Recommended Vitamin B12 Dosage for Adults with Deficiency
For adults with vitamin B12 deficiency, the recommended treatment is 1000 μg (1 mg) daily orally or 1000 μg intramuscularly, with frequency depending on the cause and severity of deficiency. 1, 2
Initial Treatment Protocol
For Deficiency with Neurological Involvement:
- Administer hydroxocobalamin 1 mg intramuscularly on alternate days until no further improvement is observed 1
- Then transition to maintenance therapy 1
For Deficiency without Neurological Involvement:
- Initial treatment is hydroxocobalamin 1 mg intramuscularly three times a week for 2 weeks 1
- Alternatively, oral administration of high-dose vitamin B12 (1-2 mg daily) is as effective as intramuscular administration for correcting anemia and neurologic symptoms 3
- Intramuscular therapy leads to more rapid improvement and should be considered in patients with severe deficiency or severe neurologic symptoms 3
Maintenance Therapy
Based on Cause of Deficiency:
- Malabsorption issues (pernicious anemia, ileal resection, bariatric surgery): 1 mg intramuscularly every 2-3 months for life 1
- Dietary insufficiency: Oral vitamin B12 at 125-250 μg daily 4
- Pernicious anemia: Oral vitamin B12 at 1 mg daily or intramuscular injections 4
- Post-bariatric surgery: 1 mg oral vitamin B12 daily indefinitely 3
Special Populations:
- Patients with ileal resection >20 cm: Prophylactic vitamin B12 injections (1000 μg) monthly for life 1
- Elderly patients: Higher risk of deficiency, may require more frequent monitoring 1
- Pregnant and lactating women: 4 μg daily as recommended by the Food and Nutrition Board 2
Monitoring Recommendations
- Check serum B12 levels and homocysteine every 3 months until stabilization, then once yearly 1
- Target homocysteine level of <10 μmol/L for optimal results 1
- During initial treatment of patients with pernicious anemia, monitor serum potassium closely for the first 48 hours 2
- Monitor hematocrit and reticulocyte counts daily from the fifth to seventh days of therapy until the hematocrit normalizes 2
Important Considerations and Pitfalls
- Never administer folic acid before treating vitamin B12 deficiency, as it may mask the deficiency and precipitate subacute combined degeneration of the spinal cord 1, 2
- Patients with pernicious anemia should understand they require lifelong supplementation 2
- Clinical and patient experience suggests up to 50% of individuals may require more frequent administration (ranging from daily to every 2-4 weeks) to remain symptom-free 5
- "Titration" of injection frequency based solely on measuring biomarkers like serum B12 or methylmalonic acid is not recommended 5
- Patients following vegetarian or vegan diets should take regular vitamin B12 supplements 2
- Vitamin B12 requirements increase during pregnancy and lactation 2
Route of Administration Considerations
- Oral administration of high-dose vitamin B12 (1-2 mg daily) is as effective as intramuscular administration for most patients 3
- For patients with severe deficiency, neurological symptoms, or malabsorption issues, intramuscular administration is preferred 1, 3
- For patients with thrombocytopenia requiring vitamin B12, intramuscular administration can be safely performed with dose adjustments based on platelet count severity 1