(See also Overview of Disorders of Magnesium Concentration Overview of Disorders of Magnesium Concentration Magnesium is the 4th most plentiful cation in the body. A 70-kg adult has about 2000 mEq (1000 mmol) of magnesium. About 50% is sequestered in bone and is not readily exchangeable with magnesium... read more .)
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 Hypothyroidism Hypothyroidism is thyroid hormone deficiency. It is diagnosed by clinical features such as a typical facial appearance, hoarse slow speech, and dry skin and by low levels of thyroid hormones... read more 
or Addison disease Addison Disease Addison disease is an insidious, usually progressive hypofunctioning of the adrenal cortex. It causes various symptoms, including hypotension and hyperpigmentation, and can lead to adrenal crisis... read more 
.
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
Calcium gluconate
Diuresis or dialysis
Treatment of severe magnesium toxicity consists of circulatory and respiratory support and administration of 10% calcium gluconate 10 to 20 mL IV. Calcium gluconate may reverse many of the magnesium-induced changes, including respiratory depression.
Administration of IV furosemide can increase magnesium excretion when renal function is adequate; volume status should be maintained.
Hemodialysis Hemodialysis In hemodialysis, a patient’s blood is pumped into a dialyzer containing 2 fluid compartments configured as bundles of hollow fiber capillary tubes or as parallel, sandwiched sheets of semipermeable... read more 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 Peritoneal Dialysis Peritoneal dialysis uses the peritoneum as a natural permeable membrane through which water and solutes can equilibrate. Compared to hemodialysis, peritoneal dialysis is Less physiologically... read more is an option.
