What is the treatment for hypomagnesemia?

Treatment of Hypomagnesemia

For severe or symptomatic hypomagnesemia (serum Mg <0.5 mmol/L or <1.2 mg/dL), administer intravenous magnesium sulfate immediately; for mild asymptomatic cases (0.5-0.7 mmol/L), use oral magnesium supplementation. 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 the patient first to correct secondary hyperaldosteronism, as water and sodium depletion drive renal magnesium wasting—magnesium replacement will fail if hyperaldosteronism persists 1
• Discontinue offending medications including proton pump inhibitors, loop/thiazide diuretics, aminoglycosides, cisplatin, cetuximab, and amphotericin B 1, 3
• Verify adequate renal function before any magnesium administration, as impaired kidney function can lead to dangerous hypermagnesemia 2

Concurrent Electrolyte Abnormalities Must Be Addressed

Hypomagnesemia rarely occurs in isolation and creates a cascade of other deficiencies:

• Correct magnesium FIRST before attempting to treat refractory hypokalemia or hypocalcemia, as magnesium deficiency impairs parathyroid hormone release (causing hypocalcemia) and increases renal potassium wasting 1
• Expect coexisting hypocalcemia and hypokalemia that will not respond to direct replacement until magnesium is repleted 1

Intravenous Magnesium for Severe/Symptomatic Cases

Life-Threatening Arrhythmias (Torsades de Pointes or 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 regardless of baseline magnesium level 4

Severe Hypomagnesemia Without Cardiac Arrest

• For adults: Give 1 g (8.12 mEq) magnesium sulfate IM every 6 hours for 4 doses, OR 5 g (40 mEq) added to 1 liter of D5W or normal saline infused over 3 hours 5
• For severe deficiency: Up to 250 mg/kg (approximately 2 mEq/kg) may be given IM over 4 hours if necessary 5
• Maximum infusion rate: Do not exceed 150 mg/minute (1.5 mL of 10% solution) except in eclamptic seizures 5
• Dilution requirement: All IV solutions must be diluted to ≤20% concentration before administration 5

Monitoring During IV Replacement

• Do not exceed 30-40 g total daily dose in patients with normal renal function 5
• In renal insufficiency: Maximum dose is 20 g per 48 hours with frequent serum magnesium monitoring 5
• Target serum level: Aim for 6 mg/100 mL (approximately 2.5 mmol/L) for seizure control in eclampsia 5

Oral Magnesium for Mild Asymptomatic Cases

For patients with serum magnesium 0.5-0.7 mmol/L without symptoms:

• Magnesium oxide 12-24 mmol daily (typically 4 mmol capsules given at night when intestinal transit is slowest for better absorption) 1
• Oral replacement is more effective at slowly restoring total body stores compared to IV boluses 3
• Reduce dose in renal insufficiency or constipation to avoid toxicity 6
• Avoid oral magnesium-containing antacids in hypophosphatemia as they are contraindicated 6

Special Clinical Contexts

Patients with High GI Losses (Short Bowel, Jejunostomy)

• Encourage glucose-saline replacement solutions with sodium ≥90 mmol/L 1
• Restrict hypotonic drinks that worsen electrolyte losses 1
• Measure 24-hour urine magnesium to assess ongoing losses 1
• Do not rely solely on serum levels—intracellular depletion can exist with normal serum magnesium 1

Cancer Patients on Chemotherapy

• Monitor magnesium levels regularly in patients receiving cisplatin or cetuximab, as these commonly cause significant hypomagnesemia 1

Critically Ill Patients on Continuous Renal Replacement Therapy

• Use dialysis solutions containing magnesium rather than IV supplementation, as 60-65% of critically ill patients on continuous KRT develop hypomagnesemia 1

Pregnancy (Pre-eclampsia/Eclampsia)

• Initial dose: 4-5 g IV in 250 mL D5W or NS infused, plus simultaneous IM doses of up to 10 g (5 g in each buttock) 5
• Maintenance: 4-5 g IM into alternate buttocks every 4 hours OR 1-2 g/hour continuous IV infusion 5
• Critical warning: Do not continue magnesium sulfate beyond 5-7 days in pregnancy as it causes fetal abnormalities 5

Common Pitfalls to Avoid

• Never give IV potassium bolus for cardiac arrest suspected to be from hypokalemia—this is a Class III (Harm) recommendation 4
• Never skip rehydration in volume-depleted patients, as hyperaldosteronism will negate magnesium replacement efforts 1
• Never ignore symptoms at "normal" serum levels—symptoms typically appear below 1.2 mg/dL, but intracellular depletion can occur with normal serum values 2, 1
• Never exceed renal excretory capacity during replacement, particularly in patients with any degree of renal impairment 5