Rice Bran Wax-Based Matrix Tablets for Sustained Release of Diclofenac Sodium: Effects of Processing and Sintering

Background/Objectives: Rice bran wax (RBW), a natural hydrophobic byproduct of rice bran oil refining, was evaluated as a lipid matrix former for the sustained oral delivery of diclofenac sodium (DFS). Methods: Matrix tablets containing 100 mg DFS and 45–60% (w/w) RBW, corresponding to 180–240 mg RBW per 400 mg tablet, were prepared using five techniques: simple mixing, dry granulation, extrusion–spheronization, partial melt granulation, and melt granulation. These techniques were selected to represent progressively different thermal, mechanical, and solvent-processing histories, ranging from simple physical blending to high-shear wet processing and extensive distribution of molten wax. Results: Processing method, wax concentration, and thermal sintering significantly influenced matrix structure and drug release. Scanning electron microscopy of the processed powders and granules indicated that melt granulation produced more extensively integrated wax-containing structures, although the internal continuity of the tablet matrix was not directly examined. FTIR and DSC analyses showed no evidence of major drug–excipient interactions and confirmed the retention of a detectable RBW melting transition. Melt granulation produced the greatest release retardation, followed by partial melt granulation, while extrusion–spheronization and dry granulation showed broadly similar release-retarding performance, and simple mixing was the least effective. The optimized formulation, containing 55% (w/w) RBW, prepared by melt granulation and sintered at 80 °C for 2 h, showed sustained release consistent with diffusion through the hydrophobic matrix. It met the dissolution limits specified in the USP–NF monograph for Diclofenac Sodium Extended-Release Tablets and showed a dissolution profile that was broadly comparable to that of the commercial reference product based on descriptive profile analysis. During a preliminary 4-week accelerated stability study, no statistically significant changes were observed in the physicochemical properties subjected to inferential analysis, while friability remained below 1%. The 55MG2 formulation also retained a broadly comparable dissolution profile, although a modest increase in drug release was observed. Conclusions: These findings support the potential of RBW as a natural lipid excipient for controlled oral drug delivery.