Regarding MgSO4 therapy for preeclampsia, which statement is true?

Regarding MgSO4 therapy for preeclampsia, which statement is true?

• A. The therapeutic range is 10 to 15 mEq/L.
• B. Reflex loss correlates with serum magnesium levels around 10 mEq/L.
• C. Excessive magnesium levels cause widening of the QRS complex.
• D. The antidote for magnesium toxicity is neostigmine.

Answer: (C)

Magnesium sulfate used for seizure prevention in preeclampsia can become toxic when levels rise, and the heart’s electrical conduction is particularly sensitive to this. As magnesium levels climb, it slows conduction pathways in the heart. This can show up on an ECG as widening of the QRS complex, a sign of impaired ventricular conduction and a risk for more serious arrhythmias. That direct link between higher magnesium and a measurable ECG change is why this statement is true. For context, the therapeutic window is much lower, typically about 4–7 mEq/L. Loss of deep tendon reflexes tends to occur at higher levels, around the 8–10 mEq/L range, and severe toxicity can lead to respiratory depression and cardiovascular collapse. The specific antidote for magnesium toxicity is calcium gluconate, not neostigmine.

Magnesium sulfate used for seizure prevention in preeclampsia can become toxic when levels rise, and the heart’s electrical conduction is particularly sensitive to this. As magnesium levels climb, it slows conduction pathways in the heart. This can show up on an ECG as widening of the QRS complex, a sign of impaired ventricular conduction and a risk for more serious arrhythmias. That direct link between higher magnesium and a measurable ECG change is why this statement is true.

For context, the therapeutic window is much lower, typically about 4–7 mEq/L. Loss of deep tendon reflexes tends to occur at higher levels, around the 8–10 mEq/L range, and severe toxicity can lead to respiratory depression and cardiovascular collapse. The specific antidote for magnesium toxicity is calcium gluconate, not neostigmine.