What are the medical uses of magnesium?

Medical Uses of Magnesium

Intravenous magnesium sulfate is most strongly indicated for treatment of severe refractory asthma, where it can improve pulmonary function and reduce hospital admissions, particularly in patients with very low FEV1 (<20% predicted). 1

Primary Therapeutic Applications

1. Acute Severe Asthma

• IV magnesium sulfate (2g over 20 minutes) is recommended for patients with:
  • Severe refractory asthma not responding to standard treatments
  • FEV1 <30% predicted, especially <20% predicted
  • Mechanism: Causes bronchial smooth muscle relaxation independent of serum magnesium level 1
  • Side effects are generally minor (flushing, light-headedness) 1

2. Cardiac Arrhythmias

• Effective for treatment of:
  • Ventricular fibrillation/ventricular tachycardia, particularly when associated with acute myocardial infarction 1
  • Torsades de Pointes (TdP) 1
  • Dosing for VF/VT: 8 mmol bolus followed by 2.5 mmol/h infusion 1
• Mechanism: Blocks neuromuscular transmission and decreases acetylcholine release at nerve endings 2

3. Electrolyte Disorders

• Treatment of hypomagnesemia (<1.3 mEq/L) 1
  • Early symptoms may develop within 3-4 days or weeks
  • Predominant effects are neurological (muscle irritability, clonic twitching, tremors)
  • Often accompanied by hypocalcemia and hypokalemia 2
• Parenteral therapy repairs plasma deficit and resolves deficiency symptoms 2

4. Eclampsia/Pre-eclampsia

• Prevents or controls convulsions by:
  • Blocking neuromuscular transmission
  • Decreasing acetylcholine release at motor nerve end-plates
  • CNS depressant effect without adverse effects on mother, fetus, or neonate when used as directed 2

Pharmacology and Mechanism of Action

• Normal plasma magnesium levels: 1.5-2.5 mEq/L
• Therapeutic anticonvulsant levels: 2.5-7.5 mEq/L
• Physiologic effects at different plasma levels:

  • 4 mEq/L: Deep tendon reflexes decrease

  • ~10 mEq/L: Deep tendon reflexes disappear, risk of respiratory paralysis

  • 12 mEq/L: Potentially fatal 2

• Peripheral vasodilation:
  • Low doses: Flushing and sweating
  • Higher doses: Blood pressure reduction 2
• Calcium administration can antagonize central and peripheral effects of magnesium toxicity 2

Pharmacokinetics

• IV administration:
  • Immediate onset of anticonvulsant action
  • Duration approximately 30 minutes
• IM administration:
  • Onset in about one hour
  • Duration 3-4 hours
• Excretion solely by kidneys at rate proportional to plasma concentration and glomerular filtration 2

Monitoring and Safety

• Monitor deep tendon reflexes as clinical indicator of toxicity
• Use with caution in patients with kidney disease due to renal excretion 2
• Magnesium toxicity (levels 6-10 mmol/L) can result in:
  • Atrioventricular nodal conduction block
  • Bradycardia
  • Hypotension
  • Cardiac arrest 1

Other Potential Applications

• Possible role in preventing postoperative arrhythmias after cardiac surgery, though evidence is mixed 1
• May help reduce symptoms in conditions associated with magnesium deficiency:
  • Metabolic syndrome
  • Glucose and insulin metabolism disorders
  • Dysmenorrhea
  • Leg cramps during pregnancy 3

Important Caveats

• Not recommended for routine treatment of asthma but permitted in severe cases not responding to standard therapy 4
• Despite widespread use for constipation and dyspepsia, evidence is limited 3
• Magnesium supplementation trials have shown inconsistent benefits and potential adverse effects with overload 5
• Currently no firm recommendation for routine supplementation except when hypomagnesemia is proven or suspected as cause for cardiac arrhythmias 5