Immediate-type hypersensitivity to pyridoxal 5'- phosphate: Study of in vivo and in vitro cross-reactivity and identification of the antigenic determinant

Background: A case in which a 45-year-old female patient with peritonitis experienced immediate-type hypersensitivity on two occasions after administration of preparations containing six different medications was referred to us for closer inspection. Methods/Results: Skin tests performed on the six medications revealed a positive reaction to the vitamin B6 preparation Biosechs (Wakamoto Pharmaceutical, Tokyo, Japan). Further investigation showed that the principal ingredient, pyridoxal 5'-phosphate (PLP), produced a positive reaction, whereas the injection solvent with the principal ingredient removed produced a negative reaction. When compounds similar to PLP were tested, pyridoxine (PN), pyridoxamine and pyridoxal produced a negative reaction, whereas pyridoxine 5'-phosphate and pyridoxamine 5'-phosphate (PMP) produced a positive reaction. Adenosine 2'-phosphate and adenosine 5'-diphosphate were also tested and these produced a negative reaction. When a histamine-release test was performed, PLP and PMP produced a positive reaction, whereas PN produced a negative reaction. When all tests were performed on three control subjects, the results were all negative. Conclusions: In this very rare case, phosphate radical conjugates with a pyridine nucleus became haptenic-epitope and an immediate-type reaction occurred. In past cases involving hypersensitivity to vitamin B6, two cases involved a photoallergic reaction caused by PN and one case involved an immediate-type hypersensitivity caused by PLP In the past cases, closely related substances had not been tested and an epitope was not identified