Hypermagnesemia

Hypermagnesemia is an electrolyte disturbance in which there is an abnormally elevated level of magnesium in the blood. Usually this results in excess of magnesium in the body.

Hypermagnesemia occurs rarely because the kidney is very effective in excreting excess magnesium. It usually develops only in people with kidney failure who are given magnesium salts or who take drugs that contain magnesium (e.g. some antacids and laxatives). It is usually concurrent with hypercalcemia and/or hyperkalemia.

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Metabolism

For a detailed description of magnesium homeostasis and metabolism see hypomagnesemia.

Symptoms

• Weakness, nausea and vomiting
• Hypotension
• Impaired breathing
• Arrhythmia and asystole, most prominent cardiac symptoms are due to conduction delays, since magnesium acts as physiologic calcium blocker.

Clinical consequences related to serumconcentration:

• 4.0 mEq/l hyporeflexia
• >5.0 mEq/l Prolonged atrioventricular conduction
• >10.0 mEq/l Complete heart block
• >13.0 mEq/l Cardiac arrest

Causes

Since magnesium is excreted through the kidneys, renal failure can result in hypermagnesemia. The most important cause however is suppletion.

Predisposing conditions

• Hemolysis, magnesium concentration in erythrocytes is approximately three times greater than in serum, therefore hemolysis can increase plasma magnesium. Hypermagnesemia is expected only in massive hemolysis.
• Renal insufficiency, excretion of magnesium becomes impaired when creatinine clearance falls below 30 ml/min. However, hypermagnesemia is not a prominent feature of renal insufficiency unless magnesium intake is increased.
• Other conditions that can predispose to mild hypermagnesemia are diabetic ketoacidosis, adrenal insufficiency, hyperparathyroidism and lithium intoxication.

Therapy

Prevention of hypermagnesemia usually is possible. In mild cases, withdrawing magnesium suppletion is often sufficient. In more severe cases the following treatments are used:

• Intravenous calcium gluconate, because the actions of magnesium in neuromuscular and cardiac function are antagonized by calcium.

Definitive treatment of hypermagnesemia requires increasing renal magnesium excretion through:

• Intravenous diuretics, in the presence of normal renal function
• Dialysis, when kidney function is impaired and the patient is symptomatic from hypermagnesemia