The Magpie Trial (2002) established magnesium sulfate as the drug of choice for eclampsia prevention. Compared to phenytoin and diazepam, which of the following best describes the proposed neuroprotective mechanism of magnesium in preventing eclamptic seizures?

• A Sodium channel blockade preventing depolarization in cortical neurons
• B GABA-A receptor potentiation causing neuronal hyperpolarization
• C NMDA receptor antagonism reducing calcium influx and cerebral vasospasm ✓
• D COX-2 inhibition reducing prostaglandin-mediated cerebral oedema

Explanation

Magnesium sulfate exerts its anticonvulsant effect primarily through NMDA (N-methyl-D-aspartate) receptor antagonism — magnesium ions block the NMDA receptor channel in a voltage-dependent manner, reducing calcium influx into neurons and thereby preventing the neuronal hyperexcitability that underlies eclamptic seizures. Additionally, magnesium causes cerebral vasodilation (reversing vasospasm), which reduces ischaemia-reperfusion injury. Sodium channel blockade is the mechanism of phenytoin; GABA-A potentiation is the mechanism of benzodiazepines and barbiturates; COX-2 inhibition is not a mechanism of magnesium.

Reference: Williams Obstetrics, 26th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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