Abstract
The Higuchi model was used to interpret the release characteristics of sulfamethoxazole from gelatin-acacia coacervated microcapsules. For dissolution tests in distilled water and disintegration test solutions No. 1 and 2 (J.P. IX), linear correlations were obtained up to 60-80% drug release from the microcapsules. In addition, the in vitro 50% dissolution time (T50) was found to correlate with the coating performance, i.e., thickening and hardening of the microcapsule wall. The release rate decreased with increasing wall thickness of the microcapsules, which effectively delayed the release probably by inhibiting or retarding the diffusion rate of the solute into the medium or out from the microcapsule. An increase of formalization with formaldehyde clearly delayed the release rate. The leaching out of the soluble complex from the microcapsules was illustrated by the dissolution profile, and somewhat enhanced the release rate of sulfamethoxazole. The apparent diffusion coefficient of sulfamethoxazole through the microcapsule wall was found to be 1.63×10-9 to 283×10-9 cm2/sec, and this was a function of coacervation pH and the amount of formaldehyde used as a hardening agent. Tortuosity in the microcapsule wall was determined to be 0.86×102 to 11.4×102, based on the dissolution data in distilled water, and was also influenced by coacervation pH and amount of formaldehyde used.
