Vitamin B12 Injection — Supplements
Intramuscular B12 for rapid repletion in deficiency states bypassing GI absorption barriers.
Overview
Intramuscular vitamin B12 (typically as hydroxocobalamin or cyanocobalamin) provides direct systemic delivery bypassing GI absorption limitations that are common in pernicious anemia, atrophic gastritis, post-bariatric surgery, and malabsorption syndromes. IM injection achieves rapid repletion of B12 stores and is the standard of care for pernicious anemia. Loading dose protocols rapidly correct deficiency, followed by monthly maintenance injections. Hydroxocobalamin is preferred in most clinical guidelines for its longer tissue retention and ability to bind cyanide.
Indications
- Pernicious anemia treatment
- Severe B12 deficiency with neurological symptoms
- Post-bariatric surgery B12 maintenance
- Malabsorption syndromes (Crohn's, celiac)
- Rapid B12 repletion in symptomatic deficiency
Mechanism of Action
IM injection bypasses intrinsic factor requirement and GI absorption barriers, delivering B12 directly to systemic circulation
Dosing
| Compound | Dose | Frequency | Notes |
|---|---|---|---|
| Vitamin B12 (Injectable) | 1,000 mcg | Weekly x 8-12 weeks (loading), then monthly (maintenance) | Hydroxocobalamin preferred; loading then maintenance protocol |
Safety & Contraindications
- Injection site pain, redness, and swelling are common
- Very rare anaphylaxis to injectable B12; have epinephrine available
- Hydroxocobalamin may cause temporary reddish discoloration of urine
- Must be administered by healthcare professional