Cross-reactivity in beta-lactams after a non-immediate cutaneous adverse reaction: experience of a reference centre for toxic bullous diseases and severe cutaneous adverse reactions.

After a suspected BL-induced non-immediate CADR, a large allergologic exploration is needed to confirm the diagnosis and evaluate cross-reactivity. In our population including cases of severe CADRs and MPE with late delay of onset, cross-reactivity was frequent and PT was sufficient to this purpose. The frequent cross-reactivity among penicillins encourages stopping this whole family and to test cephalosporins, aztreonam and carbapenems for which cross-allergies are rarer.