In vitro and in vivo evaluation of coated capsules for colonic delivery

The aim of the present study was to design and evaluate the combination of pH-dependent and time-dependent polymers for colon-specific drug delivery using response surface methodology (RSM). Theophylline was selected as a model drug and Eudragit® FS 30D (pH-dependent), Eudragit® RL 30D and Eudragit® RS 30D (as time-dependent) were used as coating polymers. Dissolution test was carried out in different pH media mimicking the transit of capsules from stomach to colon. The morphology of coated capsules was evaluated by scanning electron microscopy (SEM). In vivo studies were performed using fluorescent imaging in order to trace the movement of capsules in gastrointestinal (GI) tract. The results of in vitro studies showed that optimized formulation had suitable release profile at different pH values, which were in agreement with the predicted value by RSM. The SEM images revealed that surface coated capsules were smooth and also fluorescent imaging indicated that coated capsules disintegrated at the targeted colon region. These findings provide novel insights for the development of enteric coated capsule in order to specify drug delivery to colon.