The American College of Obstetricians and Gynecologists and the Society for Maternal-Fetal Medicine continue to support the use of magnesium sulfate injection during pregnancy in limited circumstances and for short periods of time, despite a warning from the Food and Drug Administration that the drug has the potential to harm a developing fetus.
In 2013, the Food and Drug Administration issued a safety announcement warning against the prolonged use of intravenous magnesium sulfate (beyond 5-7 days) to treat preterm labor, citing risks of bone changes and low calcium levels in the developing fetus. Agency officials also changed the Pregnancy category classification for magnesium sulfate from a category A to a category D.
The FDA announcement highlighted that although use of magnesium sulfate for preterm labor longer than 5-7 days was considered “off label,” it is approved for the treatment of preeclampsia.
But in a committee opinion issued on Dec. 22, ACOG and the Society for Maternal-Fetal Medicine (SMFM) pointed out that the FDA changes were prompted by reports of fractures and bone demineralization after magnesium sulfate treatment for “a much longer duration and much higher dose than is currently recommended for obstetric use.” In the cases cited by the FDA, average exposure was 9.6 weeks with an average total maternal dose of 3,700 g, according to the committee opinion (Obstet Gynecol. 2016;127:e52-3.).
Magnesium sulfate has been used and studied in obstetrics for many years without concerns for fractures or bone demineralization being raised, including in recent trials of magnesium for neuroprotection, ACOG and SMFM officials wrote.
The updated committee opinion outlines the continued short-term (less than 48 hours) use of magnesium sulfate for certain conditions:
• Prevention and treatment of seizures in women with preeclampsia or eclampsia.
• Preterm labor at less than 32 weeks’ gestation for fetal neuroprotection.
• Prolonging pregnancy for up to 48 hours to allow for administration of antenatal corticosteroids in women at risk for preterm delivery within 7 days.
“Practitioners should not stop using magnesium sulfate for these indications based on the FDA reclassification,” ACOG and SMFM committee members wrote. “In all of these conditions, prolonged use of magnesium sulfate is never indicated. Therefore, the FDA’s change in the pregnancy classification of magnesium sulfate addresses an unindicated and nonstandard use of this medication.”
