What is the recommended treatment for vitamin B12 deficiency?

Treatment of Vitamin B12 Deficiency

The recommended treatment for vitamin B12 deficiency is 1000 μg intramuscular injections initially (every other day for a week, then weekly until normalization), followed by monthly injections for life in cases of permanent malabsorption, or daily oral supplementation of 1000-2000 μg for those with normal intestinal absorption. 1, 2, 3

Diagnosis and Assessment

Before initiating treatment, proper diagnosis is essential:

• Measure serum B12 level with the following interpretation thresholds:

  • <180 ng/L: Confirmed deficiency
  • 180-350 ng/L: Indeterminate (requires further testing)

  • 350 ng/L: Unlikely deficiency 1

• For indeterminate results, measure methylmalonic acid (MMA) and homocysteine:

  • MMA is elevated in 98.4% of B12 deficient patients
  • Homocysteine is elevated in 95.9% of B12 deficient patients 1

• Complete blood count and folate levels should also be assessed 1

Treatment Protocol Based on Etiology

1. Pernicious Anemia

• Initial treatment: 100 mcg daily intramuscular injections for 6-7 days
• If clinical improvement and reticulocyte response occur:
  • Continue with same dose on alternate days for 7 doses
  • Then every 3-4 days for 2-3 weeks until hematologic values normalize
  • Maintenance: 100 mcg monthly for life 2, 3
• Oral therapy is not dependable for pernicious anemia according to FDA labeling 2, 3
• However, recent research suggests high-dose oral therapy (1000 μg/day) may be effective even in pernicious anemia 4

2. Crohn's Disease with Ileal Involvement/Resection

• For patients with >20 cm of distal ileum resected: 1000 mg vitamin B12 by intramuscular injection monthly for life 5
• For patients with clinical deficiency: 1000 mg intramuscular injection every other day for a week, then monthly for life 5

3. Normal Intestinal Absorption

• Initial treatment similar to pernicious anemia depending on severity
• Chronic treatment can use oral B12 preparation 2, 3
• Oral administration of 1000-2000 μg daily is effective for correcting anemia and neurological symptoms 1, 6

4. Post-Bariatric Surgery

• 1 mg oral vitamin B12 daily indefinitely 6

Route of Administration Considerations

Intramuscular Administration

• Preferred for:
  • Severe deficiency
  • Severe neurological symptoms
  • Pernicious anemia (traditionally)
  • Malabsorption conditions
• Leads to more rapid improvement 6
• Avoid intravenous route as most vitamin will be lost in urine 2, 3

Oral/Sublingual Administration

• Effective for:
  • Patients with normal absorption
  • Maintenance therapy
  • Patients on anticoagulants
  • Patients with needle phobia
• Sublingual B12 has been shown to be as effective or even superior to IM injections in some studies 7
• High-dose oral therapy (1000-2000 μg daily) can overcome malabsorption issues 1, 6

Special Populations and Monitoring

• Elderly patients: Consider screening those >75 years 6
• Vegetarians/vegans: Should consume fortified foods or take supplements 6
• Metformin users: Monitor B12 levels regularly 1, 8
• Patients with ileal disease/resection: Screen yearly for B12 deficiency 5

Important Caveats

• Vitamin B12 deficiency left untreated for >3 months may cause permanent spinal cord damage 1
• Folic acid should be administered concomitantly if needed 2, 3
• Patients with sulfasalazine or methotrexate treatment should receive prophylactic folic acid supplementation 5
• Treatment response can be used as confirmation when diagnosis is uncertain 1

Treatment Duration

• For reversible causes: Until normalization and resolution of underlying cause
• For permanent malabsorption (pernicious anemia, ileal resection >20 cm): Lifelong therapy 5, 2, 3