Abstract
The porous ethylcellulose (EC) film-coating technique was applied to prepare the film-coated (so-called capsule-type) controlled release dosage form of phenylpropanolamine hydrochloride (PPA), which was used as a highly water-soluble model drug. To prepare EC film-coated beads with various film-porosities, the PPA-loaded uncoated beads were spray-coated 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 was found that the profiles were well superimposed on the same curve, suggesting that the drug release obeyed the same mechanism. To examine the mechanism of drug release from the EC film-coated beads of PPA, drug release behaviors were investigated under the condition of various osmotic pressure differences. The drug release rate was decreased by decreasing the osmotic pressure difference. The contribution of an osmotic pumping to the drug release was estimated for the EC film-coated beads with different coating porosities. The driving force for drug release from the porous EC film-coated beads was found to be mainly an osmotic pumping mechanism, irrespective of film porosity.
