**4.9 Sustained release applications**

Recently, MCC has been widely used in the formulation of multiparticulate and matrix tablet dosage forms for sustained release drug delivery system. In general, hydrophilic polymers in matrix tablet formulation are included to form a viscous, gelling layer which can retard water penetration and acts as a barrier to drug release. Drug release is accomplished by diffusion through the gel layer and at the same time through erosion of this layer. Some studies proved that zero-order release profiles can be achieved by selection of appropriate polymers in addition of Avicel as fillers/ binders.
