Hypermagnesemia is a serum magnesium concentration > 2.6 mg/dL (>
(See also Overview of Disorders of Magnesium Concentration.)
Symptomatic hypermagnesemia is fairly uncommon. It occurs most commonly in patients with renal failure after ingestion of magnesium-containing drugs, such as antacids or purgatives. Hypermagnesemia may also occur in patients with hypothyroidism or Addison disease.
Even asymptomatic hypermagnesemia is rare in patients with normal renal function.
Symptoms and signs include hyporeflexia, hypotension, respiratory depression, and cardiac arrest.
Diagnosis of Hypermagnesemia
Serum magnesium concentrations > 2.6 mg/dL (> 1.05 mmol/L)
At serum magnesium concentrations of 6 to 12 mg/dL (2.5 to 5 mmol/L), the ECG shows prolongation of the PR interval, widening of the QRS complex, and increased T-wave amplitude.
Deep tendon reflexes disappear as the serum magnesium concentration approaches 12 mg/dL (5.0 mmol/L); hypotension, respiratory depression, and narcosis develop with increasing hypermagnesemia. Cardiac arrest may occur when blood magnesium concentration is > 15 mg/dL (6.0 to 7.5 mmol/L).
Treatment of Hypermagnesemia
Diuresis or dialysis
Calcium gluconate may temporarily reverse many of the magnesium-induced changes, including respiratory depression.
Hemodialysis may be valuable in severe hypermagnesemia, because a relatively large fraction (about 70%) of blood magnesium is not protein bound and thus is removable with hemodialysis. When hemodynamic compromise occurs and hemodialysis is impractical, peritoneal dialysis is an option.
