How to correct hypomagnesemia?

How to Correct Hypomagnesemia

For mild hypomagnesemia, start with oral magnesium oxide 12-24 mmol daily (given at night when intestinal transit is slowest), but first correct any water and sodium depletion to address secondary hyperaldosteronism that perpetuates magnesium wasting. 1

Initial Assessment and Preparation

Before starting magnesium replacement, address these critical factors:

• Correct volume depletion first with IV saline if the patient has sodium and water depletion, as secondary hyperaldosteronism increases renal magnesium and potassium losses, making supplementation ineffective 1, 2
• Check renal function and avoid magnesium supplementation if creatinine clearance is <20 mL/min due to hypermagnesemia risk 1
• Measure serum magnesium, potassium, and calcium levels, as hypomagnesemia commonly causes refractory hypokalemia and hypocalcemia 3, 4

Treatment Algorithm by Severity

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

Oral magnesium oxide is first-line therapy:

• Dose: 12 mmol initially at night, increasing to 12-24 mmol daily (approximately 480-960 mg elemental magnesium) based on response 1, 2
• Administer at night when intestinal transit is slowest to maximize absorption 1, 2
• For mild deficiency in adults, the FDA-approved regimen is 1 g (8.12 mEq) IM every 6 hours for 4 doses 5

Alternative oral formulations if magnesium oxide is poorly tolerated:

• Organic magnesium salts (aspartate, citrate, lactate) have higher bioavailability than magnesium oxide or hydroxide 2
• However, most magnesium salts are poorly absorbed and may worsen diarrhea or stomal output in patients with GI disorders 1, 2

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

Parenteral magnesium sulfate is required:

• For severe deficiency: 1-2 g IV magnesium sulfate over 15 minutes 1
• FDA-approved dosing: Up to 250 mg/kg (approximately 2 mEq/kg) IM within 4 hours if necessary 5
• Alternative: 5 g (40 mEq) added to 1 liter of D5W or normal saline for slow IV infusion over 3 hours 5
• Maximum rate: Do not exceed 150 mg/minute IV (1.5 mL of 10% solution) except in severe eclampsia with seizures 5

Life-Threatening Presentations

For cardiac arrhythmias (torsades de pointes, ventricular arrhythmias):

• Administer 1-2 g magnesium as IV bolus over 5 minutes regardless of measured serum magnesium level 1
• For QTc >500 ms, replete magnesium to >2 mg/dL as an anti-torsadogenic measure 1

Special Clinical Scenarios

Short Bowel Syndrome or Malabsorption

These patients require higher doses due to significant GI losses:

• Start with oral magnesium oxide 12-24 mmol daily, but expect that oral therapy may fail 1, 2
• If oral supplementation doesn't normalize levels, consider oral 1-alpha hydroxy-cholecalciferol (0.25-9.00 μg daily) to improve magnesium balance, while monitoring serum calcium regularly 1, 2
• For refractory cases, use IV or subcutaneous magnesium sulfate (4-12 mmol added to saline bags) 1

Post-Transplant Patients (Calcineurin Inhibitor Use)

Hypomagnesemia is common with cyclosporine and tacrolimus:

• Increased dietary magnesium intake may be attempted initially 6
• However, the amount required typically necessitates magnesium supplements rather than dietary modification alone 6
• Monitor calcium, phosphorus, and magnesium levels according to transplant protocols 6

Patients on Continuous Renal Replacement Therapy

Hypomagnesemia occurs in 60-65% of critically ill patients on CRRT:

• Use dialysis solutions containing magnesium to prevent ongoing electrolyte derangements 1
• This is particularly important when regional citrate anticoagulation is used 1

Monitoring and Target Levels

• Target serum magnesium: >0.6 mmol/L (1.5 mg/dL) as a minimum, with optimal range 1.8-2.2 mEq/L 1, 2
• Monitor for resolution of clinical symptoms if present 1
• Check for secondary electrolyte abnormalities, particularly potassium and calcium, which often accompany hypomagnesemia 1
• Correct magnesium before attempting to correct hypokalemia, as magnesium deficiency causes dysfunction of potassium transport systems and makes hypokalemia resistant to treatment 1

Critical Pitfalls to Avoid

Do not supplement magnesium without first correcting volume status in patients with diarrhea, high-output stomas, or other causes of sodium/water depletion—ongoing hyperaldosteronism will cause continued renal magnesium wasting despite supplementation 1, 2

For hypomagnesemia-induced hypocalcemia, magnesium replacement must precede calcium supplementation, as hypocalcemia will not respond to calcium alone 1

Avoid magnesium supplementation in renal insufficiency (CrCl <20 mL/min) due to hypermagnesemia risk 1

Monitor for magnesium toxicity including hypotension, bradycardia, respiratory depression, drowsiness, and muscle weakness 1

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