ABSTRACT External otitis and its treatment. Is a group III steroid without antibiotics sufficient therapy? – Experimental and clinical studies Per Emgård, Department of Otorhinolaryngology, University of Umeå and Ystad Hospital, Umeå and Ystad, Sweden External otitis is one of the most common ear, nose and throat (ENT) diagnoses in out-patient clinics. The clinical course of external otitis includes itching, pain, redness, swelling and effusion of the external auditory canal (EAC) with normal tympanic membrane status. The inflammatory condition is often associated with infection by bacteria, e.g. Pseudomonas aeruginosa, or skin bacteria such as Staphylococcus species. Fungi are present only in a low percentage of cases and if present Candida albicans infection is the most frequent in northern countries such as Sweden and the UK. Topical therapy is recommended in most countries and dominates the therapy in most studies. Topical drugs used are usually a combination of antibiotics and a steroid. However, external otitis is treated with surprisingly many strategies – eleven different ones in Sweden, for example, and 18 in the UK. The aims of the present studies were to – -establish an animal model, infected and uninfected, suitable for testing various treatment strategies of external otitis; and -perform a clinical study in patients to elucidate whether a group III steroid alone is as efficient for treatment of external otitis as is the commonly used topical drug containing a combination of a steroid and antibiotics. The animal model was established through mechanical irritation of the external ear canal skin of Sprague-Dawley rats. An evaluation scale for characterization of the clinical status of the ear canal was introduced, recording redness, swelling and occurrence of effusion in a standardized way. Specimens of the ear canal skin were analysed by histological techniques. A topical solution of 0.05% bethametasone dipropionate (BD) was compared with a 1% hydrocortisone solution with antibiotics oxytetracycline and polymyxin B added (HCPB), administered in the external otitis model infected or non-infected with bacteria (P. aeruginosa) and a fungus (C. albicans). The same drugs were tested in a randomized parallel-group multi-centre study in 51 patients. The clinical status of the external otitis patients was evaluated on a similar scale as used in the animal model. Early normalization of the ear canal skin status and frequency of relapses during the 6-month follow-up period were used as end-points of the study. The studies showed the following: -An animal model for external otitis, infected or uninfected, could be established. -A new scale for evaluation of the external ear canal status with regard to redness, swelling and occurrence of effusion was introduced for the animal model as well as for the investigations in patients. -Treatment with a group III steroid topical solution without antibiotics was superior to treatment with a group I steroid with antibiotics added in achieving resolution of external otitis. -The effectiveness of the topical drugs in the clinical studies in external otitis patients was similar to that in animal external otitis models. We conclude that a group III steroid solution cures external otitis more effectively than does a solution containing a group I steroid combined with antibiotics, whether infected by bacteria or by fungi. No difference was evident regarding adverse effects. Furthermore, costs favour a solution without any antibiotic components. In view of these observations a group III steroid solution is preferred for remedy of external otitis in the clinical situation. Key words: external otitis, external auditory canal (EAC), animal model, treatment, betamethasone, hydrocortisone, antibiotics, human study, Pseudomonas aeruginosa, Candida albicans.