I remember when my wife, in labor with our firstborn, had to take magnesium sulfate to prevent preecamplesia-related seizures. She had the baby, and mother and baby were fine, if sluggish for a day or two.
So I paid attention to recent headlines that said the FDA had curtailed the use of magnesium because it may weaken a developing baby's bones. Had my wife and newborn been given a dangerous drug? When I read the article carefully, I learned that it wasn't so.
The real concern is that people might, after a cursory read of the headlines, be less willing to get a short-term prescription for magnesium, a vital tool in managing pregnancies, said Joseph Biggio Jr., M.D., director of Division of Maternal and Fetal Medicine within the UAB Department of Obstetrics & Gynecology.
In most cases, he said, magnesium is used for just a few hours or days in women who develop preeclampsia, a form of pregnancy-related high blood pressure that can lead to seizures. Magnesium is much more effective than any other anti-seizure medications for this use, said Dr. Biggio.
Last week’s FDA advisory concerned instead a second, less common use of magnesium, where things are not so clear cut. In some cases, physicians have administered the drug continiously for a few months in hopes of delaying otherwise premature births (before 32 weeks gestation).
Recent data suggests that magnesium might protect the brains of potentially premature babies from cerebral palsy. That finding, and the lack of good drugs for the delay of preterm labor, may have encouraged more doctors to use magnesium sulfate for longer periods, said Dr. Biggio. The new FDA advisory is meant to curb attempts to stretch the boundaries of the drug’s traditional, short-term use.
The theory on how magnesium might delay labor proceeds from its similarity to calcium, which muscle cells rely on to contract. If magnesium has slipped into muscle cells in place of calcium, they can’t contract to deliver the baby. Magnesium taken by mothers also gets into their babies, which are often born listless, with low muscle tone for a couple of days after birth.
If around long enough, magnesium can compete with calcium in a second, essential role: forming bones. Bones formed in the presence of magnesium over several months may be weaker and prone to fracture.
Specifically, the FDA advised clinicians not to give pregnant women magnesium sulfate to prevent preterm labor for more than five to seven days because it may harm weaken fetal bones. It also reiterated that magnesium is approved for short-term prevention of seizures in preeclampsia, but not for longer off-label administration of magnesium to delay labor.
“No infant treated with magnesium for just the standard one or two days had any bone problems,” said Dr. Biggio, whose continued support of short-term magnesium use was echoed by the Society for Maternal-Fetal Medicine.