ABSTRACT:
Development of oral controlled release tablets for highly water-soluble drugs with the maintenance of a predetermined constant drug release rate has always been a challenge to pharmaceutical technologist. The variety of versatile controlled release layered matrix system have been reported to achieve zero-order or near zero-order release profiles with each individual layer of the matrix possibly exhibiting a different release mechanism for example, first layer swellable, second layer erodible, and third disintegrating. Simply by changing the position of layers strategically it is possible to modify the drug release kinetics. Introduction of barrier-inert layers (either hydrophobic or hydrophilic) on both faces of tablet is one of the smart techniques to modulate the drug release of conventional matrix tablets. Barrier layers keep the core layer away from its interaction with dissolution medium; as a result release rate retarded due to an increase in diffusional resistance and/or a decrease in effective area at the diffusion front. By the continuous diffusion of drug from core layer to barrier layer diffusional length is increased, improving the probability of continuous constant rate release. Current article focuses on design and development of such multi-layered devices and their industrial applicability by replacing earlier used different geometries and diverse coated systems for controlled release formulations.