What does magnesium sulfate do to the uterus?

KindProtein groupOrganismHumansPharmacological action

Yes

Actions

Inhibitor

Blocker

The magnesium regulates the channel gating by binding to the EF-hand motif region in the COOH-terminal tail of the α-subunit of the channel.

General FunctionVoltage-gated calcium channel activitySpecific FunctionVoltage-sensitive calcium channels (VSCC) mediate the entry of calcium ions into excitable cells and are also involved in a variety of calcium-dependent processes, including muscle contraction, hor...

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2. Bara M, Guiet-Bara A: Magnesium regulation of Ca2+ channels in smooth muscle and endothelial cells of human allantochorial placental vessels. Magnes Res. 2001 Mar;14(1-2):11-8. [Article]
3. Kuo CC, Hess P: Block of the L-type Ca2+ channel pore by external and internal Mg2+ in rat phaeochromocytoma cells. J Physiol. 1993 Jul;466:683-706. [Article]
4. Zhao M, Feng R, Shao D, Liu S, Lei M, Wang H, Sun X, Guo F, Hu H, Kameyama M, Hao L: Mg(2+)-dependent facilitation and inactivation of L-type Ca(2+) channels in guinea pig ventricular myocytes. J Pharmacol Sci. 2015 Nov;129(3):143-9. doi: 10.1016/j.jphs.2015.08.001. Epub 2015 Aug 7. [Article]
5. Lin CY, Tsai PS, Hung YC, Huang CJ: L-type calcium channels are involved in mediating the anti-inflammatory effects of magnesium sulphate. Br J Anaesth. 2010 Jan;104(1):44-51. doi: 10.1093/bja/aep336. [Article]

Magnesium sulfate, or mag for short, is used in pregnancy to prevent seizures due to worsening preeclampsia, to slow or stop preterm labor, and to prevent injuries to a preterm baby's brain.

Magnesium sulfate is given as an intravenous infusion or intramuscular injection in the hospital over 12 to 48 hours. It relaxes smooth muscle tissues, which helps to prevent seizures and slow uterine contractions.

Verywell / Alexandra Gordon

Magnesium sulfate infusions have been a common practice on obstetrical floors for more than 60 years. It's a well-studied drug, so doctors know very well how it affects moms and babies. Here is how it is used:

Magnesium sulfate is a tocolytic that has been used to slow or stop premature labor. Research shows that mag, like other tocolytics, doesn't work very well to actually prevent preterm birth, but it may help stall labor for a short time.

Doctors may treat preterm labor with 48 hours of magnesium sulfate, hoping to buy enough time to complete a course of steroids to help the baby's lungs develop.

Preeclampsia is a common complication of pregnancy that causes high blood pressure and protein in the urine. If not treated, preeclampsia can develop into eclampsia, a seizure disorder.

The only cure for preeclampsia and eclampsia is delivery of the baby, but magnesium sulfate can help prevent seizures in women with severe preeclampsia.

Premature babies, especially those who are born before about 32 weeks gestation, have immature brains at birth. As they grow, they are at risk for cerebral palsy, a disorder that affects movement and intelligence.

Short-term (24 hours or less) infusions of magnesium sulfate have been shown to help protect the baby's brain by reducing the incidence of cerebral palsy.

Magnesium sulfate infusion is safe and effective when administered for up to a week. However, its side effects can be very uncomfortable. In mothers, the side effects include:

• Flushing or hot flashes
• Feeling tired and lethargic
• Nausea and vomiting
• Dizziness
• Blurred vision
• Muscle weakness

These side effects during labor may make vaginal delivery difficult resulting in a C-section. However, magnesium sulfate administration is also shown to reduce post-operative pain. In addition, women who were given magnesium sulfate may experience a delay in milk production by up to 10 days.

In rare cases, respiratory depression can occur. This can be reversed with a calcium infusion and is more common in women with kidney problems.

Magnesium sulfate crosses the placenta to the baby, and babies may experience side effects that include poor muscle tone and low Apgar scores. These side effects are usually gone in a day or so and don't cause long-term problems.

Mag should not be given for longer than seven days, as long-term mag therapy can cause low calcium in the baby's bones.

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• American College of Obstetricians and Gynecologists. Magnesium Sulfate Use in Obstetrics. //www.acog.org/Resources_And_Publications/Committee_Opinions/Committee_on_Obstetric_Practice/Magnesium_Sulfate_Use_in_Obstetrics

• Drugs and Lactation Database (LactMed) [Internet]. Magnesium Sulfate. Bethesda (MD): National Library of Medicine (US); 2006. //www.ncbi.nlm.nih.gov/books/NBK501339

• Merrill L. Magnesium sulfate during anticipated preterm birth for infant neuroprotection. Nurs Womens Health. 2013;17(1):42-51. doi: 10.1111/1751-486X.12005.

• Riaz M, Porat R, Brodsky NL, Hurt H. The effects of maternal magnesium sulfate treatment on newborns: a prospective controlled study. J Perinatol. 1998;18(6 Pt 1):449-54.

• Smith JM, Lowe RF, Fullerton J, et al. An integrative review of the side effects related to the use of magnesium sulfate for pre-eclampsia and eclampsia management. BMC Pregnancy Childbirth. 2013;13:34. doi: 10.1186/1471-2393-13-34.

• US Food and Drug Administration. Magnesium Sulfate: Drug Safety Communication - Recommendation Against Prolonged Use in Pre-term Labor. //www.fda.gov/Safety/MedWatch/SafetyInformation/SafetyAlertsforHumanMedicalProducts/ucm354603.htm

High-end arteriolar resistance limits uterine artery blood flow and restricts fetal growth in preeclampsia and gestational hypertension at high altitude.

Browne VA, Toledo-Jaldin L, Davila RD, Lopez LP, Yamashiro H, Cioffi-Ragan D, Julian CG, Wilson MJ, Bigham AW, Shriver MD, Honigman B, Vargas E, Roach R, Moore LG. Browne VA, et al. Am J Physiol Regul Integr Comp Physiol. 2011 May;300(5):R1221-9. doi: 10.1152/ajpregu.91046.2008. Epub 2011 Feb 16. Am J Physiol Regul Integr Comp Physiol. 2011. PMID: 21325643 Free PMC article.

About half of the women who receive magnesium sulfate have some side effects. Potential side effects include flushing, feeling uncomfortably warm, headache, dry mouth, nausea, and blurred vision. Women often say they feel wiped out, as though they have the flu. These side effects can be uncomfortable, but they are not dangerous.

When given in high doses, magnesium sulfate can cause cardiac arrest and respiratory failure. Fortunately, women can be monitored for increases in the magnesium blood levels. If the levels become too high, the dose can be lowered.

One of the most common signs that nurses watch for is the loss of the knee-jerk reflex (a jerk that usually occurs when your leg is tapped just below the knee). Your urine output will also probably be measured every hour in the hospital to avoid toxicity.

If for some reason the levels get too high, another medication, called calcium gluconate, can help reverse the effects of magnesium sulfate.

For the Baby

Since magnesium sulfate relaxes most muscles, babies who have been exposed to magnesium for an extended period of time may be listless or floppy at birth. This effect typically goes away as the drug clears from the baby’s system.