Determination of the percolation thresholds for polyethylene oxide and polyacrylic acid matrix tablets

Abstract

The purpose of this study was to implement the concepts of percolation theory in the characterization of drug release from hydrophilic matrix tablets. Percolation theory is a powerful statistical tool that enables mathematical insight into geometrically complex and disordered systems. Matrix tablets are effective substrate for the implementation of percolation theory because of their inherent disordered structure. The objective was to predict percolation thresholds of polyethylene oxide and polyacrylic polymers in diclofenac sodium hydrophilic matrices. Matrix tablets were prepared using polyethylene oxide or polyacrylic acid as matrix forming materials and diclofenac sodium was used as a model drug substance. Ten formulations with different drug/excipient ratios were prepared using the direct compression method. Dissolution studies were performed using the paddle apparatus method. For estimating percolation threshold the change of the kinetic parameters in aspect to the volumetric fraction of excipient plus initial porosity of the tablets was studied. Observed critical points with sudden changes in behavior of kinetic parameters can be attributed to the percolation thresholds. Percolation threshold is found to be 60.22% v/v polyethylene oxide + initial porosity and 39.94% v/v polyacrylic acid + initial porosity. The results obtained demonstrate that percolation theory can be used to design and develop matrix tablet formulations. Determination of percolation threshold is a useful tool for preparing robust formulations.