Study of the critical points of experimental HPMC-NaCMC hydrophilic matrices

The purpose of the present work was to study the existence of critical points on the drug release and water uptake behaviour of ternary hydrophilic matrix tablets and to study the possibility of simplifying a ternary to a binary system. The ternary hydrophilic matrix tablets were prepared between 40 and 100% (w/w) of KCl, HPMC and NaCMC. Dissolution studies were carried out using the paddle method and the water uptake studies were measured using the modified Enslin apparatus and the behaviour of the kinetic parameters was studied. According to the percolation theory, both studies confirm the existence of critical points; those were related to the excipients percolation tresholds. The percolation thresholds for the binary hydrophilic matrix tablets were found between 28.7-40.7% (v/v) of HPMC and 38.6-53.9% (v/v) of NaCMC. For the ternary hydrophilic matrix tablets, the existence of a critical barrier between 54 and 61% (v/v) KCl (60-70%, w/w of KCl) was found. In the studied ternary systems HPMC and NaCMC showed that is not possible to simplify the system but they present a partial collaboration in order to establish the gel layer. The knowledge of this critical barrier will be useful in order to optimize the design of the ternary hydrophilic matrix systems.