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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. Accessed August 21, 2012.

  • Serum magnesium >2 mEq/L (>1 mmol/L)

  • Caused by decreased renal excretion or excessive intake of magnesium.

  • Magnesium concentrations steadily increase as GFR decreases below 30 mL/min/1.73 m2 (0.29 mL/s/m2).

  • Rarely occurs except with stage 4 or 5 chronic kidney disease (CKD).

  • Age: elderly prone to hypermagnesemia due to reduced glomerular filtration rate (GFR) and use of magnesium-containing antacids and vitamins.
  • CKD

Signs and Symptoms

  • Symptoms rare with serum magnesium concentration <4 mEq/L (<2 mmol/L)
  • Sequence of neuromuscular signs as serum magnesium increases from 5 mEq/L to 12 mEq/L (2.5-6 mmol/L):
    • Sedation
    • Hypotonia
    • Hyporeflexia
    • Somnolence
    • Coma
    • Muscle paralysis
    • Respiratory depression
  • Sequence of cardiovascular signs as serum magnesium increases from 3 mEq/L to 15 mEq/L (1.5-7.5 mmol/L):
    • Hypotension
    • Cutaneous vasodilation
    • QT-interval prolongation
    • Bradycardia
    • Primary heart block
    • Nodal rhythms
    • Bundle branch block
    • QRS- and then PR-interval prolongation
    • Complete heart block
    • Asystole

Means of Confirmation and Diagnosis

  • Serum magnesium >2 mEq/L (>1 mmol/L)

Laboratory Tests

  • Metabolic panel
  • Serum magnesium

Differential Diagnosis

  • Reverse neuromuscular and cardiovascular manifestations.
  • Decrease serum magnesium concentration.
  • Identify and treat underlying cause.

  • In dialysis patients, change hemodialysis prescription to magnesium-free dialysate.
  • Emergency hemodialysis will correct hypermagnesemia within 4 hours.

  • Treatment regimen depends on severity of signs and symptoms and degree of serum magnesium concentration elevation.
  • Options:
    • Reduce magnesium intake.
    • Enhance magnesium elimination.
      • Forced diuresis with saline and loop diuretics (e.g., furosemide 40 mg IV) in patients with normal renal function or stage 1, 2, or 3 CKD
    • Antagonize physiologic effects.
      • IV calcium (100–200 mg of elemental calcium; e.g., calcium gluconate 2 g IV)
        • Repeat hourly in life-threatening situations.

  • Evaluate serum magnesium concentration hourly when administering IV calcium until symptoms abate and magnesium concentration decreases below 3.3 mEq/L (1.64 mmol/L).
  • Continuously monitor ECG.
  • Assess urine output and for physical signs of volume overload.

  • Dependent on underlying condition and presenting symptoms.
  • Forced diuresis with saline and furosemide should reduce serum magnesium concentration within 6–12 hours.

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