Middle ear instillation of gentamicin and streptomycin in chinchillas: Morphologic appraisal of selective ototoxicity

Objective: To determine selective cochlear and vestibular ototoxicity of tw o aminoglycoside antibiotics (gentamicin and streptomycin) in the chinchill a model. Middle ear application of these agents mirrors the clinical practi ce of chemical vestibular ablation used in Meniere's disease. Background: Middle ear instillation of gentamicin or streptomycin has becom e a popular form of vestibular ablative treatment for disabling Meniere's d isease. The vestibular selectivity of these two drugs applied in this fashi on has clinical support but is not fully established in humans. Our underst anding in this regard has largely been limited to animal models exposed to systemic infusion of aminoglycosides. Method: Ten chinchillas underwent left middle ear instillation of one of th ree agents using variable dosing schedules: gentamicin (n = 6), streptomyci n (n = 2), and saline (n = 2) as control. Animals were sacrificed for tempo ral bone studies using scanning electron microscopy. Morphologic changes in the cochlear and vestibular neuroepithelia were identified. Results: Widespread cochlear and vestibular neuroepithelial injuries were o bserved with both gentamicin and streptomycin. Contralateral ototoxicity wa s variable and not related to the total dose of drug delivered. The effect of these two aminoglycosides on the dark cells of the vestibular system app eared negligible. Conclusion: We were unable to confirm the selective damage of vestibular en d-organ in the chinchilla by either gentamicin or streptomycin, a phenomeno n that is generally perceived to occur in humans. Chinchillas, like other s mall mammals, may not be an ideal model for the study of human ototoxicity.