Interaction between Eudragit® E100 and anionic drugs: Addition of anionic polyelectrolytes and their influence on drug release performance

In this work, we report results concerning the study of solid complexes compounded by a cationic polymethacrylate (Eudragit® E100, Eu) and mesalazine (M) (Eu-Mx complex). The influence of an anionic polyacrylic acid polymer (carbomer, C) on dissolution behavior of M from the complex was evaluated (Eu-MxCy complex). The dissolution profiles and solvent front movements of solid matrices in different media (water, buffer pH 7.4, 0.9% NaCl) were investigated and ionic interactions among Eu, M, and C were determined through Fourier transform infrared (FT‐IR) spectroscopy. For Eu-Mx complexes, the affinity between M and Eu modulated the delivery of free M in solution, with the dissolution media affecting the delivery rate mainly due to an ionic interchange process between M and anionic electrolytes (i.e., Cl−). FTIR spectroscopy allowed the ionic interaction between Eu and M to be verified. The addition of C (Eu-MxCy) influenced the dissolution behavior of these matrices. As the amount of C was increased, the release mechanism changed from diffusion (Eu-M50) or anomalous (Eu-M100) to zero order (Eu-MxC50). This variation in rate delivery was also affected by the dissolution media, as occurred with Eu-Mx complexes. The formation of the gel layer during the dissolution process, as consequence of Eu-MxCy matrices hydration, was influenced by C amount and dissolution media. © 2011 Wiley‐Liss, Inc. and the American Pharmacists Association J Pharm Sci 100:4664-4673, 2011