Magnesium Sulfate — Use

Magnesium sulfate (MgSO4) is a central nervous system depressant that reduces neuromuscular excitability. In preeclampsia and eclampsia, it is the first-line drug for seizure prophylaxis — not blood pressure control. It works by stabilizing neuronal cell membranes and raising the seizure threshold, preventing the tonic-clonic convulsions of eclampsia that threaten both maternal and fetal life. The therapeutic serum magnesium level for seizure prevention is 4–7 mEq/L (4.8–8.4 mg/dL). A typical protocol is a 4–6 g IV loading dose over 15–30 minutes, followed by a maintenance infusion of 1–2 g/hour. In preterm labor, MgSO4 is used as a tocolytic to relax uterine smooth muscle, slowing or stopping contractions to buy time — usually 24–48 hours — for antenatal corticosteroids to promote fetal lung maturity. It also provides fetal neuroprotection when delivery before 32 weeks is anticipated, reducing the risk of cerebral palsy. The underlying mechanism is related in both uses — magnesium competes with calcium at the neuromuscular junction, decreasing muscle contractility — but the specific pathways overlap rather than being identical, and the clinical rationale differs entirely.