Marked hypocalcemia after tocolytic magnesium sulphate therapy

Symptomatic hypocalcemia has been reported infrequently in association with magnesium sulfate (MgSO (4)) tocolytic therapy. We report a 38-year-old woman who presented in preterm labor at 24 3/7 weeks. Twenty hours after starting MgSO (4), 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 MgSO (4) can result in severe hypocalcemia, raising the question of whether Ca levels should be routinely monitored.