[Sensitivity of cationic polymer Eudragit RL to electrolytes and its effect on drug release from Eudragit RL matrix]

The swelling behavior of acrylic polymer Eudragit RL in different concentration and species of electrolyte aqueous media, and the effect of media and polymer swelling on drug release from Eudragit RL matrix system were investigated with nifedipine, chlorpheniramine maleate and indomethacin as model drugs. It was found that Eudragit RL was sensitive to the electrolytes in aqueous media. The swelling of Eudragit RL decreased with increasing electrolyte concentration and was significantly affected by the electrolyte species. The swelling behavior was reversible. The release of 3 drugs from Eudragit RL matrix was remarkably affected by the electrolytes in the media. The rates of release of nifedipine and chlorpheniramine maleate from the polymer matrices were controlled by the polymer swelling behavior, and the rate of release correlated well with the swelling behavior. However, the rates of release of indomethacin from the Eudragit RL matrix were controlled not only by the polymer swelling but also by the drug displacement by the medium anion, which was attributed to the presence of an interaction between indomethacin and Eudragit RL.