Hypermagnesemia

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, hypotension

• In severe cases, respiratory muscle paralysis, complete heart block, 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 QT prolongation

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 may be indicated

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