Generalized urticaria to cyclophosphamide: Type I hypersensitivity to an immunosuppressive agent.

A 6-yr-old white boy, Patient L. B., who was receiving cyclophosphamide (CY) for chemotherapy of a localized undifferentiated small cell sarcoma of the chest wall, developed generalized urticaria on three separate occasions immediately after CY administration. Serum samples were obtained 2 and 5 wk after the patient's last reaction and were examined for reaginic activity to the drug. Homocytotropic antibody activity to CY was found in the 2-wk postreaction sample by Prausnitz-Küstner type passive transfer skin testing to chimpanzees. This homocytotropic antibody was found to be of the IgE type, by means of an in vitro double-antibody coprecipitation assay measuring binding of free 14C-CY by specific immunoglobulin E and G fractions. Sera from 3 CY-treated patients who did not have adverse reactions to the drug and 6 normal, age-matched volunteers were used as control samples for the coprecipitation assay. None of the 3 CY-treated control patients had significant binding of 14C-CY by IgE when compared to normal individuals. However, it was found that all CY-treated patients had significant binding of 14C-CY by their IgG fraction when compared to normal subjects.