Dry Powder Coating of Pellets with Micronized Eudragit®RS for Extended Drug Release

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Abstract
Purpose. To develop a novel powder coating technology for extended-release pellets based on the acrylic polymer, Eudragit® RS. Methods. A mixture of micronized Eudragit® RS plus talc and a liquid feed (plasticizer plus binder solution) were sprayed separately onto propranolol hydrochloride-loaded pellets in a fluidized bed coater. The coated pellets were heat-cured under different conditions (40°C to 60°C, 2 h to 24 h). The coalescence (film formation) of the polymer particles was studied via the determination of the glass transition and the minimum polymer-softening temperatures (MST). The coated pellets were characterized with respect to their morphologic, release, and stability properties. Results. The optimum plasticizer type and concentration and process temperatures could be identified by the determination of the MST. High concentrations of plasticizer (40% based on the polymer) and a thermal treatment were necessary to achieve complete film formation and extended drug release. Curing the pellets resulted in release profiles, which did not change during storage for 3 years. The coated pellets had a smooth, continuous surface and a dense film structure after curing. Conclusions. This novel coating technique avoids the use of organic polymer solutions or latex dispersions, has short processing times, and results in stable extended-release profiles.