What is the recommended treatment for a patient with vitamin B12 deficiency?

Treatment of Vitamin B12 Deficiency

For patients with vitamin B12 deficiency, oral supplementation with 1500-2000 mcg daily for 3 months is as effective as intramuscular administration for most patients and should be the first-line treatment. 1

Diagnosis Before Treatment

Before initiating treatment, confirm B12 deficiency using:

• Serum B12 levels with the following interpretation:
  • <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) levels
• Additional helpful tests: homocysteine levels, complete blood count, and folate levels 1

Treatment Algorithm

1. For Most Patients with B12 Deficiency:

• Oral vitamin B12 supplementation: 1500-2000 mcg daily for 3 months 1
• Benefits: Better patient compliance, cost-effectiveness, and suitable for patients on anticoagulants or with needle phobia 1
• Mechanism: Even in patients with malabsorption issues, 1-2% of high-dose oral B12 is absorbed via passive diffusion 1

2. For Patients with Pernicious Anemia:

• Intramuscular (IM) injection is the recommended treatment 2, 3
• Initial regimen: 100 mcg daily for 6-7 days by IM injection
• If clinical improvement and reticulocyte response occur:
  • Continue with 100 mcg on alternate days for 7 doses
  • Then 100 mcg every 3-4 days for 2-3 weeks
  • Maintenance: 100 mcg monthly for life 2, 3

3. For Patients with Severe Deficiency or Neurological Symptoms:

• Start with intramuscular administration 4, 5
• This leads to more rapid improvement in patients with severe symptoms 4
• Consider switching to oral therapy once stabilized

Special Populations

• Patients after bariatric surgery: 1 mg oral vitamin B12 daily indefinitely 4
• Vegans/strict vegetarians: Regular supplementation or consumption of fortified foods 1
• Elderly patients (>75 years): Consider more aggressive screening and earlier intervention 1
• Patients on metformin (>4 months) or PPIs (>12 months): Monitor B12 levels regularly 1

Monitoring and Maintenance

• Assess response after 3 months by measuring serum B12 levels 1
• Monitor platelet count until normalization 1
• For long-term maintenance:
  • Reversible causes: May not require long-term supplementation if the cause is addressed
  • Irreversible causes (like pernicious anemia): Lifelong supplementation required 1

Important Considerations

• Sublingual B12 offers comparable efficacy to intramuscular administration 1
• Recent evidence suggests that oral vitamin B12 (1000-2000 mcg) is non-inferior to intramuscular administration for most patients 5, 6
• The British National Formulary suggests that many individuals with B12 deficiency due to malabsorption can be managed with 1000 µg intramuscular hydroxocobalamin once every two months after initial loading 7

Pitfalls to Avoid

• Don't rely solely on serum B12 testing without considering clinical symptoms and additional biomarkers 1
• Don't delay treatment in patients with neurological symptoms, as untreated vitamin B12 deficiency may cause permanent degenerative lesions of the spinal cord 1
• Don't use intravenous administration, as most of the vitamin will be lost in the urine 2, 3
• Don't "titrate" injection frequency based solely on measuring biomarkers like serum B12 or MMA 7
• Don't forget to administer folic acid concomitantly if needed 2, 3