Mamas on Bedrest: Magnesium Sulfate and Your Baby’s Bones

May 31st, 2013

Magnesium Sulfate has long been used in obstetrics to prevent seizures associated with pre-eclampsia, eclampsia, pregnancy induced hypertension and preterm labor. On May 30, 2013, the United States Food and Drug Administration issued a drug safety alert stating that clinicians should not prescribe Magnesium Sulfate for seizure prevention during pregnancy for more than 5-7 days because of the risk of low calcium and bone abnormalities in the fetus.

Magnesium Sulfate has been used for decades “off label ” (not for its originally FDA approved indication) for the prevention of preterm labor and the prevention of seizures caused by markedly increased blood pressure as seen in pre-eclampsia and eclampsia. It was first prescribed in Germany in 1906 to prevent seizures associated with eclampsia and was injected into the intrathecal cavity (at the base of the spine). In 1926 it was prescribed intra-muscularly and in  1933, the IV form of “Mag Sulfate” became available.

As recently as February 2013, researchers published a study touting the benefits of Magnesium Sulfate and saying that there were no appreciable side effects. Upon close scrutiny of  the article, one clearly sees that this particular study only addressed potential side effects to the mother. This study, like many others, completely ignored the potential harm to the developing fetus, assuming that if  magnesium sulfate is in fact safe for mamas it is safe for babies. This simply isn’t the case.

In response to 18 adverse drug reports submitted to the Safety Information and Adverse Event Reporting system, the FDA conducted its own research to see why some mothers had problems and some did not.  Babies born to these 18 women all had osteopenia (low bone mass density) and were at greater risk of sustaining fractures. The average amount of time the mamas received Magnesium sulfate was over a 10 weeks.  The FDA found that the maximum time that a mamas should take Magnesium Sulfate is a mere 5-7 days and then the FDA recommends stopping the medication. The prolonged administration of Magnesium Sulfate led to the side effects, which seem to resolve once Magnesium Sulfate is stopped.

This MedScape News Report has a couple of really good take home messages. First and foremost, clinicians must closely monitor Magnesium Sulfate administration and ensure that mamas understand that the drug is being used off label, has the potential to affect their unborn babies’ bones and that they have the right to say “no”. Second, we health care researchers have to be careful when reading studies lest we draw false conclusions and inform the public that there is no harm when there is or there is harm when there is not.


MedScape News

Jeffrey Michael Smith, Richard F Lowe, Judith Fullerton, Sheena M Currie, Laura Harris and Erica Felker-Kantor

An integrative review of the side effects related to the use of magnesium sulfate for pre-eclampsia and eclampsia management.  BMC Pregnancy Childbirth, May 2013

The US Food and Drug Administration-Safety Alerts for Human Medical Products.

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