Definition: serum [Mg2+] >2.3 mg/dL.

Etiology/Risk Factors

Hypermagnesemia is a rarely encountered electrolyte disturbance.

• Insufficient excretion: in setting of CKD.
• Excess intake is often iatrogenic: overaggressive replacement, Mg-rich laxative in CKD, administration during treatment for preeclampsia/eclampsia.

Evaluation

• Order a chem 10.
• Assess for symptoms (rarely present until Mg >4 mEq/L): areflexia, lethargy, weakness, paralysis, respiratory failure, hypotension, bradycardia, coma, cardiac arrest.
• Review medication list.

Management

• Asymptomatic: hold magnesium supplementation.
• Symptomatic:
  • 1 gram calcium gluconate IV over 10 minutes to antagonize Mg.
  • Support ventilation and heart rate if necessary.

Note: definitive therapy requires dialysis if renal excretion is inadequate to normalize serum magnesium in a timely manner.

Key Points

• Clinically relevant hypermagnesemia is rare and is usually related to excessive magnesium administration in the setting of renal failure or otherwise impaired excretion.
• Severe hypermagnesemia may require dialysis.

Weisinger JR, Bellorin-Font E. Magnesium and phosphorus. Lancet 1998;352:391-396.

Agus ZS. Hypomagnesemia J Am Soc Nephrol 1999;10:1616-1622.