A 34-year-old woman with severe pre-eclampsia at 33 weeks is receiving intravenous magnesium sulfate at 2 g/hour. Her urine output over the last 4 hours is 60 mL. Serum creatinine is 1.4 mg/dL. Which of the following is the most appropriate immediate adjustment to her magnesium sulfate regimen?
- A Reduce the infusion rate to 1 g/hour and check serum magnesium level urgently ✓
- B Increase the infusion rate to 3 g/hour to ensure therapeutic levels
- C Continue the same rate and recheck magnesium levels in 24 hours
- D Switch to oral magnesium supplementation
Correct answer: A. Reduce the infusion rate to 1 g/hour and check serum magnesium level urgently
Explanation
Magnesium is excreted renally. Oliguria (<100 mL/4 hours or <25-30 mL/hour) and elevated creatinine indicate impaired renal function, placing the patient at high risk for magnesium toxicity. The infusion rate should be reduced and serum magnesium levels checked urgently. Therapeutic range is 4-7 mEq/L; toxicity occurs above 8-10 mEq/L. Continuing the same rate or increasing it risks life-threatening toxicity. Oral magnesium is not used for seizure prophylaxis.
Reference: Williams Obstetrics, 26th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.