INFLUENCE OF MAGNESIUM-SULFATE TOCOLYSIS ON CALCIUM-METABOLISM

Objective: Our objective was to clarify the short-term and long-term effects of magnesium sulfate treatment on calcium homeostasis. Methods: Serum levels of magnesium, ionized calcium, and calcium-regulating hormones and the urinary excretion of magnesium and calcium were measured serially over 72 h in 10 pConclusion: The increase of 1,25-dihydroxyvitamin D-3 in response to hypocalcemia in the setting of hypermagnesemia does not compensate fully for the increasing urinary calcium loss or for the suppressive effects of hypermagnesemia on parathyroid hormone secretion, regnant women who were receiving intravenous magnesium sulfate for the suppression of preterm labor. Results: After the administration of magnesium sulfate, serum magnesium levels rose rapidly (P < 0.01) after 1 h and remained elevated for more than 72 h. The changes of urinary magnesium/creatinine ratios and calcium/creatinine ratios were parallel to those of serum magnesium levels. Serum ionized calcium levels fell gradually to the hypocalcemic range at 6 fi (P < 0.01), The decrease in parathyroid hormone levels preceded the maximum reduction in serum ionized calcium levels by 5 h (P < 0.01) and thereafter returned toward base level after 6 h. Levels of 1,25-dihydroxyvitamin D-3 increased significantly at 12 h (P < 0.05), There was no significant change in serum calcitonin level. Conclusion: The increase of 1,25-dihydroxyvitamin D-3 in response to hypocalcemia in the setting of hypermagnesemia does not compensate fully for the increasing urinary calcium loss or for the suppressive effects of hypermagnesemia on parathyroid hormone secretion.