In human medicine, certain systemic drugs used to treat diseases can have profound negative effects on hearing and balance.

Injectable antibiotics, mainly the amino­glycosides, and the cancer drug cisplatin seem to cause deafness in many children and adults. Some topical medications placed into the ear canals of children have caused hearing deficits and vestibular disease.

In human medicine, the symptoms of being dizzy or losing hearing can be detected very early in the course of treatment with ototoxic medications, so if an ototoxic reaction occurs, the drug can be stopped. In dogs and cats, these subtle signs cannot be easily detected, and ototoxicity is often only suspected when there is major neuro­logic damage to either the cochlea, manifesting in deafness, or the semicircular canals, resulting in vestibular signs.

The primary method of treatment of ear disease in dogs and cats is with topical products. It is well documented that more than 50% of dogs with chronic ear disease have absent or perforated eardrums, so an understanding of the potential for many of these drugs and/or chemicals to cause neurologic problems is necessary.^1,2