What is the recommended dose and frequency for vitamin B12 (cobalamin) injections?

Vitamin B12 Injection Dosing and Frequency Recommendations

For vitamin B12 (cobalamin) deficiency, the recommended dosing is 1000 μg intramuscular hydroxocobalamin with 5-6 biweekly injections for loading, followed by monthly injections for maintenance therapy. 1, 2

Initial Diagnosis and Assessment

Before initiating treatment, proper diagnosis is essential:

• Confirm B12 deficiency using either:
  • Total B12 (<180 ng/L indicates deficiency)
  • Active B12 (<25 pmol/L indicates deficiency)
  • For indeterminate results (Total B12 180-350 ng/L), measure serum methylmalonic acid (MMA) 1

Injection Protocol Based on Deficiency Cause

For Pernicious Anemia or Malabsorption:

1. Loading Phase:

   • 1000 μg intramuscular hydroxocobalamin every other day for 1-2 weeks (5-6 injections total) 2

2. Maintenance Phase:

   • 1000 μg intramuscular hydroxocobalamin once monthly for life 3, 2
   • Note: Up to 50% of patients may require more frequent administration (every 2-4 weeks) to remain symptom-free 2

For Dietary Deficiency:

• Oral supplementation with 1500-2000 μg daily for 3 months is generally sufficient 1
• If oral therapy is not feasible, follow the injection protocol above but discontinue once the underlying cause is addressed

Important Considerations

• Urgent treatment is critical: Vitamin B12 deficiency left untreated for longer than 3 months may cause permanent degenerative lesions of the spinal cord 3
• Monitoring: During initial treatment of pernicious anemia, monitor serum potassium in the first 48 hours and replace if necessary 3
• Follow-up testing: Check hematocrit and reticulocyte counts daily from days 5-7 of therapy until hematocrit normalizes 3
• Individualization: While the British National Formulary suggests maintenance with 1000 μg every two months, clinical experience indicates many patients require more frequent dosing 2
• Avoid "titration": Adjusting injection frequency based solely on serum B12 or MMA levels is not recommended; instead, base frequency on symptom control 2

Special Populations

• Elderly patients: Higher risk of deficiency; consider 1000 μg monthly injections for maintenance 4
• Post-bariatric surgery: These patients should receive 1 mg of vitamin B12 daily indefinitely 5
• Vegetarians/vegans: Should consume B12-fortified foods or supplements; if deficient, follow standard protocol 5

Oral vs. Intramuscular Administration

• High-dose oral vitamin B12 (1000-2000 μg daily) can be as effective as intramuscular administration for most patients 1, 5
• However, for severe deficiency, neurological symptoms, or malabsorption issues, intramuscular therapy leads to more rapid improvement and is preferred 5
• A recent clinical trial showed comparable effectiveness between oral (1 mg/day) and IM administration at 8 weeks, though differences emerged at 52 weeks 6

Common Pitfalls to Avoid

1. Delayed treatment: Never delay treatment as neurological damage can become irreversible 3
2. Folic acid masking: Doses of folic acid exceeding 0.1 mg daily may produce hematologic remission while allowing neurological damage to progress 3
3. Inadequate monitoring: Failure to monitor response can miss complicating illnesses that might inhibit marrow response 3
4. Insufficient maintenance: Patients with pernicious anemia require lifelong treatment; failure to maintain therapy will result in recurrence 3