Hypomagnesemia

Hypomagnesemia is a plasma magnesium concentration less than 1.4 meq/L (< 0.7 mmol/L).

Possible causes include inadequate intake and absorption of magnesium, increased excretion due to hypercalcemia or drugs such as furosemide. Symptoms of hypomagnesemia are related to concomitant hypokalemia and hypocalcemia and include lethargy, tremor, tetany, seizures, and arrhythmias. Treatment involves replacing the magnesium deficiency.

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Causes hypomagnesemia

• Alcoholism - Due to inadequate intake and excessive renal excretion
• Gastrointestinal losses - Chronic diabetes, steatorrhea
• Pregnancy related - Preeclampsia and eclampsia, lactation (increased magnesium requirement)
• Primary renal losses - Excessive excretion of magnesium without obvious cause (Gittelman syndrome)
• Secondary renal losses - Loop and thiazide diuretics; hypercalcemia; after removal of a parathyroid tumor; diabetic ketoacidosis; hypersecretion of aldosterone, thyroid hormones, ADH; nephrotoxins (amphotericin B, cisplatin, cyclosporine, aminoglycosides)

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Symptoms hypomagnesemia

Plasma magnesium concentrations, even when free ions are measured, may be within normal limits despite decreased cellular or bone magnesium stores. Decreased magnesium levels are usually due to inadequate intake, as well as impaired renal retention or GI absorption.

Symptoms of hypomagnesemia include anorexia, nausea, vomiting, lethargy, weakness, personality disorder, tetany (eg, positive Trousseau or Chvostek signs or spontaneous carpopedal spasm), tremor, and muscle fasciculations. Neurologic signs, especially tetany, correlate with the development of concomitant hypocalcemia and/or hypokalemia. Electromyography reveals myopathic potentials but is also characteristic of hypocalcemia or hypokalemia. Severe hypomagnesemia may cause generalized tonic-clonic seizures, especially in children.

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Diagnostics hypomagnesemia

Diagnosis is based on finding a serum magnesium level of less than 1.4 mEq/L (less than 0.7 mmol/L). Severe hypomagnesemia is usually seen when the level is less than 1.0 mEq/L (less than 0.5 mmol/L). Associated hypocalcemia and hypocalciuria are often seen in patients with steatorrhea, alcoholism, or other causes of magnesium deficiency. Hypokalemia with increased renal potassium secretion and metabolic alkalosis may be present. Thus, unexplained hypocalcemia and hypokalemia suggest the possibility of decreased magnesium levels.

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Treatment hypomagnesemia

In asymptomatic or persistent magnesium deficiency with a level of less than 1.0 mEq/L (less than 0.5 mmol/L), treatment with magnesium salts (sulfate or chloride) is indicated. Patients with alcoholism are treated empirically. In such cases, a deficiency of up to 12-24 mg/kg is possible. Patients with normal renal function should be prescribed twice the amount of the calculated deficiency, since about 50% of the consumed magnesium is excreted in the urine. Magnesium gluconate is administered orally at a dose of 500-1000 mg 3 times a day for 3-4 days. Parenteral administration is performed in patients with severe hypomagnesemia or when oral administration is impossible. For parenteral administration, a 10% solution of magnesium sulfate (1 g/10 ml) is used for intravenous administration and a 50% solution (1 g/2 ml) for intramuscular administration. During treatment, plasma magnesium levels must be monitored, especially with parenteral administration or in patients with renal insufficiency. Treatment is continued until normal plasma magnesium levels are achieved.

For severe hypomagnesemia with significant symptoms (eg, generalized seizures, magnesium level less than 1 mEq/L), 2 to 4 g of magnesium sulfate should be given intravenously over 5 to 10 minutes. If seizures continue, the dose may be repeated up to a total of 10 g over a further 6 hours. If seizures are controlled, 10 g may be infused in 1 liter of 5% dextrose over 24 hours, followed by up to 2.5 g every 12 hours to replace the deficit in total magnesium stores and prevent further decline in plasma magnesium levels. If plasma magnesium levels are below 1 mEq/L (less than 0.5 mmol/L) but symptoms are not severe, magnesium sulfate in 5% dextrose may be given intravenously at a rate of 1 g per hour for up to 10 hours. In less severe cases of hypomagnesemia, gradual replacement can be achieved by parenteral administration of small doses over 3-5 days until plasma magnesium levels are normalized.