Gel Strength of Hydrophilic Matrix Tablets in Terms of In Vitro Robustness

PURPOSE: The purpose of this study was to correlate the gel strength of swollen matrix tablets with their in vitro robustness against agitation intensity and applied mechanical forces. Five commercial products, i.e. Glucophage®, Alfuzosin®, Tromphyllin®, Preductal® MR and Quetiapin® formulated as water-soluble/erodible matrix tablets were investigated. METHODS: Effect of agitation speed (50–150 rpm) on drug release, hydration/erosion and gel strength was investigated using USP paddle apparatus II. The gel strength of matrix tablets during dissolution at different conditions was characterized by a texture analyzer. RESULTS: Commercial tablets formulated with HPMC of higher viscosity, such as K15M or K100M, demonstrated the gel strength in swollen state >0.02 MPa. In this case, the release mechanism was predominantly diffusional and, therefore, not affected by stirring speed and mechanical stress. In contrast, the Quetiapin® matrix tablet, formulated with HPMC K 4 M in amount of approx. 25%, demonstrated the gel strength dropped below 0.02 MPa after 6 h of release. In this case, the drug was predominantly released via erosional mechanism and very susceptible to stirring speed. CONCLUSION: Sufficient gel strength of swollen tablets is an important prerequisite for unchanged in vitro performance in consideration of mechanical stress.