Pharm 101: Magnesium

Class

Electrolyte

Pharmacodynamics

• Unclear mechanism, but has been found to have antiarrhythmic effects in some patients with normal serum magnesium levels
• Recognised to influence Na/K ATPase, Na channels, certain K channels, and Ca channels

Clinical uses

• Anti-convulsant effect
  • Pre-eclampsia and eclampsia, for prevention and treatment of life-threatening seizures
• Bronchodilator effect
• Anti-arrhythmic:
  • Torsades de pointes even if serum magnesium normal
  • Atrial fibrillation
  • Digitalis-induced arrhythmia if hypomagnesaemia present

Toxicity

• > 4 mmol/L
  • Muscle weakness
  • Hyporeflexia
  • Nausea/vomiting
• > 10 mmol/L
  • Hypoventilation
  • Arrhythmia
  • Neuromuscular paralysis
  • Coma

Further reading

• Nickson C. CCC: Magnesium

References

• Katzung BG. Basic and Clinical Pharmacology. 14e. 2018