Dermographia caused by IgE mediated penicillin allergy.

A patient developed symptomatic dermographia while taking penicillin. The dermographia disappeared when the penicillin was stopped. The patient usually was negative for dermographia testing up to 400 g pressure. While taking penicillin a dermographic response occurred at 50 g pressure. Passive transfer skin testing established that the reaction was mediated by an IgE antibody to penicillin breakdown products. Interestingly, in both the subject and the passive transfer recipient skin testing to Pen G, M.D.M. and B.P.L. was negative. We concluded that the dermographia in our patient resulted from specific IgE penicillin interactions not recognized by the usual testing reagents.