It has been well-established that cell surfaces of gram-negative bacteria are damaged after exposure to EDTA. Tromethamine is a synthetic buffer that enhances the chelating effect of EDTA. The goal of this study was to evaluate the in vitro activity of an ear rinse containing a combination of EDTA-tromethamine and benzyl alcohol on bacteria pathogens isolated from patients with otitis. Three test solutions were evaluated in this study: The combination product described above, EDTA and tromethamine, and sterile water (control). Bacterial isolates included Staphylococcus intermedius (n = 11), Staphylococcus species (n = 4), Pseudomonas aeruginosa (n = 5), Proteus species (n = 5), and beta-hemolytic Streptococcus (n = 11). Bacterial isolates were mixed with test solutions, and samples for culture were obtained at 0, 15, 30, 45, and 60 minutes after contact and cultured. Colony-forming units were counted as a measure of efficacy. In this study, the time of contact for efficacy was important-at least 15 minutes was required for a significant decrease in growth of Pseudomonas aeruginosa and beta-hemolytic Streptococcus, 30 minutes for Proteus, and 60 minutes for Staphylococcus. The ear rinse solution without benzyl alcohol had no effect on growth of Staphylococcus organisms. Study funded by IVX Animal Health Corporation, St Joseph, MO

COMMENTARY: Otitis externa and otitis media are common diseases in dogs. Successful treatment is often dependent on a combination of appropriate topical and systemic therapy and concurrent ear cleaners or rinses. Tris-buffered EDTA solutions have been known for years to be useful adjunct therapies for otitis; however, until these solutions became available commercially, use was limited to only those veterinarians who had access to formulating pharmacies. This study shows that the combination of EDTA, tromethamine, and benzoyl alcohol was effective for controlling growth of common organisms isolated from dogs with otitis. Of note, recurrent allergic and seborrheic otitis externa is often complicated by Staphylococcus organisms and ear rinse solution may be beneficial as an adjuvant for long-term management of these patients.

In vitro activity of an ear rinse containing tromethamine, EDTA, and benzyl alcohol on bacterial pathogens from dogs with otitis. Cole L, Dao HL, Paivi RK, et al. AM J VET RES 67:1040-1043, 2006.