Patent ID: 7618656

Claim:
A method of treating hyperphosphatemia in a subject comprising: (i) obtaining a crude lanthanum carbonate composition comprising lanthanum carbonate having the formula La 2 (CO 3 ) 3 .xH 2 O wherein x has a value from 3 to 6 and lanthanum hydroxy carbonate; (ii) subjecting the crude lanthanum carbonate to a purity assay comprising the steps: (a) obtaining an X-ray diffraction pattern of the crude lanthanum carbonate composition; (b) obtaining a plurality of reference samples containing the lanthanum hydroxy carbonate; (c) obtaining a plurality of X-ray diffraction patterns of the reference samples; and (d) performing Rietveld analysis on the X-ray diffraction patterns to obtain: the detection limit, minimum quantitation limit (MQL), and/or upper analytical limit from the reference samples and the predicted impurity concentration value from the crude lanthanum carbonate composition pattern, and (iii) when the lanthanum carbonate composition contains no more than 0.55% lanthanum hydroxycarbonate form (I) or no more than 0.29% lanthanum hydroxycarbonate form (II) according to the assay of (ii), administering to said subject an amount of the lanthanum carbonate composition effective to treat said hyperphosphatemia.