Treatment of Hypomagnesemia
For severe or symptomatic hypomagnesemia (serum Mg <0.5 mmol/L or life-threatening arrhythmias), administer intravenous magnesium sulfate immediately; for mild asymptomatic cases (0.5-0.7 mmol/L), oral magnesium supplementation is appropriate. 1
Critical First Step: Address Underlying Causes
Before initiating magnesium replacement, you must correct water and sodium depletion through rehydration to prevent renal magnesium wasting from secondary hyperaldosteronism 1. Simultaneously identify and discontinue offending medications including:
- Diuretics, proton pump inhibitors 1
- Chemotherapy agents (cisplatin, cetuximab) 1, 2
- Aminoglycosides, amphotericin B 1, 2
Intravenous Magnesium Sulfate for Severe Cases
Life-Threatening Arrhythmias (Torsades de Pointes)
Administer 1-2 g IV bolus push immediately 1, 3, 4. The rate of IV injection should generally not exceed 150 mg/minute except in severe eclampsia with seizures 4.
Severe Hypomagnesemia (<0.5 mmol/L)
For symptomatic cases, administer 1 g (8.12 mEq) IM every 6 hours for four doses 4. Alternatively, add 5 g (approximately 40 mEq) to one liter of 5% dextrose or 0.9% sodium chloride for slow IV infusion over 3 hours 4. For the most severe cases, up to 250 mg/kg body weight may be given IM within 4 hours if necessary 4.
Critical monitoring point: Target serum magnesium level of 6 mg/100 mL (approximately 2.5 mmol/L) for seizure control 4. Do not exceed 30-40 g total daily dose 4.
Oral Magnesium for Mild Cases
For asymptomatic patients with serum magnesium 0.5-0.7 mmol/L, prescribe magnesium oxide 12-24 mmol daily (4 mmol capsules), preferably at night when intestinal transit is slowest 1, 3. This approach is particularly effective for patients with deficient dietary intake or malabsorption 5.
Concurrent Electrolyte Abnormalities
Hypomagnesemia frequently coexists with hypocalcemia and hypokalemia, which will not correct until magnesium is repleted first 1, 6. Check and address these simultaneously, as magnesium deficiency contributes to the persistence of both conditions 6.
Special Populations
Patients on Kidney Replacement Therapy
Use dialysis solutions containing magnesium rather than IV supplementation, as hypomagnesemia occurs in 60-65% of critically ill patients on continuous KRT 1, 3. This prevents the need for repeated IV dosing 1.
Cancer Patients on Chemotherapy
Monitor magnesium levels regularly in patients receiving cisplatin or cetuximab, as these agents commonly cause significant hypomagnesemia 1, 2.
Renal Insufficiency
In severe renal insufficiency, the maximum dosage is 20 grams per 48 hours with frequent serum magnesium monitoring 4. Exercise extreme caution to prevent exceeding renal excretory capacity 4, 5.
Pregnancy
Avoid continuous maternal administration beyond 5-7 days as this can cause fetal abnormalities 4.
Common Pitfalls to Avoid
- Do not treat magnesium in isolation: Water and sodium depletion must be corrected first 1
- Do not ignore coexisting electrolyte abnormalities: Calcium and potassium will remain low until magnesium is corrected 1, 6
- Do not use oral antacids in hypophosphatemia: These are contraindicated 5
- Reduce dosing in constipation: Magnesium can worsen this condition 5