Different Mg to Fe Ratios in the Mixed Metal MgFe Hydroxy-Carbonate Compounds and the Effect on Phosphate Binding Compared With Established Phosphate Binders

Due to the side effects of the current oral phosphate binders, there is a need for effective alternatives. A number of mixed metal hydroxy‐carbonate compounds (MMHCs) based on Mg and Fe have recently been established as effective phosphate binders. We have now carried out further studies on the MMHCs with different ratios of Mg2+:Fe3+ in different forms to assess for phosphate binding efficacy and ionic release in aqueous solution and food slurries. The compounds that provide the most promise are those with Mg2+:Fe3+ ratios of 2:1 and 4:1 in the unaged/dry form. Their phosphate binding efficacy was compared with a wide range of established phosphate binders, such as aluminum hydroxide [Al(OH)3], calcium carbonate (CaCO3), calcium acetate (CaAc2), magnesium hydroxide [Mg(OH)2], and lanthanum carbonate [La2(CO3)3] in various food slurries. The results showed that the MgFe compounds were much more effective (on a weight for weight basis) than the established binders, and their properties were relatively pH independent. Calcium compounds (CaCO3 and CaAc2) were ineffective under the experimental conditions. Mg(OH)2 was effective at low pH but not at pHs greater than 5.0, and also released two‐ to threefold more magnesium than the MgFe compounds. Al(OH)3 showed some degree of efficacy, but the binding capacity was, at best, less than 50% of the MMHCs. La2(CO3)3 required at least a 10‐fold increase in weight to give comparable binding to the MMHCs. In conclusion, MgFe hydroxy‐carbonate compounds are effective phosphate binders and may provide a better alternative to both existing and emerging binders for combating hyperphosphataemia. © 2002 Wiley‐Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 91:53–66, 2002