Cochlear and Vestibular Effects of Combined Intratympanic Gentamicin and Dexamethasone

The aim of this study is to evaluate the effects of an intratympanic gentamicin-dexamethasone combination on the inner ear.

Twenty-six Wistar albino rats were divided into four groups: Group I (Control), group II (Intratympanic dexamethasone; ITD), group III (Intratympanic gentamicin; ITG), and group IV (Intratympanic gentamicin and dexamethasone; ITGD). On the first day after basal auditory brainstem response (ABR) measurements, the ITG group received 0.03 mL of intratympanic gentamicin (26.7 mg/mL). Intratympanic injection of 0.06 mL of a solution containing 13.35 mg/mL gentamicin and 2 mg/mL dexamethasone was performed in the ITGD group. 0.03 mL of physiological intratympanic serum and dexamethasone (4 mg/mL) was applied in control and ITD groups, respectively. On the 7th day, ABR measurements were repeated and vestibular functions were evaluated. On the 21th day, ABR and vestibular tests were repeated, and the animals were sacrificed for histopathological investigation.

The ITG group's hearing thresholds deteriorated in all frequencies. The ITGD group's hearing thresholds were significantly better than the ITG group, except at 8 kHz on the 7th day and in all frequencies at the 21th day measurements. The vestibular function scores of the ITG and ITGD groups were higher than the controls. Apoptotic changes were seen in cochlea, spiral ganglion, and vestibule of the ITG group. Cochlear and vestibular structures were well preserved in the ITGD group, similar to the controls.

The ITGD combination led to a significant hearing preservation. Although in subjective vestibular tests, it seemed that vestibulotoxicity was present in both ITG and ITGD groups the histopathological investigations revealed no signs of vestibulotoxicity in the ITGD group in contrast to the ITG group. Further studies using a combination of different concentrations of gentamicin and dexamethasone are needed.