Influence of preparation conditions on the properties of Eudragit microspheres produced by a double emulsion method

Abstract

AbstractThe aim of the present work was to study the preparation and characteristics of sustained‐release microspheres. As a model drug, sodium diclofenac was encapsulated in microspheres of the polymer Eudragit RS by using a double emulsion–solvent evaporation method. Investigations were carried out on the effects of the preparation method, the rate of the first step of emulsification, and the phase volume and composition (drug and additives) on the physical parameters of the product: its drug encapsulation, and the drug release. We evaluated the resulting microsphere structure [by differential scanning calorimetry (DSC)], the particle size, the surface area (by scanning electron microscopy), the entrapment and encapsulation efficiency (applying a novel method, energy‐dispersive x‐ray fluorescence analysis), the viscosity of the primary emulsion, and the organic solvent residue (by gas chromatography). We also evaluated and compared the samples by means of the kinetic data relating to drug release. The particle size could be decreased to one third by increasing the external aqueous phase ratio. In the first step of emulsification, elevation of the stirring rate led to microspheres with unfavorable characteristics. Increase of the active agent content and the plasticizer concentration had opposite effects. We applied a covalently not bound plasticizer, which was shown to influence the structure of the microspheres considerably. Drug Dev. Res. 64:41–54, 2005. © 2005 Wiley‐Liss, Inc.