Ear Infections, Otitis Externa Otitis Interna

This is for Trinket, who recently developed an ear infection and a ruptured ear drum. We’ll cover ear infections, then in later blog, we’ll cover what’s safe to use in the ear if the drum is ruptured.

Ear Anatomy
Ear infections are also called otitis since "otic" means ear and "itis" means inflammation. If the infection involves the outer portion of the ear, it's called otitis externa. If the middle or inner ear are affected, it's otitis media or interna. The ear drum sits at the end of the ear canal and separates the external ear from the middle ear. There are 3 tiny bones in the middle ear. Just deep to the middle sits the inner ear with the nerves for hearing and balance. The middle ear is usually filled with air, but can become infected and filled with pus. The inner ear is bathed in fluid. Infections from the external ear can travel through the ear drum and involve the middle ear or inner ear if the infections are untreated.

Two Types of Infection: Bacteria & Yeast
Ear infections are usually caused by bacteria or yeast, or both bacteria and yeast. (Yeast is a type of fungus and the words are often used interchangeably so your vet might say your pet has a yeast infection or your pet has a fungal infection).

Vertical Ear Canal – Usually Yeast
To decide whether a pet has a bacterial infection or a fungal infection, your veterinarian will put material from the ear on a slide and examine it under a microscope. The ear has a long canal with a bend in it. The first part of the canal, is the part we see when we look in the ear, is called the vertical canal. The vertical canal usually has yeast organisms in it. If the number of yeast organisms if very high, if there is a strong odor or a discharge, the balance between the body’s immune system and yeast is out of whack. Your pet will need an antifungal medication to bring the yeast under control.

Horizontal Ear Canal – Usually Bacteria
The horizontal canal is the deeper extension of the vertical canal. It is difficult to visualize without pulling on the pet’s ear, but when the ear canals are examined thoroughly, veterinarians can see through them right to the ear drum.
Most pets with infected ears have yeast in the vertical canal and bacteria in the deeper horizontal canal. If a proper diagnosis is made, the swab must retrieve material from the horizontal canal as well as from the superficial vertical canal.

Treating Yeasty Ear Infections
Rinsing an ear with douche solution that is 2% acetic acid and water (vinegar) acidifies the ear canal and makes it inhospitable for yeast. Douche solution will clear up a very light yeast infection. Douche solution is also helpful prevention to rinse the ears weekly if your pet is inclined to occasionally have yeast infection. Do not get douche solution that is scented or contains anything other than acetic acid and perhaps 2% boric acid.

Douche solution is not effective if your pet has a yeast infection that is overwhelming. In this case, antifungal medications similar to those we use for athlete’s foot are put into the ear. These otic medications are modified so that they’re exactly right for treating ears, which means they will be runny and will go from the outer vertical canal all the way to the deeper horizontal canal.

Some pets with severe yeast infections also need oral antifungal antibiotics such as fluconazole or itraconazole in addition to the topical otic medications.

Treating Bacterial Ear Infections
If your pet has a bacterial ear infection, it needs an antibiotic medication. The antibiotic can be both a topical that goes into the ear and an oral that goes into the mouth and is absorbed through the gut and is carried by the blood to all parts of the body, including the ear.

Some pets have simple bacterial ear infections, but some have wicked bacterial infections caused by antibiotic-resistant pseudomonas. To fight bacteria, the antibiotic is put into the ear along with a solution that breaks down the bacterial cell wall. An example of this type of solution is TrisEDTA. For many pets it’s necessary to combine TrisEDTA and the antibiotic Baytril (enrofloxacin) to clear up pseudomonas and other gram negative infections. The pharmacist mixes 6ml of 100mg/ml enrofloxicin (large animal concentration) with 4 oz TrisEDTA.

TrisEDTA and Baytril is a liquid solution, rather like water. This is good because dogs can need up to 2 cc to fill their ear canals. We can call these liquid solutions, flushes. Usually we fill a pet’s ear with the flush, and this can take 2 cc each time. The flush is used twice a day for a week or so, then once a day for another week. Then, the vet examines the ears to ensure the infection has cleared. If it hasn’t, material from the ear can be sent to the laboratory to see whether it is resistant to the medication. Obtaining a good culture sample requires anesthesia for most pets. This is also a great time to vigorously flush the ears and to get a good look at the ear drum.

Why not use TrisEDTA and Baytril every time there’s an ear infection?TrisEDTA and Baytril ear flush are only used for bacterial infections. This flush is not a good medication for pets with yeasty ear infections because the Tris portion changes the ear pH to alkaline, and an alkaline pH contributes to yeast growth.

What's coming?
In a future Caring for Pet's blog, we'll cover otitis interna and what's safe to use when there's an infection in the inner ear and the drum is ruptured. And, we hope to let you know how Trinket is doing.