Otitis: Inside look at pathogenesis, treatment and prevention - DVM
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Otitis: Inside look at pathogenesis, treatment and prevention


DVM360 MAGAZINE


Before we discuss treatment options for bacterial otitis, I will mention briefly a few facts that can be helpful for treatment and management. When one obtains a culture and sensitivity, those values are based upon minimum inhibitory concentration on the serum or plasma that is needed to achieve a kill. Many of the antibiotics are also available in topical form and can be instilled into the ear canal directly on the bacteria, thus achieving a much higher concentration of the antibiotic in the canal. This is important because many antibiotics are more effective at higher concentrations.

Also, when microbiologists and microbiology technicians select a few colonies (after culture is complete) for sensitivity studies, the information may not reflect the resistance for the remaining colonies. That is why repeated cultures and sensitivities on the same ear canal and organism can lead to different results. I have found this phenomenon to be most frustrating.

Treating bacterial otitis externa

Generally, most cases are readily cleared with appropriate topical treatments and systemic antibiotics are not helpful. Neomycin, gentamycin and enrofloxacin containing otic preparations are the most commonly available products for treatment.

I generally recommend topical treatments with corticosteroids if inflammation is moderate and advise systemic corticosteroids if inflammation is severe. Most cases are cleared in two to three weeks and may require weekly or twice-weekly ear washes/rinse to be used as prevention. Products that contain acetic acid, boric acid, chlorhexidine with ceruminolytics or surfactants are most helpful. Clearly, identifying the primary cause is important and can include food trials and intradermal skin testing. I have not found antihistamines to benefit otitis externa.

Treatment of bacterial otitis media

As mentioned earlier, culture and sensitivity and cytological examination is very important in the proper management of otitis. After cytology is performed I advise a culture if appropriate and tend to be very aggressive with therapy. The bacterial cultures may need to be repeated several times during therapy. Initially, I advise sedation if there is a fair amount of discharge in the ear canal, pain with otoscopic examination, or if I cannot visualize the tympanic membrane readily. Routine flushes can be used to irrigate the canal during sedation and include saline or non-alcohol and surfactant containing otic preparations. I have not found an increase incident of ototoxicity with products that have a reputation for causing such damage instill into an ear canal with a ruptured ear drum.

If severe pain and/or hyperplasia is present (particularly in the Cocker Spaniel), I routinely prescribe anti-inflammatory dosages of prednisone. Recently, oral cyclo-sporine has proved beneficial in the treatment of severe and hyperplastic otitis externa. I select antibiotics based upon results of cytology and culture and sensitivity. Routinely, I use topical antibiotics as well as systemic antibiotics pending results of culture. Typically, I select aminoglycosides or fluoroquinolones for topical therapy.

For systemic therapy, I prefer oral Clavamox and sulfa-type antibiotics for non-pseudomonal infections and oral fluoroquinolones for pseudomonal infections. Outlined below are some recipes for topical therapies that will aid in the treatment of resistant pseudomonal infections.

  • Spectinomycin: 2 vials of synotic, 2 mg triamcinolone and 1 cc spectinomycin mixed in 2 oz. bottle.
  • Enrofloxacin: 2.5 cc injectable enrofloxacin, 15 cc sterile saline, 15 cc dexamethasone (2 mg/ml) mixed in 1 oz. bottle.
  • Ticarcillin: reconstitute 6 gram vial in 12 cc sterile water, divide in 2 ml portions in syringe and freeze unused portions, stable for 3 months. Thaw and mix 2 ml of the prepared solution into 40 ml of sterile saline. Divide into four 10 cc aliquots and freeze (stable for months) or refrigerate (stable for about 1 week).
  • Amikacin: 15 ml amikacin (50 mg/ml) and 15 cc sterile water.
  • Silver sulfadiazine: Add 1.5 ml cream to 13.5 ml distilled water, warm and mix well in 1/2 oz bottle.
  • Neomycin/gramicidin/polymyxin ophthalmic drops, already prepared.
  • Ciprofloxacin ophthalmic drops: already prepared.
  • Tobramycin ophthalmic drops: already prepared.

I expect most cases of severe pseudomonal otitis media to be treated for four to six weeks with topical antibiotics (eliminate the corticosteroid-containing topical preparations in three to four weeks), eight to 12 weeks with systemic antibiotics. Generally, orally administered corticosteroids are ceased in two to three weeks.

Malassezia otitis usually is not complicated to treat, however I have seen several cases of severe, chronic, somewhat refractory cases of yeast otitis in the dog.


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