Vitamin B12 Injection Dosing Guidelines
For vitamin B12 deficiency without neurological involvement, administer hydroxocobalamin 1 mg (1000 mcg) intramuscularly three times a week for 2 weeks, followed by maintenance treatment of 1 mg intramuscularly every 2-3 months lifelong. 1
Initial Treatment Dosing
- For patients with vitamin B12 deficiency without neurological symptoms: 1 mg (1000 mcg) intramuscularly three times a week for 2 weeks 2, 1
- For patients with vitamin B12 deficiency with neurological involvement: 1 mg intramuscularly on alternate days until there is no further improvement 2, 1
- Standard therapeutic dosing for severe deficiency: 1000 mcg intramuscularly three times a week for 2 weeks 3
- Oral administration of high-dose vitamin B12 (1-2 mg daily) can be as effective as intramuscular administration for correcting anemia and neurological symptoms, but intramuscular therapy leads to more rapid improvement 4, 5
Maintenance Dosing
- After initial treatment, maintenance dose is 1 mg intramuscularly every 2-3 months lifelong 2, 1
- For patients with neurological involvement: 1 mg intramuscularly every 2 months after symptoms improve 2, 3
- Monthly administration of 1000 mcg IM may be more effective than 3-monthly injections 1
- Patients with pernicious anemia require monthly injections of vitamin B12 for the remainder of their lives 6
Special Populations
- For patients after bariatric surgery: 1 mg every 3 months via intramuscular injection or 1 mg daily orally 3, 1
- For patients with more than 20 cm of distal ileum resected: 1000 mcg intramuscularly monthly for life 1
- For patients after bariatric surgery planning pregnancy: B12 levels should be checked every 3 months 1
- Patients who have had bariatric surgery should receive 1 mg of oral vitamin B12 per day indefinitely 4
Important Clinical Considerations
- Never administer folic acid before treating vitamin B12 deficiency, as it may mask underlying B12 deficiency and precipitate subacute combined degeneration of the spinal cord 2, 1
- With cyanocobalamin (the only B12 preparation available in the US), much greater amounts of the vitamin are retained with a 1000 mcg injection than with 100 mcg 7
- Methylcobalamin or hydroxocobalamin may be preferable to cyanocobalamin in patients with renal dysfunction 1
- Serum B12 and total homocysteine should be measured to assess vitamin B12 status, with a target homocysteine level of <10 μmol/L for optimal results 1
Oral vs. Intramuscular Administration
- Oral vitamin B12 at doses of 1000-2000 mcg daily can be as effective as intramuscular injections for correcting deficiency 3, 5, 8
- Intramuscular therapy should be considered in patients with severe deficiency or severe neurologic symptoms for more rapid improvement 4, 5
- Oral treatment has been shown to cost less than intramuscular treatment 9
- For patients who prefer oral therapy, 1000-2000 mcg daily can be used after discussing advantages and disadvantages of both treatment options 8
Monitoring Recommendations
- During initial treatment of patients with pernicious anemia, serum potassium must be observed closely the first 48 hours 6
- Hematocrit and reticulocyte counts should be repeated daily from the fifth to seventh days of therapy and then frequently until the hematocrit is normal 6
- In patients with deficiency, monitoring should occur every 3 months until stabilization, then once a year 1
- If reticulocytes have not increased after treatment or if reticulocyte counts do not continue at least twice normal as long as the hematocrit is less than 35%, diagnosis or treatment should be reevaluated 6