Vitamin B-12 also known as cobalamin is a water-soluble vitamin that plays an important role in the formation of healthy red blood cells and in the maintenance of healthy nerve cells, according to MedlinePlus. Lack of vitamin B-12 leads to pernicious anemia. Patients with pernicious anemia are usually prescribed vitamin B-12 injections. Vitamin B-12 should not be used in patients with certain medical conditions.
Allergies
Vitamin B-12 injections should not be used in patients allergic to cobalamin, cobalt and other product ingredients, according to MayoClinic.com. Symptoms of allergic reactions caused by vitamin B-12 include wheezing, hives, rashes, problems breathing, swelling of the face, eyelids, lips, tongue and throat and itching.
Leber's Disease
Vitamin B-12 is contraindicated in patients with Leber's disease, according to MayoClinic.com. Leber's disease is a type of hereditary disease in which the optic nerve becomes atrophied. Vitamin B-12 can cause severe swift optic atrophy in patients with Leber's disease.
Megablastic Anemia
Vitamin B-12 should not be used in patients with megablastic anemia, according to MayoClinic.com. Treatment of megablastic anemia with vitamin B-12 can result in gout and fatal hypokalemia. Hypokalemia is low potassium levels in the body that lead to disturbance in electrical conduction in the heart, which can be fatal.
