As a general guideline, 5-10 drops (depending on the dog’s size) of topical antimicrobial agent should be applied to the ear twice daily, but in cases with ruptured tympanic membranes, all topically applied antibiotics are potentially ototoxic.
When the tympanic membrane is not intact or its patency is unknown, pet owners must be warned of potential adverse reactions. However, such cases are rare, and the benefits of topical antibiotics outweigh the risk of ototoxicity.
In acute Pseudomonas otitis cases, first-line topical antibiotics include neomycin, polymyxin and gentamicin.
Cases that fail to respond to initial therapy or cases of chronic Pseudomonas otitis call for second-line topical antibiotics such as tobramycin, amikacin, enrofloxacin, ticarcillin and silver sulfadiazine.
In these circumstances, presoaking the ear canal with Tris-EDTA enhances the activity of the subsequently applied topical antibiotic. Tris-EDTA disrupts the cell membranes of gram-negative bacteria, such as Pseudomonas species, allowing the antibiotics to permeate the bacteria and work more effectively.