Vestibular ototoxicity following intratympanic applications of chlorhexidine gluconate in the cat.

Our previous studies have shown that the disinfectant chlorhexidine gluconate (CH) has an ototoxic effect on the cochlea following its topical application in the middle ear space. The purpose of the present investigation was to demonstrate morphologically if CH also has the potential to injure the vestibular organs in the inner ear and, if so, what structures are most strongly damaged. Nine cats were used for the study. The drug dose of CH and the number of its applications to the middle ear were the same as used in our previous study to produce middle ear injuries. In the 2% CH group of cats pronounced degeneration was found in afferent nerve endings and both types of sensory cells. These nerve terminals showed edematous dilatations and contained degenerated mitochondria. Highly dark-stained degenerated mitochondria were distributed in the sensory cells and the afferent nerve terminals in the 0.05% CH group, but these degenerative changes were much less than in the 2% CH group. No otolithic crystals or synaptic vesicles could be seen in the 2% CH group. The results from this study showed that CH as a disinfectant has an ototoxic effect on the labyrinthine vestibule in which the sensory cell-nerve ending complex is affected as the main target. Even when used in dilute clinical concentrations, vestibular disturbances are a likely complication if the drug solution flows into the middle ear through a perforated eardrum.