Percolation thresholds in ultrasound compacted tablets

Twenty matrix systems with different KCl content las drug model, from 10 to 90% w/w) and Eudragit(R) RS-PM las inert excipient) were prepared using an ultrasound-assisted press and a traditional eccentric machine. The release behavior from both types of matrices was examined; the kinetic parameters for the release (intrinsic dissolution) and the technological properties of the final tablets (total porosity) were used to estimate the percolation t hreshold for the drug model and the excipient in both systems. For the syst ems compacted by ultrasound (US) the estimated value for the excipient perc olation threshold ranges from 13.4 to 20.2% v/v (lower than that found for traditional tablets), that agrees with a continuum percolation model sugges ting the presence of a continuum phase inside the tablet. This depends on a thermoplastic deformation of Eudragit(R) RS-PM under ultrasound, that dest royed the particulate system of the excipient and transform it into a conti nuum medium. The percolation threshold for KCl ranged from 58.6 to 61.0% v/ v for US and from 26.7 to 42.2% V/V for the traditional tablets. The higher value for ultrasound compacted tablets can be explained by the difficulty of KCI to outcome from a matrix containing insoluble phase that surrounds K Cl crystals. (C) 2000 Elsevier Science B.V. All rights reserved.