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 p rocessing and film formation from acrylic polymers with poor film Term ing 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 fi lm structures are generally obtained from blends containing an associa tion of hard acrylic polymers (Eudragit(R) RS30D, S100) with the soft Eudragit(R) NE30D when the drying temperature is lower than the minimu m film forming temperature (MFT) of the hard acrylic polymers. The Tg and MFT values of the hard acrylic polymers are not modified in the pr esence of the soft polymer as shown by the thermograms of these blends which are generally characterized by two individual glassy transition s. On the other hand, a wide range of drug dissolution profiles can be obtained from film coated pellets either by using, in different propo rtions, the insoluble but readily permeable Eudragit(R) RL30D in assoc iation with the less permeable Eudragit(R) RS30D in order to obtain pH -independent permeability membrane, or by mixing the anionic methacryl ic acid copolymers (L30D, S100) with the neutral NE30D in order to obt ain pH-dependent permeability film coated pellets showing higher disso lution release rates at intestinal pH values.