What is the therapeutic magnesium level for severe preeclampsia?

From the Guidelines

The therapeutic magnesium level for severe preeclampsia should be maintained between 4.8 to 8.4 mg/dL (2.0 to 3.5 mmol/L) to prevent eclampsia and ensure maternal and fetal well-being. This is achieved through intravenous magnesium sulfate administration, usually with a loading dose of 4-6 grams given over 20-30 minutes, followed by a maintenance infusion of 1-2 grams per hour 1. Regular monitoring of serum magnesium levels is essential, typically every 4-6 hours until stable levels are achieved, then less frequently. Clinical assessment for signs of magnesium toxicity is also crucial, including monitoring deep tendon reflexes, respiratory rate, and urine output. If toxicity occurs (levels >9.6 mg/dL or 4 mmol/L), the infusion should be reduced or temporarily stopped. Magnesium sulfate works as a central nervous system depressant and vasodilator, preventing seizures by blocking N-methyl-D-aspartate (NMDA) receptors and calcium channels, thereby reducing cerebral irritability and preventing eclampsia in women with severe preeclampsia.

Key considerations in managing severe preeclampsia include:

• Urgent treatment of severe hypertension (>160/110 mm Hg) with acceptable agents such as oral nifedipine or intravenous labetalol or hydralazine 1
• Treatment of BPs consistently at or >140/90 mm Hg to reduce the likelihood of developing severe maternal hypertension and other complications 1
• Assessment of women with preeclampsia in hospital when first diagnosed, with possible outpatient management thereafter if the condition is stable 1
• Administration of MgSO4 for convulsion prophylaxis in women with preeclampsia who have proteinuria and severe hypertension, or hypertension with neurological signs or symptoms 1

It is essential to note that the management of severe preeclampsia requires a multidisciplinary approach, with clear protocols and guidelines in place to ensure optimal care and prevent complications 1. Regular monitoring and assessment of both maternal and fetal well-being are crucial in managing severe preeclampsia and preventing adverse outcomes.

From the FDA Drug Label

Serum magnesium levels usually sufficient to control convulsions range from 3 to 6 mg/100 mL (2.5 to 5 mEq/L). A serum magnesium level of 6 mg/100 mL is considered optimal for control of seizures.

The therapeutic magnesium level for severe preeclampsia is between 3 to 6 mg/100 mL (2.5 to 5 mEq/L), with an optimal level of 6 mg/100 mL for control of seizures 2.

From the Research

Therapeutic Magnesium Level for Severe Preeclampsia

• The therapeutic level of magnesium for severe preeclampsia is generally considered to be between 4.8 to 8.4 mg/dL 3.
• A study comparing serum magnesium levels during magnesium sulfate infusion at 1 gram/hour versus 2 grams/hour found that serum magnesium levels were higher in the 2-gram/hour group, but the 1-gram/hour group had fewer side effects 4.
• Another study found that the rate of achievement of the therapeutic level of magnesium was higher in the 2-gram/hour group than in the 1-gram/hour group, both before and after delivery 3.
• The American Society of Health-System Pharmacists notes that therapeutic serum magnesium levels cause cerebral vasodilation, thereby reversing the ischemia produced by cerebral vasospasm during an eclamptic episode 5.
• A study on ionized and total magnesium concentration in patients with severe preeclampsia-eclampsia undergoing magnesium sulfate therapy found that the putative level of 4 mEq/L of total magnesium was not obtained in up to 42% of patients during treatment 6.
• A randomized study comparing 12-hour versus 24-hour maintenance dose of magnesium sulfate found that a 12-hour maintenance dose was effective and safe for the management of severe pre-eclampsia 7.

Maintenance Dose of Magnesium Sulfate

• A maintenance dose of 1 gram/hour of magnesium sulfate was found to be as effective as a 2-gram maintenance dose, with fewer side effects 4.
• A study found that the therapeutic level of magnesium in overweight mothers with preeclampsia could be more frequently achieved with a dose of 2 grams per hour of magnesium sulfate infusion 3.
• The standard regimen of magnesium sulfate may not provide the proposed therapeutic level of magnesium in all patients 6.