A multiparous woman develops grand mal seizure at 36 weeks gestation. Magnesium sulfate is administered. Six hours later she becomes oliguric with urine output of 15 mL/hour. Her serum magnesium level is 9 mEq/L. The FIRST intervention should be:

• A Increase IV fluid rate to 200 mL/hour
• B Administer calcium gluconate 1 g intravenously ✓
• C Stop magnesium sulfate infusion immediately
• D Administer furosemide to restore urine output

Explanation

Serum magnesium of 9 mEq/L is in the toxic range (therapeutic: 4–7 mEq/L; toxicity: loss of patellar reflexes at 7–10, respiratory paralysis at 10–13). With oliguria signaling reduced excretion, calcium gluconate 1 g IV is the antidote and must be given first to reverse magnesium toxicity. Stopping the infusion is important but calcium gluconate directly antagonizes the toxic effects at the neuromuscular junction and is the immediate priority.

Reference: Williams Obstetrics, 26th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.