Vitamin B12 Replacement Therapy
For vitamin B12 deficiency, the recommended treatment is hydroxocobalamin 1 mg intramuscularly three times a week for 2 weeks followed by maintenance treatment with 1 mg intramuscularly every 2-3 months for life in patients without neurological involvement. 1
Initial Treatment Based on Clinical Presentation
Patients WITH Neurological Involvement
- Administer hydroxocobalamin 1 mg intramuscularly on alternate days until there is no further improvement 1
- After improvement, transition to maintenance with hydroxocobalamin 1 mg intramuscularly every 2 months 1
- Seek urgent specialist advice from neurologist and haematologist for patients with unexplained sensory, motor, or gait symptoms 1
Patients WITHOUT Neurological Involvement
- Administer hydroxocobalamin 1 mg intramuscularly three times a week for 2 weeks 1
- Follow with maintenance treatment of 1 mg intramuscularly every 2-3 months lifelong 1
Treatment Based on Cause of Deficiency
Malabsorption (Pernicious Anemia, Bariatric Surgery, Ileal Resection)
- Parenteral (intramuscular) vitamin B12 is the recommended treatment and will be required for the remainder of the patient's life 2, 3
- For patients with ileal resection (>20 cm of distal ileum), prophylactic vitamin B12 injections (1000 μg) monthly for life 2
Normal Intestinal Absorption
- Where oral route is not deemed adequate, initial treatment similar to that for patients with pernicious anemia 3
- Chronic treatment can be with an oral B12 preparation 3, 4
- Oral therapy with 1000 μg daily can be effective for patients with normal absorption 5, 4
Important Considerations
Diagnostic Testing
- Use either total B12 (serum cobalamin) or active B12 (serum holotranscobalamin) as the initial test 1
- Consider measuring methylmalonic acid (MMA) as a confirmatory test when initial results are indeterminate 1
Critical Warnings
- 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
- Check both vitamin B12 and folate levels, as folate deficiency may coexist 1
Monitoring
- Monitor clinical response and hematological parameters 2, 5
- For patients with deficiency, monitoring should occur every 3 months until stabilization, then once a year 2
Alternative Approaches
Oral Supplementation
- Oral vitamin B12 at doses of 1000 μg daily can be effective in some patients, particularly those without malabsorption issues 5, 4, 6
- However, for malabsorption conditions, parenteral therapy remains the gold standard 2, 5
Dosing Variations
- Some evidence suggests that up to 50% of individuals may require more frequent administration than the standard regimen, ranging from daily or twice weekly to every 2-4 weeks, to remain symptom-free 5
- Using 1000 μg rather than 100 μg injections may result in greater retention with no disadvantage in cost or toxicity 7
Special Populations
- Elderly patients have higher risk of B12 deficiency, with metabolic B12 deficiency present in 18.1% of patients over 80 years 2
- Patients after bariatric surgery require close monitoring and supplementation 2
- For patients with thrombocytopenia requiring vitamin B12, intramuscular administration can be safely performed with platelet count >50 × 10⁹/L 2