Vitamin B9 (Folate)

Folic acid is the synthetic form of vitamin B9 or folate and it is not found in nature. Folate conversion to the active form requires reduction to tetrahydrofolate, a reaction that is catalyzed by dihydro-folate reductase, which is expressed in the intestine and other peripheral tissues. Folic acid is the lonely vitamin able to induce severe anaphylactic shock following its oral assumption or through any route of administration, i.e. intravenously or intramuscularly. The sensitizing strength of the folic acid might be due to its accumulation in blood, caused by its property to exhaust the enzymatic pathways responsible for its metabolism. Specific IgE to folic acid has been isolated by different research groups, thus suggesting immediate-type reactions to folic acid have genuinely a reaginic pathomechanism. Furthermore, derivative drugs like folinic acid or antifolate drugs like methotrexate have been produced and they may show an allergic cross-reactivity with folic acid. Isolated cases of folic acid desensitization have been performed but poorly described in literature whereas a wellelaborated desensitization protocol would be desirable, given the importance of folic acid during pregnancy to prevent neural tube malformations in the newborn.

Keywords: Anaphylaxis, Calcium Folinate, Cereals, Delayed-type Reaction, Folate, Folic Acid, Folinic Acid, IgE, Immediate-type Reaction, Methotrexate, Pteroyl-glutamic Acid, Skin Tests, Urticaria, Vitamin B9.