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Key Features

  • Serum magnesium > 3.0 mg/dL (> 1.25 mmol/L)

  • Almost always the result of advanced stages of chronic kidney disease (CKD) and impaired magnesium excretion

  • Pregnant patients may have severe hypermagnesemia from intravenous magnesium therapy for preeclampsia and eclampsia

  • Magnesium replacement should be done cautiously in patients with CKD, and dose reductions up to 75% may be necessary to avoid hypermagnesemia

Clinical Findings

  • Muscle weakness

  • Decreased deep tendon reflexes

  • Mental obtundation

  • Confusion

  • Weakness, even flaccid paralysis

  • Ileus, urinary retention, hypotension

  • In severe cases, respiratory muscle paralysis or cardiac arrest

Diagnosis

  • Serum magnesium > 3.0 mg/dL (> 1.25 mmol/L)

  • In the common setting of CKD, elevated blood urea nitrogen, serum creatinine, phosphate, and uric acid; serum K+ may be elevated

  • Serum Ca2+ is often low

  • ECG may show increased PR interval, broadened QRS complexes, and peaked T waves, probably related to associated hyperkalemia

Treatment

  • Exogenous sources of magnesium should be discontinued

  • Calcium antagonizes Mg2+ and may be given intravenously as calcium chloride, 500 mg or more at a rate of 100 mg (4.1 mmol)/min

  • Hemodialysis or peritoneal dialysis may be indicated

  • Long-term use of magnesium hydroxide and magnesium sulfate should be avoided in patients with advanced stages of CKD

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