Correction of Hypomagnesemia Using Sodium/Water Depletion Management

Rehydration to correct secondary hyperaldosteronism is the most important first step in treating hypomagnesemia. 1

Pathophysiology and Mechanism

Sodium and water depletion leads to secondary hyperaldosteronism, which increases renal magnesium losses 1, 2
Hyperaldosteronism increases renal retention of sodium at the expense of both magnesium and potassium, leading to high urinary losses of these electrolytes 2
This mechanism is particularly significant in patients with short bowel syndrome, especially those with jejunostomy 1, 2

Begin with intravenous normal saline (0.9% NaCl) to correct dehydration and secondary hyperaldosteronism 1
For severe depletion, administer 2-4 L/day of intravenous saline while keeping the patient "nil by mouth" for 1-2 days 1
Target urine volume of at least 800-1000 ml with a random urine sodium concentration greater than 20 mmol/l 1
In patients with high-output stoma, saline bags may have 4-12 mmol magnesium sulfate added 1

After correcting fluid and electrolyte balance, initiate oral magnesium supplementation 1, 2
Magnesium oxide is commonly given as gelatine capsules of 4 mmol (160 mg) to a total of 12-24 mmol daily 1, 2
Administer magnesium at night when intestinal transit is assumed to be slowest for better absorption 1, 2
If oral supplements don't normalize levels, consider adding oral 1-alpha hydroxy-cholecalciferol (0.25-9.00 μg daily) to improve magnesium balance, but monitor serum calcium to avoid hypercalcemia 1

For severe hypomagnesemia (<1.2 mg/dL) with symptoms, administer intravenous magnesium sulfate 3, 4
Dosage: 1-2 g IV over 15 minutes for acute severe deficiency 3
For maintenance, 5 g (approximately 40 mEq) can be added to one liter of 5% Dextrose or 0.9% Sodium Chloride for slow IV infusion over a three-hour period 3
Alternatively, magnesium can be given as an intravenous or subcutaneous infusion with saline 1

Most magnesium salts are poorly absorbed orally and may worsen diarrhea/stomal output 1
Reduce/avoid excess lipid in diet to improve magnesium absorption 1
Monitor serum magnesium levels regularly to assess response to treatment 2, 4
In patients with renal insufficiency, use caution with magnesium supplementation due to risk of hypermagnesemia 2, 5
Hypomagnesemia is often associated with other electrolyte abnormalities, particularly hypokalemia and hypocalcemia, which may also require correction 6, 7

Failing to correct sodium and water depletion before attempting magnesium replacement 1, 2
Overlooking the underlying cause of hypomagnesemia (e.g., short bowel syndrome, medication effects) 4, 8
Administering oral magnesium supplements without addressing secondary hyperaldosteronism 1
Inadequate monitoring of serum magnesium levels during replacement therapy 2
Excessive magnesium supplementation in patients with renal insufficiency 2, 5