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Source: Brophy DF, Frumin J. Disorders of Potassium and Magnesium Homeostasis. In: DiPiro, JT, Talbert RL, Yee GC, Matzke GR, Wells BG, Posey LM. Pharmacotherapy: A Pathophysiologic Approach. 8th ed. http://accesspharmacy.com/content.aspx?aid=7984069. Accessed August 21, 2012.

  • Serum magnesium <1.4 mEq/L (<0.70 mmol/L)

  • Drugs or disorders that interfere with intestinal absorption or increase renal excretion of magnesium can cause hypomagnesemia.
    • Small bowel disease most common cause worldwide.
    • Commonly associated with alcoholism.

  • Primary renal magnesium wasting caused by:
    • Defect in renal tubular magnesium reabsorption
    • Inhibition of sodium reabsorption in which magnesium transport follows passively
    • Thiazide and loop diuretics

  • Common problem in both ambulatory and hospitalized patients.
  • Up to 65% of intensive care unit patients are magnesium deficient.

  • Include green vegetables such as spinach in diet.

  • Alcoholism
  • Malnutrition
  • Excessive vomiting

Signs and Symptoms

  • Neuromuscular disturbances earliest manifestations.
    • Tremor
    • Fasciculations
    • Tetany
    • Chvostek’s sign
    • Trousseau’s sign
    • Generalized convulsions
  • Cardiovascular
    • Palpitations
    • Arrhythmias
    • Sudden cardiac death
    • Hypertension
    • Electrocardiogram (ECG) changes:
      • Mild hypomagnesemia
        • Widened QRS complex
        • Peaked T waves
      • Moderate to severe hypomagnesemia
        • Prolonged PR interval
        • Progressive widening of QRS complex
        • Flattened T waves
  • Other electrolyte disturbances

Means of Confirmation and Diagnosis

  • Serum magnesium <1.4 mEq/L (<0.70 mmol/L)

Laboratory Tests

  • Metabolic panel
    • Serum calcium
    • Serum potassium
  • Serum magnesium

Diagnostic Procedure

  • ECG

Differential Diagnosis

  • Resolve signs and symptoms.
  • Restore normal magnesium concentrations.
  • Correct concomitant electrolyte abnormalities.
  • Identify and correct underlying cause of magnesium depletion.

  • Severity of magnesium depletion and presence of symptoms dictate route of magnesium supplementation (Table 1).
    • Diarrhea dose-limiting toxicity with oral therapy.
    • Intramuscular magnesium painful and should be reserved for patients with severe hypomagnesemia and limited venous access.
    • IV bolus injection associated with flushing, sweating, and sensation of warmth.
  • Optimal replacement regimen unknown.
    • Serum magnesium >1 mEq/L (>0.5 mmol/L): use oral products
    • Serum magnesium <1 mEq/L (<0.5 mmol/L): Common approach administer 8–12 g of IV magnesium sulfate in first 24 hours, followed by 4–6 g/day for 3–5 days to adequately replace body stores.
      • Approximately 50% of administered dose excreted in urine.

Table 1. Guidelines for Treatment of Magnesium Deficiency in Adults

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