Action of magnesium sulphate is?

RUHS, Jaipur, M.Sc Nursing Entrance Exam-2016

Pharmacology

Easy

Appeared in: RUHS, Jaipur, M.Sc Nursing Entrance Exam-2016

Explanation

Magnesium sulphate acts as a central nervous system (CNS) depressant.
Its primary mechanism involves blocking neuromuscular transmission by reducing the release of the neurotransmitter acetylcholine at nerve endings and blocking NMDA receptors in the brain.
This action reduces overall CNS excitability, making it a highly effective anticonvulsant for preventing and treating eclamptic seizures.
It also causes peripheral vasodilation, which can contribute to a modest reduction in blood pressure.

Option B: While magnesium is an essential mineral and can be taken as a dietary supplement (e.g., magnesium oxide), magnesium sulphate is administered parenterally for acute, specific medical conditions like eclampsia, not as a routine dietary supplement.
Option C: This is partially correct as magnesium sulphate does cause muscle relaxation. However, this effect is a consequence of its primary action as a CNS depressant and neuromuscular blocker. 'CNS depressant' is the more fundamental and comprehensive description of its mechanism.
Option D: This is incorrect. Magnesium sulphate is a depressant; its effects, such as drowsiness, decreased reflexes, and respiratory depression, are the opposite of a CNS stimulant.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Pharmacological action of Magnesium Sulphate as background academic context rather than a clinical decision trigger.
Magnesium sulphate is the first-line drug for seizure prophylaxis and treatment in patients with severe preeclampsia and eclampsia.
Nurses must perform frequent assessments for signs of magnesium toxicity. The loss of the patellar (knee-jerk) deep tendon reflex is the earliest sign and requires stopping the infusion immediately.
The antidote, calcium gluconate, must always be readily available at the bedside whenever a patient is receiving a magnesium sulphate infusion.

How to Approach the Question

This is a factual recall question about a common and critical medication used in obstetrics.
Identify the drug in the stem: 'magnesium sulphate'.
Recall its primary pharmacological class and therapeutic use. It is most famously used to prevent seizures in preeclampsia.
Consider how it prevents seizures. It does so by depressing the central nervous system.
Evaluate the options based on this primary action. 'CNS depressant and anticonvulsant' directly aligns with its main use and mechanism.
Eliminate the distractors. It is not a stimulant. While magnesium is a mineral, magnesium sulphate is used therapeutically, not as a general supplement. 'Muscle relaxant' is a secondary effect of its primary CNS depressant action.

Concept Tested & Keywords

QGRc4a1Q0-3ANSGuUF7pDi

E6 Obstetrics Williams p. 31-52

E6 Nursing Brunner Adult Health 3SA Vol 1 Part 1 p. 156-158