Ototoxicity in dogs and cats

Ears are special sense organs whose principal functions are hearing and maintaining equilibrium. Aminoglycoside antibiotics, erythromycin, polymyxin B, and cisplatin can affect either or both of these functions by binding with, injuring, and/or destroying special receptor cells associated with these functions. Severe hearing loss manifests itself as deafness, whereas loss of equilibrium will present as abnormal righting reflexes, nausea, and vomiting. Damage is proportional to levels of these ototoxins in the endolymphatic fluids. Evidence suggests that toxicity may be influenced by endolymphatic calcium concentrations, and levels of cAMP and cGMP are altered in specialized cochlear cells during ototoxicity, suggesting an additional mechanism for ototoxicity. The administration of salicylates and loop diuretics may potentiate the action of ototoxins, especially aminoglycoside antibiotics, probably by increasing the levels of these toxins in the endolymphatic fluid. Although many of these assessments have been made in laboratory animals, applicability may also be expected in small domestic animals, and extreme care should be taken in prescribing potentially ototoxic drugs to small animals. Cochlear damage from ototoxic compounds occurs initially in the cells detecting high-frequency sounds located at the lower basal region. In aging dogs and humans, this sensitivity of receptors in the lower basal region is enhanced. Early auditory damage is detectable by BAER and cochlear microphonic potentials. Vestibular responses can also be detected early as vestibular ocular reflexes and visual-vestibulo-ocular reflexes. Early detection is especially important because early changes can sometimes be reversible. Cavinton (apovincaminic acid) and fosfomycin represent examples of experimental agents being evaluated in laboratory animals for application as potential treatments to limit the ototoxicity associated with various drugs.