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Serum magnesium has a normal range of 0.8-1.2 mMol/L. Magnesium homeostasis is regulated by renal and gastrointestinal mechanisms. Hypermagnesemia is usually iatrogenic and is frequently seen in conjunction with renal insufficiency.

Clinical Evaluation of Hypermagnesemia

Renal. Creatinine clearance <30 mL/minute.

Nonrenal. Excessive use of magnesium cathartics, especially with renal failure; iatrogenic overtreatment with magnesium sulfate.

Less Common Causes. Hyperparathyroidism, Addison's disease, hypocalciuric hypercalcemia, lithium therapy.

Hypermagnesemia is commonly caused by overzealous replacement of magnesium, inadequate adjustment of Mg dosage for renal insufficiency, and overuse of magnesium-containing cathartics.

Cardiovascular Manifestations of Hypermagnesemia

Lower levels of hypermagnesemia <10 mEq/L. Delayed interventricular conduction, first-degree heart block, prolongation of the Q-T interval.

Levels greater than 10 mEq/L. Heart block progressing to complete heart block and asystole occurs at levels greater than 12.5 mMol/L (>6.25 mMol/L).

Neuromuscular Effects

Hyporeflexia occurs at a Mg level >4 mEq/L (>2 mMol/L); an early sign of magnesium toxicity is diminution of deep tendon reflexes caused by neuromuscular blockade.

Respiratory depression due to respiratory muscle paralysis occurs at levels >13 mEq/L (>6.5 mMol/L).

Somnolence and coma occur at very elevated levels.

Hypermagnesemia should always be considered when these symptoms occur in patients with renal failure, in those receiving therapeutic laxative abuse.

Treatment of Hypermagnesemia

Asymptomatic, Hemodynamically Stable Patients

Moderate hypermagnesemia can be