MATRIX OR MONOLITHIC systems

Matrix or monolithicsystems can be considered to date as the easiest and least expen-sive means of controlling drug release. The principle of these dosage forms is based on the uniform dispersion of the active ingredient in an inert solid polymeric excipi-ent. This excipient forms a skeleton in which the drug is trapped and released by ero-sion and/or diffusion. The aim of this work is to show the progress in the formulation of these dosage forms, their conception, design, and resulting biopharmaceutical properties. The first part is related to the classical matrix study according to the kind of excipient used. A more or less arbitrary classification can be considered: plastic, lipidic. and hydrophilic matrices. The various excipients used, the mechanisms allowing the drug to be released, and the formulation parameters influencing these dosage forms in in vitro/in vivo are also presented. The secondpart is dedicated to the new matrixsystems. Their technology and con-ception derive directly from the experience of the classical matrices and advances achieved in the study and the synthesis of the polymers. Among these new types of matrices, two types can be distinguished: those resulting from the combination of the matrix technology with the coating technics and those deriving from the association of various matrix excipients from different origins; the multiple unit matrices and the dosage forms presenting a well-defined physiological behavior associated with biopharmaceutical matrix properties