Polymers with pH-dependent solubility: Possibility of use in the formulation of gastroresistant and controlled-release matrix tablets

Polymers usually utilized for gastroresistant film coating of tablets or pe llets such as cellulose acetate phthalate (CAP), cellulose acetate trimelli tate (CAT), hydoxy-propylmethylcellulose phthalate (HPMCP), and Eudragit L and S were used in the preparation of drug/polymer matrix tablets. These ta blets were prepared either by direct compression of both powders or by the formulation of microspheres that were then compressed. The microspheres wer e characterized by scanning electron microscopy (SEM), differential scannin g calorimeter (DSC), and X-ray diffractometry analyses. Dissolution studies were finally carried out to verify if the tablets possessed gastroresistan t or controlled-release characteristics. Except for Eudragit L, the polymer s can be used under certain conditions in the formulation of modified-relea se tablets.