Vitamin B12, also known as cobalamin, is one of the few organo-metallic compounds occurring in nature and was the last hydro-soluble vitamin to be identified. The cobalamin biochemical structure and its metabolism are highly complex, and diseases related to its deficiency are associated with hematological and neurological alterations. The complex chemical structure of cobalamin gives it a high molecular weight, making cobalamin an immunogenic molecule. Moreover, the presence of the cobalt atom in the corrin ring of cobalamin may cause an allergic contact dermatitis flare-up in patients previously sensitized to cobalt. Immediate-type reactions induced by the parental administration of vitamin B12 have been reported in the literature, and they are linked to the used cobalamin moiety or its delivery route. They are reputed to be genuinely IgE mediated. Two “time patterns” of sensitization have been evidenced and probably two patterns of immune recognition also exist. Desensitization protocols have been used as an alternative method to administer vitamin B12 in patients needing it when all the other strategies fail.
Keywords: Adenosylcobalamin, Allergic Contact Dermatitis, Anaphylaxis, Cobalamin, Cobalt, Cyanocobalamin, Drug Desensitization, Hydroxocobalamin, IgE, Skin Tests, Transcobalamin II, Urticaria, Vitamin B12.