Pharmaceutical Technology: Controlled Drug Release, Volume 2

120 CH. 10] CONTROLLED DELIVERY OF THEOPHYLLINE
Fig. 1—Effect of polyisobutadiene concentration on in vitro release of theophylline microcapsules (theophylline:RS 100
ratio, 1:2; particle size 540 µm): □, 2.5% (w/w); ○, 3.0% (w/w); ∆, 4.0% (w/w).
take food until 2.5 h after dosing. Then a standardized breakfast, without tea or coffee, was given.
A light meal was served at 11.30 a.m. and dinner was served at 8.30 p.m. The subjects refrained
from taking any other drugs during this study. A cross-over schedule was adopted and a minimum
interval of one week was allowed between each dosing. All subjects received a single oral dose of
the different oral dosage forms in each schedule.
Blood samples were taken at 0.25, 0.5, 1.5, 2.5, 4.5, 6.5, 8.5, 10.5 and 12.5 h and the
concentration of theophylline in serum was assayed by a spectrophotometric method [7]. The
samples were analysed in duplicate. Bioavailability was calculated from the area under the
concentration curve following the trapezoidal rule.
RESULTS AND DISCUSSION
Scanning electron micrography of the micromatrices revealed that the products were
homogeneous with corrugated surfaces and pores. Higher magnification revealed surface shrinkage.
After dissolution the micromatrices did not change in shape, which suggests that the drug diffused
out through the minor pores and channels. After being solubilized by the dissolution media.
Electron micrographs of the microcapsules showed that there were a few pores on the surface of
the microcapsules. Shapes were irregular owing to the amorphous nature of the drug particles
used.