Recommended Intramuscular Vitamin B12 Dosing 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 of 1 mg intramuscularly every 2-3 months lifelong. 1, 2
Initial Treatment Protocol Based on Clinical Presentation
- For patients with neurological involvement: 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 1, 2
- For patients without neurological involvement: Administer hydroxocobalamin 1 mg intramuscularly three times a week for 2 weeks 1, 2
- For patients with pernicious anemia: Administer cyanocobalamin 100 mcg daily for 6-7 days intramuscularly, then every other day for 7 doses, then every 3-4 days for 2-3 weeks, followed by 100 mcg monthly for life 3
Maintenance Therapy
- After initial treatment of vitamin B12 deficiency, provide maintenance treatment with 1 mg intramuscularly every 2-3 months lifelong 1, 2
- For patients with pernicious anemia, maintenance dose is 100 mcg monthly for life 3
- For patients who have had bariatric surgery or with more than 20 cm of distal ileum resected, monthly vitamin B12 injections (1000 μg) are recommended for life 2, 4
Important Clinical 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 1, 2
- Seek urgent specialist advice from neurologist and haematologist if there is possible neurological involvement, such as unexplained sensory and/or motor and gait symptoms 1
- Intramuscular administration should be preferred over intravenous administration, as intravenous administration will result in most of the vitamin being lost in the urine 3
- While oral vitamin B12 supplementation (1-2 mg daily) has been shown to be effective in some patients 4, 5, intramuscular therapy leads to more rapid improvement and should be considered in patients with severe deficiency or severe neurologic symptoms 4, 6
Monitoring and Follow-up
- Monitor clinical response including hematologic values and neurological symptoms 3, 6
- Measurement of serum methylmalonic acid should be used to confirm deficiency in asymptomatic high-risk patients with low-normal levels of vitamin B12 4, 7
- Do not use "titration" of injection frequency based on measuring biomarkers such as serum B12 or methylmalonic acid as this is not evidence-based 6
Common Pitfalls to Avoid
- Failing to recognize and treat vitamin B12 deficiency promptly can lead to irreversible neurological damage 6
- Using intravenous route for vitamin B12 administration results in most of the vitamin being lost in urine 3
- Administering folic acid before correcting vitamin B12 deficiency can mask B12 deficiency and worsen neurological complications 1
- Relying solely on serum B12 levels without considering methylmalonic acid levels in borderline cases may lead to missed diagnoses 4, 7