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Magnesium Sulfate for Seizure Prevention During Pregnancy


Generic Name
magnesium sulfate

Magnesium sulfate is used to prevent or stop seizures (eclampsia) during pregnancy. It is usually given through a vein (intravenously, or IV) or injected into a muscle (intramuscularly, or IM). Treatment to prevent seizures is usually continued for 24 hours after delivery.

Getting magnesium sulfate through a vein (IV) is less painful than through IM injection because the IM injections must be given frequently. The IM delivery route may be used when:

  • A pump for adjustable and reliable IV delivery is not available.
  • Continuous monitoring of the health of the mother and fetus is not possible.
  • The mother must be transferred to another location for treatment.

How It Works

It is not known exactly how magnesium prevents or stops seizures during pregnancy. But it may work by blocking or reducing activity in certain areas of the brain.

Why It Is Used

Magnesium sulfate is used to:

  • Prevent seizures in a woman with moderate to severe preeclampsia. When magnesium sulfate is used during labor and delivery, it is usually continued for at least 24 hours after delivery.
  • Stop seizures when they are occurring.

How Well It Works

Magnesium sulfate is effective in reducing the risk of seizures in women who have severe preeclampsia.1 It also prevents repeat seizures in women who have eclampsia.1

Side Effects

Common side effects of this medicine include:

See Drug Reference for a full list of side effects. (Drug Reference is not available in all systems.)

What To Think About

In rare cases, symptoms of magnesium toxicity (nausea, muscle weakness, loss of reflexes) occur during magnesium sulfate treatment. The medicine calcium gluconate is given to treat the problem.

Magnesium sulfate:

  • Affects the central nervous system (brain and spinal cord) of the mother. Part of normal care when intravenous magnesium sulfate is given includes checking the mother's reflexes. If too much magnesium sulfate is given, the mother's reflexes will be slowed. Reflexes are usually checked about every 2 to 4 hours while the mother is on this medicine.
  • Affects the fetus's central nervous system. If this medicine has been given to the mother in large doses and the baby is born before the drug has had time to clear the mother's body, the baby may have temporary problems with breathing right after birth. These problems are quickly reversed with medicine.
  • Leaves the mother's body in her urine. The amount of urine she produces is closely monitored to ensure that this medicine does not build up in her bloodstream.

Mothers on magnesium sulfate are closely monitored. Blood pressure and pulse are checked about every 30 minutes for at least the first few hours of treatment.

Complete the new medication information form (PDF)(What is a PDF document?) to help you understand this medication.


  1. Duley L (2011). Pre-eclampsia, eclampsia, and hypertension; search date February 2010. Online version of BMJ Clinical Evidence:

By Healthwise Staff
Primary Medical Reviewer Sarah Marshall, MD - Family Medicine
Specialist Medical Reviewer William Gilbert, MD - Maternal and Fetal Medicine
Current as of November 5, 2012

WebMD Medical Reference from Healthwise

Last Updated: November 05, 2012
This information is not intended to replace the advice of a doctor. Healthwise disclaims any liability for the decisions you make based on this information.

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