Contact allergy to various components of topical preparations for treatment of external otitis.

Patients suffering from chronic external otitis had developed contact allergies to one or more compounds of topical preparations in 40% of 142 tested patients. Neomycin and framycetin caused most of the allergic reactions (16.2%) followed by chinoform (7.0%), chloramphenicol and polymyxin (4.2%). Preservatives of the topical otic preparations such as benzethonium chloride (8.5%), benzalkonium chloride (6.3%) and thimerosal (merthiolate) (5.6%) were also common causes of allergic reactions. An epicutaneous test (patch test) using compounds in topical preparations should be done in cases of prolonged, treatment resistant external otitis.