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    Drugs & Diseases > Nephrology

    Hypomagnesemia Treatment & Management

    Updated: Aug 23, 2018
    • Author: Tibor Fulop, MD, PhD, FACP, FASN; Chief Editor: Vecihi Batuman, MD, FASN  more...
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    Treatment

    Approach Considerations

    Hypomagnesemia often leads to hypocalcemia, a phenomenon largely explained by inhibition of parathyroid hormone bioactivity. Hypocalcemia does not resolve until the magnesium deficiency has been corrected.

    Patients with hypomagnesemia have an excellent prognosis once the deficiency is corrected. For the most part, the symptoms are reversible with treatment.

    Diet

    Green vegetables such as spinach are good sources of magnesium, which is contained in the chlorophyll molecule. Some legumes (beans and peas), nuts and seeds, and whole, unrefined grains are also good sources of magnesium. [106]

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    Pharmacologic Therapy

    The route of magnesium repletion varies with the severity of the clinical manifestations. For example, the hypocalcemic-hypomagnesemic patient with tetany or the patient who is suspected of having hypomagnesemic-hypokalemic ventricular arrhythmias should receive 50 mEq of intravenous magnesium, given slowly over 8-24 hours. This dose can be repeated as necessary to maintain the plasma magnesium concentration above 1.0 mg/dL (0.4 mmol/L or 0.8 mEq/L). In the normomagnesemic patient with hypocalcemia, it has been suggested that this dose be repeated daily for 3-5 days.

    It must be appreciated that the plasma magnesium concentration is the major regulator of magnesium reabsorption in the loop of Henle, the major site of active magnesium transport. Thus, an abrupt elevation in the plasma magnesium concentration will partially remove the stimulus for magnesium retention, and up to 50% of the infused magnesium will be excreted in the urine.

    Furthermore, because magnesium is subject to slow equilibration between serum and the intracellular spaces and tissues (eg, bone, red blood cells, muscle), the serum magnesium level may appear artificially high if measured too soon after a magnesium dose is administered. Large magnesium depletion requires sustained correction of the hypomagnesemia.

    For these reasons, oral replacement should be given in the asymptomatic patient, preferably with a sustained-release preparation, given the ability of magnesium to induce diarrhea. Bioavailability of oral preparations is assumed to be 33% in the absence of intestinal malabsorption. Several preparations are available: Mag-Ox 400, containing magnesium oxide; Slow-Mag, containing magnesium chloride; and Mag-Tab, containing magnesium lactate. These preparations provide 5-7 mEq (2.5-3.5 mmol or 60-84 mg) of magnesium per tablet. Six to 8 tablets should be taken daily in divided doses for severe magnesium depletion. Two to 4 tablets may be sufficient for mild, asymptomatic disease. Mag-Ox 400 contains 242 mg (20 mEq) of elemental magnesium, but absorption is less efficacious.

    Patients with concomitant hypokalemia or hypocalcemia should also receive potassium and calcium replacement, because these disorders may take several days to correct when treated with magnesium alone. In the presence of hypocalcemia, tetany can occur during the administration of magnesium-sulfate if calcium is not supplemented, as ionized calcium levels can drop acutely from complexing of calcium with sulfate ions and increased urinary excretion. [111]

    Sulfate ions also cause the generation of more negative transepithelial potential difference in renal tubules, which promotes kaliuresis and thereby can worsen hypokalemia. Patients undergoing intravenous magnesium replacement should be monitored for evidence of acute hypermagnesemia (eg, respiratory depression, areflexia). Patients with renal dysfunction are particularly at increased risk for hypermagnesemia during treatment, and only 25-50% of the normal dose magnesium dose should be given to patients when plasma creatinine levels are greater than 2 mg/dL.

    Intravenous calcium chloride or gluconate represent the antidotes for hypermagnesemia, and 1-2 ampules should be administered immediately if symptomatic or otherwise serious hypermagnesemia develops. Calcium chloride (1000 mg, 13.6 mEq of calcium) should be infused via a central venous catheter over 10 minutes; however, calcium gluconate 1-3 g (4.56-13.7 mEq of elemental calcium) can be infused via a peripheral intravenous catheter over 3-10 minutes. [112]

    Diuretic-induced hypomagnesemia

    Patients with diuretic-induced hypomagnesemia who cannot discontinue diuretic therapy may benefit from the addition of a potassium-sparing diuretic (eg, amiloride or triamterene) or from changing plain thiazide-type diuretic medications to thiazide diuretic/potassium-sparing diuretic combinations. These drugs may decrease magnesium excretion by increasing its reabsorption in the collecting tubule. These drugs also may be useful in Bartter and Gitelman syndrome or in cisplatin nephrotoxicity.

    These patients should also be placed on a magnesium-rich diet, which includes such foods as meat, green vegetables, dairy products, nuts, cereals, and seafood. In addition, these patients should be examined frequently for evidence of magnesium deficiency and should be monitored for regular serum magnesium. If hypomagnesemia persists, these patients should be treated with an oral sustained-release preparation.

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