The development and in-vitro evaluation of novel mixed metal hydroxy-carbonate compounds as phosphate binders

The currently available phosphate binders are relatively inefficient and su ffer from clinical side-effects of increased absorption of calcium and alum inium and the diarrhoea-inducing effects of magnesium. A new class of compo unds based on mixed metal hydroxides has been developed and evaluated for t heir potential as phosphate binders. The mixed metal hydroxides were prepar ed using a standard procedure for hydrotalcite (Al2Mg6 (OH)(16). CO3.4H(2)O ) by substituting Fe3+ for Al3+ with Mg2+ or Ca2+ as the divalent metal ion . Phosphate precipitation (binding) was examined at different pH values in aqueous solution and in various food mixtures in comparison with hydrotalci te, Al(OH)(3), CaCO3 and Mg(OH)(2) on the same weight-to-weight basis. A se ries of compounds with differing ratios of metal ions (Fe:Mg/Ca 1:2 or 1:3) gave analytically similar ratios to those predicted from the initial amoun ts added. CTFeCa bound > 90 % phosphate in aqueous solution compared with 6 5 % binding with CTFeMg, 85 % binding with MS(OH),, and less than 30 % bind ing for CaCO3 and Al(OH)(3). The mixed metal compounds also bound up to 80 % phosphate in various food matrices, which was relatively independent of c hanges in pH, compared with MS(OH),, where binding decreased from 85% at pH 3.0 to 25% at pH 8.0, Al(OH)(3) and CaCO3 were relatively ineffective phos phate binders under all the conditions tested. The mixed metal hydroxides c ompounds show considerable promise as phosphate binders over those currentl y available and warrant further patient-based in-vivo testing.