Like
penicillins,
cephalosporins may cause
IgE-mediated reactions such as
urticaria,
angioedema, and
anaphylactic shock, which occur because of sensitization to determinants shared with
penicillins or to unique
cephalosporin haptens. In particular, side-chain structures may be responsible for selective sensitization or cross-reactivity. For this reason, individual free
cephalosporins are usually employed in skin testing, in addition to the classic
penicillin reagents.
Cephalosporin skin tests are sensitive in diagnosing
immediate hypersensitivity to these betalactams. As far as in vitro tests are concerned,
IgE assays for
cephalosporins, specifically
sepharose-radioimmunoassays, are a potentially useful tool in evaluating immediate reactions and could be used as complementary tests. In selected cases displaying negative results in both skin tests and
IgE assays, a graded challenge with the implicated
cephalosporin can be performed.
Cephalosporin IgE-mediated hypersensitivity may be a transient condition; therefore, allergologic exams should be repeated in patients with negative initial allergologic work-ups, including challenges. Performing allergologic tests with
cephalosporins other than the culprit, as well as with
penicillin reagents, allows the identification of cross-reactivity with
penicillins, selective responses, or cross-reactivity among
cephalosporins. In the latter group, cross-reactivity is more frequently related to R1 than to R2 side-chain recognition. In assessing the selectivity of the response, negative results in skin testing with
cephalosporins other than the responsible one appear to be a reliable
indicator of tolerability.