Chitosan (CS) gel beads were prepared in 10% amino acid solution (pH 9) and
implanted into air pouches (AP) prepared subcutaneously on the dorsal surf
ace of mice. No inflammatory response was observed, and degradation of the
beads in the AP increased as their degree of deacetylation decreased. Degra
dation could be altered by changing the nature of the CS or by increasing t
he CS concentration. The release of prednisolone (PS) in vivo from CS gel b
eads was similar to the release in vitro. When a suspension of PS was injec
ted into the AP, the PS had almost completely disappeared 24 h after inject
ion. Retention of PS in the AP was not increased by using a viscous CS solu
tion. Alginate (Alg) gel beads, which were not degraded, released PS slowly
into the AP over 3 d. The in vitro release profile of PS using 1% CS (deac
etylation: 70% (7B) and 80% (8B)) and 1.5% CS (deacetylation: 90% (9B)) gel
beads was similar to that with Alg gel beads. However, the in vivo release
of PS was affected by the degradability of the gel beads. CS7B and 8B (1%)
gel beads had released PS into the AP earlier than 3 d according to their
rate of degradation. CS9B (1.5%) gel beads were not degraded after 3 d and
went on to release PS into the AP for 3 d similar to the release profile of
Alg gel beads. CS9B (2%) gel beads were also not degraded after 3 d and th
e release of PS from these beads into the AP was sustained; 76% and 27% of
administered PS remained in the gel beads after 1 and 3 d, respectively. Th
erefore, degradation and drug release of CS gel beads can be controlled by
changing the structure of the gel matrix, which appears to make these beads
a promising biodegradable vehicle for sustained drug delivery.