Comparative frequency of patch test reactions to topical antibiotics

SummaryBackground Neomycin, clioquinol and fusidic acid are all topical antibiotics widely used in dermatological practice in the U.K., either as a single agent or in combination with topical corticosteroids. However, an adverse effect of topical antibiotics is contact sensitization. Objectives To examine the frequency of positive patch test reactions to fusidic acid, clioquinol and neomycin. Methods To compare the frequency of allergic patch test reactions over 1 year, we patch tested all patients attending the St John's Institute of Dermatology contact dermatitis clinic for one calendar year with fusidic acid, neomycin and clioquinol. Results We patch tested 1119 patients. Postitive patch test reactions to neomycin were noted in 40 patients (3·6%), compared with eight patients (0·7%) to clioquinol and three patients (0·3%) to fusidic acid. The frequency of medicament allergy to neomycin was thus five times more common than to clioquinol and ten times more common than to fusidic acid. Although fusidic acid is not part of our extended standard series, it is in our medicaments series. Therefore, in the second part of our study, we reviewed all cases of positive patch test reactions to fusidic acid over the last 20 years. We found that the frequency of hypersensitivity has decreased since the early 1980s despite increasing usage; the current average frequency being 1·62 patch-tested patients per year (1·45%) of those patch tested to the medicaments series). The most common diagnosis in such patients was stasis dermatitis (54·2%). Conclusions The frequency of fusidic acid allergy in an eczema population is low and is comparable with published data from over 10 years ago.