POROSITY-CONTROLLED ETHYLCELLULOSE FILM COATING .5. MECHANISM OF DRUG-RELEASE FROM BEADS COATED WITH POROUS ETHYLCELLULOSE FILM

The porous ethylcellulose CEC) film-coating technique was applied to p repare the film-coated (so-called capsule-type) controlled release dos age form of phenylpropanolamine hydrochloride (PPA), which was used as a highly water-soluble model drug. To prepare EC film-coated beads wi th various film-porosities, the PPA-loaded uncoated beads were spray-c oated with an aqueous ethanolic or ethanolic solution of EC, and their drug release behaviors or drug release mechanisms were investigated. Although the amount of coating of the beads was equal, the PPA release rate differed according to the ethanolic concentration in the coating solution, that is, the lower the ethanolic concentration, the faster the release rate. The release profiles were normalized using a reduced time method to compare the profiles of different release rates. It wa s found that the profiles were well superimposed on the same curve, su ggesting that the drug release obeyed the same mechanism. To examine t he mechanism of drug release from the EC film-coated beads of PPA, dru g release behaviors were investigated under the condition of various o smotic pressure differences. The drug release rate was decreased by de creasing the osmotic pressure difference. The contribution of an osmot ic pumping to the drug release was estimated for the EC film-coated be ads with different coating porosities. The driving force for drug rele ase from the porous EC film-coated beads was found to be mainly an osm otic pumping mechanism, irrespective of film porosity.