What is the dosing for cyanocobalamin (Vitamin B12) for at-home injection use?

Cyanocobalamin Dosing for At-Home Injection Use

For at-home intramuscular vitamin B12 injections, use cyanocobalamin 1000 mcg (1 mg) monthly for maintenance therapy, or 1000 mcg every 2-3 months if using hydroxocobalamin. 1, 2

Standard Dosing Protocol

Initial Treatment Phase (Loading Dose)

• For deficiency without neurological symptoms: Administer 1000 mcg IM three times weekly for 2 weeks 1, 2
• For deficiency with neurological involvement: Give 1000 mcg IM on alternate days until no further improvement occurs 1, 2
• Alternative loading regimen: 1000 mcg IM given 5-6 times over 2 weeks (biweekly injections) 3

Maintenance Therapy

• Standard maintenance dose: 1000 mcg IM once monthly for life 1, 2, 3
• Alternative maintenance: 1000 mcg IM every 2-3 months (though monthly dosing may be more effective in meeting metabolic requirements) 1, 2
• The FDA-approved formulation contains cyanocobalamin 1000 mcg per mL 4

Special Population Considerations

Post-Bariatric Surgery Patients

• Recommended dose: 1000 mcg IM every 3 months for life 1, 2
• This applies particularly to Roux-en-Y gastric bypass or biliopancreatic diversion procedures 1

Patients with Ileal Resection

• If >20 cm of distal ileum resected: 1000 mcg IM monthly for life as prophylaxis 1, 2
• Crohn's disease with ileal involvement: Monthly injections recommended even without resection if >30-60 cm involved 1

Patients with Renal Dysfunction

• Important caveat: Consider using hydroxocobalamin or methylcobalamin instead of cyanocobalamin in patients with renal impairment, as cyanocobalamin requires renal clearance of the cyanide moiety and is associated with increased cardiovascular events (HR 2.0) in diabetic nephropathy 1

Injection Technique and Safety

Administration Details

• Injection site: Avoid the buttock routinely due to sciatic nerve injury risk; if used, only inject in the upper outer quadrant with needle directed anteriorly 1
• Preferred sites: Deltoid or vastus lateralis muscles
• Formulation: Each mL contains 1000 mcg cyanocobalamin with benzyl alcohol 0.015 mL as preservative 4

Special Precautions for Thrombocytopenia

• Platelet count >50 × 10⁹/L: Standard IM administration is safe 1
• Platelet count 25-50 × 10⁹/L: Use smaller gauge needles (25-27G) and apply prolonged pressure (5-10 minutes) at injection site 1
• Platelet count <25 × 10⁹/L with neurological symptoms: Prioritize treatment despite low platelets; consider platelet transfusion if <10 × 10⁹/L 1

Critical Clinical Pitfalls

Folic Acid Warning

• Never administer folic acid before treating vitamin B12 deficiency, as it may mask B12 deficiency and precipitate subacute combined degeneration of the spinal cord 1, 2

Dosing Considerations

• The 1000 mcg dose is recommended over lower doses (100 mcg) because significantly greater amounts of vitamin are retained with the higher dose, with no disadvantage in cost or toxicity 3
• Monthly dosing of 1000 mcg IM is more effective than 3-monthly injections in maintaining adequate B12 levels 2

Lifelong Therapy

• Do not discontinue B12 supplementation even if levels normalize—patients with malabsorption will require lifelong therapy 1
• Monitor for recurrence of neurological symptoms (paresthesias, gait disturbances, cognitive changes) and consider increasing injection frequency if symptoms return 1

Monitoring Parameters

• Check serum B12 levels and homocysteine every 3 months until stabilization, then once yearly 1, 2
• Target homocysteine level <10 μmol/L for optimal outcomes 1
• Evaluate for resolution of deficiency symptoms including neurological manifestations 1