Sustained drug release from electrostatic powder coated tablets with ultrafine ethylcellulose powders

In the present study, tablets were successfully coated with ultrafine ethylcellulose powders by using an electrostatic dry powder coating technology and sustained drug release was successfully achieved. The angle of repose (AOR) of the ultrafine powders of ethylcellulose was significantly reduced by adding nano sized colloidal silicon dioxide, indicating a significant improvement of flowability. Variations in charging voltage of the electrostatic gun had a significant influence on the coating powder adhesion and coating efficiency. Lactose and triethyl citrate (TEC) were used as the solid and liquid plasticizers to reduce the glass transition temperature (Tg) of ethylcellulose. The presence of liquid plasticizer could also increase the electrical conductivity of drug tablets so as to promote the coating powder adhesion. Other factors that affect the film formation include curing time and curing temperature. Dissolution tests indicated that the drug release from electrostatic dry powder coated tablets could be altered by adjusting coating level or pore former ratio in the coating formulation.