Development of sustained-release oral tablets using xanthan and tragacanth gums as release modifiers

Hydrophilic matrix systems are widely used to regulate drug release from oral dosage forms and remain one of the most established approaches for achieving sustained drug delivery. However, despite growing interest in natural polysaccharides as matrix-forming excipients, their comparative release performance and mechanisms governing drug release remain insufficiently understood. This study evaluates xanthan gum (XG) and tragacanth gum (TG) as natural hydrophilic matrix-forming excipients in tablets prepared by direct compression at various polymer loadings. Caffeine, ibuprofen, and 5-aminosalicylic acid were selected as model drugs representing BCS Classes I, II, and IV, respectively, to assess the effects of polymer type, concentration, and drug solubility on release behaviour. Drug release was characterized using dissolution testing, kinetic modeling, and complementary gel-layer, swelling, and erosion analyses to elucidate the dominant release mechanisms. Both polymers enabled controlled release, but their performance depended strongly on hydration behaviour and gel structure. XG matrices exhibited rapid hydration and extensive swelling, forming thick, highly hydrated gel layers that promoted faster drug diffusion. Effective release control required polymer loadings of at least 25%, whereas lower concentrations led to rapid disintegration and burst release. In contrast, TG formed thinner but more cohesive gel structures, attributed to its dual-phase composition, which provided a stronger diffusion barrier and sustained release even at polymer loadings as low as 5%. Korsmeyer-Peppas modeling revealed distinct release mechanisms for the two polymers: XG exhibited predominantly diffusion-controlled release at moderate loadings and anomalous transport at higher concentrations, whereas TG showed anomalous transport across a broader composition range. Blending these gums with other polysaccharides further improved release; however, TG-containing formulations consistently showed superior performance, providing more sustained and uniform drug release than XG-based systems. Overall, TG outperformed XG by achieving prolonged and uniform drug release at substantially lower polymer content. The balanced contributions of diffusion, matrix swelling, and relaxation in TG systems enabled effective release control even at low polymer concentrations and in blended polysaccharide matrices. These findings identify TG as a highly efficient natural matrix-forming excipient and provide mechanistic insight into the design of hydrophilic matrix tablets for controlled oral drug delivery.