An eclamptic patient receives 4 g IV magnesium sulfate as a loading dose followed by 1 g per hour infusion. Two hours later she has another seizure. Her reflexes are present and respiratory rate is 16 per minute. Serum magnesium level drawn now is most likely to be:

• A Above 12 mg/dL, the lethal range
• B Between 7 and 10 mg/dL, the therapeutic range
• C Between 10 and 12 mg/dL, the toxic range
• D Below 4 mg/dL, indicating subtherapeutic levels ✓

Explanation

Recurrent seizure on adequate magnesium dosing with preserved reflexes and normal respiration points to subtherapeutic levels, usually below the therapeutic window of 4 to 7 mg/dL (roughly 4.8 to 8.4 mg/dL by some conventions). Loss of deep tendon reflexes appears around 9 to 12 mg/dL and respiratory depression above 12 mg/dL, both absent here. Management would be a further 2 g bolus while monitoring levels, per standard protocols.

Reference: Williams Obstetrics, 26th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.