S. Narisawa et al., POROSITY-CONTROLLED ETHYLCELLULOSE FILM COATING .5. MECHANISM OF DRUG-RELEASE FROM BEADS COATED WITH POROUS ETHYLCELLULOSE FILM, Chemical and Pharmaceutical Bulletin, 42(10), 1994, pp. 2131-2134
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.