Differing Effects on the Inner Ear of Three Gentamicin Compounds: GM-C1, -C2 and -C1a.

Abstract

Objective—Gentamicin (GM) has been used to ablate the vestibular system function as a form of treatment for Ménière's disease. Generally, clinicians have not recognized that commercial GM comprises three major compounds – GM-C1, -C2 and -C1a – and the effects of the individual compounds on the inner ear have not been elucidated. In this study we investigated differences in cochleo- and vestibulotoxicity between the three compounds.Material and Methods—Hartley guinea pigs were treated for 2 weeks with daily subcutaneous injections (100 mg/kg) of the GM complex or the GM-C1, -C2 or -C1a compounds. After a further 2 weeks, we assessed the inner ear by measuring the auditory brainstem response (ABR) and performing a sinusoidal rotation test (SRT) and morphological analyses.Results—The ABR thresholds in the C2 group were found to be more impaired than those in the other groups In the SRT, the nystagmus counts in the C2 group were lower than those in the controls and in the C1 group. The counts in the C1a group were lower than those in the C1 group. Morphological analyses revealed that the proportion of remaining outer hair cells was less in the C2 group than in the other groups.Conclusions—Our results suggest that characterization of differences in ototoxicity may be useful for treatment of Ménière's disease with GM.