What is the use of magnesium sulfate (MgSO4)?

From the Guidelines

Magnesium sulfate should be administered to all preeclamptic women, especially in low- and middle-income countries, as it prevents eclampsia and has a significant cost-benefit advantage, with approximately 100 women needing treatment to prevent one seizure 1. The dosing regimens used in the Eclampsia and MAGPIE trials should be followed, which typically include a 4-6 gram IV loading dose over 15-20 minutes, followed by a maintenance infusion of 1-2 grams per hour, continuing for 24 hours after delivery or the last seizure. Key points to consider when using magnesium sulfate include:

• Monitoring for signs of toxicity, such as flushing, hypotension, respiratory depression, and loss of deep tendon reflexes, which require immediate dose reduction or discontinuation
• Maintaining serum magnesium levels between 4-7 mg/dL for seizure prophylaxis
• Using the medication cautiously in patients with renal impairment
• Having calcium gluconate available as an antidote for magnesium toxicity Recent guidelines have consistently recommended magnesium sulfate for the treatment and prevention of eclampsia in women with severe preeclampsia or serious end-organ involvement 1. It is essential to have a consistent policy on the use of magnesium sulfate, incorporating appropriate monitoring, recognition of risks, and assessment of maternal and fetal outcomes.

From the FDA Drug Label

In the treatment of mild magnesium deficiency, the usual adult dose is 1 g, equivalent to 8. 12 mEq of magnesium (2 mL of the 50% solution) injected IM every six hours for four doses (equivalent to a total of 32.5 mEq of magnesium per 24 hours). For severe hypomagnesemia, as much as 250 mg (approximately 2 mEq) per kg of body weight (0. 5 mL of the 50% solution) may be given IM within a period of four hours if necessary. Alternatively, 5 g (approximately 40 mEq) can be added to one liter of 5% Dextrose Injection, USP or 0. 9% Sodium Chloride Injection, USP for slow IV infusion over a three-hour period. The usual dose of magnesium sulfate for mild magnesium deficiency is 1 g every six hours for four doses, and for severe hypomagnesemia, it is 250 mg per kg of body weight within four hours or 5 g added to one liter of solution for slow IV infusion over three hours 2.

• The dosage may vary depending on the severity of the condition and the patient's response.
• It is essential to monitor serum magnesium levels and renal function to avoid exceeding the renal excretory capacity.

From the Research

Magnesium Sulfate Usage

• Magnesium sulfate (MgSO4) is commonly used for treating eclampsia and preventing eclampsia in patients with severe pre-eclampsia 3.
• The drug can be administered through intramuscular or intravenous routes, with the intramuscular regimen typically involving a 4 g intravenous loading dose, followed by 10 g intramuscularly and then 5 g intramuscularly every 4 hours 3.
• The intravenous regimen involves a 4 g dose, followed by a maintenance infusion of 1 to 2 g/h by controlled infusion pump 3.

Pharmacokinetics and Toxicity

• After administration, about 40% of plasma magnesium is protein bound, and the unbound magnesium ion diffuses into various tissues and fluids, including the fetus and amniotic fluid 3.
• Magnesium is almost exclusively excreted in the urine, with 90% of the dose excreted during the first 24 hours after an intravenous infusion of MgSO4 3.
• Maternal toxicity is rare when MgSO4 is carefully administered and monitored, with the first warning of impending toxicity being loss of the patellar reflex at plasma concentrations between 3.5 and 5 mmol/L 3.

Clinical Usage and Efficacy

• Magnesium sulfate is effective in preventing and controlling seizures in patients with pre-eclampsia and eclampsia 4, 5, 6.
• The drug has been shown to reduce the risk of eclampsia and maternal death, although it may increase the risk of side effects such as flushing and respiratory depression 6.
• A systematic review and meta-analysis found no statistically significant differences in efficacy and safety between 12-hour and 24-hour regimens of magnesium sulfate in managing patients with pre-eclampsia and eclampsia 7.

Dosage and Administration

• The initial loading dose of magnesium sulfate typically consists of 4 gm administered as a 20% solution intravenously over 10-15 minutes, followed by 5 gm intramuscularly into each buttock 4.
• The dose may be repeated if the patient develops convulsions, and careful monitoring of maternal and fetal outcomes is necessary to prevent toxicity and ensure effective treatment 4, 5, 6.