What is the treatment for hypomagnesemia (low magnesium levels)?

Treatment of Hypomagnesemia

For severe or symptomatic hypomagnesemia (serum Mg <0.5 mmol/L or <1.2 mg/dL), administer intravenous magnesium sulfate 1-2 g IV push for life-threatening arrhythmias, or 1 g IM every 6 hours for four doses; for mild asymptomatic cases (0.5-0.7 mmol/L), use oral magnesium supplementation at 12-24 mmol daily. 1, 2

Critical First Step: Correct Underlying Causes Before Magnesium Replacement

Before initiating any magnesium therapy, you must address the root cause to prevent futile replacement:

• Rehydrate first to correct secondary hyperaldosteronism, as water and sodium depletion must be corrected before magnesium replacement or the kidneys will continue wasting magnesium 1
• Identify and discontinue offending medications including loop diuretics, thiazide diuretics, proton pump inhibitors, aminoglycosides, cisplatin, cetuximab, and pentamidine 1, 3
• Correct concurrent electrolyte abnormalities as hypomagnesemia commonly coexists with refractory hypokalemia and hypocalcemia that will not correct until magnesium is repleted first 1, 3

Route Selection Based on Clinical Severity

Life-Threatening Presentations (Torsades de Pointes, Cardiac Arrest)

• Administer 1-2 g magnesium sulfate IV push immediately for polymorphic ventricular tachycardia or cardiac arrest with suspected hypomagnesemia 4, 1
• This is a Class I recommendation from the American Heart Association for cardiotoxicity and cardiac arrest 4

Severe Symptomatic Hypomagnesemia (Serum Mg <1.2 mg/dL or <0.5 mmol/L)

• Give 1 g magnesium sulfate (8.12 mEq) IM every 6 hours for four doses (total 32.5 mEq per 24 hours) 2
• Alternatively, for extremely severe cases: 250 mg/kg IM within 4 hours if necessary 2
• Or 5 g (40 mEq) added to 1 liter of IV fluid infused over 3 hours 2
• The IV infusion rate should generally not exceed 150 mg/minute 2

Mild Asymptomatic Hypomagnesemia (Serum Mg 0.5-0.7 mmol/L)

• Use oral magnesium oxide 12-24 mmol daily (typically 4 mmol capsules given at night when intestinal transit is slowest) 1
• Oral magnesium-containing antacids in normal dosage may be effective for prolonged therapy in patients with deficient diet or malabsorption 5

Special Clinical Contexts

Pre-eclampsia/Eclampsia

• Initial dose: 4-5 g IV in 250 mL fluid infused, plus 10 g IM (5 g in each buttock) simultaneously 2
• Maintenance: 4-5 g IM into alternate buttocks every 4 hours as needed, or 1-2 g/hour by continuous IV infusion 2
• Target serum magnesium level of 6 mg/100 mL for seizure control 2
• Do not exceed 30-40 g total daily dose, and limit to 20 g/48 hours in severe renal insufficiency 2
• Critical warning: Continuous maternal administration beyond 5-7 days can cause fetal abnormalities 2

Cancer Patients on Chemotherapy

• Monitor magnesium levels regularly as cisplatin and cetuximab commonly cause significant hypomagnesemia 1

Critically Ill Patients on Continuous Kidney Replacement Therapy

• Use dialysis solutions containing magnesium rather than IV supplementation, as hypomagnesemia occurs in 60-65% of these patients 1

Short Bowel/Jejunostomy Patients

• Encourage glucose-saline replacement solutions with sodium ≥90 mmol/L, restrict hypotonic drinks, measure 24-hour urine magnesium loss, and provide oral magnesium supplementation 1
• Do not rely solely on serum levels as intracellular depletion can exist with normal serum magnesium 1

Monitoring and Safety Considerations

Renal Function Assessment

• Establish adequate renal function before administering any magnesium supplementation to prevent exceeding renal excretory capacity 2, 6
• In severe renal insufficiency, reduce dosing and obtain frequent serum magnesium concentrations 2

Contraindications and Dose Adjustments

• Lower magnesium dose in renal insufficiency or constipation 5
• Avoid oral antacids in hypophosphatemia 5

Diagnostic Workup to Guide Treatment

• Measure fractional excretion of magnesium and urinary calcium-creatinine ratio to determine if losses are gastrointestinal (<2% fractional excretion) or renal (>2% fractional excretion) 6
• This distinction helps identify whether the problem is Bartter syndrome/loop diuretics (associated with hypercalciuria) versus Gitelman syndrome/thiazide diuretics (associated with hypocalciuria) 6

Common Pitfalls to Avoid

• Do not attempt to correct hypokalemia or hypocalcemia before correcting magnesium, as these will remain refractory until magnesium is repleted 1, 3
• Do not give bolus potassium for cardiac arrest suspected to be secondary to hypokalemia, as this is ill-advised (Class III recommendation) 4
• Do not continue magnesium sulfate in pregnancy beyond 5-7 days due to risk of fetal abnormalities 2
• Do not overlook the need for rehydration first in patients with gastrointestinal losses, as hyperaldosteronism will perpetuate magnesium wasting 1