Abstract
Chitosan with excellent biodegradable and biocompatible characteristics has received attention as an oral drug delivery vehicle for controlled-release formulations. In this study an enteric-coated capsule containing theophylline-chitosan beads based on 23 factorial designs was prepared as a colon drug delivery system. The theophylline-chitosan gel beads were formulated by adding the drug-containing solution of chitosan into tripolyphosphate solutions, dropwise. The obtained beads were washed with water and freeze-dried before filling into the capsules. Eudragit® S100 was then used to enteric-coat the prepared capsules. Drug entrapment efficiency and the effects of different variables including: bead morphology, swelling behavior of the beads and the release behavior of the system on these parameters were investigated. Results showed that the highest and lowest swelling ratio is obtained at pH 4.5 and 7.2, respectively. These studies have shown that chitosan concentration and drug polymer weight ratio significantly affect the drug entrapment. Decreasing the drug solubility in external phase caused a significant increase in drug loading. External phase saturation with theophylline and tripolyphosphate, as well as decreasing temperature, have increased drug loading. Furthermore, the lowering of temperature had a significant effect on bead's hardness. The release of theophylline from freeze-dried beads filled in enteric-coated capsules was also investigated. Release of theophylline was prolonged with saturation of both drug and tripolyphosphate in the external phase. Results showed that the release of theophylline from chitosan beads is possibly due to more than one mechanism, possibly dissolution, diffusion and relaxation of the polymer chains.
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