What is the role of Magnesium sulfate (MgSO4) in preventing postpartum seizures?

From the Guidelines

Magnesium sulfate is the first-line treatment for prevention and management of postpartum seizures associated with preeclampsia and eclampsia, and it should be administered for 24 hours postpartum. The recommended loading dose is 4-6 grams IV over 15-20 minutes, followed by a maintenance infusion of 1-2 grams per hour for 24 hours after the last seizure or delivery, whichever occurs last 1. For recurrent seizures while on magnesium, an additional 2-gram bolus can be administered. Therapeutic serum magnesium levels should be maintained between 4-7 mEq/L (2-3.5 mmol/L). During administration, patients require close monitoring of vital signs, deep tendon reflexes, respiratory rate (should remain above 12 breaths/minute), and urine output (should exceed 30 mL/hour). Calcium gluconate (1 gram IV) should be immediately available as an antidote for magnesium toxicity. Magnesium works by stabilizing neuronal membranes through NMDA receptor antagonism and by causing cerebral vasodilation, which reduces cerebral ischemia. It also lowers blood pressure modestly and has anticonvulsant properties. Renal function should be assessed before administration, as magnesium is excreted by the kidneys, and dose adjustments are necessary for patients with renal impairment.

Some key points to consider when administering magnesium sulfate include:

• The importance of close monitoring of patients during administration, as recommended by the ISSHP guidelines 1
• The need for a consistent policy on the use of magnesium sulfate, incorporating appropriate monitoring and assessment of maternal and fetal outcomes 1
• The potential benefits of magnesium sulfate in preventing eclampsia, with approximately 100 women needing to be treated to prevent one seizure 1
• The recommendation to continue magnesium sulfate for 24 hours postpartum, as suggested by recent studies 1

Overall, the use of magnesium sulfate for the prevention and management of postpartum seizures associated with preeclampsia and eclampsia is a crucial aspect of maternal care, and its administration should be guided by the most recent and highest-quality evidence available 1.

From the FDA Drug Label

In severe pre-eclampsia or eclampsia, the total initial dose is 10 to 14 g of magnesium sulfate. Intravenously, a dose of 4 to 5 g in 250 mL of 5% Dextrose Injection, USP or 0. 9% Sodium Chloride Injection, USP may be infused. Simultaneously, IM doses of up to 10 g (5 g or 10 mL of the undiluted 50% solution in each buttock) are given Alternatively, the initial IV dose of 4 g may be given by diluting the 50% solution to a 10 or 20% concentration; the diluted fluid (40 mL of a 10% solution or 20 mL of a 20% solution) may then be injected IV over a period of three to four minutes Subsequently, 4 to 5 g (8 to 10 mL of the 50% solution) are injected IM into alternate buttocks every four hours as needed, depending on the continuing presence of the patellar reflex and adequate respiratory function. Alternatively, after the initial IV dose, some clinicians administer 1 to 2 g/hour by constant IV infusion. Therapy should continue until paroxysms cease A serum magnesium level of 6 mg/100 mL is considered optimal for control of seizures. A total daily (24 hr) dose of 30 to 40 g should not be exceeded.

Magnesium sulfate dosage for postpartum seizure: The dosage of magnesium sulfate for postpartum seizure is not explicitly stated in the provided drug labels. However, for severe pre-eclampsia or eclampsia, the total initial dose is 10 to 14 g of magnesium sulfate, with subsequent doses of 4 to 5 g every four hours as needed.

• The optimal serum magnesium level for control of seizures is 6 mg/100 mL.
• The total daily dose should not exceed 30 to 40 g. 2

From the Research

Magnesium Sulfate for Postpartum Seizure Prophylaxis

• Magnesium sulfate is the standard of care for maternal seizure prophylaxis in women with preeclampsia 3, 4, 5, 6
• The duration of postpartum magnesium sulfate administration is crucial, with traditional regimens continuing infusions for 24 hours postpartum 4
• A systematic review and meta-analysis found that women who received less than 24 hours of postpartum magnesium sulfate had a significantly faster time to ambulation postpartum and shorter durations of indwelling urinary catheter placement, but the results did not show a difference in the rate of eclampsia 4
• Studies have compared the efficacy of magnesium sulfate with phenytoin for preventing seizures in hypertensive women during labor, with magnesium sulfate being superior to phenytoin 3, 7, 5, 6

Comparison with Phenytoin

• Magnesium sulfate is associated with a substantial reduction in the recurrence of seizures compared to phenytoin 3, 7, 5, 6
• Phenytoin may be considered for treatment of special conditions such as mild preeclampsia, but magnesium sulfate is more effective for prevention of convulsion in eclampsia and severe preeclampsia 3, 7
• The use of phenytoin should be abandoned in favor of magnesium sulfate for women with eclampsia, as it reduces the risk of recurrence of seizures and probably reduces the risk of maternal death 6

Maternal and Fetal Outcomes

• Magnesium sulfate is associated with a higher incidence of cesarean section compared to phenytoin 3, 7
• There were no significant differences in fetal outcomes between magnesium sulfate and phenytoin in some studies 3, 7, but magnesium sulfate was associated with fewer admissions to a special care baby unit and fewer babies who died or were in the unit for more than seven days in another study 6