A woman with severe pre-eclampsia at 34 weeks is started on magnesium sulphate. Four hours later she has absent deep tendon reflexes but is still conscious and breathing. Her urinary output in the last hour is 15 mL. What is the most appropriate immediate action?

• A Administer calcium gluconate 1 g IV ✓
• B Increase magnesium dose to achieve therapeutic levels
• C Stop magnesium and check serum magnesium level
• D Administer diazepam as a substitute for magnesium

Explanation

Loss of deep tendon reflexes is the earliest sign of magnesium toxicity (serum Mg ~7–10 mEq/L); the oliguria (15 mL/hour) indicates impaired renal excretion, further elevating levels. The antidote is calcium gluconate 1 g IV (10 mL of 10% solution) administered over 3 minutes. Increasing the dose would worsen toxicity; diazepam is not an antidote for magnesium.

Reference: Williams Obstetrics, 26th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.