Background: Selective reactions to clavulanic acid (CLV) account for around 30% of
immediate reactions after administration of amoxicillin‐CLV. Currently, no immunoas‐
say is available for detecting specific IgE to CLV, and its specific recognition in pa‐
tients with immediate reactions has only been demonstrated by basophil activation
testing, however with suboptimal sensitivity. The lack of knowledge regarding the
structure of the drug that remains bound to proteins (antigenic determinant) is ham‐
pering the development of in vitro diagnostics. We aimed to identify the antigenic
determinants of CLV as well as to evaluate their specific IgE recognition and potential
role for diagnosis.
Methods: Based on complex CLV degradation mechanisms, we hypothesized the for‐
mation of two antigenic determinants for CLV, AD‐I (N‐protein, 3‐oxopropanamide)
and AD‐II (N‐protein, 3‐aminopropanamide), and designed different synthetic analogs
to each one. IgE recognition of these structures was evaluated in basophils from pa‐
tients with selective reactions to CLV and tolerant subjects. In parallel, the CLV frag‐
ments bound to proteins were identified by proteomic approaches.
Results: Two synthetic analogs of AD‐I were found to activate basophils from allergic
patients. This determinant was also detected bound to lysines 195 and 475 of CLV‐
treated human serum albumin. One of these analogs was able to activate basophils in
59% of patients whereas CLV only in 41%. Combining both results led to an increase
in basophil activation in 69% of patients, and only in 12% of controls.
Conclusion: We have identified AD‐I as one CLV antigenic determinant, which is the
drug fragment that remains protein‐bound.
