چکیده (انگلیسی):

The aim of this work was to establish whether alginate gel
formed spontaneously in hard gelatin capsules which modifies
release of a model drug, theophylline. The effects of
the alginate composition, the calcium addition, and the dissolution
medium on drug release were also investigated.
After the capsule shell dissolved in water, at neutral pH the
gel layer of sodium alginate was formed immediately as the
sodium alginate hydrated and swelled on contact with the
aqueous medium. In acidic pH, the contents remained intact
and the matrix shape was the same. Theophylline release
from capsules containing different grades of alginate demonstrated
different release patterns, depending on alginate
composition and the pH of the medium. The capsules containing
sodium/calcium salts of alginate showed the slowest
drug release at neutral pH but the fastest in acidic medium.
The presence of calcium acetate in the formulations influenced
the drug release kinetics. The drug release in acidic
medium showed a non-Fickian diffusion-controlled release,
while those in water at neutral pH exhibited a Super Case II
transport mechanism. The study also provides evidence that
the behavior of alginate in forming the hydrated gel layer
may explain the drug release behavior at different pHs.