Formulation, Evaluation and Optimization of Metformin Hydrochloride 500 mg Sustained-Release Tablets Using a Quality-By-Design Approach: A Comprehensive Review

Metformin hydrochloride is a first-line oral antihyperglycemic agent widely used for the management of type 2 diabetes mellitus. Despite its therapeutic effectiveness, its high aqueous solubility, relatively limited membrane permeability, dose-related gastrointestinal effects and restricted intestinal absorption window can complicate the development of prolonged-release oral formulations. Sustained-release (SR) matrix tablets provide a rational strategy for controlling drug release, reducing dosing frequency, improving dosing convenience and maintaining more consistent systemic exposure. This review presents a Quality-by-Design (QbD)-oriented framework for the formulation, evaluation and optimization of 500-mg metformin hydrochloride SR matrix tablets. The framework incorporates the Quality Target Product Profile (QTPP), Critical Quality Attributes (CQAs), Critical Material Attributes (CMAs), Critical Process Parameters (CPPs), risk assessment, Design of Experiments (DoE), formulation optimization and lifecycle control. Particular emphasis is placed on hydrophilic matrix systems containing hydroxypropyl methylcellulose (HPMC), together with the roles of hydrophobic and natural polymers and functional excipients. Key formulation and process variables, including polymer concentration, viscosity grade, drug-to-polymer ratio, compression force, porosity and manufacturing conditions, are considered in relation to matrix hydration, gel formation, diffusion, erosion and drug-release behavior. Evaluation includes pre-formulation, powder properties, tablet quality, assay, content uniformity, compatibility, swelling, dissolution, release kinetics and stability. Emerging tools such as process analytical technology, physiologically based biopharmaceutic modeling, artificial intelligence, machine learning and continuous manufacturing may further enhance predictive development, robustness, scalability, and lifecycle control of metformin SR tablets. Keywords: Metformin Hydrochloride; Sustained-Release Tablets; Quality By Design; Design Of Experiments; Matrix Tablets.