Due to their simple and low-cost manufacturing process, matrix tablets are pharmaceutical dosage forms most widely used for the formulation of oral controlled release of drugs (1). These systems involve dispersion of one or more drugs in a support structure, which in the majority of the cases is of polymeric nature.Inert matrices are systems that consist of a polymeric porous solid network, which is insoluble and indigestible in the gastrointestinal tract (2). Drug release from these dosage forms occurs by drug diffusion through the pores of the matrices, including the initial pores and the pores that appear when the drug or soluble excipients have been dissolved (3).Ethylcellulose is a water insoluble polymer that has been used in the manufacturing of different solid oral dosage forms. It is used in the preparation of microcapsules and microspheres, as a barrier membrane in reservoirs, and as inert matrix-former for oral Percolation theory has been applied to study the drug release behaviour in multicomponent inert matrices containing ethylcellulose as a matrix forming polymer. Global influence of major formulation factors such as polymer viscosity, polymer particle size, drug and filler solubility and porosity of the tablets in drug release kinetics has been studied for the first time. Batches containing three viscosity grades of Ethocel™, microcrystalline cellulose (MCC) and lactose as fillers, a lubricant and flow aid mixture and three drugs with different solubility have been manufactured. For some batches, compression pressure was varied in order to obtain matrices with five levels of initial porosity. The behaviour of inert matrices was explained based on the percolation ranges of the main components of the formulation. The effect of the porosity percolation threshold was observed and the existence of a tricoherent drug-polymer-filler system is hypothesized.
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