The evaluation of novel mixed metal hydroxy-carbonates as phosphate binders: an in-vivo study in the rat

A number of novel phosphate binders based on mixed metal hydroxide structur es incorporating Fe and Ca, or Fe and Mg (classified as CT, Crosfield test compounds), were compared with the established phosphate binders Mg(OH)(2), Al(OH)(3), CaCO3 and a commercial hydrotalcite (Al- and Mg-based) using a rat model. The changes in urine and soluble faecal phosphate were used to e valuate efficacy of phosphate binding. The binders were mixed into a standa rd rat maintenance food at a concentration of 1 % (w/w). Four rats were use d for each binder study group and fed over 7 days. Urine and faeces were co llected (in a metabolic cage) over the last 24-h study period and the phosp hate content measured. The urinary phosphate was significantly reduced (P < 0.001) with CTFeCa (72 +/- 44 mum), CTFeMg (13 +/-4 mum). CT100 (26 +/- 11 pm), and Mg(OX), (65 +/- 53 mum), compared with control (766 +/- 188 mum), Al(OH)(3) (1256 +/- 279 mum), and CaCO3 (857 +/- 25 mum). The soluble phos phate content of the faeces was significantly reduced (P < 0.05) by up to 6 0% with CTFeCa, CTFeMg and Mg(OH)(2), and up to 40% with CT100 and Al(OH)(3 ), compared with 30% in controls and 10% with CaCO3. The new mixed metal hy droxy-carbonate compounds based on FeCa or FeMg are effective phosphate bin ders in-vivo and warrant further testing in patients.