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Hypermagnesemia
Last reviewed: 07.07.2025
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Hypermagnesemia is a condition when magnesium is elevated above 2.1 mEq/L (> 1.05 mmol/L). The main cause is renal failure.
Symptoms of hypermagnesemia include hypotension, respiratory depression, and cardiac arrest. Diagnosis is by measuring serum magnesium levels. Treatment includes intravenous calcium gluconate and possibly furosemide; hemodialysis may be effective in severe cases.
Pathogenesis
Magnesium is the fourth most abundant cation in the body. A 70 kg adult contains about 2000 mEq of magnesium. About 50% is sequestered in bone tissue and does not participate in exchange with other spaces. Only 1% of the total magnesium in the body is in the ECF. The rest is in the intracellular space. Normal magnesium concentration is 1.4-2.1 mEq/L (0.7-1.05 mmol/L).
Maintenance of plasma magnesium concentrations depends on dietary intake and effective renal and intestinal retention. After 7 days of starting a magnesium-restricted diet, renal and GI magnesium excretion falls by 1 mEq/day (0.5 mmol/L per day).
About 70% of plasma magnesium is filtered by the kidney; the remainder is bound to proteins. Protein binding is pH-dependent. Plasma magnesium concentrations and total body magnesium levels are not closely related. However, severe hypomagnesemia may reflect decreased body magnesium stores.
Magnesium activates many enzymes, some of which depend on it. Magnesium is necessary for all enzymatic processes involving ATP and for many enzymes involved in nucleic acid metabolism. Magnesium is necessary for the cofactor activity of thiamine pyrophosphate and stabilizes the structure of DNA and RNA macromolecules. Magnesium is also associated with calcium and potassium metabolism, although the mechanism is not fully understood.
Hypermagnesemia is more common in patients with renal failure after taking magnesium-containing medications such as antacids or laxatives.
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Symptoms hypermagnesemia
At plasma magnesium concentrations of 5-10 mEq/L (2.5-5 mmol/L), the ECG shows prolongation of the PR interval, widening of the QRS complex, and increased amplitude of the T wave. Deep tendon reflexes disappear when plasma magnesium concentrations rise to 10 mEq/L (5.0 mmol/L); with progressive hypermagnesemia, hypotension, respiratory depression, and narcosis develop. Cardiac arrest may occur when blood magnesium levels are above 12-15 mEq/L (6-7.5 mmol/L).
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Treatment hypermagnesemia
Severe hypermagnesemia is treated with methods such as: circulatory and respiratory support with 10-20 ml of intravenous calcium gluconate. Calcium gluconate can reverse many of the changes induced by magnesium, including respiratory depression. Intravenous furosemide can increase magnesium excretion if renal function is normal. Hemodialysis may be effective in severe hypermagnesemia, since a relatively large proportion (about 70%) of blood magnesium is nonprotein bound and therefore ultrafilterable. If hemodynamic failure occurs and hemodialysis is inappropriate, peritoneal dialysis may be an option.