What medication is used to treat hypomagnesemia?

Treatment of Hypomagnesemia

For mild hypomagnesemia, give oral magnesium oxide 12-24 mmol daily, starting with 12 mmol at night; for severe or symptomatic hypomagnesemia, administer IV magnesium sulfate 1-2 g as initial therapy. 1, 2, 3

Treatment Algorithm Based on Severity

Mild Hypomagnesemia (Asymptomatic, Mg >1.2 mg/dL)

Oral magnesium oxide is the first-line treatment:

• Start with 12 mmol at night when intestinal transit is slowest to maximize absorption 1
• Increase to 24 mmol daily (divided doses) if needed based on response 1
• Magnesium oxide is preferred because it contains more elemental magnesium than other salts and converts to magnesium chloride in the stomach 1

Alternative oral preparations if magnesium oxide is poorly tolerated:

• Organic magnesium salts (aspartate, citrate, lactate) have higher bioavailability than magnesium oxide or hydroxide 1, 2
• These alternatives may cause less diarrhea in susceptible patients 1

Severe Hypomagnesemia (Symptomatic or Mg <1.2 mg/dL)

IV magnesium sulfate is required:

• For mild deficiency: 1 g (8.12 mEq) IM every 6 hours for 4 doses 3
• For severe deficiency: Up to 250 mg/kg IM over 4 hours (maximum approach with caution) 3
• Alternatively: 5 g (40 mEq) in 1 liter of D5W or normal saline IV over 3 hours 3
• Rate should generally not exceed 150 mg/minute to avoid hypotension and bradycardia 3

For life-threatening presentations (cardiac arrhythmias, torsades de pointes):

• Give 1-2 g IV bolus over 5 minutes regardless of measured serum magnesium levels 1, 2
• This applies even if serum magnesium appears normal, as intracellular depletion may exist 4

Critical First Step: Correct Sodium and Water Depletion

Before starting magnesium replacement, address volume status:

• Correct water and sodium depletion first, as secondary hyperaldosteronism worsens magnesium deficiency 5, 1
• This is particularly important in patients with high-output jejunostomy, ileostomy, or short bowel syndrome 5

Special Considerations for Malabsorption

In patients with short bowel syndrome or malabsorption:

• Start with IV magnesium sulfate initially, then transition to oral magnesium oxide and/or 1-alpha cholecalciferol 5, 1
• If oral therapy fails, consider 1-alpha hydroxy-cholecalciferol in gradually increasing doses to improve magnesium balance 1
• Monitor serum calcium regularly when using cholecalciferol to avoid hypercalcemia 1
• For chronic maintenance, subcutaneous magnesium sulfate (4 mmol) with saline 1-3 times weekly is an option 1, 2

Monitoring and Target Levels

Target serum magnesium:

• Aim for >0.6 mmol/L (approximately 1.5 mg/dL) as a minimum target 1, 2
• Normal range is 1.3-2.2 mEq/L or 1.8-2.2 mEq/L depending on laboratory 2, 6

Monitor for magnesium toxicity:

• Watch for hypotension, drowsiness, muscle weakness, and loss of deep tendon reflexes 2
• Have calcium chloride available to reverse potential magnesium toxicity 2

Important Pitfalls and Caveats

Refractory electrolyte abnormalities:

• Hypokalemia and hypocalcemia often coexist with hypomagnesemia and will be resistant to potassium or calcium replacement until magnesium is corrected 5, 2, 4
• Always check and correct magnesium first when encountering refractory hypokalemia 5

Gastrointestinal side effects:

• Most oral magnesium salts are poorly absorbed and may worsen diarrhea or stomal output 1
• Administering at night and dividing doses throughout the day can help minimize this 1
• Reducing excess dietary lipids can improve magnesium absorption 1

Renal function considerations:

• Establish adequate renal function before administering magnesium supplementation 6
• In severe renal insufficiency, maximum dosage is 20 g/48 hours with frequent serum monitoring 3

Pregnancy warning:

• Continuous maternal administration beyond 5-7 days can cause fetal abnormalities 3

Fractional excretion testing:

• If the cause is unclear, measure fractional excretion of magnesium: <2% suggests GI losses, >2% indicates renal wasting 6