Vitamin B12 Replacement Therapy

Initial Treatment Based on Clinical Presentation

The recommended treatment for vitamin B12 deficiency without neurological involvement 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 1, 2, 3
For patients with neurological involvement, administer hydroxocobalamin 1 mg intramuscularly on alternate days until there is no further improvement 1, 2, 3
After improvement in patients with neurological involvement, transition to maintenance with hydroxocobalamin 1 mg intramuscularly every 2 months 2, 3

For patients with malabsorption, parenteral vitamin B12 is the recommended treatment and will be required for the remainder of the patient's life 4
For patients with ileal resection (>20 cm of distal ileum), prophylactic vitamin B12 injections (1000 μg) monthly for life 4

Use either total B12 or active B12 as the initial test, and consider measuring methylmalonic acid as a confirmatory test when initial results are indeterminate 5, 6
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, 3
Check both vitamin B12 and folate levels, as folate deficiency may coexist 2

Elderly patients have a higher risk of B12 deficiency, with metabolic B12 deficiency present in 18.1% of patients over 80 years 4
Patients after bariatric surgery require close monitoring and supplementation 4
For patients with thrombocytopenia requiring vitamin B12, intramuscular administration can be safely performed with platelet count >50 × 10⁹/L 4