What is the magnesium sulfate (MgSO4) dose regimen for managing preeclampsia?

From the Guidelines

The recommended magnesium sulfate regimen for preeclampsia management consists of a loading dose of 4 grams IV and 10 grams IM (5 grams in each buttock), followed by a maintenance dose of 5 grams IM every 4 hours. This regimen is based on the most recent and highest quality study available, which provides a clear protocol for the treatment and prevention of eclampsia 1. The study suggests that the loading dose should be administered as an intravenous dose and intramuscular dose, and the maintenance dose should be administered every 4 hours for 24 hours in alternate buttocks. Key points to consider when administering magnesium sulfate include:

• Prior to administration, baseline vital signs, deep tendon reflexes, respiratory rate, and urine output should be assessed.
• During treatment, continuous monitoring is essential with hourly assessment of maternal reflexes, respiratory rate, and urine output.
• Therapeutic serum magnesium levels range from 4-7 mEq/L or 4.8-8.4 mg/dL.
• Calcium gluconate (1 gram IV) should be readily available as an antidote for magnesium toxicity. It is also important to note that magnesium sulfate works by causing vasodilation, reducing cerebral ischemia, and blocking NMDA receptors in the brain, thereby preventing seizures 1. Additionally, the study highlights the importance of clear protocols for magnesium sulfate use in each health facility/unit, and that task-shifting guidelines should be available for both MgSO4 and antihypertensive treatment 1. Overall, the recommended magnesium sulfate regimen is effective in preventing seizures and reducing the risk of progression from preeclampsia to eclampsia.

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 total daily (24 hr) dose of 30 to 40 g should not be exceeded.

The magnesium sulfate (MgSO4) dose regimen for managing preeclampsia is as follows:

• Initial dose: 10 to 14 g of magnesium sulfate
• IV dose: 4 to 5 g in 250 mL of 5% Dextrose Injection, USP or 0.9% Sodium Chloride Injection, USP
• IM dose: up to 10 g (5 g or 10 mL of the undiluted 50% solution in each buttock)
• Subsequent doses: 4 to 5 g (8 to 10 mL of the 50% solution) IM every 4 hours as needed
• Alternative: 1 to 2 g/hour by constant IV infusion after the initial IV dose
• Maximum daily dose: 30 to 40 g 2

From the Research

Magnesium Sulfate Dose Regimen for Managing Preeclampsia

• The magnesium sulfate (MgSO4) dose regimen for managing preeclampsia typically involves a loading dose followed by maintenance doses 3.
• The intramuscular regimen is most commonly a 4 g intravenous loading dose, immediately followed by 10 g intramuscularly and then by 5 g intramuscularly every 4 hours in alternating buttocks 3.
• The intravenous regimen is given as a 4 g dose, followed by a maintenance infusion of 1 to 2 g/h by controlled infusion pump 3.
• A study compared the success rates of yielding the standard therapeutic level of magnesium among overweight mothers with preeclampsia after receiving 1 gram and 2 gram per hour of magnesium sulfate maintenance infusion, and found that the rate of achievement of the therapeutic level of magnesium in the experimental group was higher than that of the control group both before delivery and after delivery 4.
• Another study found that a single dose of magnesium sulfate is equally effective as standard dose regimen in terms of seizure prophylaxis in severe pre-eclamptic women, with added advantage of reduced maternal toxicity and better neonatal outcome 5.
• A randomized controlled trial compared the efficacy of a 12-h versus 24-h regimen of intramuscular magnesium sulfate in the management of eclampsia and preeclampsia, and found that 12 hours of intramuscular magnesium sulfate showed similar rates of seizures, with fewer side effects and shorter inpatient admission 6.
• A systematic review of tested regimens of magnesium sulphate for prevention and treatment of eclampsia in low and middle income countries found that all studies were effective at preventing the initiation and/or recurrence of eclamptic seizures, and that most studies administered MgSO4 by the IV route, at least in part 7.

Key Findings

• The therapeutic level of magnesium is typically considered to be between 4.8 to 8.4 mg/dL 4.
• Maternal toxicity is rare when MgSO4 is carefully administered and monitored, and the first warning of impending toxicity in the mother is loss of the patellar reflex at plasma concentrations between 3.5 and 5 mmol/L 3.
• The dose of magnesium sulfate may need to be adjusted based on the patient's weight and other factors, such as renal function 4.
• The use of magnesium sulfate for seizure prophylaxis in severe pre-eclamptic women has been shown to be effective in reducing the risk of seizures and improving maternal and neonatal outcomes 5, 6.