Tablet Erosion Under Heterogeneous Flow in USP Apparatus II

Background/Objectives: Although hydrodynamic heterogeneity in USP Apparatus II has been extensively studied, few experimental studies have examined how it affects the dosage form. This study investigated how paddle rotation speed, radial tablet position, and bottom-surface exposure affect dissolution and post-dissolution erosion patterns of paracetamol model tablets, and whether residual tablet shape provides complementary information on local hydrodynamic heterogeneity. Methods: Two paracetamol model tablet types were used: model tablets (MT) for visualization of post-dissolution shape by micro-computed tomography and photography, and MT with an embedded steel washer (SW-MT) for height measurements. SW-MT dissolution was tested at 25–75 rpm at 0D, 0.5D, and 1D positions, with and without bottom-surface coating, and evaluated using the fraction dissolved after 40 min (Q40), while height changes were quantified using erosion height loss (EH) and height asymmetry (AH). Computational fluid dynamics (CFD) results aided erosion-pattern interpretation. Results: Increasing paddle rotation speed increased dissolution and erosion extent, whereas radial displacement affected erosion distribution. At 0D, residual MT shapes were comparatively symmetrical, while 0.5D and 1D produced pronounced erosion patterns. Greater erosion extent did not correspond to greater asymmetry: for uncoated SW-MT at 75 rpm, EH increased from 36% at 0.5D to 40% at 1D, whereas AH decreased from 19% to 9%. Directional erosion in MT was consistent with spatial differences in velocity and predicted surface erosion rate from CFD. Conclusions: Post-dissolution tablet shape complements dissolution profiles by revealing the spatial distribution of material loss and may serve as a complementary approach to assessing local hydrodynamic heterogeneity in USP Apparatus II.