Vitamin B12 Dosage Recommendations for Deficiency Treatment
For patients with vitamin B12 deficiency, the recommended intramuscular (IM) dosage is 1000 mcg hydroxocobalamin three times weekly for 2 weeks (loading phase), followed by 1000 mcg monthly for maintenance therapy; while intranasal administration should follow a regimen of 1000 mcg every 3 days for effective treatment. 1, 2
Intramuscular (IM) Administration
Initial Treatment for B12 Deficiency
- For vitamin B12 deficiency with neurological involvement: 1000 mcg hydroxocobalamin IM on alternate days until no further improvement is observed 1
- For vitamin B12 deficiency without neurological involvement: 1000 mcg hydroxocobalamin IM three times weekly for 2 weeks 1, 3
- For pernicious anemia: 100 mcg cyanocobalamin daily for 6-7 days IM, followed by alternate-day dosing for seven doses, then every 3-4 days for 2-3 weeks 4
Maintenance Therapy
- Standard maintenance: 1000 mcg hydroxocobalamin IM every 2-3 months for life 1, 3
- Monthly administration (1000 mcg IM) is more effective than 3-monthly injections 3
- For pernicious anemia: 100 mcg cyanocobalamin IM monthly for life 4
- For patients with ileal resection >20 cm: 1000 mcg IM monthly for life 1
Special Considerations for IM Administration
- In patients with thrombocytopenia (platelet count >50 × 10⁹/L): Standard IM administration can be safely performed 1
- For severe thrombocytopenia (25-50 × 10⁹/L): Use smaller gauge needles (25-27G) and apply prolonged pressure at injection site 1
- For critical thrombocytopenia (<25 × 10⁹/L): Consider platelet transfusion before IM administration 1
Intranasal Administration
Dosing Regimens
- Effective regimen: 1000 mcg every 3 days, which provides steady increase in vitamin B12 levels 2
- Alternative loading dose regimen: 1000 mcg daily for 14 days, followed by weekly administration 2
- Both intranasal regimens effectively normalize vitamin B12 levels and metabolic markers (methylmalonic acid and homocysteine) 2
Monitoring and Follow-up
- Check serum B12 levels and homocysteine every 3 months until stabilization, then annually 1
- Target homocysteine level should be <10 μmol/L for optimal results 1
- Monitor for neurological symptoms and consider increasing frequency of injections if symptoms recur 1, 5
- Do not discontinue B12 supplementation even if levels normalize, as patients will likely require lifelong therapy 1
Important Cautions
- Never administer folic acid before treating vitamin B12 deficiency, as it may mask B12 deficiency and precipitate neurological complications 1, 3
- Avoid intravenous administration of cyanocobalamin as most of the vitamin will be lost in urine 4
- Methylcobalamin or hydroxocobalamin may be preferable to cyanocobalamin in patients with renal dysfunction 3
- Treatment should be individualized based on symptom response rather than solely on laboratory values 5