Urine composition in patients with urolithiasis during treatment with magnesium oxide.

Fifteen patients with recurrent renal stone formation were treated with 400 mg magnesium oxide daily. Urine composition was analyzed before the start of treatment and after 6-12 months. The urinary excretion of magnesium before and during treatment was 321 +/- 120 (mean +/- SD) and 409 +/- 140 mmol per mol creatinine respectively, a difference that was not statistically significant. Urinary calcium increased from 473 +/- 186 to 662 +/- 213 mmol per mol creatinine (p less than 0.05). All patients who increased their excretion of magnesium also increased the urinary output of calcium and, as a result of this, the calcium/magnesium-quotients were unaffected by the treatment. No significant effect was observed on urine oxalate excretion. Serum concentrations of calcium, magnesium and urate all remained at the pre-treatment level. From the results obtained in this study, magnesium oxide in this dosage cannot be recommended for use in treatment of patients with urolithiasis.