What is the recommended oral magnesium supplementation regimen for magnesium repletion?

Oral Magnesium Repletion Protocol

For oral magnesium repletion, begin with magnesium oxide at 12-24 mmol daily (approximately 350-420 mg elemental magnesium for men and 320 mg for women), preferably administered at night to maximize absorption, with gradual dose increases based on tolerance and clinical response. 1

Recommended Magnesium Formulations

• First-line option: Magnesium oxide 12-24 mmol daily (350-420 mg elemental magnesium)

  • Despite relatively poor bioavailability (4% absorption) 2, magnesium oxide remains recommended by guidelines due to higher elemental magnesium content per dose
  • Preferably administered at night to maximize absorption 1

• Alternative formulations (for patients with GI intolerance):

  • Magnesium citrate: Preferred for patients at risk of kidney stones 1
  • Liquid or dissolvable magnesium products: Better tolerated than pills 3
  • Magnesium chloride, lactate, or aspartate: Higher bioavailability than oxide 2
  • Effervescent magnesium tablets: Show 40% better bioavailability than capsules 4

Dosing Considerations

• Initial dosing: Start at recommended daily allowance (350 mg daily for women; 420 mg daily for men) 3
• Gradual titration: Increase gradually according to tolerance due to potential gastrointestinal side effects 3
• Severe deficiency: May require up to 600-6500 mg daily in divided doses 3
• Renal impairment: Avoid in severe renal impairment (creatinine clearance <20 mg/dL) 1

Monitoring Protocol

• Check serum magnesium levels 6-24 hours after completion of magnesium course 5
• Monitor for diarrhea, which can worsen with magnesium supplementation 1
• Assess associated electrolytes (calcium, phosphorus, potassium) 1
• For patients with renal insufficiency: More frequent monitoring is required 1

Special Considerations

1. Rehydration first: Correct dehydration before magnesium repletion to address secondary hyperaldosteronism 1

2. Potassium repletion: Correct hypomagnesemia before addressing hypokalemia, as potassium replacement may be ineffective until magnesium is repleted 6

3. Refeeding syndrome: For severely malnourished patients, magnesium requirements are approximately 0.4 mmol/kg/day orally (or 0.2 mmol/kg/day if supplied intravenously) 3

4. Medication interactions: Be aware that diuretics, proton pump inhibitors, certain antibiotics, and chemotherapeutic agents can cause hypomagnesemia 1

5. Short bowel syndrome: These patients may require 12-24 mmol daily of magnesium oxide for repletion 1 and may benefit from magnesium diglycinate which shows better absorption in patients with ileal resection 7

When to Consider IV Magnesium Instead

• For severe symptomatic hypomagnesemia (cardiac manifestations, seizures)
• When oral supplementation is not tolerated or ineffective
• In critical care settings requiring rapid repletion

IV magnesium provides greater and more rapid elevations in serum magnesium concentration compared to oral supplementation 5, but oral supplementation is preferred for long-term management and outpatient repletion.