Two cases of toxic epidermal necrolysis caused by delayed hypersensitivity to beta-lactam antibiotics

The authors describe two cases of toxic epidermal necrolysis (TEN) caused by delayed hypersensitivity to semisynthetic penicillins. The first patient developed erythema of the lower limbs following an i.m. injection of ampicillin, which progressed to TEN as therapy was continued. Fever and eosinophilic leukocytosis were also present. In the second case, TEN developed following oral amoxicillin therapy, and was preceded by a diffuse, maculopapular eruption. In both cases, symptoms resolved with the prompt administration of steroids. Both patients underwent allergological testing: prick test and, if results were negative, intradermal tests with penicilloyl-polylysine (PPL), minor determinant mixture (MDM), penicillin, amoxicillin and ampicillin. Patch testing with penicillin, ampicillin and amoxicillin was also performed. Both patients developed positive reactions to the intradermal tests after 6 h, and to patch tests after 48-72 h (for ampicillin, amoxicillin and penicillin in the first case, and for ampicillin and amoxicillin in the second). The lymphocyte transformation test (LTT), performed only in the first case, was positive for ampicillin. As these cases demonstrate, delayed hypersensitivity should be suspected in cases of drug-related TEN. Patch testing is a simple and useful allergological test for these types of cases.