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

A polymeric matrix system for controlled drug release was developed employing the model drugs, salicylic acid and chlorpheniramine maleate, along with two acrylic resin polymers of varying permeability (Eudragits RL and RS). During drug release studies and sorption experiments with salicylic acid and the Eudragit RL polymer, the presence of an interaction between the drug and polymer was found. The physical and chemical properties of this drug-polymer complex were investigated to elucidate the mechanisms of interaction. The solubility of the salicylic acid 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 polymer and the matrix existed as a solid solution. X-ray diffraction studies revealed that sorbed salicylic acid was in solution with the polymer rather than present as dispersed crystalline material. These Eudragit polymers interacted with acidic compounds in a manner similar to ion exchange resins which contain quaternary ammonium groups, as found in these polymers. Both reversible and irreversible binding of salicylic acid were observed during desorption studies, suggesting the presence of more than one type of binding interaction. The reversibility of salicylic acid binding with a change in ionic conditions supported the theory that the drug interacted with these polymers primarily via ionic electrostatic interactions. The absence of observed changes in the location or breadth of specific infrared absorption bands, suggested that hydrogen bonding between the salicylic acid and the polymer was minimal in the drug-polymer interaction. No evidence of new covalent chemical bond formation between the drug and the polymer was found. The dissolution release profiles for salicylic acid and chlorpheniramine maleate were directly correlated to the drug-polymer interactions. Decreases in pH or increases in ionic strength which minimized ionization of the anionic drug resulted in decreased drug sorption and increased drug release from the matrix films.