Dissolution kinetics for coprecipitates of indomethacin with polyvinylpyrrolidone.

Dissolution profiles of indomethacin/polyvinylpyrrolidone (PVP) coprecipitates (involving a crystallization process) were investigated kinetically by the dispersed amount and rotating disk methods in comparison with those of physical mixtures. The dissolution rate constant, kt, the rate constant of the crystallization process, kr, and saturated concentrations before and after the crystallization, CSM and CSO, were calculated from the dissolution data by a curve fitting procedure. The effects of the content and molecular weight of PVP in the coprecipitates on these dissolution parameters were also investigated in detail. It was found that increase of the content and the molecular weight of PVP correlated well with retardation of the crystallization process. In order to obtain desirable dissolution patterns, we attempted to estimate the optimum content of PVP in the coprecipitates by analysis of the dissolution parameters.