Vitamin B12 Injection Treatment Protocol for Deficiency
For vitamin B12 deficiency without neurological involvement, administer hydroxocobalamin 1 mg intramuscularly three times a week for 2 weeks, followed by maintenance treatment with 1 mg intramuscularly every 2-3 months lifelong. 1
Initial Treatment Based on Clinical Presentation
For patients with vitamin B12 deficiency with neurological involvement (such as unexplained sensory, motor, or gait symptoms), administer hydroxocobalamin 1 mg intramuscularly on alternate days until there is no further improvement, then transition to maintenance with hydroxocobalamin 1 mg intramuscularly every 2 months 2, 1
For patients with vitamin B12 deficiency without neurological involvement, administer hydroxocobalamin 1 mg intramuscularly three times a week for 2 weeks 2, 1
Seek urgent specialist advice from neurologist and hematologist if there is possible neurological involvement 2
Maintenance Therapy
After initial treatment of vitamin B12 deficiency, provide maintenance treatment with hydroxocobalamin 1 mg intramuscularly every 2–3 months lifelong 2, 1
For patients after bariatric surgery, vitamin B12 supplementation at 1 mg every 3 months via intramuscular injection is recommended 1
Patients with more than 20 cm of distal ileum resected should receive prophylactic vitamin B12 injections (1000 μg) monthly for life 1
Important Considerations
Never administer folic acid before treating vitamin B12 deficiency, as it may mask underlying B12 deficiency and precipitate subacute combined degeneration of the spinal cord 2, 1
For patients with pernicious anemia, parenteral vitamin B12 is the recommended treatment and will be required for the remainder of the patient's life 3
When using cyanocobalamin (the only B12 preparation available in the US), the FDA recommends 100 mcg daily for 6-7 days by intramuscular injection, followed by 100 mcg monthly for life for pernicious anemia 3
Some evidence suggests that higher doses of cyanocobalamin (1000 mcg) may be more effective for maintenance therapy 4
Monitoring
Biochemical B12 deficiency is diagnosed based on low serum cobalamin levels and elevated functional biomarkers such as homocysteine or methylmalonic acid 1
In patients with deficiency, monitoring should occur every 3 months until stabilization, then once a year 1
For patients after bariatric surgery planning pregnancy, B12 levels should be checked every 3 months 1
Alternative Administration Routes
While intramuscular administration is the standard approach, oral administration of high-dose vitamin B12 (1 to 2 mg daily) can be effective for correcting anemia and neurologic symptoms in patients with normal intestinal absorption 5
However, intramuscular therapy leads to more rapid improvement and should be considered in patients with severe deficiency or severe neurologic symptoms 5
Oral formulations with absorption enhancers may improve bioavailability but are not yet standard of care 6
Special Populations
Elderly patients have a higher risk of B12 deficiency, with metabolic B12 deficiency present in 18.1% of patients over 80 years 1
Patients who have had bariatric surgery should receive vitamin B12 supplementation indefinitely 5
Patients with ileal Crohn's disease involving more than 30-60 cm of ileum are at risk for B12 deficiency even without resection 1