We present nine patients with delayed allergic reactions to beta-lacta
ms. Four of them developed reactions to ampicillin; the diagnostic stu
dies suggested the involvement of a type IV hypersensitivity mechanism
to an antigenic determinant in the side-chain structure, with intrade
rmal and patch tests positive to ampicillin but good tolerance to benz
ylpenicillin. Three patients showed delayed hypersensitivity reactions
to benzylpenicillin (positive delayed skin tests and/or challenges).
Arthus-type reactions were seen in two other patients. Specific IgE of
uncertain relationship to benzylpenicillin and ampicillin was later d
etected in four cases.