Studies on different dissolution models. IV. Erosion of tablets.

A comparative study of the action of erosion on non disintegrating theophylline tablets was performed in the three USP XX dissolution models, the rotating basket, the paddle and the modified disintegration apparatus, as well as in a new (sandwich) model. The results show erosion to be dependent on the mechanical strength of the tablets and to be promoted by the phenomenon of softening of the tablets during the process of dissolution. A considerable and moderate erosion was found for 'soft' tablets in the rotating basket and disintegration apparatus, respectively, whereas no or only slight erosion was observed in the paddle and sandwich models. The phenomenon of dissolution intensified erosion and erosion intensified dissolution is shown to affect the description of the release profiles. The dissolution profiles of the 'hard' tablets in the models preferred to be described by the square root equation, whereas the profiles of the 'soft' tablets in the case of erosion showed a tendency to a better fit with the cube root of mass versus time relation.