EVALUATION OF THERMAL AND FILM-FORMING PROPERTIES OF ACRYLIC AQUEOUS POLYMER DISPERSION BLENDS - APPLICATION TO THE FORMULATION OF SUSTAINED-RELEASE FILM-COATED THEOPHYLLINE PELLETS

Aqueous acrylic polymer dispersions were blended in order to improve processing and film formation from acrylic polymers with poor film Terming properties and/or to obtain sustained-release film coated pellets with optimal barrier properties according to the physico-chemical and pharmacokinetic requirements of the active substance. Heterogeneous film structures are generally obtained from blends containing an association of hard acrylic polymers (Eudragit(R) RS30D, S100) with the soft Eudragit(R) NE30D when the drying temperature is lower than the minimum film forming temperature (MFT) of the hard acrylic polymers. The Tg and MFT values of the hard acrylic polymers are not modified in the presence of the soft polymer as shown by the thermograms of these blends which are generally characterized by two individual glassy transitions. On the other hand, a wide range of drug dissolution profiles can be obtained from film coated pellets either by using, in different proportions, the insoluble but readily permeable Eudragit(R) RL30D in association with the less permeable Eudragit(R) RS30D in order to obtain pH-independent permeability membrane, or by mixing the anionic methacrylic acid copolymers (L30D, S100) with the neutral NE30D in order to obtain pH-dependent permeability film coated pellets showing higher dissolution release rates at intestinal pH values.