Sustained release coating of tablets with Eudragit^® RS/RL using a novel electrostatic dry powder coating process

The objectives of this study were to develop an electrostatic dry powder coating process for sustained coating tablets with Eudragit^® RS/RL and to investigate the effects of various factors and operating conditions on the coating process and drug release profile. A liquid plasticizer (triethyl citrate) was sprayed onto the surface of the tablets followed by spraying coating powder by an electrostatic spray gun. The powder coated tablets were cured at elevated temperature for a film formation. Liquid plasticizer played important roles in lowering down the glass transition temperature (T_g) of the coating polymer and increasing the surface electrical conduction of tablet cores. Electrostatic assisted coating deposition was confirmed by the fact that higher coating level was obtained with electrical charging than the ones without it. The micrographs of scanning electron microscopy (SEM) of coated tablets showed that the film formation mainly occurred during the curing step. Higher curing temperature and longer curing time help enhance the film formation. The in vitro drug release profiles indicated that curing time, temperature, coating level and ratio of Eudragit^® RS/RL were the main factors affecting the sustained release profile. The electrostatic dry powder coating process has been demonstrated to be an alternative for tablet sustained release coating with Eudragit^® RS and RL.