Stabilization of sulfamerazine suspensions by xanthan gum

Suspensions of sulfamerazine (10%) containing 0.2% docusate sodium were deflocculated because of repulsion between the negatively charged particles. Flocculation was induced by salts or by xanthan gum, which is anionic, in the presence of salts at concentrations below those at which salt flocculation resulted. The amount of gum necessary to produce a flocculated system was lower the higher the concentration of salt present. Calcium chloride and magnesium chloride were considerably more effective in this regard than sodium chloride. Gum flocculation produced aggregates with fewer particles and weaker bonding forces than did salt flocculation. The sedimentation rate of the suspensions decreased 5 to 10 times for each 0.1% increase in the gum concentration.