Symptomatic hypocalcemia after tocolytic therapy with magnesium sulfate and nifedipine

In this study, we presented 2 cases and evaluated the evidence for symptomatic hypocalcemia after treatment with magnesium sulfate alone or combined with use of nifedipine.

Case reports, such as the one that follows, and literature review were used. A 25-year-old gravida presented at 33 weeks' gestation with advanced preterm labor. She received magnesium sulfate followed by nifedipine and experienced bilateral hand contractures 12 hours after discontinuation of magnesium sulfate. Total serum calcium was 5.4 mg/dL. A 35-year-old gravida presented at 26 weeks' gestation with ruptured membranes and received magnesium sulfate until it was discontinued prematurely because of pulmonary edema. Twenty hours later she experienced bilateral hand contractures; total serum calcium was 5.9 m/dL. Symptoms for both patients resolved with calcium gluconate therapy.

Hypocalcemia is a well-recognized complication of magnesium sulfate infusion. These are the fifth and sixth symptomatic case reports, as identified by Medline Search. Our first case is the only report in which the subsequent use of nifedipine may have been a factor. Little has been reported on the possible toxicity associated with the combined or sequential use of magnesium sulfate and nifedipine.

Marked hypocalcemia is clearly associated with magnesium sulfate infusion, is likely dose related, and may appear after discontinuation of magnesium sulfate therapy. Moreover, while the evidence for synergistic toxicity of magnesium sulfate and nifedipine is sparse, caution is advised when these agents are used together.