Therapy for Chronic Canine Otitis

Treatment errors, over and under treatment, or inappropriate use of antimicrobial medication can result in a chronically diseased ear. The key to successful management of chronic canine otitis is early intervention, identifying a cause of the condition, and employing specific and appropriate therapy.

Ears with highly proliferative, chronic disease require deep cleaning and flushing before any topical therapy can be expected to help resolve the condition. Should a myringotomy be performed, the contents of the middle ear can be aspirated as soon as rupture occurs, and the middle ear can be flushed with normal saline or Tris-EDTA using a feline, open-tipped urinary catheter. “Just before the animal wakes, Tris-EDTA and a topical antimicrobial solution should be instilled and a parenteral prednisolone administered.”

“The pathogens isolated most frequently from chronic external and middle-ear infections include Staphylococcus intermedius, Malassezia pachydermatis, Pseudomonas species, Proteus species, Escherichia coli, and enterococcus. Selection of both systemic and topical antimicrobial medication is based on cytologic evaluation and culture and sensitivity results. Systemic antibiotics are mandatory... Treatment should continue until the infection is resolved (a minimum of 4 weeks). It is not uncommon for treatment of otitis media to continue uninterrupted for 8 to 12 weeks.”

Patricia D. White, DVM, MS of Atlanta Veterinary Skin & Allergy Clinic suggests that several compounded preparations may be appropriate.

Compendium on Continuing Education 21:8 August 1999, pg 716-28

Importance of Medication Vehicle

“Topical antimicrobial therapy is an important part of the treatment regimen, and the vehicle is as important as the active ingredient. Most otic preparations are combination drugs (glucocorticoid plus antibiotic) in an oil or ointment base. Oils and ointments are occlusive, may hold or trap exudate, and may increase the risk of ototoxicity; such preparations are not desirable in cases of chronic otitis in which a moist exudate is present, the canal is stenotic, or the eardrum may be ruptured. The goal of treating a wet ear is to dry it. Solutions and suspensions are primarily composed of water; may contain an astringent (e.g., aluminum acetate); and are designed to evaporate over time, thus helping to dry the ear.” Topical antibiotics that are selected initially should be adjusted when the culture and sensitivity results are known.

“There is no single topical otic preparation that will satisfactorily treat all conditions. Practitioners tend to dispense a product based on clinical impressions or pick a favorite product rather than selecting one that has specific application for the current condition.” Direct application of medication to the ear canal will result in a higher concentration than that obtained with systemic medication.
Once you have identified the problem, we can compound an otic preparation to most appropriately treat each animal.

Compendium on Continuing Education 21:8 August 1999, pgs. 716-728

Helpful Hints Regarding Otitis Therapy

Ototoxicity manifested as deafness or vestibular toxicity is a potential adverse effect of some medications used to treat otitis, such as aminoglycosides (tobramycin, gentamicin, amikacin and neomycin) and chloramphenicol. Numerous alternatives exist.
Enrofloxacin, a fluoroquinolone effective against Pseudomonas species, can be compounded as a solution and applied to the ear canal twice daily. “Topical enrofloxacin may achieve a higher antibiotic concentration at the site more economically than systemic medication.”
Silver sulfadiazine is effective in vitro against Pseudomonas species, Staph aureus, Proteus species, and others; a 0.1% to 1% emulsion every 12 hours is adequate to kill Pseudomonas.

Topical otic products may contain potent glucocorticoids in ointment or oil bases. However, solutions may be a preferable vehicle, and it may be advisable to use a less potent steroid because the degree of absorption of topical steroids can not be controlled. We can compound a preparation containing your choice of steroid in the most appropriate vehicle to treat the condition.

“Commercial otic drying agents should be avoided in inflamed, chronically diseased ears because most contain isopropyl alcohol and varying concentrations of benzoic, acetic, salicylic, or boric acid. Each of these products individually can be extremely irritating to an already traumatized epithelium.”

Acetic acid solution can be used to decrease the bacterial population by lowering the pH within the ear canal. Pseudomonas can be killed by 1 minute of contact with a 2% solution. This treatment is especially beneficial when the organism is resistant to other antibacterials. Staph and Strep may be killed by 5 minutes of contact with a 5% solution, according to Kirk’s Current Veterinary Therapy XII Small Animal Practice. However, inflammation (which can be severe) is an occasional side effect of treatment with acetic acid concentrations higher than 2.5%.

Compendium on Continuing Education 21:8 August 1999, pgs. 716-728
Kirk’s Current Veterinary Therapy XII Small Animal Practice, 1995, Bonagura & Kirk, ed.

Treatment of Canine Otitis with Norfloxacin 1% & Ketoconazole 1%
by T. D. Flack, D.V.M. Scottsdale, AZ

The common therapy for fungal otitis externa in dogs utilizes an antifungal and topical steroid, sometimes in combination with systemic antibiotics. The three organisms which have been isolated and are thought to be the most common pathogens in recurrent canine otitis externa are Malassezia, Pseudomonas, and Proteus spp. Using a fluoroquinolone along with an antifungal, we are able to have good coverage on all virulent pathogens. For treatment of resistant infections, the synergism of norfloxacin and ketoconazole provides a broader spectrum of coverage than many other therapies, as ketoconazole is a more active antifungal than clotrimazole. We have utilized a compounded otic gel containing norfloxacin 1% and ketoconazole 1% more than 20 times with a very high success rate.

“Infectious otitis externa is a common disease in dogs. Systemic antibiotic therapy is not always required. Thirty-six dogs of mixed sex, breed, and age were treated for... the purpose of evaluating the efficacy of a ketoconazole 1% and norfloxacin 1% otic gel... Treatment consisted of 0.5 to 1.0 ml of the otic gel in each affected ear twice a day for 7 days. Results showed 91.66% satisfactory responses at 7 and 14 days treatment... Failures (8.33%) were related to Staphylococcus associated with Proteus, Malassezia, and Candida... The 7-day treatment was successful in 21 cases. However, since 12 dogs required 14 days of treatment, it would be sensible to recommend a 14-day therapy.”

Canine Practice, Vol. 21, No. 2, pp. 26-28

Tris-EDTA Solution for Canine Otitis
Richard E. Wooley, D.V.M., Ph.D., Harry W. Dickerson, B.V.Sc., Ph.D.,
and William R. Engen, D.V.M.,
Department of Medical Microbiology, College of Veterinary Medicine, Univ. of Georgia, Athens

The authors reported the successful use of Tris-EDTA in the treatment of otitis externa. In 24 dogs with clinical otitis, the Tris-EDTA (tris[hydroxymethyl] aminomethane and ethylenediaminetetraacetate) combination was tested against Bacillus spp., Staphylococcus aureus, Candida spp., Pseudomonas aeruginosa, Esherichia coli, Proteus vulgaris, Trichosporon spp., and an a-streptococcus. “Fifteen of the 24 cases were acute; all were evaluated with bacterial culture before and after treatment. The treatment consisted of applying lavage solution to the ears t.i.d. until resolution or for three weeks if there was no clinical response. Dogs were examined for irritation of the ears after treatment... 23 of 24 cases were resolved; no adverse effects were seen, but duration of follow-up was not specified. The case that failed to respond was a chronic, mixed infection of E. Coli and Proteus spp.; inflammation was reduced, but the infection persisted. Most cases responded within one week, but P. aeruginosa infections required one to three weeks of treatment.”

Veterinary Forum, June 1999, p. 52

Tris-EDTA solution (buffered to pH 8.0) has a direct bactericidal effect on some bacteria by chelating metal ions in the cell wall. “Dogs with chronic disease (e.g. atopy, idiopathic seborrhea) will be predisposed to recurrent otitis; a topical antibiotic solution or Tris-EDTA used two to three times weekly may prevent an infection from occurring with each flare-up of the primary disease.”

The bactericidal effects of Tris-EDTA are synergistic with aminoglycosides. Although an antibiotic can be added to the Tris-EDTA solution, Patricia D. White, DVM, MS states that she prefers to use Tris-EDTA 5 to 10 minutes before the topical antibiotic. The Tris-EDTA/antibiotic combination is ineffective against yeast.

Compendium on Continuing Education 21:8 Aug. 1999, pgs. 716-728