Intratympanic gentamicin treatment for Ménière's disease: a randomized, double-blind, placebo-controlled trial on dose efficacy - results of a prematurely ended study.

BACKGROUND: Gentamicin is used as a therapeutic agent for Ménière's disease because of its vestibulotoxicity causing chemo-ablation of the vestibular sensory epithelia. Its use has increased in recent years. However, there is still no consensus about the dose regimen of gentamicin in the treatment of Ménière's disease. In this study two different dose regimen treatment protocols are compared in a placebo controlled study design. The primary objective is to quantify the treatment effect on dizziness, the secondary objective is hearing evaluation. METHODS: We performed a randomized, double-blind, placebo-controlled study in adults with unilateral Ménière's disease according to the AAO-HNS guidelines resistant to conservative medication. Three groups received four injections, administered weekly (four intratympanic injections with 40 mg/mL gentamicin solution, two injections gentamicin solution and two injections of placebo in random order, or four injections with placebo). Outcome measures were the score on the Dizziness Handicap Inventory and pure tone audiometry (PTA). Intended follow-up was 2 years. RESULTS: During follow-up one patient exceeded the accepted amount of hearing loss. Further, enrollment was very slow (until 12 months between two patients) and new insights showed an apparent benefit of intratympanic gentamicin treatment (ITG). Therefore we performed an unscheduled interim analysis which showed that PTA threshold shifts reached the stopping criteria in two more patients. Because of this, this study was ended. Of the three patients with the significant PTA threshold shift two were enrolled in the gentamicin group. CONCLUSION: No conclusions can be drawn concerning doses regimens. Now that new publications have shown that ITG treatment can be an effective and safe treatment, a placebo-controlled randomized controlled trial may not pass the ethical committee because of these recent reports in literature. Still, a dose regimen study (without placebo) on ITG treatment needs to be performed. TRIAL REGISTRATION: This trial was registered in The University Medical Center Utrecht/ Gelre hospital Apeldoorn. Protocol ID: 07/343, EudraCT number 2006-005913-37.

Does vestibular end-organ function recover after gentamicin-induced trauma in Guinea pigs?

Until 1993 it was commonly accepted that regeneration of vestibular hair cells was not possible in mammals. Two histological studies then showed structural evidence for spontaneous regeneration of vestibular hair cells after gentamicin treatment. There is less evidence for functional recovery going along with this regenerative process; in other words, do regenerated hair cells function adequately? This study aims to address this question, and in general evaluates whether spontaneous functional recovery may occur, in the short or long term, in mammals after ototoxic insult. Guinea pigs were treated with gentamicin for 10 consecutive days at a daily dose of 125 mg/kg body weight. Survival times varied from 1 day to 16 weeks. Vestibular short-latency evoked potentials (VsEPs) to linear acceleration pulses were recorded longitudinally to assess otolith function. After the final functional measurements we performed immunofluorescence histology for hair cell counts. Auditory brainstem responses (ABRs) to click stimuli were recorded to assess cochlear function. As intended, gentamicin treatment resulted in significant loss of utricular hair cells and accompanying declines in VsEPs. Hair cell counts 8 or 16 weeks after treatment did not significantly differ from counts after shorter survival periods. Maximal functional loss was achieved 1-4 weeks after treatment. After this period, only 2 animals showed recovery of VsEP amplitude - all other animals did not reveal signs of regeneration or recovery. In contrast, after initial ABR threshold shifts there was a small but significant recovery. We conclude that spontaneous recovery of otolith function, in contrast to cochlear function, is very limited in guinea pigs. These results support the concept of intratympanic gentamicin treatment where gentamicin is used for chemoablation of the vestibular sensory epithelia.

Deafness induction in mice.

HYPOTHESIS: How to induce most efficiently severe sensorineural hearing loss in mice using a single coadministration of an aminoglycoside antibiotic and a loop diuretic? BACKGROUND: The coadministration of aminoglycosides and a loop diuretic has been widely used to induce hair cell and spiral ganglion cell loss in guinea pigs. However, the development of new treatment strategies against sensorineural hearing loss, such as tissue engineering techniques, requires the use of mouse models. Previous attempts to induce hearing loss in mice have rendered inconsistent results because of resistance to aminoglycoside-induced ototoxicity. Especially inner hair cells seem to be resistant to aminoglycoside-induced ototoxicity. METHODS: In the present study, we aim to optimize hearing loss in mice, using a single high-dose kanamycin (700 and 1,000 mg/kg) injection followed by a furosemide (100 mg/kg) administration. Although previous studies used intraperitoneal furosemide injections 30 minutes after kanamycin administration, we used intravenous furosemide injections administered within 5 minutes after kanamycin treatment. RESULTS: Auditory brain stem responses illustrated severe threshold shifts, and histologic analysis showed marked outer hair cell destruction as well as spiral ganglion cell loss. The present protocol results in more severe inner hair cell loss when compared with the results of previous researches. CONCLUSION: We conclude that severe sensorineural hearing loss can be induced in mice. Moreover, we found that this mouse model can be augmented via the use of rapid intravenous furosemide administrations to maximize inner hair cell loss.

Combined administration of kanamycin and furosemide does not result in loss of vestibular function in Guinea pigs.

Aminoglycoside antibiotics are known to damage the vestibular and auditory sensory epithelia. Although loop diuretics enhance the cochleotoxic effect of aminoglycosides, it is not known whether concomitant administration of an aminoglycoside and a loop diuretic affects the vestibular system. The aim of our study was to investigate the effect of co-administration of kanamycin and furosemide upon the otolith organs and to compare it to the known vestibulotoxic effect of gentamicin. Five guinea pigs were injected with a single dose of both kanamycin (400 mg/kg, s.c.) and furosemide (100 mg/kg, i.v.), 5 animals received gentamicin (100 mg/kg, i.p.) for 10 days, and 5 untreated animals served as controls. After 7 days, vestibular function was assessed by measuring vestibular short-latency evoked potentials (VsEPs) to linear acceleration stimuli and cochlear function by auditory brainstem responses (ABRs) to clicks. Hair cell densities were determined in phalloidin-stained whole mounts of the utricles and saccules, and in midmodiolar sections of resin-embedded cochleae. Co-administration of kanamycin and furosemide had no significant effect on VsEPs and hair cell densities in the utricles and saccules were not reduced. ABR thresholds were increased to a great extent (by ∼60 dB), and histologically a severe loss of cochlear hair cells was observed. The effect of gentamicin, both on vestibular and cochlear function, was just the opposite. VsEP thresholds to horizontal stimulation were elevated and suprathreshold amplitudes showed a decrease, whereas cochlear function was not reduced. With this protocol, we have a tool to selectively induce cochlear or vestibular damage, which may be of interest to researchers and clinicians alike.