Magnesium Sulphate: Clinical Uses, Pharmacology, Physiology, and Toxicity

Magnesium sulphate (MgSO4) is a versatile compound with wide-ranging clinical applications due to its physiological importance. In this article, we will explore its clinical uses, basic pharmacology, physiology, and potential toxicity.

Clinical Uses

Clinical ConditionMechanism of Action
Pre-eclampsia and EclampsiaReduces systemic vascular resistance, CNS excitability.
TocolysisInduces uterine relaxation.
Acute ArrhythmiasEffective in abolishing various arrhythmias.
HypomagnesaemiaCorrects magnesium deficiency.
TetanusTreats muscle spasm and autonomic instability.
EpilepsyControls status epilepticus.
Subarachnoid HemorrhagePrevents cerebral vasospasm.
AsthmaActs as a bronchodilator in severe refractory cases.
AnalgesiaUsed as an epidural adjunct for postoperative pain relief.
Constipation and DyspepsiaFunctions as a laxative and antacid.

Pharmacology and Physiology

Aspect of MagnesiumFunction
Mode of ActionActs as a natural calcium antagonist, inhibits Ca2+ influx.
Competes with calcium for binding sites on sarcoplasmic
reticulum. Acts as an NMDA receptor antagonist.
PhysiologyFourth most abundant cation in the body, important intracellular cation.
Activates over 300 enzyme systems.
Affects neurons, myocardial and skeletal muscle, vasomotor
tone, and hormone receptor binding.

Effects on Systems

  • Central and Peripheral Nervous Systems: Depresses CNS, sedating, cerebral vasodilator, interferes with neurotransmitter release, and affects muscle function.
  • Cardiovascular: Reduces vascular tone, inhibits catecholamine release, decreases cardiac conduction, and contractile force.
  • Respiratory: Weakens respiratory muscles, reduces bronchomotor tone.
  • Uterus: Powerful tocolytic, useful in hypertensive disease of pregnancy.
  • Renal: Acts as a vasodilator and diuretic.


Magnesium Level (mmol/l)Effects
0.7–1.0Normal blood level.
4.0–8.0Therapeutic level.
15.0Respiratory paralysis.
15.0Complete SAN and AV block.
25.0Cardiac arrest.

Magnesium can cross the placenta rapidly, potentially affecting the neonate, leading to hypotonia and apnea.

Magnesium sulphate is a vital compound in medical practice due to its diverse clinical applications, ranging from obstetrics to cardiology and neurology. Understanding its pharmacological properties, physiological roles, and potential toxicity is crucial for its safe and effective use in various medical scenarios.

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