Spherical solid dispersion containing amorphous tolbutamide embedded in enteric coating polymers or colloidal silica prepared by spray-drying technique.

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Abstract
Spherical solid dispersion particles of tolbutamide were prepared by spray-drying a diluted ammonia solution of the drug with additives. Enteric coating polymers (Eudragit L100-55, hydroxypropyl methylcellulose phthalate) and colloidal silica (Aerosil) were useful as additives for the solid dispersions. Most of the tolbutamide was dispersed in the amorphous state in the solid dispersion particles when the drug and the additive were formulated in the ratio of 1 : 1. It was a characteristic of the spray-dried solid dispersions that the additive content was smaller than that of dispersions prepared by conventional solvent evaporation or by a grinding method. The drug dissolution in vitro was investigated using the disintegration solution No. 2 (pH 6.8) specified in JPX. The dissolution rate from the solid dispersions was markedly improved compared with that from the original or spray-dried drug powder. The rapid dissolution rate from the solid dispersion with enteric coating polymers was attributed to improved wettability and rapid dissolution of the polymer, while that from the dispersion with colloidal silica was found to have a close relationship with the drug crystallinity as well as the wettability.