The effect of oral administration of magnesium oxide on the crystallization in urine of calcium oxalate and brushite was determined in 4 cases of recurrent calcium nephrolithiasis. Each patient was evaluated while on a constant metabolic diet before, during and after therapy with magnesium (1,000 mg. magnesium as magnesium oxide per day). During magnesium therapy urinary hydrogen ion concentration increased by approximately 0.5 unit in all 4 patients and urinary calcium increased about 50 mg per day in 2. Urinary oxalate decreased significantly in 1 patient and urinary phosphorus was reduced in 2. The urinary activity product ratio of brushite (state of saturation) increased, owing largely to the rise in urinary hydrogen ion concentration but that of calcium oxalate was not changed significantly by magnesium treatment. Although urinary magnesium increased significantly there was no significant change in the urinary formation product ratio (limit of metastability) or the rate of crystal growth of brushite or calcium oxalate. Thus, no beneficial effect of magnesium therapy could be demonstrated in this short-term study.
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