ABSTRACT OF THE WEEK

Journal of Small Animal Practice
Volume 59 | Issue 1 (January 2018)

Brainstem auditory evoked responses in 37 dogs with otitis media before and after topical therapy.

J Small Anim Pract. January 2018;59(1):10-15.

S Paterson¹

¹ Department of Dermatology, Rutland House Veterinary Hospital, Abbotsfield Road, St Helens, Merseyside WA9 4HU, UK.

Abstract

OBJECTIVES:The objective of this study was to determine whether intra-aural administration of aqueous solutions of marbofloxacin, gentamicin, tobramycin and ticarcillin (used off-licence) was associated with changes in hearing as measured by brainstem auditory evoked responses.

MATERIALS AND METHODS:Dogs diagnosed with otitis media (n=37) underwent brainstem auditory evoked response testing and then were treated for their ear disease. First, the external ear canal and middle ear were flushed with sterile saline followed by EDTA tris with 0·15% chlorhexidine. Then, a combination of aqueous antibiotic mixed with an aqueous solution of EDTA tris was instilled into the middle ear. Follow-up examinations were undertaken for each dog, and treatment was continued until there were no detected infectious organisms or inflammatory infiltrate. Brainstem auditory evoked response testing was repeated after resolution of the infection and discontinuation of therapy.

RESULTS:Brainstem auditory evoked responses in dogs treated with aqueous solutions of marbofloxacin or gentamicin remained unchanged or improved after therapy of otitis media but were impaired in dogs treated with ticarcillin or tobramycin.

CLINICAL SIGNIFICANCE:If off-licence use of topical antibiotics is deemed necessary in cases of otitis media, aqueous solutions of marbofloxacin and gentamicin appear to be less ototoxic than aqueous solutions of ticarcillin or tobramycin.

Companion Notes

Retrospective report on brainstem auditory evoked responses before and after topical therapy in 37 dogs with otitis media

Introduction on otitis media (OM) in the dog

- affected dogs commonly have reduced hearing as measured by BAER

(BAER = brainstem auditory evoked responses)

- this hearing loss may be associated with the following:

- altered conduction due to narrowing of ear canal lumen

- damage to tympanic membrane

- accumulated fluid within middle ear

- sensorineural damage

- due to penetrating bacterial toxins or ototoxic drugs

- through round window causing cochlear damage

- treatment recommendations: flush tympanic bulla and then instill topicals

- in human medicine:

- very few good clinical trials on ototoxicity from ear medications

- most data comes from animal reports and case reports

- fluoroquinolones currently recommended as first-line drugs for OM

- topical ciprofloxacin shown very safe for OM

(there’s no data on topical marbofloxacin for OM)

- shown very safe in mice, guinea pigs and humans

- in canine and feline medicine:

- very few good clinical trials on ototoxicity of ear medications

- most data comes from guinea pigs, mice, rabbits and chinchillas

- or anecdotal case reports

Study design

- study population: dogs seen at Rutland House Veterinary Hospital, UK

- clinic has a standard treatment protocol

- BAER always performed at dog's first examination

- repeated after complete clinical and cytological resolution

- diagnosis of OM made by referring DVM

- otoscopy confirmed the absence of a tympanic membrane, all cases

- owners told of potential problems with use of off-license drugs for OM

- drugs potentially might have ototoxic effects

- told they’re currently no drugs licensed to treat OM

- history & signalment

- cocker spaniel, 6 cases

- Labrador, 6

- West Highland White terrier, 4

- clinical signs

- bilateral OM in 17 cases and unilateral OM in 20 (54 ears)

- procedure:

- all dogs underwent brainstem auditory evoked response testing

- minimum hearing threshold determined

- mucopurulent material taken from tympanic bulla by aspiration

(5 Fr catheter)

- some submitted for culture and sensitivity

- some smeared on microscope slide

- all discharge then flushed from canal with sterile saline

- clean 5 Fr catheter via working channel of the video-otoscope

- 2^nd flush when canal was clean with “further clean catheter”

- ethylene diamine tetra-acetic acid (EDTA) with 0.15% chlorhexidine

(Trizchlor flush, Dechra Veterinary Products)

- then aqueous (off-license) antibiotic mixed with aqueous EDTA tris

(Trizaural flush, Dechra Veterinary Products)

- antibiotic choice based on culture and susceptibility

- marbofloxacin used if culture and susceptibility not available

- 5 mL of 200 mg/ml marbofloxacin added to 118 mL of EDTA tris

(Marbofloxacin, Marbocyl SA injection (Vetoquinol animal health))

(0.85% solution)

- apply 0.5 mL into the ear once daily after cleaning

- 17 cases

- 80 mg/2 mL (Gentamicin (Roche) (0.27% solution)), 11 cases

- 8 mL added to 118 mL of EDTA tris

- apply 0.5 mL into the ear once daily after cleaning

- 40 mg/mL (Tobramycin (1% solution)), 5 cases

- 8 mL added to 32 mL of EDTA tris

- apply 0.5 mL into the ear once daily after cleaning

- 3.2 g (Ticarcillin vials (2.5% solution)), 4 cases

- 3.2g mixed with 6 mL sterile water

- frozen in aliquots for weekly use

- 1 mL of defrosted solution added to 20 mL of sterile water each week

- apply 0.5 mL into the ear once daily after cleaning

- dogs discharged with two solutions

- EDTA with 0.15% chlorhexidine flush solution

(Trizchlor flush, Dechra Veterinary Products)

- EDTA tris flush with antibiotic (treatment solution)

(Trizaural flush, Dechra Veterinary Products)

- owner to flood ear with flush solution daily

- before instilling 0.5 mL of treatment solution once or twice daily

- recheck exams performed for each dog at 3-week intervals

- treatment continued until clinical cure

(no detected infectious organisms or inflammatory infiltrate)

- brainstem auditory evoked response testing repeated

(after infection resolved and therapy discontinued)

Results

- brainstem auditory evoked responses

- unchanged or improved after therapy in 2 groups

- dogs treated with aqueous solutions of marbofloxacin

- dogs treated with aqueous solutions of gentamicin

- impaired after therapy in 2 groups

- dogs treated with ticarcillin

- dogs treated with tobramycin

- culture and susceptibility

- Pseudomonas species, 28 cases

- with concurrent Staphylococcus spp in 9 of the 28 cases

- Staphylococcus species as only isolate, 24 cases

- Proteus species, 2 cases (1 with concurrent Staphylococcus spp)

“Linked article: This article is commented on by G.M. Strain., p. 60 in this issue”

[article comments on chlorhexidine and gentamicin ototoxicity]

[https://beta.vin.com/doc/?id=8348021]

“Veterinary surgeons must therefore try to select drugs for therapy that have the lowest potential for ototoxicity whilst being mindful that a failure to treat infection adequately may lead to hearing loss and vestibular disease through the elaboration of exotoxins from the bacteria…”

“The author is a veterinary adviser for Vetruus and has received consultancy fees from Dechra Animal Health and Elanco over the last two years.”

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Comment In J Small Anim Pract. 2018 Jan;59(1):60

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