Patch testing - a valuable tool for investigating non-immediate cutaneous adverse drug reactions to antibiotics.

BACKGROUND: Antibiotics are among the most frequent causes of cutaneous adverse drug reactions (CADR); patch testing may be an important tool in their evaluation and management. We assessed the role of patch testing as a diagnostic tool in non-immediate CADR to antibiotics, and evaluated cross-reactivity among them.

METHODS: We reviewed data from all patients with non-immediate CADR attributed to antibiotics, which were patch tested between 2000 and 2014 at our dermatology department.

RESULTS: Patch tests were performed in 260 patients, and showed overall reactivity to antibiotics of 21.5%, especially in the context of drug reactions with eosinophilia and systemic symptoms (DRESS) (31.6%), maculopapular exanthema (MPE) (21.8%), Stevens-Johnson syndrome/toxic epidermal necrolysis (20%) and acute generalized exanthematous pustulosis (AGEP) (18.1%). Patch test reactivity was higher for amoxicillin, mainly in DRESS (44.4%) and MPE (25.6%), and dicloxacillin (50% in AGEP and 37.5% in MPE). Reactivity to clindamycin occurred, especially in the setting of MPE (23.2%). In AGEP and DRESS, patch tests were useful in detecting reactivity to quinolones (50-100%). Overall reactivity was lower for vancomycin (9.1%), co-trimoxazole (8.6%), macrolides (4.8%) and cephalosporins (4.4%). Positive patch tests for more than one antibiotic occurred in 29/56 cases (51.8%), mostly explained by cross-reactions. Twenty of 24 cases reacted to both amoxicillin and ampicillin. All five cases reacting to ciprofloxacin cross-reacted with other quinolones.

CONCLUSION: Although oral rechallenge is considered the gold standard for confirming drug imputability in CADR, patch testing could be suggested as a first choice in the study of non-immediate reactions, since it is a safe and valuable procedure.