Marked Hypocalcemia after Tocolytic Magnesium Sulphate Therapy

ABSTRACT

Symptomatic hypocalcemia has been reported infrequently in association with magnesium sulfate (MgSO₄) tocolytic therapy. We report a 38-year-old woman who presented in preterm labor at 24 3/7 weeks. Twenty hours after starting MgSO₄, she developed chest pain. Studies revealed therapeutic serum Mg level, total serum calcium (Ca) = 5.5 mg/dL, 24-hour urine Ca = 763.9 mg, and low serum uric acid and phosphate levels. All studies corrected day 1 postpartum; urine Ca level corrected on day 2. Even short courses of MgSO₄ can result in severe hypocalcemia, raising the question of whether Ca levels should be routinely monitored.

Magnesium sulfate - tocolysis - asymptomatic hypocalcemia

REFERENCES

• 1 Koontz S L, Friedman S A, Schwartz M L. Symptomatic hypocalcemia after tocolytic therapy with magnesium sulfate and nifedipine.  Am J Obstet Gynecol. 2004;  190 1773-1776
• 2 Agus Z S, Wasserstein A, Goldfarb S. Disorders of calcium and magnesium homeostasis.  Am J Med. 1982;  72 473-488
• 3 Cholst I N, Steinberg S F, Tropper P J, Fox H E, Segre G V, Bilezikian J P. The influence of hypermagnesemia on serum calcium and parathyroid hormone levels in human subjects.  N Engl J Med. 1984;  310 1221-1225
• 4 Mayan H, Hourvitz A, Schiff E, Farfel Z. Symptomatic hypocalcaemia in hypermagnesaemia-induced hypoparathyroidism, during magnesium tocolytic therapy-possible involvement of the calcium-sensing receptor.  Nephrol Dial Transplant. 1999;  14 1764-1766
• 5 Smith L G, Burns P A, Schanler R J. Calcium homeostasis in pregnant women receiving long-term magnesium sulphate therapy for preterm labor.  Am J Obstet Gynecol. 1992;  167 45-51