EFFECT OF DIFFERENT POLYMER-PLASTICIZER COMBINATIONS ON IN-VITRO RELEASE OF THEOPHYLLINE FROM COATED PELLETS

Plasticizers are added to the polymer coating of sustained-release gra nules to improve the mechanical properties of the coating shell. The p resent investigation evaluated the influence of different plasticizer/ polymer combinations on theophylline (TH) release from pellets coated with latex aqueous dispersions of ethylcellulose (EC) or acrylic polym ers (ACR). The plasticizers, present in the coating films in amounts r anging from 8 to 30%, were acetylated monoglycerides (AMG), diethyl ph thalate (DEP), dibutyl phthalate (DBP) and dibutyl sebacate (DBS). The release profiles of TH from the coated pellets were influenced by the type and amount of plasticizer and of coating material, and by the ra tio polymer-plasticizer. For both types of coating, the drug release r ate decreased with increasing plasticizer content. A correlation was f ound between the permeability coefficients (P-WV) to water vapour of f ree films, having the same composition as those used for coating, and drug release.