Oral Magnesium Repletion Options
Magnesium oxide at 12-24 mmol daily (typically as 4 mmol/160 mg capsules) is the recommended first-line oral option for magnesium repletion, preferably administered at night when intestinal transit is slowest to maximize absorption. 1
Recommended Oral Magnesium Preparations
First-Line Options:
- Magnesium oxide: 12-24 mmol daily (4 mmol/160 mg capsules)
- Contains more elemental magnesium than other salts
- Best administered at night when intestinal transit is slowest
- Typical dosing: 400-800 mg daily in divided doses (198-396 mg of elemental magnesium) 2
Alternative Options:
- Magnesium citrate: Increases muscle and brain magnesium levels in a dose-independent manner 3
- May be preferred for patients at risk of developing kidney stones 1
- Magnesium acetyl taurate: Shows good brain penetration 3
- Magnesium glycinate: Better absorbed than inorganic compounds 3
Dosing Considerations
General Population:
- RDA for magnesium: 320 mg/day for women and 420 mg/day for men
- Tolerable Upper Intake Level from supplements: 350 mg/day 2
For Specific Conditions:
- Hypomagnesemia: Initial dose 400-800 mg daily in divided doses 2
- Stone formers with hypomagnesuria: 250-500 mg/day supplementation significantly increases urinary magnesium and citrate levels 4
- Short bowel syndrome: 12-24 mmol daily of magnesium oxide 1
Clinical Pearls and Pitfalls
Absorption Considerations:
- Organic magnesium compounds (citrate, malate, acetyl taurate, glycinate) generally have better absorption than inorganic compounds 3
- Splitting high doses does not necessarily improve tissue magnesium levels 3
- Rehydration to correct secondary hyperaldosteronism is an important first step before magnesium repletion 1
Common Side Effects:
- Most magnesium salts may worsen diarrhea/stomal output, particularly at higher doses 1
- Diarrhea is the most common dose-limiting side effect 5
Special Situations:
- In patients with refractory hypomagnesemia despite oral supplements, oral 1-alpha hydroxy-cholecalciferol in gradually increasing doses (0.25-9.00 mg daily) may improve magnesium balance, but requires regular monitoring of serum calcium 1
- For patients with short bowel syndrome or malabsorption, higher doses may be needed 1
- In patients with refeeding syndrome, magnesium requirements are approximately 0.4 mmol/kg/day orally 1
Monitoring:
- Monitor serum magnesium levels along with associated electrolytes (calcium, phosphorus, potassium)
- More frequent monitoring needed in patients with renal dysfunction or those on medications that deplete magnesium 2
- Correct hypomagnesemia before addressing hypokalemia, as potassium replacement may be ineffective until magnesium is repleted 2
Contraindications and Cautions
- Use with caution in patients with kidney disease as magnesium is excreted renally 6
- Avoid in patients with hypermagnesemia
- Consider potential drug interactions, particularly with medications that affect renal magnesium handling
By following these evidence-based recommendations for oral magnesium repletion, clinicians can effectively address magnesium deficiency while minimizing adverse effects.