Formulation and In-Vitro Evaluation of Diclofenac Sodium Sustained Release Matrix Tablets Using Chitosan as a Natural Polymer : A Comprehensive Review

Abstract

Oral drug delivery remains the most preferred route of administration due to its convenience, cost-effectiveness, and high patient compliance. Conventional immediate-release (IR) formulations, however, suffer from a characteristic 'peak-and-valley' plasma concentration profile, leading to toxicity during peak phases and subtherapeutic effects during trough phases. Sustained-release (SR) tablet technology offers a viable solution by controlling the rate of drug release to maintain therapeutic plasma concentrations over an extended period, thereby reducing dosing frequency and improving patient outcomes.
Natural polymers have gained considerable attention as matrix-forming agents in SR tablet development due to their biocompatibility, biodegradability, low cost, and widespread availability. Chitosan, a deacetylated derivative of chitin, is one of the most extensively investigated natural polymers in this regard. Its unique properties — including mucoadhesion, pH-dependent swelling, hydrogel formation, and cationic character — make it particularly suited for controlled oral drug delivery.
This review comprehensively discusses the pathophysiology of sustained-release systems, classification of matrix tablets, the physicochemical and biopharmaceutical properties of chitosan, formulation strategies for SR tablets using natural polymers, evaluation methods (preformulation, in vitro dissolution, and kinetic modelling), and recent advances in natural polymer-based SR formulations. Diclofenac sodium — a model NSAID with a short half-life and significant gastric adverse effects — is used as a case study throughout this review to illustrate the formulation and evaluation aspects.

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