CHARACTERIZATION OF ACRYLIC RESIN MATRIX FILMS AND MECHANISMS OF DRUG-POLYMER INTERACTIONS

A polymeric matrix system for controlled drug release was developed em ploying the model drugs, salicylic acid and chlorpheniramine maleate, along with two acrylic resin polymers of varying permeability (Eudragi ts RL and RS). During drug release studies and sorption experiments wi th salicylic acid and the Eudragit RL polymer, the presence of an inte raction between the drug and polymer was found. The physical and chemi cal properties of this drug-polymer complex were investigated to eluci date the mechanisms of interaction. The solubility of the salicylic ac id and chlorpheniramine maleate in the polymeric films was determined to be greater than 10% w/w using DSC, SEM and powder x-ray diffraction . At a 10% drug loading, the drug molecules were dissolved in the poly mer and the matrix existed as a solid solution. X-ray diffraction stud ies revealed that sorbed salicylic acid was in solution with the polym er rather than present as dispersed crystalline material. These Eudrag it polymers interacted with acidic compounds in a manner similar to io n exchange resins which contain quaternary ammonium groups, as found i n these polymers. Both reversible and irreversible binding of salicyli c acid were observed during desorption studies, suggesting the presenc e of more than one type of binding interaction. The reversibility of s alicylic acid binding with a change in ionic conditions supported the theory that the drug interacted with these polymers primarily via ioni c electrostatic interactions. The absence of observed changes in the l ocation or breadth of specific infrared absorption bands, suggested th at hydrogen bonding between the salicylic acid and the polymer was min imal in the drug-polymer interaction. No evidence of new covalent chem ical bond formation between the drug and the polymer was found. The di ssolution release profiles for salicylic acid and chlorpheniramine mal eate were directly correlated to the drug-polymer interactions. Decrea ses in pH or increases in ionic strength which minimized ionization of the anionic drug resulted in decreased drug sorption and increased dr ug release from the matrix films.