A 32-year-old woman with pre-eclampsia with severe features at 36 weeks is started on IV labetalol and magnesium sulfate. Two hours later she becomes oliguric (urine output 15 mL/hr) and her serum magnesium level is 8.5 mEq/L. Her patellar reflexes are absent. The IMMEDIATE next step is:

• A Administer calcium gluconate 1 g IV over 10 minutes ✓
• B Stop magnesium and give furosemide 40 mg IV
• C Reduce magnesium infusion rate by half
• D Obtain serum magnesium and await result before acting

Explanation

Loss of patellar reflexes occurs at serum magnesium 7–10 mEq/L and signals impending toxicity; respiratory arrest occurs at 10–13 mEq/L. The immediate antidote is calcium gluconate 1 g (10 mL of 10% solution) given IV over 10 minutes, which antagonises magnesium at the neuromuscular junction. Magnesium infusion should also be stopped, but calcium gluconate is the life-saving immediate action. Furosemide is secondary and waiting for labs is dangerous.

Reference: Williams Obstetrics, 26th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.