Ear canals should first be opened, as ear canal epithelial inflammation and stenosis hinder effective topical treatment, and most cases therefore require topical and/or systemic corticosteroid treatment.2
Ears should be cleaned by flushing, which removes dried medication and cerumen that may interfere with examination and treatment. Sterile saline flushing should be selected when tympanic membrane status is unknown to minimize concern for ototoxicity.9 Squalene is an effective ceruminolytic agent with demonstrated safety in the middle ear and is an alternative option when perforation is suspected.10 During treatment, at-home flushes containing salicylic acid or other mild ceruminolytics should be administered 2 to 3 times per week to maintain ear canal cleanliness.
Treatment selection is based on pathogen identification (yeast vs Pseudomonas spp vs other bacteria), exudate characteristics, and chronic ear canal changes. Because external ear canal volume varies among dog breeds (eg, brachycephalic breeds, 0.47 mL; mesaticephalic and dolichocephalic breeds, up to 5.86 mL),11 extra-label dosing (0.5-1 mL) of most topical ear medications should be used for each affected ear to allow medication to sufficiently coat the ear canals. Antimicrobial medications, excluding long-acting, FDA-approved florfenicol otic medications, are applied twice daily (extra-label) to ensure maintenance of adequate antimicrobial concentrations and inflammation reduction. For stenotic canals, a solution is preferred over an ointment.
Topical antibiotics (eg, fluoroquinolones, amikacin, tobramycin, silver sulfadiazine, ceftazidime) are frequently used to treat Pseudomonas spp. Due to drug inactivation, gentamicin and neomycin are ineffective against Pseudomonas spp otitis, seemingly more so than other aminoglycosides such as amikacin and tobramycin, which have been effective for treatment of Pseudomonas spp otitis in the authors’ experience.12,13 Florfenicol is also ineffective against Pseudomonas spp otitis due to its spectrum limitations.12,13 Using a tris-EDTA–containing flush, which serves as a calcium-chelating agent, can help the effectiveness of topical antimicrobial treatment. These flushes are commercially available and increase the medication permeability of gram- negative organisms by damaging the outer cell wall membrane. The calcium-chelating flush should be applied as pretreatment in conjunction with topical therapy for improved treatment efficacy against Pseudomonas spp otitis.14
Systemic antibiotics should be reserved for the treatment of otitis media and are ineffective in the treatment of otitis externa.2,15