A pharmaceutical composition comprises a salt of a rare earth metal (S1) and at least one nontoxic counterion (C1). (S1) Is optionally hydrated. ACTIVITY : Nephrotropic； Uropathic. MECHANISM OF ACTION : Oxalate Absorption Inhibitor. Stock sodium oxalate solution (50 ml) containing sodium chloride (8.5 g/l) was adjusted to either pH 3 or pH 7. Prior to the addition of lanthanum carbonate, a 2 ml sample was taken as a zero time point sample. The volume of buffer was made up to 50 ml, pH was adjusted and lanthanum carbonate was added so that a concentration of 0.1 M was present in the 50 ml of either pH 3 or pH 7 phosphate/oxalate buffer. A timer was started and 2 ml samples were removed at pre-determined time intervals over twenty minutes and analyzed. A phosphorus assay was performed as given in Sigma procedure 670. The results indicated that even in the presence of 10-fold excess phosphate, lanthanum carbonate bind oxalate.
