Vitamin B₁₂ (Cyanocobalamin)

Category:

• Vitamin

Description:

• Dietary supplement; water-soluble vitamin

Indications:

• 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.

Contraindications:

• Sensitivity to cobalt

Precautions:

• 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 Leber’s 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

Dosage:

• 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