Experts concur that systemic antibiotics are inadequate to squash the bad-boy bugs of otitis externa. They also concur that some animals won’t hold still for clients to topically medicate their ears.
"I have rarely found that systemic antimicrobials alone are sufficient to resolve a severe otitis externa case, which typically has copious amounts of organic material in the canal,” said Jon Plant, DVM, owner of the SkinVet Clinic in Lake Oswego, Ore. "If one tries this approach, it is important to thoroughly clean the ear canal. In situations when pet owners are unable to medicate ears topically, I’ve had some success using compounded lanolin-based ear medications that provide a repository effect.”
Paul B. Bloom, DVM, Dipl. ACVD, Dipl. ABVP, also uses a compounded product to pack ears weekly in problem patients until the infection resolves. A combination of gentamicin 0.3 percent, ketoconazole 2.0 percent and triamcinolone 0.1 percent is favored by Bloom, owner of the Allergy, Skin and Ear Clinic for Pets in Livonia, Mich. Alternatively, he offers clients the choice of bringing in the animal daily to have the ears medicated.
Zymox, a non-prescription, enzyme-based family of products manufactured by Pet King Brands Inc. in Westmont, Ill., is a treatment program favored by some veterinarians. The otic products are based on an antimicrobial enzyme system containing lactoperoxidase, lactoferrin and lysozyme, explained Deborah Brown, advertising and marketing vice president.
Zymox products are antifungal, anti-yeast and partially antibacterial, Brown said. Because they work enzymatically, antibiotic resistance is not a factor. Moreover, these solutions thrive on dirty ears, Brown said.
"It’s a totally different protocol than antibiotics,” she said. The enzymes use the microbes in ear debris to emit minute particles of hydrogen peroxide, which she said eliminates even the initial cleaning step.
The client fills the pet’s ear canal with Zymox once daily, massages the base of the ears, then cleans off the excess, Brown said. Treatment protocol is two weeks. "Compliance goes up and it’s more comfortable for the animal.”
Advanced Formula Zymox Plus, introduced in January, is a veterinary-exclusive product aimed at resistant otitis externa due to microbes that form biofilm, a slimy, protective matrix that makes tough infections more resistant to antimicrobials, Brown said. Chief offenders are Pseudomonas, Staphylococcus aureus, methicillin-resistant staph (MRSA) and coagulase-negative staph. The new product contains four additional enzymes to bust the biofilm.
Zymox products come in hydrocortisone-free and 1.0 percent hydrocortisone formulas.
Merck’s Otomax, a combination of gentamicin, clotrimazole and betamethasone, has been popular for years and is virtually the "Coca-Cola” of otic topicals, complete with a posse of generic copycats. A more recent product, Mometamax, contains mometasone furoate in place of betamethasone , and is labeled for once-daily dosing, versus twice-daily for Otomax.
Merial’s Tresaderm is another veteran otic which is labeled for twice-daily use in cats as well as dogs. It contains thiabendazole, dexamethasone and neomycin sulfate.
Easotic Suspension for dogs is Virbac Corp.’s new ear medication that delivers a precise 1-mL dose no matter how the bottle is held. Active ingredients are gentamicin sulfate, miconazole nitrate and hydrocortisone aceponate (HCA), a newer-generation corticosteroid.
Heidi Lobprise, DVM, Virbac’s senior technical manager, said HCA is rapidly hydrolyzed by skin esterases to a potent anti-inflammatory compound. As esterase activity continues into the lower skin layers, the drug is weakened, progressively released into the bloodstream and inactivated, she said.
Easotic is labeled for a once-daily, five-day treatment course.
"Studies show persistence of gentamicin and miconazole in ear canals 10 days after treatment, suggestive of prolonged antimicrobial effects beyond treatment administration,” Lobprise said.
A product cited by Bloom is Surolan otic suspension. Manufactured by Vetoquinol USA Inc., this twice-daily formula contains miconazole nitrate, polymyxin B sulfate and prednisolone acetate.
Baytril Otic contains enrofloxacin, a broad-spectrum flouroquinolone antibiotic that works on more than 400 infectious agents, said Cristiano von Simson, DVM, of Bayer Healthcare LLC Animal Health.
While some might see the lack of an anti-inflammatory ingredient as a negative, von Simson noted, "Many times with steroids, symptoms are reduced or alleviated but the problem is not really solved. Then the infection comes back with a vengeance.”
Since some otitis cases are linked to atopy, the animal often needs systemic corticosteroid treatment, he said.
Regarding use of oral Baytril to treat ear infections, von Simson said one study showed that 82 percent of animals with otitis externa also had otitis interna.
"In many cases, you have to use both the topical and systemic products,” he said.
For those who prefer an anti-inflammatory drug with their flouroquinolone, there is Posatex Otic suspension by Merck. Active ingredients are orbifloxacin, mometasone furoate monohydrate and posaconazole.