The IgE response, the involvement of the different penicillins availab
le for therapeutic use, and the specificity of the IgE antibodies foun
d in a group of penicillin-allergic subjects from Italy were studied.
Thirty subjects with a history of allergic reactions to penicillins we
re studied. In vivo and in vitro specific IgE antibodies were determin
ed to different penicillin determinants. Fifteen subjects developed an
aphylactic responses and the remainder urticaria and angioedema. The d
rug most frequently involved in the patients' allergic reactions was a
mpicillin (AMP). The benzylpenicilloyl (BPO) skin test was positive in
16 (53.3%) patients, whereas 23 (76.6%) patients were positive to min
or determinant mixture (MDM), benzylpenicillin (PG), AMP, or amoxicill
in (AX). When classified according to initial reaction type, most anap
hylactic patients (93.3%) were associated with minor determinant react
ivity, whereas most urticaria patients (80%) reacted to BPO. RAST resu
lts for the anaphylactic and urticaria subgroups were similar. RAST in
hibition showed that most sera contained highly cross-reactive IgE ant
ibodies. There was evidence of a specific response to AX and PG (one p
atient each). These data show that in a population of penicillin-aller
gic patients from Italy, AMP was the main drug inducing the allergic r
eaction. In skin tests and RAST, patients exhibited heterogeneous IgE
responses with little indication of specific reactivity to AMP.