FDA warns against prolonged use of magnesium sulfate to stop preterm labor

FDA advised healthcare professionals not to use magnesium sulfate injection for more than 5-7 days to stop preterm labor in pregnant women, according to a May 30 drug safety communication.

Such use of the drug is off-label, and may lead to low calcium levels and bone problems in a fetus, including osteopenia and bone fractures. Magnesium sulfate is approved to prevent seizures in preeclampsia and eclampsia.

The safety announcement did not specify the shortest duration of magnesium sulfate injection that results in harm to babies.

FDA found 18 case reports in its Adverse Events Reporting System describing skeletal abnormalities in neonates exposed in utero to magnesium sulfate. All had appeared in the medical literature. The magnesium was given to mothers for tocolysis in pregnancy. The average duration of utero exposure was 9.6 weeks and the average maternal dose was 3,700 g.

In those cases, neonates developed skeletal abnormalities and multiple fractures involving the ribs and long bones.

FDA is also adding new safety information to the drug label for Magnesium Sulfate Injection, USP 50%. That new information includes a warning that continuous administration of magnesium sulfate injection beyond 5-7 days to stop preterm labor can cause bone changes; a new Teratogenic Effects section; and a new labor and delivery section emphasizing that continuous use of magnesium sulfate injection to treat preterm labor is not approved.