Phosphate binding gels: balancing phosphate adsorption and aluminum toxicity

The phosphate binding capacity of five commercial aluminum hydroxide phosphate-binding gels and two crystalline forms of aluminum hydroxide was studied by an in vitro procedure which simulated passage through the stomach to the small intestine. The potential for aluminum toxicity was estimated by determining the fraction of the dose which was converted into soluble aluminum species by acid neutralization at pH 3, 37 degrees C. The commercial products varied widely both in phosphate binding capacity and production of soluble aluminum species. The evidence suggests that the ideal phosphate binder will have a surface area small enough to minimize the formation of soluble aluminum species during the gastric residence time but also large enough to adsorb a clinically significant amount of phosphate.