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Elizabeth Bellavance

Elizabeth Bellavance, DVM, MBA, CEPA


Søren R. Boysen

Scott Weese,



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Trisha Dowling,



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David Francoz,



Fraser Hale

Fraser Hale,



Danny Joffe

Danny Joffe,

DVM, DABVP (canine/feline)

Steve Noonan,


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Susan Little,

DVM, DABVP (feline)

Ernie Prowse

Ernie Prowse,


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John Tait, BSc,


Scott Weese

Søren R. Boysen, DVM, DACVECC

Joseph C. Wolfer

Joseph C. Wolfer, DVM, DACVO


Clayton MacKay,


Adronie Verbrugghe,


Stephen Waisglass,


Jayne Takahashi,




Canadian Vet is unique in that it keeps Canadian veterinarians informed about the latest companion animal, livestock, equine, avian, exotic and other animal species health issues. Each issue also includes useful practice management articles. Canadian Vet is written by our own team of expert medical writers, and is reviewed for accuracy.

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Otis externa: listening to what is new

TORONTO, ON - Otitis externa is a common presenting complaint in veterinary and referral practice, with prevalence in dogs is as high as 10-20%, and in cats around 2-10%. Often, character and smell of the discharge, along with bacterial culture and sensitivity testing are procedures used in the diagnosis of otitis externa, said Anthony Yu, DVM, MS, ACVD, speaking at the Veterinary Education Today Conference. He cautioned that these findings are often unreliable and inconsistent and noted that more suitable diagnostic techniques exist, along with therapeutic approaches that minimize the need for 3rd and 4th generation antibiotics. 

Diagnosis of otitis externa

Dr. Yu said that in this day of methicillin-resistant and biofilm-producing bacteria, along with other zoonotic conditions, he advises that veterinarians avoid sniffing infected ears.  Both smell and visual character of the discharge may be misleading.

The otic examination and ear cytology are the clinician’s best diagnostic tools. Otic examination can be used to rapidly visualize ear mites, tumours and foreign bodies, as well as provide a clinical baseline from which to correlate relevant laboratory diagnostics.

Otic cytology gives a rapid indication of the relative number of morphologically different species of organisms present in the outer ear canal, providing direction with empirical selection of otic therapy.  Dr. Yu said that he only pursues otic bacterial culture and sensitivity when:

  1. Otitis interna is present (head tilt noted), especially if systemic antibiotics are to be used.
  2. The client is not able to treat the ears topically due to severe hyperplastic ear disease or a non-cooperative patient.

Dr. Yu emphasized that otic cultures should always be interpreted with reference to concurrent cytology done at the time of sampling, and the results of both these diagnostic tests should be interpreted in light of the otic examination.

To treat otitis externa, Dr. Yu prefers using topically applied otic products as they typically achieve concentrations well above 10 to 1000 times the minimum inhibitory concentrations (MIC) for systemically-delivered antimicrobials by avoiding the first-pass effect and need for vascular delivery of the medication to the site of infection. Selection of appropriate topical therapies should be based primarily on cytology, as current laboratory assays often do not reflect sensitivity patterns for concentrations of topically applied medications and thus may mislead clinicians by reporting false resistance patterns.

Treatment of acute otitis externa

Acute otitis externa may present as emergencies.  These are often one-time occurrences that can be treated immediately and do not require long-term follow up. 

Parasitic otitis externa

Otodectes cynotis is responsible for 50% of parasitic otitis externa in cats and 5 - 10% in dogs.   Brown to black waxy, dry exudate is indicative of a mite infestation and they are often visible on otologic examination. However, a subset of patients with Otodectes may have low numbers of mites with otic inflammation consistent with a hypersensitivity reaction, noted Dr Yu.

Treatment of mites is easily accomplished by selamectin, milbemycin and moxidectin-based topical or systemically administered medication at their labeled doses for 3 successive treatments 7-14 days apart when an active infection is noted.  The off-label shorter interval of administration will break the life cycle of the mites.  Once controlled, the owner may return to labeled-monthly dosing.  Recently isoxazoline-based products (Bravecto®, NexGard®, Simparica® and soon to come Credelio®) also have demonstrated efficacy against most external parasites with a single or repeated doses.  It’s important to treat all in-contact pets to prevent re-infestation. 

Aural hematomas

Aural hematomas have many underlying factors including bacterial, fungal or parasitic otitis, atopic dermatitis, food allergies, trauma, flea infestation, sarcoptic mange and vasculopathy.  These factors should be addressed concomitantly with treatment of the aural hematoma.

Medical options available for treatment include the following:

  1. Drainage and injection of 1mg Triamcinolone acetonide.  This treatment may be in conjunction with oral prednisone pending severity of clinical signs. 
  2. Drainage and intralesional injection of 2 mg/kg of methylprednisolone acetate, repeated on day 7 if the hematoma is still present.  In a very recent study, this procedure resulted in a 68% success rate for dogs as a monotherapy.
  3. Drainage and instillation of dexamethasone 0.2% diluted with saline injected into the hematoma cavity.  This can be repeated daily, usually for 3-5 days.
  4. Oral prednisone (or prednisolone for cats) can be used solely as a non-surgical treatment option with or without prior drainage. Doses range from 1-2 mg/kg per os every 12 to 24 hours based on the severity of clinical signs, tapering as the hematoma resolves.

Foreign body or tumours

A video-otoscope and grasping forceps can be used by the clinician to identify and extract any foreign bodies, displaced hairs or spicules.  A hand-held otoscope with canula and a snare or alligator forceps may be used to perform extraction of foreign material.  Use of ophthalmic anesthetics in the ear may help dampen any sensation without having to use sedation or general anesthesia.

Tumour types in the ear include multiple to singular aural inflammatory polyps in dogs and cats, ceruminoliths, apocrine gland cysts, ceruminous gland adenoma or adenocarcinoma.  Intra-aural surgery using a video-otoscope and a CO2 or diode LASER may allow clinicians to salvage the ear canal, and avoid the need for a total ear canal ablation and bulla osteotomy (TECA-BO).

Hyperplastic/stenotic otitis externa

Presentation may involve severe hyperplasia of the intra-aural tissue resulting in partial to complete stenosis of the ear canal.  Intralesional injections into the hyperplastic tissue in a “ring-block” fashion every two weeks for a total of 3 treatments has proven successful as a salvage technique, often circumventing the need for a TECA-BO.  Triamcinolone is used to decrease inflammation, fibrosis and calcification. The ear should be cleaned thoroughly under sedation or general anesthesia.  Using a Luer-lock or swedged-on needle and syringe, 6-10 mg per ear of triamcinolone can be injected intralesionally in multiple locations working from the external ear inward on subsequent visits. During the entire treatment period, infections and underlying etiologies need to be addressed.  A final assessment of this salvage approach is made at 8 weeks where if no significant improvement is noted, TECA-BO should be considered.

Acute ulcerative otitis externa

When patients present with severe pain, inflammation and ulceration, use of oral steroids for 7-14 days will help to calm the otitis to the point where the owners can now approach the infected ear(s) topically without risk of causing discomfort or being bitten, said Dr. Yu.  Another recently introduced alternative is a long-acting topically applied adaptable gel containing betamethasone, terbinafine and florfenicol (Osurnia®, Elanco) that is instilled after cleansing the ear(s) at the veterinary hospital and another ampule is instilled in one week without further cleansing, thus eliminating the need for owner involvement and compliance.

Recurrent otitis externa

Dr. Yu emphasized that the inflamed ear is an extremely moist and warm environment favorable for bacterial and yeast overgrowth, including those species unable to reproduce successfully in the normal ear canal.  Chronicity of ear disease often worsens this problem, he said.

A three-pronged approach is key to the successful treatment of all recurrent otitis externa:

  1. Identify and address the underlying etiology
  2. Calm the microenvironment such that it is not conducive for bacterial or yeast overgrowth
  3. Identify and treat the secondary infection

1) Identify the underlying etiology
The top three underlying etiologies for recurrent otitis externa are adverse food reactions, environmental allergies, and hypothyroidism.  

Many adverse food reaction patients present with otitis externa as their only clinical complaint.  It behooves us, therefore, to consider a dietary restriction using limited ingredient novel or hydrolyzed protein sources in patients with recurrent otitis externa, commented Dr. Yu.  

Environmental allergies should be considered in a patient that started with a history of seasonally recurrent otitis externa.  Allergy testing and immunotherapy or symptomatic medical management may result in control of the otitis externa without the need for otic therapy.

Hypothyroidism causes a ceruminous otitis externa with alterations in cerumen lipid composition to low levels of free fatty acids in surface lipids along with increased levels of surface triglycerides, which both in turn act as fodder for the microorganisms.  The bacteria and/or yeast are also allowed to propagate and establish an infection in hypothyroid patients as a result of their compromised immune system.

2) Calm the microenvironment
Decreasing inflammation using topical and/or oral anti-inflammatory medications is key to making the microenvironment less conducive to bacterial or yeast overgrowth, Dr. Yu noted. 
(See Chart 1)

Chart 1:  Commonly incorporated anti-inflammatory ingredients

Topical anti-inflammatory

Systemic anti-inflammatory


Cyclosporine – 5mg/kg PO for 30 days, then taper


Dexamethasone – 0.05 mg/kg PO for 7 days then taper


Prednisolone – 0.5-1.0 mg/kg PO for 7 days then taper


Prednisolone-trimeprazine – 1 tablet/10kg for 7 days then taper


Triamcinolone intralesional – 6-10 mg/ml per ear q 2week X 3





  3) Treat the secondary infection(s)

Many topical products contain antiyeast, antibacterial and anti-inflammatory agents…a shotgun approach. Dr. Yu said that in general these products work well for uncomplicated first and even repeated cases of otitis externa, and knowledge of the active ingredients within these products will help the clinician select the appropriate therapy for the patient. (See Chart 2)

Cleansing and/or flushing the ear canals, either with or without sedation or general anesthesia based on patient co-operation, is dependent on the amount of debris, the consistency of the debris, the chronicity of the ear infections and the response to previous therapies.  In general, if Pseudomonas is present, use of Tris-EDTA to breakdown virulence factors is preferred.  If Staphylococcus or Malassezia are present, then Dr. Yu recommends a cleanser containing a cerumenolytics to breakdown the ear wax and flush out the ear canal.

Chart 2:  Commonly used topical otic antimicrobial ingredients

Topical anti-yeast


Topical antibiotic

Clotrimazole (Malassezia)

Enrofloxacin (Pseudomonas; MSSP)

Enilconazole (Malassezia)

Florfenicol (Pseudomonas@30mg/ml; MRSP, MSSP)

Nystatin (Candida)

Fusidic acid (MRSP, MSSP)

Miconazole (Malassezia)

Gentamicin (Pseudomonas; MSSP)

Posaconazole (Malassezia)

Marbofloxacin (Pseudomonas; MSSP)

Terbinafine (Malassezia)

Mupirocin (MRSP, MRSP)


Orbifloxacin (Pseudomonas; MSSP)


Polymyxin B (Pseudomonas)


Ceftazidime, Piperacillin, Imipinem (Pseudomonas; MSSP)

MSSP – Methicillin Sensitive Staphylococcus Pseudintermedius
MRSP - Methicillin Resistant Staphylococcus Pseudintermedius


In an ear with a ruptured tympanic membrane, ototoxicity concerns are decreased if the oval and round window that divide the middle from the inner ear are intact.  Administration of Vitamin E 20 IU/kg PO 3 times daily or aspirin 5-10mg/kg BID PO (if not currently on steroids) for the duration of topical treatment with ear medications may prevent hearing loss in predisposed individuals (more mature pets) by scavenging free oxygen radicals. CV