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

Abstract

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 contrast only few data exist about delayed reactions such as morbilliform or maculopapular rash. Objective To assess the predictive value of immediate skin tests, skin‐patch tests, specific IgE and lymphocyte transformation tests with regard to the diagnosis of delayed skin eruptions. Methods Skin and in vitro tests were performed in 18 subjects. Twelve subjects had penicillin‐ or amoxicillin‐induced morbilliform exanthema and six were controls without hypersensitivity reaction, tested before and after exposure. 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, respectively, but negative in all six controls. Conclusion These findings substantiate a T‐cell‐mediated immune pathomechanism in the majority of penicillin‐induced delayed skin reaction. Moreover, they underline the necessity to adapt the test procedures to underlying pathomechanisms and support the diagnostic value of skin‐patch testing and LTT in delayed cutaneous reactions to penicillins.