Vitamin B2 (Riboflavin) and Magnesium Supplementation
Vitamin B2 (Riboflavin) Dosing
For general supplementation, riboflavin 1.1-1.3 mg/day meets the recommended dietary allowance for adults, with higher doses of 3.6-10 mg/day recommended for patients requiring enteral or parenteral nutrition. 1
Standard Dosing
- Adult males: 1.3 mg/day 1
- Adult females: 1.1 mg/day 1
- Pregnancy: 1.4 mg/day 1
- Lactation: 1.6 mg/day 1
- Parenteral nutrition: 3.6-10 mg/day 1
- Enteral nutrition (in 1500 kcal): 1.2 mg minimum 1
Therapeutic Dosing for Migraine Prevention
- High-dose riboflavin: 400 mg/day has shown significant benefit for migraine prevention at 3-4 months after initiation 1
- This dose is substantially higher than the RDA and should be viewed as therapeutic intervention 2
- Adverse events are minimal even at high doses 2
- Evidence supports use in adults for migraine prevention, but pediatric use is not proven 2
Key Precautions for Riboflavin
- Riboflavin is light-sensitive and decomposes after irradiation; store protected from light 1
- Well absorbed in the proximal small intestine through active transport 1
- Not stored in ample amounts in the body, requiring constant dietary supply 1
- In inflammatory states, plasma riboflavin decreases by 30-40%, though erythrocyte concentrations remain stable 1
Magnesium Dosing
For general supplementation, start with the recommended daily allowance of 320 mg/day for women and 420 mg/day for men, with specific clinical conditions requiring substantially higher doses up to 12-24 mmol (480-960 mg elemental magnesium) daily. 3
Standard Dosing
- Adult males: 420 mg/day 3
- Adult females: 320 mg/day 3
- Parenteral nutrition: 3-5 mg/day for home/long-term PN 1
- Enteral nutrition (in 1500 kcal): 10-20 mg minimum 1
Therapeutic Dosing by Indication
Chronic constipation:
- Start with magnesium oxide 400-500 mg daily 3
- Titrate based on symptom response and side effects 3
- Clinical trials used up to 1.5 g/day (approximately 900 mg elemental magnesium) 3
Short bowel syndrome:
- Magnesium oxide 12-24 mmol daily (approximately 480-960 mg elemental magnesium) 3
- Administer at night when intestinal transit is slowest to improve absorption 3
- Critical first step: Correct water and sodium depletion with IV saline to address secondary hyperaldosteronism before magnesium supplementation 3
- If oral supplementation fails, consider IV or subcutaneous magnesium sulfate (4-12 mmol added to saline) 3
Migraine prevention:
- Magnesium 300-400 mg/day has shown benefit in some studies 4, 5
- Evidence is mixed, with some studies showing benefit over placebo while others show no difference 1, 5
Erythromelalgia:
- Start at RDA (320-420 mg/day) and increase gradually according to tolerance 3
- Liquid or dissolvable forms are better tolerated than pills 3
- IV administration (2g infused over 2 hours every 2-3 weeks) may be considered, though evidence is limited 3
Cardiac emergencies (torsades de pointes):
- 1-2 g IV bolus over 5-15 minutes for acute treatment 3
- For QTc prolongation >500 ms, replete magnesium to >2 mg/dL regardless of baseline level 3
Magnesium Formulations
- Magnesium oxide: Most commonly used, causes more osmotic diarrhea due to poor absorption 3
- Organic salts (aspartate, citrate, lactate): Better bioavailability than oxide or hydroxide 3
- Avoid magnesium hydroxide or sulfate (Epsom salts) orally for supplementation as they are potent laxatives with poor absorption 3
Critical Precautions and Contraindications
Renal Function Assessment
Check renal function before initiating magnesium supplementation; avoid entirely if creatinine clearance <20 mL/min due to life-threatening hypermagnesemia risk. 3
- Absolute contraindication: CrCl <20 mL/min 3
- Extreme caution: CrCl 20-30 mL/min (avoid unless life-threatening emergency) 3
- Reduced doses with close monitoring: CrCl 30-60 mL/min 3
Common Side Effects
- Magnesium: Diarrhea, abdominal distension, gastrointestinal intolerance 3
- Most magnesium salts are poorly absorbed and may worsen diarrhea or stomal output in patients with GI disorders 3
- Riboflavin: Minimal adverse events even at high doses 2
Drug Interactions
- Separate calcium and iron supplements by 2 hours from magnesium-containing multivitamins 1
- Single calcium doses should not exceed 600 mg 1
- Magnesium deficiency is listed as a potential risk factor for fluoroquinolone-associated tendon disorders 3
Monitoring Protocol
Initial Assessment
- Check serum magnesium, potassium, calcium, and renal function at baseline 3
- Assess for volume depletion and correct with IV saline if present 3
Follow-up Monitoring
- 2-3 weeks after starting: Recheck magnesium level and assess for side effects 3
- After dose adjustments: Recheck levels 2-3 weeks following any change 3
- Stable maintenance: Monitor every 3 months once dose is stable 3
- High-risk patients (short bowel syndrome, high GI losses, renal disease, or on medications affecting magnesium): Monitor more frequently 3
Special Clinical Scenarios
Refractory Hypokalemia
Magnesium deficiency causes dysfunction of potassium transport systems and increases renal potassium excretion, making hypokalemia resistant to potassium treatment until magnesium is corrected. 3
- Always suspect and rule out hypomagnesemia in cases of refractory hypokalemia 3
- Correct sodium and water depletion first to avoid secondary hyperaldosteronism 3
- Normalize serum magnesium before or simultaneously with potassium supplementation 3
Refeeding Syndrome Prevention
- In patients with minimal food intake for ≥5 days, supply no more than half of calculated energy requirements during first 2 days 1
- Supply vitamin B1 in daily doses of 200-300 mg before and during nutritional repletion 1
- Magnesium requirement approximately 0.2 mmol/kg/day IV or 0.4 mmol/kg/day orally 1
- Monitor and substitute potassium (2-4 mmol/kg/day) and phosphate (0.3-0.6 mmol/kg/day) as needed 1