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Patients with early Leber's disease (hereditary optic nerve atrophy) who were treated with vitamin B12 suffered severe and swift optic atrophy.

Hypokalemia and sudden death may occur in severe megaloblastic anemia which is treated intensely with vitamin B12. Folic acid is not a substitute for vitamin B12 although it may improve vitamin B12-deficient megaloblastic anemia. Exclusive use of folic acid in treating vitamin B12-deficient megaloblastic anemia could result in progressive and irreversible neurologic damage.

Anaphylactic shock and death have been reported after parenteral vitamin B12 administration. No such reactions have been reported in clinical trials with Nascobal (cyanocobalamin) Nasal Spray or Nascobal (cyanocobalamin) Nasal Gel.

Blunted or impeded therapeutic response to vitamin B12 may be due to such conditions as infection, uremia, drugs having bone marrow suppressant properties such as chloramphenicol, and concurrent iron or folic acid deficiency.



An intradermal test dose of parenteral vitamin B12 is recommended before Nascobal (cyanocobalamin) Nasal Spray is administered to patients suspected of cyanocobalamin sensitivity. Vitamin B12 deficiency that is allowed to progress for longer than three months may produce permanent degenerative lesions of the spinal cord. Doses of folic acid greater than 0.1 mg per day may result in hematologic remission in patients with vitamin B12 deficiency. Neurologic manifestations will not be prevented with folic acid, and if not treated with vitamin B12, irreversible damage will result.

Doses of vitamin B12 exceeding 10 mcg daily may produce hematologic response in patients with folate deficiency. Indiscriminate administration may mask the true diagnosis.

The validity of diagnostic vitamin B12 or folic acid blood assays could be compromised by medications, and this should be considered before relying on such tests for therapy.

Vitamin B12 is not a substitute for folic acid and since it might improve folic acid deficient megaloblastic anemia, indiscriminate use of vitamin B12 could mask the true diagnosis.

Hypokalemia and thrombocytosis could occur upon conversion of severe megaloblastic to normal erythropoiesis with vitamin B12 therapy. Therefore, serum potassium levels and the platelet count should be monitored carefully during therapy.

Vitamin B12 deficiency may suppress the signs of polycythemia vera. Treatment with vitamin B12 may unmask this condition.

If a patient is not properly maintained with Nascobal® (cyanocobalamin) Nasal Spray, intramuscular vitamin B12 is necessary for adequate treatment of the patient. No single regimen fits all cases, and the status of the patient observed in follow-up is the final criterion for adequacy of therapy.

The effectiveness of Nascobal (cyanocobalamin) Nasal Spray in patients with nasal congestion, allergic rhinitis and upper respiratory infections has not been determined. Therefore, treatment with Nascobal (cyanocobalamin) Nasal Spray should be deferred until symptoms have subsided.

Laboratory Tests

Hematocrit, reticulocyte count, vitamin B12, folate and iron levels should be obtained prior to treatment. If folate levels are low, folic acid should also be administered. All hematologic parameters should be normal when beginning treatment with Nascobal® (cyanocobalamin) Nasal Spray.

Vitamin B12 blood levels and peripheral blood counts must be monitored initially at one month after the start of treatment with Nascobal® (cyanocobalamin) Nasal Spray, and then at intervals of 3 to 6 months.

A decline in the serum levels of B12 after one month of treatment with B12 nasal spray may indicate that the dose may need to be adjusted upward. Patients should be seen one month after each dose adjustment; continued low levels of serum B12 may indicate that the patient is not a candidate for this mode of administration.

Patients with pernicious anemia have about 3 times the incidence of carcinoma of the stomach as in the general population, so appropriate tests for this condition should be carried out when indicated.

Carcinogenesis, Mutagenesis, Impairment Of Fertility

Long-term studies in animals to evaluate carcinogenic potential have not been done. There is no evidence from long-term use in patients with pernicious anemia that vitamin B12 is carcinogenic. Pernicious anemia is associated with an increased incidence of carcinoma of the stomach, but this is believed to be related to the underlying pathology and not to treatment with vitamin B12.


Pregnancy Category C: Animal reproduction studies have not been conducted with vitamin B12. It is also not known whether vitamin B12 can cause fetal harm when administered to a pregnant woman or can affect reproduction capacity. Adequate and well-controlled studies have not been done in pregnant women. However, vitamin B12 is an essential vitamin and requirements are increased during pregnancy. Amounts of vitamin B12 that are recommended by the Food and Nutrition Board, National Academy of Science - National Research Council for pregnant women should be consumed during pregnancy.

Nursing Mothers

Vitamin B12 appears in the milk of nursing mothers in concentrations which approximate the mother's vitamin B12 blood level. Amounts of vitamin B12 that are recommended by the Food and Nutrition Board, National Academy of Science-National Research Council for lactating women should be consumed during lactation.

Pediatric Use

Intake in pediatric patients should be in the amount recommended by the Food and Nutrition Board, National Academy of Science-National Research Council.


This monograph has been modified to include the generic and brand name in many instances.

Last reviewed on RxList: 12/12/2016


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