Amorphous Iron (III) Hydroxide as Phosphate-binding Agent fnr Oral Administration

Abstract

Effective and safety phosphate binding agent for oral administration is desired for patients of renal failure. The feasibility of amorphous iron (III) hydroxide as the agent was investigated in vitro, because the toxicity of iron (III) hydroxide and Fe³⁺ ion is lower than that of Al³⁺. Amorphous iron (III )hydroxide showed large phosphate binding capacity per gram (PBC) in a wide pH range (1.5-8). In the presence of phosphate, amorphous iron (III) hydroxide was dissolved little at pH 2 corresponding to the pH value in stomach. It was considered that phosphate ions were bound to the amorphous iron (III) parti cles by ligand exchange with OH^- on the surface of particles under weakly acidic conditions, and that phosphate ion was precipitated as amorphous iron (III) phosphate under strongly acidic conditions, where iron (III) hydroxide is not stable. The molar ratio of (bound phosphate/Fe in the agent) was able to increase by controlling the composition of iron (III) hydroxide and cellulose, even though PBC decreased.