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Vestibular destruction by slow infusion of gentamicin into semicircular canals
Ming Lii1, Dalian Ding, Xiang-Yang Zheng
1Department of Otolaryngology, Yueyang Hospital of Shanghai Traditional Medical and Pharmacy University, Shanghai, China.
Abstract:
Intratympanic or round window application of gentamicin is often used to alleviate disabling vertigo arising from unilateral Meniere's disease; however, treatment is often accompanied by hearing loss because the drug initially enters the cochlea before diffusing to the vestibular system. In order to enhance vestibular damage and reduce the risk of hearing loss, gentamicin was infused directly into the vestibular system. An osmotic pump containing 50, 100, 200 or 400 microg/ml of gentamicin was infused into the superior semicircular canal of the chinchilla for 7 days. Afterwards, vestibular damage was evaluated by measuring the decline in hair cell density in the utricle, saccule and superior semicircular canals. Auditory damage was assessed with distortion product otoacoustic emissions (DPOAE) and outer hair cell (OHC) and inner hair cell (IHC) loss. Infusion with the two lowest gentamicin concentrations resulted in significant hair cell loss and reduced duration of the nystagmus response, but had little or no effect on OHC or DPOAE. Higher doses of gentamicin damaged cochlear hair cells and reduced the DPOAE. In conclusion, slow infusion of a low dose of gentamicin into the semicircular canals mainly damages the vestibular hair cells and inactivates the nystagmus response without damaging cochlear hair cells or DPOAE.
Insights
Directly infusing low-dose gentamicin into the vestibular system effectively treats vertigo by damaging vestibular hair cells. This method minimizes cochlear damage and preserves hearing, unlike traditional applications.
Area of Science:
- Ototoxic effects of gentamicin
- Vestibular system pharmacology
- Meniere's disease treatment
Background:
- Intratympanic gentamicin is a common Meniere's disease treatment.
- Current methods risk cochlear damage and hearing loss due to drug diffusion.
- Targeting the vestibular system directly could improve efficacy and safety.
Purpose of the Study:
- To evaluate direct vestibular gentamicin infusion for Meniere's disease.
- To determine if vestibular targeting reduces cochlear damage.
- To assess dose-dependent effects on vestibular and auditory function.
Main Methods:
- Gentamicin was infused into the superior semicircular canal of chinchillas using osmotic pumps (50-400 microg/ml) for 7 days.
- Vestibular damage assessed by hair cell density in the labyrinth.
- Auditory function evaluated using distortion product otoacoustic emissions (DPOAE) and hair cell counts.
Main Results:
- Low gentamicin doses (50, 100 microg/ml) caused significant vestibular hair cell loss and reduced nystagmus.
- These low doses minimally impacted outer hair cells (OHC) and DPOAE.
- Higher doses led to cochlear hair cell damage and reduced DPOAE, indicating a narrow therapeutic window.
Conclusions:
- Slow, direct infusion of low-dose gentamicin into the vestibular system selectively damages vestibular hair cells.
- This approach effectively inactivates nystagmus with minimal risk to cochlear function and hearing.
- Direct vestibular gentamicin infusion offers a promising strategy for Meniere's disease treatment.
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