Interaction of two diclofenac acid salts with copolymers of ammoniomethacrylate: Effect of additives and release profiles

The copolymer of ammoniomethacrylate Eudragit RL(R) (ERL) interacted with d iclofenac acid salts (sodium and diethylamine salts) in aqueous solutions, forming a complex. Sorption experiments were done in aqueous solutions of e ither sodium lauryl sulfate (SLS), Tween 20 or Tween 80. The SLS competed s trongly with the drug, even at low concentrations, and reduced significantl y the amount of drug sorbed by ERL. Tweens at high concentrations exhibited two phase profiles: the sorption phase, which was short and during which d rug concentration dropped sharply, and the release phase, Juring which the drug was released slowly over 24 hr and which was accompanied by dispersion of ERL particles into the colloidal dispersion. The interaction was depend ent an temperature, ionic strength and nature of the additives. The extent of interaction in water and phosphate buffer solutions was in the following order: water > pH 6 > pH 7-8. In-vitro dissolution studies of the dried co mplex were done over 24 hr. In water, the drug remained bound to the polyme r In aqueous surfactant solutions (SLS, Tween 20 and Tween 80) and phosphat e buffer at pH 6.8 a linear relationship between drug concentration and the square root of time was obtained indicating a matrix diffusion-controlled mechanism. However, 100% release was not reached, and resorption was observ ed in the phosphate buffer solution.