[Allergic reaction after intravenous application of vitamin B12]

Allergic reactions of parenteral vitamin B12 (cobalamin) for therapy of pernicious anaemia are very rare, but repeatedly described in the literature. In case of allergic reactions oral instead of intravenous substitution of vitamin B12 is tolerated. Very high dosages of vitamin B12 (1,000-2,000 microg per day) are necessary due to the underlying vitamin B12 malabsorption.