Bilayer coating of drug spheroids with a fixed inner coat of plasticiz
ed hydrophilic cellulose ether and varying amount of plasticized metha
crylic acid copolymer outer coat was formulated. These coated spheroid
s were able to demonstrate a greater sustained-release effect at pH 1
than spheroids coated with solely plasticized methacrylic acid copolym
er. The swelling dynamics of the cellulose ether had an important role
in achieving the desirable sustained release property as was well dem
onstrated by spheroids coated with an inner coat of plasticized hydrox
ypropylmethyl cellulose of high viscosity grade and an outer coat of p
lasticized Eudragit L30D. However, substituting the inner coat with fa
st-disintegrating sodium carboxymethyl cellulose of moderate viscosity
grade was less superior in its sustained release effect than an inter
ior coat of plasticized hydroxypropylmethyl cellulose. When plasticize
d methacrylate ester copolymer was utilized as the outer coat, the inc
orporation of plasticised cellulose ether whether hydroxypropylmethyl
cellulose or sodium carboxymethyl cellulose, as the inner coat, showed
faster release than the plasticized Eudragit RS30D coat alone at both
pH 1 and pH 72. Nevertheless, the results provided a useful basis for
rite design and formulation of bilayer coated spheroids consisting of
a swellable inner layer, made of high viscosity plasticized hydroxypr
opylmethyl cellulose and an outer coat of an enteric material. The und
issolved and intact membrane coat that swelled to different extent was
directly correlated to the coating level or thickness of the outer L3
0D-PEG6000 coat. The swollen coat had attained a constant diffusion pa
thway for drug release, exhibiting a zero-order drug release kinetics
nt gastric pH.