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

Treatment of Hypomagnesemia

Critical First Step: Correct Volume Depletion Before Magnesium Replacement

Before initiating any magnesium therapy, you must correct water and sodium depletion with IV saline to eliminate secondary hyperaldosteronism, which drives renal magnesium wasting—this is particularly crucial in patients with high gastrointestinal losses, diarrhea, or high-output stomas. 1

• Secondary hyperaldosteronism from volume depletion increases renal retention of sodium at the expense of magnesium and potassium, making magnesium replacement futile until volume status is corrected 1
• Each liter of jejunostomy fluid contains approximately 100 mmol/L sodium, representing significant losses that must be replaced 2

Route Selection Based on Severity and Symptoms

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

For life-threatening arrhythmias (torsades de pointes), administer 1-2 g magnesium sulfate IV push over 5 minutes immediately, regardless of baseline magnesium level. 1, 2

• This is an American Heart Association Class I recommendation with the strongest evidence 1
• For severe symptomatic hypomagnesemia without cardiac arrest, give 1-2 g magnesium sulfate IV bolus over 5-15 minutes, followed by continuous infusion 2
• In pediatric patients, administer 25-50 mg/kg (maximum 2 g) IV/IO over 10-20 minutes for hypomagnesemia with pulses, and as a bolus for pulseless torsades 2

FDA-approved dosing for severe hypomagnesemia: As much as 250 mg (approximately 2 mEq) per kg body weight may be given IM within four hours if necessary, or alternatively 5 g (approximately 40 mEq) added to one liter of fluid for slow IV infusion over three hours 3

• The rate of IV injection should generally not exceed 150 mg/minute (1.5 mL of a 10% concentration) 3
• Solutions for IV infusion must be diluted to a concentration of 20% or less prior to administration 3

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

Oral magnesium oxide at 12-24 mmol daily (typically given at night when intestinal transit is slowest) is the first-line treatment for mild, asymptomatic hypomagnesemia. 1, 2

• Start with 12 mmol given at night as the initial dose, with total daily doses ranging from 12-24 mmol depending on severity and response 2
• FDA-approved dosing for mild deficiency: 1 g magnesium sulfate (equivalent to 8.12 mEq) injected IM every six hours for four doses (total of 32.5 mEq per 24 hours) 3
• Most magnesium salts are poorly absorbed and may worsen diarrhea or stomal output in patients with gastrointestinal disorders 2

Address Concurrent Electrolyte Abnormalities

Always replace magnesium FIRST before attempting to correct refractory hypokalemia or hypocalcemia, as these will not respond to treatment until magnesium is normalized. 1, 2

• Hypomagnesemia impairs parathyroid hormone release, causing calcium deficiency 1
• Hypomagnesemia causes dysfunction of potassium transport systems and increases renal potassium excretion, making hypokalemia resistant to potassium treatment alone 2
• Calcium normalization typically follows within 24-72 hours after magnesium repletion begins 2
• Do not administer calcium and magnesium supplements together, as they inhibit each other's absorption—separate by at least 2 hours 2

Identify and Discontinue Offending Medications

Review and discontinue causative medications whenever possible: 1

• Cisplatin, cetuximab (chemotherapy agents)
• Aminoglycosides
• Loop and thiazide diuretics
• Proton pump inhibitors
• Amphotericin B, pentamidine, foscarnet 4

Monitoring During Treatment

Monitor for magnesium toxicity during IV replacement, particularly in patients with renal insufficiency: 2

• Loss of patellar reflexes (occurs as plasma magnesium approaches 10 mEq/L)
• Respiratory depression
• Hypotension and bradycardia
• Heart block may occur at plasma levels of 10 mEq/L or lower 3
• Serum magnesium concentrations exceeding 12 mEq/L may be fatal 3

Have calcium chloride available to reverse magnesium toxicity if needed. 2

• Effective anticonvulsant serum levels range from 2.5 to 7.5 mEq/L 3
• In severe renal insufficiency, the maximum dose is 20 grams/48 hours with frequent serum magnesium monitoring 2, 3

Special Populations

Short Bowel Syndrome/Malabsorption

• Initially use IV magnesium sulfate, then transition to oral magnesium oxide and/or 1-alpha cholecalciferol 2
• Encourage glucose-saline replacement solutions with sodium concentration ≥90 mmol/L and restrict hypotonic drinks 1
• Measure 24-hour urine magnesium loss, as intracellular depletion can exist with normal serum levels 1
• For severe malabsorption, subcutaneous magnesium sulfate (4-12 mmol added to saline bags) may be necessary 1-3 times weekly 2

Refractory Cases

• Add oral 1-alpha hydroxy-cholecalciferol (0.25-9.00 μg daily) in gradually increasing doses to improve magnesium balance 2
• Monitor serum calcium regularly to avoid hypercalcemia 2

Cancer Patients on Chemotherapy

• Regular monitoring of magnesium levels is essential, as cisplatin and cetuximab commonly cause significant hypomagnesemia 1

Kidney Replacement Therapy

• Use dialysis solutions containing magnesium to prevent hypomagnesemia rather than IV supplementation, as hypomagnesemia occurs in 60-65% of critically ill patients on continuous KRT 1, 2
• Use regional citrate anticoagulation with caution, as it increases magnesium losses in the form of magnesium-citrate complexes 2

Pregnancy (Pre-eclampsia/Eclampsia)

• Total initial dose is 10-14 g magnesium sulfate: 4-5 g IV in 250 mL fluid infused, with simultaneous IM doses of up to 10 g (5 g in each buttock) 3
• Subsequently, 4-5 g IM into alternate buttocks every four hours as needed, or 1-2 g/hour by constant IV infusion 3
• Target serum magnesium level of 6 mg/100 mL for seizure control 3
• Do not exceed 30-40 g total daily dose 3
• Continuous maternal administration beyond 5-7 days can cause fetal abnormalities 3

Common Pitfalls to Avoid

• Do not give IV potassium bolus for cardiac arrest suspected to be from hypokalemia—this is an American Heart Association Class III (Harm) recommendation 1
• Do not rely solely on serum magnesium levels in patients with significant gastrointestinal losses, as intracellular depletion can exist with normal serum levels 1
• Do not administer magnesium without first establishing adequate renal function 5
• Rapid infusion of magnesium sulfate can cause hypotension and bradycardia 2
• In renal insufficiency or constipation, lower the magnesium dose 6
• In hypophosphatemia, oral antacids containing magnesium are contraindicated 6