influence of certain additives and preparative conditions on surface adhesion of ethylcellulose microcapsules containing isoniazid

ABSTRACT

The microcapsules described in this study were prepared by the phase separation technique induced by the addition of nonsolvent. The obtained results revealed that despite of the vigorous stirring, this procedure is not suitable for forming coacervate droplets and the formation of small or perfect microcapsules becomes unreproducible due to surface adhesion during the tacky stage of the microcapsule formation. The microcapsules that resulted consisted of aggregates and not individual entities. To lessen the tendency to surface adhesion between these coacervate droplets, different amounts of cholesterol [CH], Polyisobutylene [PIB] and talc were used as additives to help in the preparation of fine or individual microcapsules. The addition of cholesterol or polyisobutylene was found to reduce the aggregation of the formed microcapsules, while talc did not show any significant effect. The formation of aggregated microcapsules were also minimized by choosing the appropriate core wall ratio, stirring speed, solvent, initial core size and method of preparation. The emulsion-induction technique used for the preparation of microcapsules allowed the optimal formation of coacervate droplets and produced fine microcapsules. Microcapsules prepared by the emulsion induction technique showed smaller mean particle diameter [200 micro. m] in comparison to that prepared by the conventional method of preparation [501 microm]. Microcapsules prepared in the presence of cholesterol showed a narrow particle size distribution curves. These microcapsules were subjected to dissolution studies. The obtained results showed that the drug release was prolonged and the presence of cholesterol also delayed the drug release. For all the microcapsules studied, drug release occurs by a diffusion controlled process as described by Higuchi for the release of drug from insoluble matrix