Middle ear instillation of gentamicin and streptomycin in chinchillas: morphologic appraisal of selective ototoxicity.
OBJECTIVE
To determine selective cochlear and vestibular ototoxicity of two aminoglycoside antibiotics (gentamicin and streptomycin) in the chinchilla model. Middle ear application of these agents mirrors the clinical practice of chemical vestibular ablation used in Meniere's disease.


BACKGROUND
Middle ear instillation of gentamicin or streptomycin has become a popular form of vestibular ablative treatment for disabling Meniere's disease. The vestibular selectivity of these two drugs applied in this fashion has clinical support but is not fully established in humans. Our understanding in this regard has largely been limited to animal models exposed to systemic infusion of aminoglycosides.


METHODS
Ten chinchillas underwent left middle ear instillation of one of three agents using variable dosing schedules: gentamicin (n = 6), streptomycin (n = 2), and saline (n = 2) as control. Animals were sacrificed for temporal bone studies using scanning electron microscopy. Morphologic changes in the cochlear and vestibular neuroepithelia were identified.


RESULTS
Widespread cochlear and vestibular neuroepithelial injuries were observed with both gentamicin and streptomycin. Contralateral ototoxicity was 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 appeared negligible.


CONCLUSIONS
We were unable to confirm the selective damage of vestibular end-organ in the chinchilla by either gentamicin or streptomycin, a phenomenon that is generally perceived to occur in humans. Chinchillas, like other small mammals, may not be an ideal model for the study of human ototoxicity.
Department of Otolaryngology, University of Toronto, Ontario.
J M
JM
Chen
A
A
Kakigi
H
H
Hirakawa
R J
RJ
Mount
R V
RV
Harrison
D000818:Animals; D000900:Anti-Bacterial Agents / Q000633:toxicity*; D002682:Chinchilla; D003051:Cochlea / Q000187:drug effects / Q000648:ultrastructure*; D004195:Disease Models, Animal; D004333:Drug Administration Routes; D004432:Ear, Middle / Q000187:drug effects*; D004848:Epithelium / Q000648:ultrastructure; D005839:Gentamicins / Q000633:toxicity*; D006198:Hair Cells, Auditory / Q000187:drug effects / Q000648:ultrastructure*; D008575:Meniere Disease; D008854:Microscopy, Electron / Q000379:methods; D013307:Streptomycin / Q000633:toxicity*; D014722:Vestibule, Labyrinth / Q000187:drug effects / Q000648:ultrastructure*
D000900:Anti-Bacterial Agents; D005839:Gentamicins; D013307:Streptomycin