At which serum magnesium level range is seizure prophylaxis used in preeclampsia management?

• A. 5-8 mg/dL
• B. 5-10 mg/dL
• C. 8-12 mg/dL
• D. 20-35 mg/dL

Answer: (A)

Magnesium sulfate is given in preeclampsia to prevent seizures by raising the brain’s seizure threshold, so the goal is to keep serum magnesium within a mid-range therapeutic window. The range of 5 to 8 mg/dL is high enough to provide anticonvulsant effect but low enough to limit toxicity, given that normal serum magnesium is about 1.7–2.2 mg/dL. Monitoring serum levels and clinical signs is essential; if levels creep higher or signs of toxicity appear—such as diminished deep tendon reflexes, slow or shallow breathing, or reduced urine output—stop the infusion and treat promptly with calcium gluconate. In short, 5–8 mg/dL is the target range for seizure prophylaxis in this setting.