The aim of this research was to investigate the effect of acid exposure and calcium re-exposure on
the diffusion of caffeine and theophylline through calcium alginate gel films. Dimsion was measured
using side-by-side glass cells, before and after thejilms were exposed to simulated gastric
fluid (SGF) USP minus pepsin. The permeability increased by about 15-fold for theophylline and
48-fold for caffeine after 5 min SGF exposure. There was no sign@cant further increase by prolonging
the exposure time to 4 hr. The diffusion of both drugs was less than through alginate gel
films that were not cross-linked with calcium but were gelled in SGF. Treatment of the calcium
alginate gel film with SGF depleted the films of all of their calcium content. Calcium alginate gel
jilms that were exposed to SGF for a constant period of 15 min, were re-exposed to 0.34 M calcium
chloride solution for periods up to 24 hr. The calcium content returned to 80% of the level
in the original calcium alginate$lms and diffusion was reduced, but not to the level that was observed
in the original calcium alginate$lms. It was concluded that the effect of SGF on calcium
alginate was very rapid and that the increase in drug diffusion observed was probably due to removal
of calcium from the gel. It was also concluded that the origiruzl diffusion properties and calcium
content could only be partially regenerated by re-exposing the acid-exposed films to calcium
chloride.