Treating otitis externa - Veterinary Practice
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InFocus

Treating otitis externa

How should the current focus on antimicrobial resistance affect our approach in treating otitis externa?

Otitis externa is a very common clinical presentation and the management of cases is reliant on identification and treatment of the underlying cause, be it predisposing, primary or perpetuating. As well as treating the infection presented in the clinic, it is often necessary to control secondary factors using topical polypharmacy ear preparations to combat infections with bacteria and yeasts, and inflammatory processes within the ear canal. Topical preparations are ideal for this type of infection, as the antibiotic chosen can be given in much higher concentrations than when dosing systemically. Therefore, antibiotics that the bacteria have shown apparent resistance to in in vitro culture and sensitivity testing can still be effective when used topically. Cytological examination of ear exudate is one of the most important steps. It can easily be performed in-house and gives quick results, allowing the identification of cocci, rods and fungal organisms such as Malassezia spp. Knowing what is present in the ear is invaluable when deciding which antibiotic to use.

The antimicrobials available in licensed topical preparations in the UK are: florfenicol, framycetin, fucidic acid, gentamicin, marbofloxacin, orbifloxacin and polymixin B. They have differing profiles for which bacteria they would be expected to be effective against depending on their classification. There are studies showing synergy between some ear-cleaning preparations and these antimicrobials, increasing the antibiotic susceptibility of certain bacteria. The likely resistance profiles of certain organisms against these antimicrobials has been researched. Orbifloxacin and marbofloxacin are fluoroquinolones and should not usually be used as first-line treatments, typically being reserved for if bacterial culture and sensitivity results indicate they would be the most appropriate antibiotics to use due to resistance of the first-line options. Your choice of antimicrobial to instil topically into the ear canal should be based on history-taking, clinical examination, cytological findings, and good antibiotic stewardship.

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