initial burst release.

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Keywords
Pellets, coating non-uniformity, electrostatic charging, process parameters, wurster, bottom spray fluid bed