POROSITY-CONTROLLED ETHYLCELLULOSE FILM COATING .4. EVALUATION OF MECHANICAL STRENGTH OF POROUS ETHYLCELLULOSE FILM

The mechanical characteristics of porous ethylcellulose (EC) film as a barrier in a controlled release dosage form were investigated. Spraye d EC films with various porosities were prepared by changing the ethan olic concentrations in the EC spraying solution, and their film porosi ties (epsilon) and tensile strength (T-s) were measured. It was found that the T-s of EC films decreased with an increase in epsilon, and th at the quantitative relationship between both parameters was considera bly adapted to the equation proposed by Bal'shin. By using the permeab ility-epsilon and T-s-epsilon relations, the mechanical strength of tw o EC films with different porosities were estimated under the assumpti on that the drug permeation rate through the two films was equal. The result suggested that, when the permeation rate was equal, a film with higher porosity would have higher mechanical strength. This was also proved by a high-shear dissolution test for theophylline beads coated with EC film. The in vivo drug release behavior from porous EC film-co ated heads agreed well with the in vitro drug release, indicating that the porous EC film-coated beads had sufficient strength to withstand the mechanical stress of the gastrointestinal tract, and that the poro us EC film coating could be used as a barrier for controlled release p reparations.