Using the percolation theory to explain the release behavior from inert matrix systems

A novel analysis of drug release process from binary matrix systems has been realized and a study of the initial stage of the process has been carried out. A fast and easy technique has allowed the acquisition of one experimental datum per second. Release data have been analyzed by means of a detailed statistical study. The dissolution profiles were studied applying different kinetic models (zero order, logarithmic, and Higuchi equation). In all the cases studied, a starting process of Zero or first order, indicative of a surface-dependent mechanism, has been found. Then, a parameter, named as critical time of kinetic change (t(c)), has enabled the authors to establish the instant at which a diffusion release mechanism, according to Higuchi equation, is consolidated. From this time until the end of the process, release mechanism of matrices was shown to be diffusion controlled. The influence of the drug loading and the particle size over the release properties of tablets has also been investigated and it has been evaluated on the basis of percolation theory. The results show a major significance of particle size over the initial drug release and a decrease of its influence along the time. On the other hand, the drug loading variable shows an important influence over the release properties along the whole process.