Recommended Dose of Vitamin B12
For healthy adults, the WHO recommends 2.4 micrograms daily for maintenance, but for those with deficiency or absorption issues, therapeutic doses of 1000-2000 micrograms daily orally or 1000 micrograms intramuscularly are required. 1
Maintenance Dosing for Healthy Adults
- 2.4 micrograms per day is the standard recommendation for healthy adults without deficiency 1, 2
- This dose should ideally come from crystalline vitamin B12 (supplements or fortified foods) rather than food-bound sources, especially in adults over 50 years, as absorption of food-bound B12 decreases with age due to atrophic gastritis 3
Therapeutic Dosing for Deficiency
Initial Treatment (Loading Phase)
For deficiency without neurological symptoms:
- Hydroxocobalamin 1000 micrograms intramuscularly three times weekly for 2 weeks 1, 4
- Alternative: Oral therapy with 1000-2000 micrograms daily is equally effective for correcting anemia and neurologic symptoms 1, 5
For deficiency with neurological involvement:
- Hydroxocobalamin 1000 micrograms intramuscularly on alternate days until symptoms improve 1, 4
- This more aggressive protocol is critical because neurological damage can become irreversible if undertreated 4
Maintenance Treatment
After initial loading:
- Hydroxocobalamin 1000 micrograms intramuscularly every 2-3 months for life 1, 4
- Monthly administration of 1000 micrograms IM is more effective than 3-monthly injections and may be necessary to meet metabolic requirements in many patients 1, 6
- Alternative: Oral supplementation 1000-2000 micrograms daily may be considered after the initial IM loading phase if the patient has no neurological symptoms 1
Special Population Dosing
Post-bariatric surgery patients:
- 1000 micrograms every 3 months via intramuscular injection OR 1000 micrograms daily orally 1, 4
- For pregnant women after bariatric surgery: continue 1000 micrograms every 3 months IM or 1000 micrograms daily orally 1
Patients with ileal resection >20 cm:
Pregnant women:
- 4 micrograms daily (increased from the standard 2.4 micrograms) 2
Lactating women:
- 4 micrograms daily 2
Pediatric patients:
- Infants up to 12 months on parenteral nutrition: 0.3 μg/kg/day 1
- Older children: 1 μg/day 1
- General intake for children: 0.5 to 3 micrograms daily depending on age 2
Elderly patients (>75 years):
- Should consume fortified foods or supplements to ensure adequate absorption, as food-bound B12 absorption decreases with age 1, 3
Critical Formulation Considerations
Preferred forms:
- Hydroxocobalamin is the preferred formulation for intramuscular therapy due to superior tissue retention and established dosing protocols 4
- Methylcobalamin or hydroxocobalamin should be used instead of cyanocobalamin in patients with renal dysfunction, as cyanocobalamin requires renal clearance of the cyanide moiety 1, 4
Common Pitfalls to Avoid
- Never administer folic acid before treating vitamin B12 deficiency, as it may mask the anemia while allowing irreversible neurological damage (subacute combined degeneration of the spinal cord) to progress 1, 4, 2
- Do not discontinue B12 supplementation even if levels normalize—patients with malabsorption require lifelong therapy 4, 2
- Do not use 100 microgram doses for maintenance therapy; 1000 micrograms is superior as much greater amounts are retained with no disadvantage in cost or toxicity 6
- Patients with pernicious anemia have 3 times the incidence of gastric carcinoma, so appropriate screening should be performed when indicated 2
Monitoring Parameters
- Check serum B12 levels and homocysteine every 3 months until stabilization, then annually 1, 4
- Target homocysteine level: <10 μmol/L for optimal outcomes 1, 4
- Monitor complete blood count to assess for resolution of megaloblastic anemia 4
- Evaluate for resolution of neurological symptoms (paresthesias, gait disturbances, cognitive changes) as improvement indicates effective therapy 4, 7