Assessment of vestibular ototoxicity of ear drops by recording of vestibular evoked potentials to acceleration impulses

Introduction: The cochlear ototoxicity of several ear drops is well documented in the literature, but very few studies exist on the vestibular ototoxicity of these topical drugs. Goal of Study: To develop an animal model for the assessment of the vestibular ototoxicity of ear drops. Materials and Methods: Two animal groups, consisting of five fat sand rats (FSRs) each, underwent unilateral labyrinthectomy. Normal saline was topically applied into the middle ear cavity of rats in the first group for 7 days (control group). Rats in the second group were treated in the same way by topical gentamicin solution. Cochlear function was assessed by the recording of auditory evoked potential (ABPs) thresholds, and vestibular function was assessed by the recording of vestibular evoked potentials (VsEPs) to angular accelerations. Results: In the control group, except for the amplitude of the first wave, there was no significant difference in the VsEPs recorded before and after topical application. In the gentamicin group, VsEPs could not be recorded after 7 days, and ABPs were recorded in one case only, with a threshold of 100 dB, sound pressure level (SPL). Conclusion: VsEPs seem to be a reliable measure for evaluating the vestibular ototoxicity of topical ear drops.