What is the recommended IV (intravenous) dose for treating vitamin B12 deficiency?

Recommended IV Dose for Vitamin B12 Deficiency

Vitamin B12 should NOT be administered intravenously—intramuscular (IM) injection is the correct parenteral route, with hydroxocobalamin 1 mg IM being the preferred formulation and dose. 1, 2, 3

Why IV Administration is Inappropriate

• Cyanocobalamin should never be given IV because rapid renal excretion prevents adequate hepatic storage, making this route therapeutically ineffective 1
• All clinical guidelines and protocols specify intramuscular (IM) administration as the standard parenteral route for vitamin B12 replacement 2, 3

Correct Intramuscular Dosing Protocols

Initial Treatment (Loading Phase)

For patients WITH neurological symptoms:

• Hydroxocobalamin 1 mg IM on alternate days until no further neurological improvement occurs 2, 3
• Then transition to maintenance therapy 2, 3

For patients WITHOUT neurological symptoms:

• Hydroxocobalamin 1 mg IM three times weekly for 2 weeks 2, 3
• Alternatively, cyanocobalamin 1,000 mcg IM on days 1-10 1
• Then transition to maintenance therapy 2, 3

Maintenance Therapy

• Hydroxocobalamin 1 mg IM every 2-3 months for life is the standard maintenance regimen 2, 3
• Some patients may require more frequent dosing (every 2-4 weeks or even twice weekly) based on symptom recurrence, as up to 50% of patients need individualized injection frequency to remain symptom-free 4
• Do not use serum B12 or methylmalonic acid levels to "titrate" injection frequency—base dosing on clinical symptoms and patient response 4

Alternative: Cyanocobalamin Dosing

If hydroxocobalamin is unavailable, cyanocobalamin can be used:

• Loading: 1,000 mcg IM given 5-6 times over 2 weeks 1, 5
• Maintenance: 1,000 mcg IM monthly 1, 5
• The 1,000 mcg dose provides superior tissue retention compared to 100 mcg doses with no additional cost or toxicity 5

Special Populations

Post-bariatric surgery patients:

• 1 mg (1,000 mcg) IM every 3 months OR 1 mg daily orally 2

Severe thrombocytopenia (platelets <25 × 10⁹/L):

• IM administration should still be prioritized if neurological symptoms are present 2
• Consider platelet transfusion support if platelets <10 × 10⁹/L before IM injection 2
• Use smaller gauge needles (25-27G) and apply prolonged pressure (5-10 minutes) at injection site 2

Critical Pitfall to Avoid

• Never administer folic acid before treating vitamin B12 deficiency, as this may mask B12 deficiency and precipitate subacute combined degeneration of the spinal cord—a devastating and irreversible neurological complication 2, 3