Comparative Evaluation of Floating and Non-Floating Controlled-release Metformin HCl Tablets: In vitro and In vivo Characterization

Objective: The present study aimed to comparatively evaluate floating and non-floating controlled-release formulations of Metformin HCl to understand the influence of formulation composition and processing variables on gastroretentive behavior, drug release characteristics, and pharmacokinetic performance. The study particularly focused on the role of rate-controlling polymer, binder grade, and granulation process in modulating formulation performance and bioavailability. Methodology: Floating gastroretentive tablets of Metformin HCl were developed using Eudragit NE 30D as the rate-controlling polymer and polyvinyl alcohol (PVA) as the granulating binder through a low-shear fluid bed granulation process. Both floating and non-floating controlled-release systems were formulated and optimized to assess the impact of binder grade and formulation parameters on tablet performance. The prepared formulations were evaluated for physicochemical properties, in vitro buoyancy behaviour, swelling index, matrix erosion, and dissolution profile. In addition, in vivo gastric retention and pharmacokinetic performance were assessed in healthy human volunteers. Results: The optimised floating formulation (MTH3) demonstrated rapid flotation within 20 seconds and sustained buoyancy for more than 16 hours. In contrast, the non-floating optimized formulation (MTH6) prepared with lower grades of PVA as a binder with the addition of controlled release polymer, maintained controlled drug release characteristics. Dissolution studies showed prolonged and near-complete drug release from both the formulations. Drug release kinetics for both the formulations followed the Higuchi model, indicating a combined diffusion and matrix erosion mechanism. Stability studies confirmed consistent dissolution similarity (f₂), demonstrating formulation robustness. In vivo pharmacokinetic evaluation revealed higher systemic exposure for the floating formulation compared with the non-floating system. The optimized floating tablets met bioequivalence criteria relative to the reference listed drug, at 90% confidence intervals for Cmax (87.60%–97.77%), AUC₀–t (84.95%–97.73%), and AUC₀–inf (85.17%–97.47%) were entirely contained within the predefined acceptance limits of 80–125%, whereas the non-floating formulation failed to achieve bioequivalence. Conclusions: The study demonstrates that formulation variables such as rate-controlling polymer selection, binder grade, and granulation conditions significantly influence the gastroretentive properties, drug release kinetics, and bioavailability of controlled-release Metformin HCl tablets. The optimised floating system provided improved gastric retention and enhanced systemic exposure, successfully achieving bioequivalence with the reference product, highlighting its potential as an effective gastroretentive controlled-release formulation.