Morbilliform Eruptions Caused by Penicillin*

Although much has been learned regarding the immunology of penicillin eruptions, the advances are largely limited to reactions mediated by humeral antibodies. Therefore, we undertook a study of the more common, but less well-understood morbilliform eruptions which occur several days to weeks following penicillin therapy. Biopsies were taken from 4 patients with such eruptions and from 4 control subjects and studied by electron microscopy as well as light microscopy. The patients were skin tested with penicillin antigens and studied for hemagglutinating antibodies. The results showed no abnormalities in hemagglutinating antibodies, no detectable skin-sensitizing antibodies or delayed sensitivity to penicillin derivatives. Electron microscopy revealed striking differences between patients with penicillin eruptions and controls. The involved skins showed intercellular edema limited to the basal area and some intracellular edema. The basement lamina remained intact. Other morphologic changes presented interesting similarities to those seen in pemphigus vulgaris including clumped perinuclear tonofibrils and “tomb-stone-like” basal keratinocytes. Fluorescence studies revealed anti-epithelial antibodies in the blood serum of 2 of the 4 patients with morbilliform penicillin eruptions.