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Trade Names:
Big Shot B-12
- Tablets 5,000 mcg

Trade Names:
Crystamine
- Injection 1,000 mcg/mL

Trade Names:
Crysti 1000
- Injection 1,000 mcg/mL

Trade Names:
Cyanoject
- Injection 1,000 mcg/mL

Trade Names:
Cyomin
- Injection 1,000 mcg/mL

Trade Names:
Rubesol-1000
- Injection 1,000 mcg/mL

Mechanism of Action

Pharmacology

Involved in protein synthesis; essential to growth, cell reproduction, hematopoiesis, and nucleoprotein and myelin synthesis.

Pharmacokinetics

Absorption

T _max is 1 h.

T _max is 1 to 2 h. C _max is about 1,414 pg/mL.

Bound to intrinsic factor during transit through the stomach; separation occurs in the presence of calcium and vitamin B ₁₂ enters the mucosal cells for absorption.

Distribution

Distributed and stored primarily in the liver and bone marrow. In the blood, it is bound to trancobalam II.

Elimination

Unbound vitamin B ₁₂ is rapidly eliminated in the urine.

50% to 98% is excreted in the urine within 48 h.

Indications and Usage

Treatment of vitamin B ₁₂ deficiency caused by inadequate utilization of vitamin B ₁₂ ; dietary deficiency of vitamin B ₁₂ occurring in strict vegetarians; malabsorption syndrome of various causes (eg, pernicious anemia, GI pathology, fish tapeworm infestation, malignancy of pancreas or bowel, gluten enteropathy, small bowel bacterial overgrowth, gastrectomy, accompanying folic acid deficiency); supplementation because of increased requirements (eg, associated with pregnancy, thyrotoxicosis, hemolytic anemia, hemorrhage, malignancy, hepatic and renal disease); vitamin B ₁₂ absorption test (eg, Schilling test).

Contraindications

Hypersensitivity to cobalt, vitamin B ₁₂ , or any component of these medications; hereditary optic nerve atrophy.

Dosage and Administration

PO 2 mcg/day.

PO 0.3 to 2 mcg/day.

PO 25 to 1,000 mcg/day.

IM or deep subcutaneous 30 mcg/day for 5 to 10 days followed by 100 to 200 mcg/mo.

IM or deep subcutaneous 100 mcg/day for 6 to 7 days. If reticulocyte response occurs, give 100 mcg every other day for 7 doses, then give 100 mcg every 3 to 4 days for 2 to 3 wk. After this regimen, give 100 mcg/mo for life.

IM 1,000 mcg (z-tract method preferred).

Storage/Stability

Protect from light. Do not freeze.

Drug Interactions

Decreases hematologic effects of vitamin B ₁₂ in patients with pernicious anemia.

Decreases GI absorption of vitamin B ₁₂ .

Laboratory Test Interactions

May invalidate vitamin B ₁₂ diagnostic microbiological blood assays.

Adverse Reactions

With parenteral administration:

Cardiovascular

Pulmonary edema; CHF; peripheral vascular thrombosis.

Dermatologic

Itching; transitory exanthema; urticaria.

EENT

Severe and rapid optic nerve atrophy.

GI

Mild transient diarrhea.

Miscellaneous

Hypersensitivity; pain at injection site; sensation of body swelling; hypokalemia; polycythemia vera; asthenia, headache, infection, glossitis, nausea, paresthesia, rhinitis (intranasal).

Precautions

Pregnancy

Category A ( Category C in doses that exceed the RDA).

Lactation

Excreted in breast milk.

Children

Some products contain benzyl alcohol, which has been associated with fatal “gasping syndrome” in premature infants.

Hypersensitivity

Anaphylactic shock and death have been associated with parenteral use.

Hypokalemia

Possibly fatal hypokalemia could occur as result of increased erythrocyte potassium requirements in severe megaloblastic anemia intensely treated with vitamin B ₁₂ .

Patient Information

• Instruct patient with pernicious anemia of need to continue therapy throughout lifetime.
• Advise patient to administer intranasal gel at least 1 h before or 1 h after ingestion of hot foods or liquids.
• Advise patient with nasal congestion, allergic rhinitis, or upper respiratory tract infections to defer treatment with intranasal gel until symptoms have subsided.
• Teach patient of need to maintain well-balanced diet. Remind patient of the following good sources of vitamin B ₁₂ : seafood, egg yolks, organ meats, fortified breakfast cereals, meat, cheeses, milk, other dairy products.
• Advise patient that folic acid is not substitute for vitamin B ₁₂ but may be taken concurrently.
• Instruct vegetarians who do not use animal products of need for daily oral vitamin B ₁₂ .
• Inform patient with pernicious anemia of need to have periodic GI evaluations.
• Instruct patient to report the following symptoms to health care provider: muscle weakness, shortness of breath, heart irregularity, vision disturbances.