Drug release from w/o/w emulsions prepared with different chitosan salts and concomitant creaming up

Water-in-oil-in-water (w/o/w) emulsions containing chitosan and tryptophan in the inner aqueous phase were prepared. The acids used to dissolve chitosan were formic, acetic, butyric and lactic acids. The effects of these organic acids and pH of the inner aqueous phase on the release of tryptophan and on the separation of the aqueous phase due mainly to creaming up during storage were studied. When the inner aqueous phase was an acidic chitosan solution, the release rate was almost the same irrespective of the acids mentioned above. When acetic and butyric acids were neutralized with sodium hydroxide, the release of tryptophan was prolonged. However, it was enhanced again by an excess amount of sodium hydroxide. On the other hand, the release was enhanced after neutralization of formic and lactic acids. Separation of the aqueous phase from the w/o/w emulsion during storage was remarkably delayed after neutralizing the chitosan solution containing acetic or butyric acids, while not so much in the cases of formic and lactic acids. It is concluded that these w/o/w emulsions were stabilized in the presence of neutralized chitosan gel suspensions containing acetate or butyrate ions in the inner aqueous phase.