Testing the applicability of classical diffusional models to polydisperse systems

Abstract The purpose of this work is the study of the applicability of the classical dissolution models to a suspension of multisized particles. The dissolution profiles were obtained with the Coulter Multisizer, using three microsieved fractions of indomethacin (5–15, 15–25 and 25–35 μm). This instrument enables the dissolution process to be followed with regard to size, size distribution and number of the undissolved particles, as a function of time. This information is crucial for the discussion of the model-associated assumptions. It was concluded that most of the premises on which the models are based are not valid for the present experimental conditions. An alternative model was then proposed which takes into account the polydisperse nature of the particles and their number variation throughout dissolution. A remarkably good agreement was achieved between the simulated and the experimental profiles, indicating that the methodology adopted here is most suitable for the study of multiparticulate polydisperse systems.