How is vitamin B12 deficiency anemia treated?

Treatment of Vitamin B12 Deficiency Anemia

Vitamin B12 deficiency anemia should be treated with intramuscular hydroxocobalamin, with the regimen determined by the presence or absence of neurological symptoms. 1, 2

Initial Treatment Based on Clinical Presentation

For Patients WITH Neurological Involvement:

• Administer hydroxocobalamin 1 mg intramuscularly on alternate days until there is no further improvement 1, 2
• After improvement, transition to maintenance therapy with hydroxocobalamin 1 mg intramuscularly every 2 months 1, 2
• Seek urgent specialist advice from a neurologist and hematologist for patients with neurological symptoms 1

For Patients WITHOUT Neurological Involvement:

• Administer hydroxocobalamin 1 mg intramuscularly three times a week for 2 weeks 1, 2
• Follow with maintenance treatment of 1 mg intramuscularly every 2-3 months lifelong 1, 2
• Alternative FDA-approved regimen: cyanocobalamin 100 mcg daily for 6-7 days intramuscularly, then alternate days for 7 doses, then every 3-4 days for 2-3 weeks, followed by 100 mcg monthly for life 3

Important Considerations

Before Starting Treatment:

• Do NOT give folic acid before treating vitamin B12 deficiency as it may mask underlying deficiency and precipitate subacute combined degeneration of the spinal cord 1, 2
• Check both vitamin B12 and folate levels, as deficiencies may coexist 2
• Consider measuring methylmalonic acid as a confirmatory test when initial B12 results are indeterminate 2, 4

Treatment Based on Cause of Deficiency:

• For patients with malabsorption (including pernicious anemia), parenteral vitamin B12 is traditionally recommended and will be required lifelong 2, 3, 5
• For patients with ileal resection (>20 cm of distal ileum), provide prophylactic vitamin B12 injections (1000 μg) monthly for life 2
• Patients who have had bariatric surgery should receive vitamin B12 supplementation indefinitely 1, 4

Emerging Evidence for Oral Therapy

• Recent research suggests high-dose oral vitamin B12 (1000-2000 mcg daily) may be effective even in pernicious anemia through passive diffusion 4, 6
• A 2024 study showed that oral cyanocobalamin at 1000 μg/day effectively treated vitamin B12 deficiency in patients with pernicious anemia, with 88.5% of patients no longer deficient after 1 month 6
• Oral therapy may be considered for patients who prefer it or have contraindications to injections, but close monitoring is essential 5, 4
• For patients with normal intestinal absorption, oral B12 preparations are appropriate for chronic treatment 3, 4

Monitoring Response to Treatment

• Expect normalization of hemoglobin level and serum B12 concentration within two months of starting treatment 7
• Neurological symptoms typically begin to improve within one month of treatment initiation 7
• Some patients may require individualized injection frequencies based on symptom control rather than serum levels 5
• For maintenance with oral therapy, intermittent administration may be needed every 1-3 months to maintain normal serum B12 levels 7, 8

Special Populations

• Elderly patients (>75 years) have higher risk of B12 deficiency and should be monitored closely 2, 4
• Vegans or strict vegetarians should consume foods fortified with vitamin B12 or take supplements 4
• For patients with thrombocytopenia requiring vitamin B12, intramuscular administration can be safely performed with platelet count >50 × 10⁹/L 2