Conductive hearing loss in four dogs associated with the use of ointment-based otic medications.

BACKGROUND: Hearing loss (HL) is classified as conductive when sound transmission is compromised in the ear canal or middle ear, or sensorineural when there is an abnormality of the receptor cells of the cochlea or auditory pathway. Hearing in dogs is evaluated using the brainstem auditory evoked response (BAER) test.

HYPOTHESIS/OBJECTIVES: Our objective was to characterize BAER findings pre- and post-ear flushing in four dogs with acute HL following application of an ointment-based otic medication containing betamethasone, clotrimazole and gentamicin in a mineral oil-based system containing a plasticized hydrocarbon gel.

ANIMALS: Dogs, ranging from 9 to 11 years old, that had been treated with the otic medication for one to three weeks prior to hearing loss and on otoscopic examination had evidence of medication in the horizontal ear canals.

METHODS: Dogs were anaesthetized for an ear flush to remove the medication from the ear canals. Hearing was assessed using BAER testing, measurements were initiated with 116 decibel peak equivalent sound pressure level (dBpeSPL) click. Estimated threshold was defined as the lowest intensity in dB in which wave V was still present.

RESULTS: Post-ear flush the estimated threshold improved in both ears of all dogs (mean 22.3 dB; range 13-41 dB), confirming conductive HL due to the otic medication. All owners noted an improvement in their dog's hearing post-ear flush, validating the BAER findings.

CONCLUSIONS AND CLINICAL IMPORTANCE: These results emphasize the importance of an ear flush to remove otic medications in dogs that experience acute HL, to determine if the HL is conductive, and if so, to restore hearing.