How to Cite This Chapter: Merali Z, Panju M, Srivaratharajah K, Mathew A, Kokot F, Franek E, Drabczyk R. Hypermagnesemia. McMaster Textbook of Internal Medicine. Kraków: Medycyna Praktyczna. https://empendium.com/mcmtextbook/chapter/B31.II. Accessed July 23, 2024.
Last Updated: December 15, 2021
Last Reviewed: December 15, 2021
Chapter Information

Definition, Etiology, PathogenesisTop

Hypermagnesemia is defined as a total serum [Mg2+] >1.2 mmol/L.


1) Excessive intake of magnesium due to the use of magnesium oxide preparations (eg, as treatment for peptic ulcer disease or hypomagnesemia).

2) Excessive absorption of magnesium from the gastrointestinal tract due to gastric or intestinal inflammatory conditions.

3) Impaired renal excretion of magnesium due to acute or chronic renal failure, adrenal insufficiency, hypothyroidism (deficiency of cortisol, aldosterone, and thyroid hormones impairs renal excretion of magnesium), or treatment with lithium salts.

Clinical FeaturesTop

Hypermagnesemia impairs neuromuscular transmission.

Clinical manifestations of hypermagnesemia include hyporeflexia; facial paresthesia; symptoms of smooth muscle paralysis (constipation, urinary retention); hypotension; and muscle weakness, particularly affecting the respiratory muscles. Electrocardiography (ECG) reveals a long PR interval, and in severe hypermagnesemia also atrioventricular and intraventricular conduction abnormalities (in extreme hypermagnesemia a heart block or even asystole may develop). Signs and symptoms of hypocalcemia may also be present (because of parathyroid hormone suppression).


The diagnosis of hypermagnesemia is based on measurement of serum [Mg2+] (>1.2 mmol/L). In all patients measure serum levels of other ions and creatinine.


1. Try to control the cause of hypermagnesemia.

2. In case of emergency (arrhythmia, ventilation abnormalities) administer Ca2+ in the form of 10 to 20 mL of 10% calcium gluconate IV. You may increase the renal magnesium excretion by IV administration of 1000 to 2000 mL of 0.9% NaCl and furosemide 20 to 40 mg. In patients with life-threatening hypermagnesemia, serum [Mg2+] may be decreased rapidly by hemodialysis using magnesium-free or low-magnesium dialysate.

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