A 32-year-old woman with pre-eclampsia with severe features at 36 weeks is on MgSO4 infusion. Her urine output has dropped to 12 mL/hour over the last 2 hours. Patellar reflexes are sluggish. Serum magnesium level is 9.5 mg/dL. What is the most appropriate immediate action?
- A Administer 10 mL of 10% calcium gluconate intravenously ✓
- B Increase the rate of MgSO4 infusion to control ongoing seizure risk
- C Perform immediate emergency caesarean section
- D Switch to IV diazepam for seizure prophylaxis
Correct answer: A. Administer 10 mL of 10% calcium gluconate intravenously
Explanation
Serum magnesium of 9.5 mg/dL (therapeutic range 4–7 mg/dL) combined with loss of patellar reflexes (which disappear at 7–10 mg/dL) and oliguria indicates magnesium toxicity. The antidote is 10 mL of 10% calcium gluconate given IV over 3 minutes. MgSO4 infusion must also be stopped. The toxicity sequence is: loss of patellar reflex (7–10 mg/dL), respiratory arrest (10–13 mg/dL), cardiac arrest (>15 mg/dL). Delivery is ultimately necessary but immediate resuscitation takes priority.
Reference: Williams Obstetrics, 26th ed.
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Written and medically reviewed by the StethoPrep medical team.