Dissolution mechanism and rate of solid dispersion particles of nilvadipine with hydroxypropylmethylcellulose

The dissolution experiments on the solid dispersion particles of nilvadipine with hydroxypropylmethylcellulose were performed in stagnant and stirring water. The particles in stagnant water instantaneously gelatinized to the water content of 84.6% w/w after dipping and those dissolved very slowly through the penetration of water. However the particles in stirring water dissolved quickly at different rates depending on stirring rate, and both components in the solid dispersion dissolved at the same rate. Such experimental results seemed to suggest the important roles of erosion for gelatinized particles and mass transfer rate at the diffusion layer. The high concentrations of nilvadipine obtained after its nucleation and growth depend on complex formation. A new dissolution mechanism and rate equation were proposed on the basis of such experimental results and the availability of the rate equation was confirmed experimentally. (C) 1997 Elsevier Science B.V.