Vitamin B12 (Cyanocobalamin)


  • Vitamin


  • Dietary supplement; water-soluble vitamin


  • Vitamin B12 deficiency

    • necessary for bone marrow and proper CNS and GI function

  • Pernicious anemia (enlarged (macrocytic) red blood cells)

  • Increased vitamin B12 requirements: 

    • Pregnancy

    • Thyrotoxicosis

    • Hemolytic anemia

    • Hemorrhage

    • Malignancies

    • Hepatic or renal disease.

  • Unlabeled uses:

    • cyanide toxicity associated with sodium nitroprusside.  Vitamin B12 binds with free cyanide to form cyanocobalamin and thereby decreasing RBC and plasma cyanide concentrations.


  • Sensitivity to cobalt


  • Pregnancy category C

  • Vitamin B12 deficiency is related to malabsorption syndrome seen in patients with:

    • Pernious anemia

    • GI pathology, dysfunction or surgery, 

    • Tapeworm infestation

    • Pancreatic or bowel malignancies

    • Sprue

    • Small bowel bacterial overgrowth

    • Gastrectomy

    • Folic acid deficiency.

  • If the patient exhibits an inadequate response, it may be due to:

    • Infection

    • Uremia

    • Bone marrow suppressive medications

    • Concurrent iron or folic acid deficiency

    • Misdiagnosis.

  • Patients with Leberís disease (hereditary optic nerve atrophy) suffer severe and swift optic nerve atrophy.

  • Long-term vitamin B12 deficiency may produce permanent degenerative lesions on the spinal cord.

  • Give a test dose of parenteral vitamin B12 due to cases of anaphylactic reactions.

  • Vitamin B12 deficiency is common in immunocompromised patients, monitor AIDS and HIV patients vitamin B12 levels.

  • The maximum amount of vitamin B12 absorbed per dose is 1-5mcg and the percentages decreases with subsequent doses.

Adverse Reactions (Side Effects):

  • Relatively non-toxic in therapeutic doses

  • Parenteral vitamin B12:

    • Cardiovascular: pulmonary edema, congestive heart failure in early treatment, peripheral vascular thrombosis

    • Itching, transitory exanthema

    • Feeling of generalized body swelling, mild transient diarrhea, injection site pain


  • Dietary sources: meat products (produced by microorganisms in animal proteins), dairy products

  • Administered in oral tablets, intranasal gel and injectable

  • Dietary supplementation (RDA: recommended daily allowance):

    • Adults: 2 mcg per day

  • Normal dosing:

    • oral: up to 1000mcg per day

    • parenteral: IM or SQ: 30mcg per day for 3-10 days, then followed by 100-200mcg on a monthly basis

  • Addisonian pernious anemia:

    • IV therapy is required for life

    • 100mcg per day for 6-7 days by deep IM or SQ injection

    • if improvement occurs, give every other day for 2 weeks, then every 3-4 days for another 2-3 weeks, then 100mcg per day for remainder of life

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