What is the recommended dose of mecobalamin (cyanocobalamin) for treating vitamin B12 deficiency?

Recommended Dose of Mecobalamin for Vitamin B12 Deficiency

For patients with clinical vitamin B12 deficiency, administer 1000 mcg (1 mg) of vitamin B12 intramuscularly every other day for one week, then 1000 mcg monthly for life. 1

Initial Treatment Protocol

For Deficiency WITHOUT Neurological Involvement

• Loading phase: Hydroxocobalamin 1 mg intramuscularly three times per week for 2 weeks 2
• Maintenance phase: 1 mg intramuscularly every 2-3 months lifelong 2

For Deficiency WITH Neurological Involvement

• Intensive loading: Hydroxocobalamin 1 mg intramuscularly on alternate days until no further neurological improvement occurs 2
• Maintenance phase: 1 mg intramuscularly every 2 months for life 2

The distinction between these protocols is critical—neurological symptoms demand more aggressive initial treatment to prevent irreversible damage. 2, 3

Prophylactic Dosing for High-Risk Patients

Patients with >20 cm of distal ileum resected (with or without ileocecal valve) should receive prophylactic vitamin B12 1000 mcg intramuscularly monthly indefinitely, even without documented deficiency. 1, 2 This recommendation stems from the inevitable malabsorption that occurs with significant ileal resection, as the terminal ileum is the primary site of B12 absorption. 1

Alternative Dosing Regimens

High-Dose Oral Therapy

Oral administration of 1-2 mg daily is as effective as intramuscular therapy for correcting anemia and neurologic symptoms in most patients. 4 However, intramuscular therapy remains the reference standard and should be prioritized in malabsorption states. 1

Frequency Adjustments

While guidelines recommend every 2-3 month maintenance dosing, clinical experience suggests up to 50% of patients require individualized regimens ranging from twice weekly to every 2-4 weeks to remain symptom-free. 3 Do not use serum B12 or methylmalonic acid levels to "titrate" injection frequency—base adjustments solely on clinical symptom resolution. 3

Form Selection Considerations

Methylcobalamin or hydroxocobalamin may be preferable to cyanocobalamin in patients with renal dysfunction. 2 Methylcobalamin is the principal circulating form and requires no conversion, while cyanocobalamin requires metabolic conversion to become biologically active. 5

Common Pitfalls to Avoid

• Never administer folic acid before treating B12 deficiency, as it may mask hematological manifestations while allowing neurological damage to progress (subacute combined degeneration of the spinal cord). 2, 5
• Do not discontinue therapy even if levels normalize—patients with malabsorption require lifelong supplementation. 2
• Do not rely on oral supplementation alone in malabsorption states (pernicious anemia, ileal resection, inflammatory bowel disease)—parenteral therapy is essential. 1, 3
• Do not use lower doses (100 mcg) for maintenance—1000 mcg injections result in significantly greater vitamin retention with no additional cost or toxicity. 6

Monitoring Requirements

• Screen CD patients with ileal involvement and/or resection yearly for B12 deficiency 1
• Check serum B12 and homocysteine every 3 months until stabilization, then annually 2
• Target homocysteine level <10 μmol/L for optimal results 2
• Monitor for resolution of neurological symptoms (paresthesias, gait disturbances, cognitive changes) as the primary indicator of treatment adequacy 2, 3