The MAGPIE trial established the role of magnesium sulfate in pre-eclampsia. Which of the following best describes its primary mechanism for preventing eclamptic seizures?
- A Antagonism of NMDA glutamate receptors, reducing neuronal hyperexcitability in the limbic system ✓
- B Inhibition of voltage-gated calcium channels in cerebral arteries, causing vasodilation and reducing ischemic threshold
- C GABA-A receptor potentiation in the cortex, mimicking benzodiazepine effect on inhibitory neurotransmission
- D Direct inhibition of sodium-potassium ATPase, stabilizing neuronal membrane resting potential
Explanation
The MAGPIE trial (2002) showed magnesium sulfate reduces eclampsia risk by 58% compared to placebo. Its primary mechanism is NMDA receptor antagonism — magnesium ions block the NMDA receptor channel in a voltage-dependent manner, reducing calcium influx and limiting neuronal hyperexcitability thought to drive eclamptic seizures. Magnesium also causes some cerebral vasodilation (option B is partially true) but this is secondary and less central to its anticonvulsant action. It does not work via GABA-A (option C, that is benzodiazepine/barbiturate mechanism) nor Na-K ATPase inhibition (option D).
Reference: Williams Obstetrics, 26th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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