A 26-year-old with pre-eclampsia with severe features at 34 weeks is on magnesium sulfate. She develops decreased deep tendon reflexes, respiratory rate drops to 10/min, and urine output falls to 15 mL/hour. The immediate antidote and correct dose is:

• A Calcium chloride 500 mg IV bolus
• B Sodium bicarbonate 1 mEq/kg IV
• C Atropine 0.6 mg IV stat
• D Calcium gluconate 1 g (10 mL of 10% solution) IV over 3 minutes ✓

Explanation

Magnesium toxicity manifests sequentially as loss of deep tendon reflexes (first sign, at ~7 mEq/L), respiratory depression (~10 mEq/L), and cardiac arrest (~15 mEq/L). The antidote is calcium gluconate 1 g (10 mL of 10% solution) given IV slowly over 3 minutes, which directly antagonises magnesium at neuromuscular junctions. Calcium chloride causes local tissue necrosis if extravasated and is not preferred; atropine and bicarbonate are not antidotes for magnesium toxicity.

Reference: Williams Obstetrics, 26th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.