What is the best formulation to replete magnesium?

Best Formulation for Magnesium Repletion

For magnesium repletion, magnesium glycinate is the recommended formulation due to its superior bioavailability and tolerability, particularly in patients with intestinal disorders. 1

Formulation Selection Based on Clinical Context

Oral Magnesium Formulations

• Magnesium glycinate: Preferred for routine oral supplementation due to:

  • Better gastrointestinal tolerability (fewer laxative effects)
  • Higher bioavailability compared to inorganic compounds
  • Particularly beneficial in patients with intestinal resection 2
  • Recommended dose: 500 mg to 1 g daily for mild to moderate hypomagnesemia 1

• Magnesium citrate: Alternative option with good absorption

  • Shown to increase muscle and brain magnesium levels in a dose-independent manner 3
  • May cause more gastrointestinal side effects than glycinate

• Magnesium oxide: Less preferred due to:

  • Lower bioavailability compared to organic compounds 4
  • Higher incidence of gastrointestinal side effects
  • However, still effective for maintaining physiological levels in healthy individuals without prior deficits 4

Parenteral Magnesium Formulations

• Magnesium sulfate: For severe deficiency or when oral route is not feasible
  • For mild deficiency: 1 g (8.12 mEq) IM every six hours for four doses 5
  • For severe hypomagnesemia: up to 250 mg/kg IM within four hours, or 5 g IV infused over three hours 5
  • Must be diluted to ≤20% concentration for IV administration 5

Administration Considerations

Dosing Strategy

• Smaller, divided doses throughout the day improve absorption compared to a single large dose 1
• Maximum recommended daily dose should not exceed 350 mg for women and 420 mg for men (elemental magnesium) 1
• For patients with jejunostomy/high output stomas, intravenous magnesium sulfate may be initially required for correction of deficiency 6

Monitoring

• Monitor serum magnesium levels, symptom improvement, and side effects (particularly gastrointestinal) 1
• Important to correct magnesium deficiency before addressing potassium or calcium abnormalities, as these may be resistant to treatment until magnesium is repleted 1

Special Populations

• Renal impairment: Contraindicated in significant renal impairment (creatinine clearance <20 mg/dL) due to risk of hypermagnesemia 1
• Intestinal disorders: Patients with ileal resection may benefit more from magnesium glycinate than magnesium oxide 2
• Pregnancy: Continuous use beyond 5-7 days can cause fetal abnormalities 5

Pitfalls and Caveats

1. Quality control issues: Up to 58.7% of magnesium supplements may contain different amounts than declared on the label, potentially resulting in underdosing or overdosing 7

2. Refeeding syndrome risk: In severely malnourished patients, magnesium should be repleted slowly along with other electrolytes (potassium, phosphate) to prevent refeeding syndrome 6

3. Absorption variability: Absorption is dose-dependent, with higher doses having proportionally lower absorption rates 4

4. Drug interactions: Magnesium supplements can interact with various medications, reducing their absorption (e.g., antibiotics, bisphosphonates) 1

By selecting the appropriate magnesium formulation based on the clinical context and patient characteristics, optimal repletion can be achieved while minimizing adverse effects.