Magnesium sulfate in obstetric care is used for what combination?

• A. It is used only as a tocolytic
• B. It is used as a tocolytic and for seizure prophylaxis in preeclampsia
• C. It is a beta-blocker
• D. It is never given IV

Answer: (B)

Magnesium sulfate is used in obstetric care for two main reasons: to stop or slow preterm labor (tocolysis) and to prevent seizures in women with preeclampsia or to treat impending eclampsia. Mechanistically, it relaxes uterine smooth muscle by reducing calcium entry into myometrial cells, which lowers contractions. It also depresses central nervous system activity, raising the seizure threshold and reducing the risk of seizures in preeclampsia. Because of these dual actions, it serves both purposes in appropriate clinical scenarios. It is not a beta-blocker, and it is commonly given IV with careful monitoring for toxicity (such as loss of deep tendon reflexes or respiratory depression), with calcium gluconate available as an antidote.