Ear Therapy

Here is a simple, logical, progressive method of providing ear therapy. Before initi­ating these steps, appropriate cytology and/or culture samples should be retrieved. Use each step and continue to the next step if necessary.

Step 1: Ear Cleaning

Clean the ear thoroughly using a non-ototoxic ear cleaner in the hospital so that a thorough otic examination can be performed, including assessment of the tympanic membrane. The author prefers an acetic acid/boric acid ear cleaner (MalAcetic Otic). Problems may arise when detergents and alcohols are used as ear cleaners in situa­tions where the eardrum may be ruptured. Use anesthesia when appropriate.

Acetic acid and boric acid in combination has been shown to be an effective combination in vivo to treat Malassezia otitis.¹ In many cases, continued daily ear cleansing by the owner at home for 1 week is all that is needed to treat the ear. Maintenance cleaning twice weekly may prevent recurrence of Malassezia. Cleaning the ear is important for removal of surface debris from the affected ear canal epithelium. Apply medications, if needed, after cleaning.

How to Clean an Ear

1. Apply approximately 5 ml (1 teaspoon) of the ear cleaner into the ear canal and massage thoroughly. A cotton ball may be inserted into the canal to protect against drenching should the pet shake its head.

2. For maximum benefit, allow the ear cleaner to remain in the ear canal for at least 5 minutes before attempting to clean manually.

3. Clean the ear by using a cotton ball at the opening of the ear canal to absorb liquid and dislodged debris. As days of treatment go by, less debris will be removed.

4. Stop daily cleaning when the cotton ball remains free of debris after cleaning.

In dry and/or irritated ears with little debris and/or wax, the cotton ball may be irritating. In these cases, a tiny bulb syringe or Water Pik can be helpful.

It is important to remember that infected ears are very acidic, which inactivates some antibiotics commonly used in the ear such as gentamycin and amikacin. Many ear cleaners are also acidic. In those cases, waiting 4 hours after cleaning to apply these antibiotics may be warranted.

Cleaning with Tris-EDTA. One non-ototoxic alkalinizing agent that the litera­ture reports to have primary antimicrobial properties is tris-ethylenediamine­tetraacetic (tris-EDTA [TrizEDTA, DermaPet]). To use tris-EDTA, one should follow the previous instructions on how to clean an ear, substituting the alkalinizing tris-EDTA for the acidic ear cleaner MalAcetic Otic. It appears that tris-EDTA pretreatment allows increased antimicrobial activity for many antibiotics used to treat ear disease. It is especially useful in stubborn Pseudomonas otitis cases. Gentamycin or enrofloxacin may be added to the tris-EDTA solution.

Step 2: Topical Therapy

Logical otic therapy is based on the results of otic examination and cytology. In bacterial infections, use antibiotics. In yeast infection, use an anti-yeast therapy.

TOPICAL EAR FORMULA (GEMISH)

Malassezia gemish

12 ml acetic acid/boric acid ear cleaner

6 mg dexamethasone sodium phosphate (for increased solubility)

Also add as appropriate:

0.5 to 1 ml medical-grade dimethyl sulfoxide (DMSO)

0.5 ml ivermectin

BACTERIAL GEMISH

12 ml tris-EDTA

60 mg Baytril injectable

6 mg dexamethasone sodium phosphate (for increased solubility)

Also add as appropriate:

0.5 to 1 ml medical-grade DMSO

TRIS-EDTA gemish

Add 600 mg Baytril LA to a 4-ounce bottle of tris-EDTA. This creates a 5% Baytril/tris-EDTA solution. The increased emphasis on topical therapy versus systemic therapy has led to the popularization of this formula. This better affords the recom­mended usage of 0.5 to 2 ml per ear twice daily, allowing sufficient volume for effective topical therapy. If sufficient volume is not used, the infected surface area cannot be thoroughly reached.

In inflammation (neutrophils on the cytology) or erythema, use topical cortico­steroids. If ear mites are present, use a topical insecticide or topical ivermectin. After the ear has been cleaned, apply the topical formula.

The use of these gemishes has many advantages over all current commercial products. The application of oils tends to have adverse consequences, including not reaching the affected sites, not covering the surface area, and ototoxicity. The fact that these products often only come in 7.5- to 15-ml packaging should not be overlooked.

Step 3: Systemic Therapy

Continue Steps 1 and 2 and, if there is inflammation or purulent material present, use a systemic antibiotic and/or a short-acting systemic corticosteroid.

Step 4: Further Complications

When Steps 1 through 3 do not cause remission of signs after 2 weeks, reexamine the ears. If there is stenosis and strangulation of the canal, using a 1.5-inch 20-gauge needle, inject approximately 0.5 ml of methylprednisolone acetate (Depo-Medrol, Pharmacia- Upjohn) between the epithelium and cartilage as distal in the canal as possible.

If the eardrum is bulging, a myringotomy may be done to relieve the pressure and pain, and a culture of the middle ear can be obtained. If the eardrum is ruptured, infuse a combination of 0.5 ml of dexamethasone sodium phosphate and 0.5 cc of enrofloxacin directly into the tympanic bulla.

Myringotomy may reveal pathology in the middle ear that, once removed and treated, will reduce cervical, head, or neck pain. An example is primary secretory otitis media (PSOM) of Cavalier King Charles Spaniels.

The use of corticosteroids is multifunctional. Although we are most familiar with their antiinflammatory properties, in cases of otitis media the reduction of viscosity of the secretions and exudate are also noteworthy goals. The tympanic bulla is covered with pseudostratified squamous epithelial cells with mucus-secreting goblet cells that need to be toned down by 2 mg/kg daily of prednisone for as long as 2 weeks.

Step 5: Step 4 and Culture and Sensitivity

Many dermatologists recommend a culture from each ear in difficult cases to assess the bacterial microflora. It is possible to have different bacteria in each ear, and it is also possible to have bacteria complicating otitis media that are not normally found in the external ear. Topical treatment (see tris-EDTA gemish) with antibiotics achieves much higher topical levels than the mean inhibitory concentration (MIC) reported by the laboratory, so bacteria resistant on the culture results may be suscep­tible to the higher topical doses.

Step 6: Tris-EDTA

In stubborn bacterial otitis externa or media, use tris-EDTA (TrizEDTA, DermaPet) before instilling the antimicrobial. Clean the ear thoroughly for 7 to 21 days. Tris- EDTA is an alkaline solution with a pH of 8.0. There are reports in the literature of the primary microbiocidal properties of tris-EDTA, particularly to Pseudomonas. Those reports also indicate the evidence for potentiation with antibiotics that other­wise are inactivated by other acidifiying ear cleansers. If Pseudomonas is suspected from cytology or cultured, use the appropriate systemic and topical antibiotics after a 15-minute pretreatment with tris-EDTA. Others recommend using the tris-EDTA gemish, allowing both cleansing, pretreatment, and treatment simultaneously.

The mechanism of action of tris-EDTA is discussed elsewhere in this book.

Step 7: Surgery

If corticosteroid injection into the ear canal epithelium fails to open up an inflamed, swollen, occluded ear canal (Step 4), if permanent pathologic changes are evident, or if there is severe calcification of the ear canal, surgery of the ear canal is indicated for relief of pain and to allow for drainage.

Reference

1. Gotthelf L, Young S: A new treatment for canine otitis externa, Vet Forum 14(8):46-53, 1997.