What is the therapeutic serum range for magnesium sulfate?

• A. 4-7 mEq/L
• B. 1-2 mEq/L
• C. 8-12 mEq/L
• D. 10-15 mEq/L

Answer: (A)

Magnesium sulfate is given to prevent seizures in severe preeclampsia/eclampsia, so it must be kept within a narrow therapeutic window. The target serum level is 4 to 7 mEq/L. At this range, magnesium provides the anticonvulsant effect without tipping into toxicity. If the level climbs higher, the risk of toxicity rises, with signs such as diminished or absent deep tendon reflexes and respiratory depression, and can progress to cardiac arrhythmias or arrest. Levels below the range may not adequately prevent seizures. Therefore, careful monitoring is essential: assess deep tendon reflexes, watch respiratory rate and depth, monitor urine output, and check magnesium levels as ordered. Have calcium gluconate available to treat toxicity if needed.