Hypomagnesemia & Hypermagnesemia

Definition

Disorders of magnesium homeostasis include hypomagnesemia (low serum magnesium <1.7 mg/dL) and hypermagnesemia (high serum magnesium >2.5 mg/dL). Magnesium is essential for enzymatic reactions, neuromuscular function, and cardiac stability.

Epidemiology

• Hypomagnesemia occurs in 12–30% of hospitalized patients; more common in critically ill or post-surgical patients
• Hypermagnesemia is less common, usually iatrogenic or in renal failure
• Magnesium disturbances can coexist with calcium, potassium, or phosphate abnormalities

Etiology

• Hypomagnesemia: GI losses (diarrhea, malabsorption), renal losses (diuretics, hyperaldosteronism), alcoholism, malnutrition, pancreatitis
• Hypermagnesemia: renal failure (most common), magnesium-containing medications (antacids, laxatives), adrenal insufficiency, iatrogenic infusion

Pathophysiology

• Magnesium is predominantly intracellular; regulates neuromuscular excitability and cardiac conduction
• Hypomagnesemia → increased neuromuscular excitability, secondary hypokalemia and hypocalcemia
• Hypermagnesemia → decreased neuromuscular excitability, hypotension, bradycardia, cardiac conduction disturbances
• Renal handling of magnesium is central in both disorders