Polyacrylate (Eudragit Retard) Microspheres for Oral Controlled Release of Nifedipine. I. Formulation Design and Process Optimization

Abstract

Nifedipine was incorporated in polyacrylate-polymethacrylate microspheres using the solvent evaporation process. Optimal experimental conditions were found for the production of large batches of nifedipine microspheres based on Eudragit polymers the amount of which ranged from 25 to 40g. It was noted that the microspheres were net quite spherical and some of them especially the large microspheres, collapsed and lost their spherical shape due to the existence of internal void volume as evidenced by SEM examination of fractured nifedipine microspheres. It appeared that the experimental conditions used in the present study favoured the formation of microspheres of a new type. They could be defined as “film type” microspheres which consisted of spherical micromatrices comprizing an internal void space and a polymeric membrane of variable thickness where the nifedipine was dispersed either in a molecular or solid state depending on the payload extent. This was confirmed by differential scanning calorimetry analysis and scanning electron microscopy which detected drug crystals embedded on the microsphere surfaces at high drug content.