Skin and laboratory tests in amoxicillin- and penicillin-induced morbilliform skin eruption

Background Cutaneous amoxicillin- and penicillin-mediated reactions can be classified as immediate and delayed-type reactions. Immediate reactions are thought to involve IgE antibodies and have been studied extensively. In co ntrast only few data exist about delayed reactions such as morbilliform or maculopapular rash. Objective To assess the predictive value of immediate skin tests, skin-patc h tests, specific IgE and lymphocyte transformation tests with regard to th e diagnosis of delayed skin eruptions. Methods Skin and in vitro tests were performed in 18 subjects. Twelve subje cts had penicillin- or amoxicillin-induced morbilliform exanthema and six w ere controls without hypersensitivity reaction, tested before and after exp osure. Results Specific IgE to penicillin and immediate penicillin skin tests were negative in amoxicillin- or penicillin-induced delayed skin eruptions. In contrast, skin-patch testing and LTT were positive in 9/12 or 10/12, respec tively, but negative in all six controls. Conclusion These findings substantiate a T-cell-mediated immune pathomechan ism in the majority of penicillin-induced delayed skin reaction. Moreover, they underline the necessity to adapt the test procedures to underlying pat homechanisms and support the diagnostic value of skin-patch testing and LTT in delayed cutaneous reactions to penicillins.