Fixed drug eruption caused by three unrelated drugs: promethazine, pethidine and omeprazole.

We report a case of fixed drug eruption (FDE) caused by three unrelated drugs. A 52-year-old woman presented with a diagnosis of FDE after taking a drug to treat a common cold. An oral provocation test and a patch test were carried out, and the patient reacted to promethazine, which is a derivative of phenothiazine. To determine the core structure of the antigen, we performed patch testing and/or an oral provocation testing with six drugs that are similar in structure to promethazine. The patient reacted to five of the six drugs, and the antigenic determinant was identified as a phenothiazine and a tricyclic structure. The patient had similar eruptions at the same sites 3 years later after taking pethidine. Seven months after that reaction, a more severe eruption was caused by oral omeprazole. This is an extremely rare case of FDE caused by three structurally unrelated drugs. © The Author(s). CED