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

S. Paterson, L. Payne

Rutland House Veterinary Hospital, St Helens, Merseyside, UK.         

In this retrospective study brainstem evoked auditory responses (BAERs) from 60 ears of 37 dogs was assessed for evidence of ototoxicity after the application of topical medications. A chlorhexidene/EDTA tris flush (TrizPlus, Dermapet) was used as a standard flush throughout treatment and topical antibiotic therapy included marbofloxacin (29), gentimicin (9), clotrimazole (27), tobramycin (2), ticarcillin (3) and silver sulphadiazine (8) were used for therapy. BAERs were measured before and after topical applications. A score was given for each drug as the difference between the two BAER readings. A positive score indicated an improvement in hearing, a negative score a deterioration. Pseudomonas spp. (27), coagulase positive staphylococcus (11) and Malassezia pachydermatis (29) were most commonly isolated from cases. Each ear was thoroughly flushed and soaked in chlorhexidene/EDTA tris for 10 minutes before 0.5ml of antibiotic solution was instilled. Intravenous dexamethasone (0.1mg/kg) was given after flushing in all cases. Owners used flush daily at home before instilling 0.5ml of antibiotic solution. At a 3 week reassessment oral prednisolone (1mg/kg body weight once daily) was prescribed. Dogs were anaesthetized at their 6- 8 week check where repeat cytology and BAER testing was performed. Mean BAER scores for each drug was recorded as marbofloxacin and gentimicin in aqueous solution +15 and +12.5 respectively. Clotrimazole solution scored +17 and silver sulphadiazine solution +6.8. Tobramycin and ticarcillin produced profound reduction in BAER scores at   -50 and -16.7 respectively suggesting they are ototoxic when applied to the middle ear.