A topical steroid without an antibiotic cures external otitis efficiently:a study in an animal model

In an animal external otitis model, inflammatory reactions were evoked by m echanical stimulation of the rat ear canal skin. The rats were in four grou ps: group A treated with a group III steroid, betamethasone dipropionate; g roup B treated with hydrocortisone combined with oxytetracycline; group C t reated with hydrocortisone with oxytetracycline and polymyxin B added; Grou p D, the controls, treated with saline. All rats were observed otomicroscop ically daily during the first 7 days after treatment and then on days 10 an d 20. A standardized scoring system was used to evaluate colour, swelling a nd effusion of the ear canal. Histological specimens were collected on days 3, 7, 10 and 20. The most rapid improvement in the ear canal status occurr ed in the animals treated with betamethasone dipropionate. The inflammatory reaction of the ear canal skin caused by mechanical stimulation was charac terized by oedema of the stroma but few inflammatory cells were present. Th e surface of the epithelium towards the connective tissue layer was smooth in the group III-treated animals (group A) whereas other groups had irregul arities of the basal membrane. From this study it is inferred that the grou p III steroid betamethasone dipropionate alone heals experimentally induced external otitis more rapidly than hydrocortisone with oxytetracycline, wit h or without polymyxin B. These findings should be considered in future cli nical trials of external otitis.