Ear Flushing and Treatment of Otitis Externa
North American Veterinary Conference, 2005
Louis N. Gotthelf, DVM
Animal Hospital of Montgomery
Montgomery, AL
Ear Flushing and Cleaning
Do not use cotton tipped applicators to clean ears! When cotton tipped ear swabs are pushed into an ear canal full of exudate, the material is pushed further toward the eardrum making cleaning more difficult and possibly causing a weakened eardrum to rupture. Cotton swabs are also very irritating to a friable epithelium and their use results in painful abrasion or ulceration to the canal epithelium.
The MedRx Video Vetscope (MedRx, Inc., Seminole, FL) is a very useful instrument to use for cleaning, drying, and examining the ear canal since it's video capability gives the examiner a clear real time image on a video monitor. The Vetscope has a 2mm working channel through which a 5 1/2 inch open ended tomcat catheter (Sherwood, St. Louis, MO), a 3 Fr. feeding tube, or 5Fr. polypropylene urethral catheter can be inserted. A 10mm Frazier Suction tip (Anthony Products, Indianapolis, IN) is used to connect the suction tubing to the catheter. The catheter is inserted into working channel.
With the Vetscope positioned in the ear canal, the catheter can be advanced to suction the canal under video visualization. Small pieces of epithelium, wax, hairs and pus can be vaccuumed out of the canal while the examiner views the procedure on a video monitor. In this manner, even the smallest pieces of detritus can be removed. Large pieces of debris and concretions can be extracted from the ear canal under visualization with the video vetscope by using a grasping type of endoscopic forcep inserted through the 2mm working channel.
Care must be taken in the selection of a flushing agent, since so many ear
cleaners contain materials that are potentially ototoxic when the eardrum is
not intact. Prior to using an ear cleaner, read the label to see if it can be
used if the eardrum is damaged. Many manufacturers are now placing a warning
on their labels.
Until a determination of the intgrity of the eardrum is made, the choice of
flushing solutions should be limited to non-detergent, non-alcoholic type of
flushing solutions. Physiologic saline and dilute povidone iodine are safe flushing
materials to use. When used as warm solutions (98 degrees F.) these solutions
act to soften wax and loosen other debris. A waterpik can be used to loosen
the exudate, but the pressure in a waterpik can be excessively high, requiring
extra caution so the eardrum is not ruptured from the high pressure.
Ear curettes are useful for scraping the ear canal to dislodge large pieces of wax and epithelial shreds. They are available in various loop sizes and angles and some have a circular cutting surface (Dermal Curettes). Curettes are also useful for harvesting cells for cytology when a tumor mass is suspected.
After the ear canal has been cleared of debris, then a determination of the
integrity of the eardrum can be made. Unfortunately, severely stenotic ear canals
prevent adequate visualization of the eardrum through the otoscope.
Treatment of Otitis Externa
Corticosteroids
Corticosteroids have a definite place in the treatment of otitis externa. Systemic
corticosteroids reduce the intense pruritis associated with acute otitis externa
and reduce the inflammation in the epithelium of the ear canal. Systemic high
doses of corticosteroids are used for several days to reduce the edema and stenosis
that prevents adequate examination of the ear canal. If the ear canal is patent,
then a potent topical corticosteroid such as dexamethasone, betamethasone, or
flucinolone may be used to relieve the intense pain and itching. As the otitis
resolves, a less potent corticosteroid such as 1% hydrocortisone (Malacetic
HC, Dermapet) may be used in the ear to act as a preventative for inflammation
in atopic dogs that may have recurrent otitis. Corticosteroids do not remove
hyperplastic epithelium or glands, so if there is no response to high dose corticosteroids
after 7-10 days, the stenosis is probably the result of increased tissue growth
rather than inflammation.
Treatment of Malassezia
Alterations in cerumen lipid composition caused by underlying skin diseases such as atopy or hypothyroidism may play a role in Malassezia otitis externa. Low levels of free fatty acids in surface lipids coupled with increased levels of surface triglycerides favors Malassezia infections. Diseases of the ear cause increases in the amount of sebaceous secretion and increases in the number and amount of lipid secretion from the apocrine (cerumen) glands. This tends to decrease the overall lipid composition of the cerumen and interferes with the moisture barrier function of the cerumen.
For otitis externa complicated by Malassezia, the author prefers the use of an acetic acid/boric acid solution (Malacetic Otic, Dermapet, Inc.). The cleansing effect and desquamating effect of the acetic acid/boric acid solution essentially removes fatty acid substrates necessary for the metabolism and reproduction of Malassezia. Malassezia produces a chemotactic factor for neutrophils that is hydrophilic and protein in nature. The presence of this factor may help explain why only a few Malassezia organisms can cause such profound erythema and pruritis. The cleansing effect of the acetic acid/boric acid solution destroys this acid-labile chemoattractant and may account for the reduction in inflammation. Boric acid, which is hygroscopic (drying out the humid ear canal) removes moisture necessary for this hydrophilic chemoattracant and may prevent attachment of Malassezia yeasts to the epithelium by inactivating adhesin molecules that allow Malassezia to stick to keratnocytes. Malacetic Otic is used daily for 7-10 days by filling the ear canal to overflowing, massaging the base of the ear, and allowing the solution to remain in the ear canal for 5 minutes. The loosened debris is wiped off of the pinnal surface with a dry cotton ball. This procedure is repeated once daily. When the ear canal is clean, the cotton ball will remain fairly white when the solution is wiped away. At that time, treatment is reduced to once weekly.
Treatment of Bacteria
Antibiotics that kill Staphylococci, Pseudomonas and other gram negative bacteria
are used in many otic preparations. They may be formulated with other topical
pharmaceuticals such as antifungals, corticosteroids, insecticides, and topical
anesthetics. First line antibiotics such as gentamycin, neomycin, and polymyxin
B are potentially ototoxic, so if there is no eardrum, these antibiotics should
be avoided. In addition, neomycin has been implicated as a sensitizer in contact
dermatitis in the ear. If the ear becomes worse with neomycin treatment, the
antibiotic should be stopped immediately. Other antibiotics such as tobramycin
and ticarcillin may be used for bacterial infections in the ear canal.
Injectible enrofloxacin (Baytril Injection, 22.7 mg/ml, Bayer) is used by the
author in a variety of forms. An enrofloxacin topical otic solution can be made
by mixing 2ml injectible enrofloxacin with 13ml of artificial tears. Also, 1cc
injectible enrofloxacin mixed in an 8ml bottle of DMSO/flucinolone (Synotic,
Ft. Dodge) provides a potent antibiotic, anti-inflammatory combination. This
solution is unstable and should not be used for more that 5 days. Baytril may
be instilled directly into the ear as a bulla infusion to get very high levels
quickly.
Baytril Otic (Bayer) has recently been introduced. It is a solution that contains 0.5% enrofloxacin and 1% silver sulfadiazine. The high concentration of enrofloxacin has been demonstrated in-vitro to provide a high enough concentration to be effective against most bacteria. However, there are a number of fluoroquinolone resistant Pseudomonas bacteria being found, and so this product is not recommended for first-line use. It's use should be based on demonstration of susceptibility of the organism to enrofloxacin. Silver sulfadiazine may have some use against the yeasts in the ear.
Ciprofloxacin 0.3% (Ciloxin Ophthalmic Solution, Alcon) eye drops can be used in the ear. Ciprofloxacin with Hydrocortisone (CiproHC Otic, Bayer) and Ciprofloxacin with dexamethasone (Ciprodex, Bayer) are now available for human use. A new topical otic fluroquinolone, ofloxacin (Floxin Otic, Daiichi) has been shown to be safe and effective in children with suppurative otitis media.
Tris-EDTA
Another useful compound as an adjunct in ear infections is tris-EDTA solution
(TrizEDTA, Dermapet, Inc.). Tris-EDTA is particularly useful for otitis externa/media
caused by gram negative bacteria. EDTA chelates metal ions, such as calcium
and magnesium, which are necessary to maintain the integrity of the cell membrane.
Tris buffer enhances this effect and acts as a buffer to keep the ear canal
at pH of 8.0, which is optimum for function of the aminoglycosides and fluoroquinolones.
The cell membrane of bacteria becomes more porous so that the antibiotic can
diffuse into the bacteria and kill it. Tris-EDTA alone has been shown in vitro
to have potent bactericidal effects.
A recent theory to explain resistance patterns in Pseudomonas involves the expression of one or more genes, selected for in resistant bacteria that cause an efflux pump mechanism to activate. The efflux pump causes antibiotics to be actively pumped out of the bacteria. EDTA seems to inactivate these pumps thus restoring the antibiotic sensitivity. In-vitro treatment of highly fluoroquinolone resistant Pseudomonas with tris-EDTA demonstrated significant reduction in the MIC after a 5 minute treatment.
Even if culture and sensitivity results indicate that a gram negative bacteria is resistant to a certain antibiotic in vitro, tris-EDTA may render it sensitive to that particular antibiotic in vivo. Clinically, tris-EDTA is used as a pre-treatment in the external ear 5 minutes prior to the instillation of topical antibiotics.
Take Home Points
Always make sure that the ear canal is clean before treating the ear. Owner
complicance is essential so that the treatment can be maximally effective. Make
sure that the appropriate antimicrobial preparation is being used (do not use
an antibiotic for a yeast otitis). Insure that the treatment is done long enough.
Re-cehck the ears including cytology until the ears are normal. Successful ear
treatment is based on identifying and treating the underlying skin disease.
And identify otitis media if it is present to prevent treatment failures.
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