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

Treatment of Hypomagnesemia

Immediate Life-Threatening Situations

For torsades de pointes or cardiac arrest with suspected hypomagnesemia, administer 1-2 g magnesium sulfate IV push immediately, regardless of baseline magnesium level. 1, 2, 3

• This is a Class I recommendation from the American Heart Association, meaning the strongest level of evidence supports this intervention 1
• The bolus should be given over 5-15 minutes for torsades de pointes 2
• In pediatric patients, use 25-50 mg/kg (maximum 2 g) IV/IO over 10-20 minutes for hypomagnesemia with pulses, or as a bolus for pulseless torsades 2
• Have calcium chloride available to reverse magnesium toxicity if needed 2

Critical First Step: Correct Underlying Fluid and Electrolyte Imbalances

Before starting magnesium replacement, correct water and sodium depletion with IV saline to eliminate secondary hyperaldosteronism, which causes renal magnesium wasting. 1, 2

• This is particularly crucial in patients with high-output stomas, diarrhea, or gastrointestinal losses, where each liter of jejunostomy fluid contains approximately 100 mmol/L sodium 2
• Hyperaldosteronism from volume depletion increases renal retention of sodium at the expense of magnesium and potassium 1
• Identify and discontinue offending medications including cisplatin, cetuximab, aminoglycosides, diuretics, and proton pump inhibitors 1

Address Concurrent Electrolyte Abnormalities First

Correct magnesium deficiency before attempting to treat refractory hypokalemia or hypocalcemia, as these will not respond to supplementation until magnesium is repleted. 1, 2

• Hypomagnesemia impairs parathyroid hormone release, causing calcium deficiency 1
• Magnesium deficiency causes dysfunction of potassium transport systems and increases renal potassium excretion 2
• Calcium normalization typically occurs within 24-72 hours after magnesium repletion begins 2

Route Selection Based on Severity

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

Use intravenous magnesium sulfate for severe or symptomatic cases. 1, 2, 3

• For severe hypomagnesemia, give 1-2 g magnesium sulfate IV bolus over 5-15 minutes, followed by continuous infusion 2
• Alternatively, add 5 g (approximately 40 mEq) to one liter of 5% dextrose or 0.9% sodium chloride for slow IV infusion over three hours 3
• For severe hypomagnesemia, as much as 250 mg (approximately 2 mEq) per kg of body weight may be given IM within four hours if necessary 3
• The rate of IV injection should generally not exceed 150 mg/minute 3

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

Use oral magnesium oxide supplementation at 12-24 mmol daily for asymptomatic patients with mild deficiency. 1, 2

• Give 4 mmol capsules, typically at night when intestinal transit is slowest 1, 2
• For mild magnesium deficiency, the usual adult dose is 1 g (equivalent to 8.12 mEq) injected IM every six hours for four doses if oral route is not feasible 3
• Most magnesium salts are poorly absorbed and may worsen diarrhea or stomal output in patients with gastrointestinal disorders 2

Monitoring During Treatment

Monitor for magnesium toxicity during IV replacement, including loss of patellar reflexes, respiratory depression, hypotension, and bradycardia. 2, 3

• A serum magnesium level of 6 mg/100 mL is considered optimal for control of seizures 3
• Monitor both magnesium and calcium levels closely and adjust treatment based on renal function 2
• Rapid infusion of magnesium sulfate can cause hypotension and bradycardia 2

Special Populations and Dosing Adjustments

Renal Insufficiency

In severe renal insufficiency, the maximum dose is 20 grams/48 hours with frequent serum magnesium monitoring. 2, 3

• Establish adequate renal function before administering any magnesium supplementation 4
• Maximum dose adjustments and frequent serum monitoring are required 2

Pregnancy (Pre-eclampsia/Eclampsia)

Do not use continuous maternal magnesium sulfate beyond 5-7 days in pregnancy as it can cause fetal abnormalities. 3

• For severe pre-eclampsia or eclampsia, the total initial dose is 10-14 g of magnesium sulfate 3
• Give 4-5 g IV in 250 mL of 5% dextrose or 0.9% sodium chloride, with simultaneous IM doses of up to 10 g (5 g in each buttock) 3
• Subsequently, give 4-5 g IM into alternate buttocks every four hours as needed, or 1-2 g/hour by constant IV infusion 3

Short Bowel Syndrome/Malabsorption

For patients with short bowel syndrome or severe malabsorption, higher doses of oral magnesium or parenteral supplementation may be required. 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
• Subcutaneous magnesium sulfate (4-12 mmol added to saline bags) may be necessary 1-3 times weekly 2
• Initially use IV magnesium sulfate, then transition to oral magnesium oxide and/or 1-alpha cholecalciferol 2

Refractory Cases

For hypomagnesemia refractory to oral therapy, 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
• This approach may be particularly useful in patients with short bowel syndrome 2

Kidney Replacement Therapy

Use dialysis solutions containing magnesium to prevent hypomagnesemia during continuous kidney replacement therapy rather than IV supplementation. 1, 2

• Hypomagnesemia occurs in up to 60-65% of critically ill patients on continuous kidney replacement therapy 1, 2
• Use regional citrate anticoagulation with caution, as it increases magnesium losses in the form of magnesium-citrate complexes 2

Administration Precautions

Do not mix magnesium sulfate with vasopressors or calcium in the same solution, and use a central venous catheter for administration to avoid tissue injury from extravasation. 2

• Solutions for IV infusion must be diluted to a concentration of 20% or less prior to administration 3
• Deep IM injection of the undiluted (50%) solution is appropriate for adults, but dilute to 20% or less for children 3

Total Daily Dose Limits

A total daily (24-hour) dose of 30-40 g should not be exceeded. 3

• In total parenteral nutrition, maintenance requirements range from 8-24 mEq (1-3 g) daily for adults and 2-10 mEq (0.25-1.25 g) daily for infants 3
• Caution must be observed to prevent exceeding the renal excretory capacity 3