MECHANISM OF RELEASE FROM PELLETS COATED WITH AN ETHYLCELLULOSE-BASED FILM

Studies were conducted to determine the mechanism of drug release from pellets coated with an ethylcellulose-based pseudolatex widely accepted for use as a sustained release coating for phar-maceuticals. Possible mechanisms for release include solution/diffusion through the continuous polymer phase and/or plasticizer channels, diffusion through aqueous pores and osmotically dri-ven release through aqueous pores. To distinguish between these mechanisms, the release rate was studied as a function of coating thickness, plasticizer content, and osmotic pressure in the dissolution medium. As the coating thickness was increased from 9 to 50 pm, the rate of release fell from 9.93. 10m3 to 1.71. 10m3 g phenylpropanolamine (PPA). HCl/lOO ml h in an inversely proportional manner. Release as a function of plasticizer content was studied over the range 12 to 24 % dibutyl sebacate (DBS). At 18 or 24 % DBS, the rates of release of PPA*HCl were virtually identical, about 50 % of PPA*HCl in six hours. At 12 % DBS through, over 80 % was released in the first hour. Surface area measurements and scanning electron microscopy @EM) showed that the larger surface area of the 12 % DBS batch was attributable to the presence of cracks in the coating. These results indicated that while the plasticizer is important in terms of forming a continuous film, diffusion through plasticizer channels is unlikely to make a significant contri