Intratympanic gentamicin for the treatment of Ménière's disease and other forms of peripheral vertigo

Meniere's disease: Pathogenesis, treatments, and emerging approaches for an idiopathic bioenvironmental disorder

Meniere's disease (MD) is a severe inner ear condition known by debilitating symptoms, including spontaneous vertigo, fluctuating and progressive hearing loss, tinnitus, and aural fullness or pressure within the affected ear. Prosper Meniere first described the origins of MD in the 1860s, but its underlying mechanisms remain largely elusive today. Nevertheless, researchers have identified a key histopathological feature called Endolymphatic Hydrops (ELH), which refers to the excessive buildup of endolymph fluid in the membranous labyrinth of the inner ear. The exact root of ELH is not fully understood. Still, it is believed to involve several biological and bioenvironmental etiological factors such as genetics, autoimmunity, infection, trauma, allergy, and new theories, such as saccular otoconia blocking the endolymphatic duct and sac. Regarding treatment, there are no reliable and definitive cures for MD. Most therapies focus on managing symptoms and improving the overall quality of patients' life. To make significant advancements in addressing MD, it is crucial to gain a fundamental understanding of the disease process, laying the groundwork for more effective therapeutic approaches. This paper provides a comprehensive review of the pathophysiology of MD with a focus on old and recent theories. Current treatment strategies and future translational approaches (with low-level evidence but promising results) related to MD are also discussed, including patents, drug delivery, and nanotechnology, that may provide future benefits to patients suffering from MD.

Bifenestral surgical and chemical labyrinthectomy, a new effective ablative surgical approach to intractable vertigo in Ménière Disease elderly Patients

INTRODUCTION

In this article, the bi-fenestral surgical chemical labyrinthectomy is introduced as a surgical demolition technique for treating resisting incurable forms of Meniere's disease in patients aged over 70 and/or with low hearing residues refractory to medical treatment.

MATERIALS AND METHODS

The results on participants fitting the inclusion criteria (n = 16) were reported using anamnesis (frequency of the crisis), Dizziness Handicap Inventory (DHI) and Functional Level Scale (FLS) before and after the intervention.

RESULTS

Vertigo control was achieved in all patients of this case series. A difference of 57 and 3.67 in mean DHI (from 68 (SD 16,7) to 11 (SD 14)) and FLS (from 4,68 (SD 0,7) to 0,1 (SD 0,3)) scores respectively were seen after an average of 16.28 months. Contextually tinnitus was reported to improve in seven patients (43,75%), aggravate in three (18,75%) and remain unchanged in the remaining six(37,5%).

CONCLUSION

Bi-fenestral surgical chemical labyrinthectomy appears a safe, immediate, and effective demolition treatment for vertigo control in a restricted class of patients affected by intractable Meniere disease.

Low Dose Intratympanic Gentamicin in Ménière’s Disease

Intratympanic gentamicin has become an accepted standard of care for Ménière's disease. But there still exists controversies regarding the dosing protocol as well as the drug concentration for optimum control of vertigo and hearing preservation. To determine if 20 mg of intratympanic gentamicin administered once a month for a maximum of 2 months can alleviate intractable vertigo caused by definite Ménière's disease with hearing preservation. Once diagnosed with definite Ménière's disease as per AAO-HNS criteria, the patient was given 0.5 ml of 40 mg/ml intratympanic gentamicin. Follow-up was done at 1-month and 6-month post-treatment. If at 1-month review patient continued to have vertigo one more dose of intratympanic gentamicin was administered. Thirty-two patients were included in the study. Seventeen patients (53.1%) received one dose and 15 patients (46.9%) received two doses of intratympanic injection. We achieved an effective vertigo control of 59.4% and complete vertigo control rate of 53.1%. Worsening of symptoms was noted in 1 patient. Hearing was preserved in all patients except for one. Among the patients who attained effective vertigo control, 72.2% had dead labyrinth at 6-month cold caloric status. A single injection of 20 mg intratympanic gentamicin can alleviate intractable vertigo caused by definite Ménière's disease with hearing preservation. Non-responders may be given a second dose after one month. Intratympanic gentamicin is a simple, cheap treatment that can be carried out in an out-patient setting.

Effects of intratympanic gentamicin and intratympanic glucocorticoids in Ménière's disease: a network meta-analysis

OBJECTIVE

Intratympanic therapies, usually including glucocorticoid and gentamicin, are becoming worldwide used in clinical practice of Ménière's disease today. However, clinical efficacy and safety of these two therapies are still in controversial.

DATA SOURCES

Electronic searches in PubMed, CENTRAL, Web of Science, EMBASE, CINAHL, ClinicalTrials.gov and the European Union Clinical Trials Register were conducted from inception until September 2020.

REVIEW METHODS

The pre-specified protocol of this systematic review and meta-analysis has been registered and published in November 2018 (PROSPERO Identifier: CRD42018114389). All randomized controlled trials of intratympanic gentamicin or glucocorticoids for Ménière's disease, compared with each other or placebo, were considered for this review.

RESULTS

Ten studies with 455 patients met the inclusion criteria. Pooled results indicated significant advantage of intratympanic gentamicin and glucocorticoids over placebo treatments in vertigo control (gentamicin vs placebo: risk rate, RR, 2.56; 95% CI 1.18-5.54; glucocorticoids vs placebo: RR, 3.02; 95% CI 1.36-6.73). There was no significant difference between gentamicin and glucocorticoids in vertigo control (gentamicin vs placebo: RR, 1.18; 95% CI 0.97-1.45). Intratympanic glucocorticoids showed better hearing protective results than gentamicin (change of pure tone audiometric, PTA, mean difference, MD, - 6.48 dB; 95% CI - 11.84 to - 1.13 dB; change of speech discrimination scale, SDS, MD 7.69%; 95% CI 0.83-14.55%).

CONCLUSIONS

Intratympanic gentamicin and glucocorticoids are two effective approaches to control vertigo symptoms for Ménière's disease. Glucocorticoids showed a potentially better hearing protective role over gentamicin.

Effect of Dexamethasone Combination with Gentamicin in Chemical Labyrinthectomy on Hearing Preservation and Vertigo Control in Patients with Unilateral Meniere's Disease: A Randomized Controlled Clinical Trial

Chemical labyrinthectomy using gentamicin is a popular method for treating intractable vertigo attacks in Meniere’s disease. However, the risk of hearing loss remains a major concern for clinicians. We investigated the effect of simultaneous dexamethasone and gentamicin application on hearing preservation and vertigo control in patients with intractable unilateral Meniere’s disease. A single-institutional, prospective, single-blinded, randomized clinical trial was conducted. Gentamicin-soaked Gelfoam^® was directly applied on the oval window following middle ear exploration. On the round window, dexamethasone-soaked Gelfoam^® was applied in the gentamicin with dexamethasone group (GD group, n = 18), and saline-soaked Gelfoam^® was applied in the gentamicin with sham reagent group (GO group, n = 19). The hearing change 8 weeks after the procedure and vertigo control 2–12 months after the procedure were investigated. The high-frequency hearing threshold was significantly increased in the GO group (p = 0.005 and 0.012 for 4 and 8 kHz, respectively), but not in the GD group. The short-term (2–6 months) vertigo control was more successful in the GD group (57.89% vs. 94.44%, p = 0.019), but long-term control (6–12 months) was insignificant. In conclusion, the combined application of gentamicin and dexamethasone in chemical labyrinthectomy is an effective method for protecting high-frequency hearing and vertigo control.

[Topical drug administration to the inner ear. Modern state of the problem and development perspectives]

The work assessed modern methods of drug delivery through biological barriers to the lesion, in particular, through the most studied - skin. The main advantages and disadvantages of the existing methods for the topical administration of drugs into the inner ear - intra-imperial and intra-labyrinth delivery are analyzed. A brief review of medicinal substances for topical administration to the inner ear, both widely used (for example, aminoglycosides, steroid drugs) and undergoing clinical trials, is given. An assessment is made of the prospects for the use of transmembrane drug delivery to the inner ear using an electric field, which has a combined electro-creative and iontophoretic effect.

Why study inner ear hair cell mitochondria?

In several systems of the body (muscle, liver, nerves), new studies have examined the internal structure of mitochondria and brought to light striking new findings about how mitochondria are constructed and how their structure affects cell function. In the inner ear field, however, we have little structural knowledge about hair cell and supporting cell mitochondria, and virtually none about mitochondrial subtypes or how they function in health and disease. The need for such knowledge is discussed in this short review.

Different medications for the treatment of Ménière's disease by intratympanic injection: A systematic review and network meta-analysis

BACKGROUND

It is generally accepted that intratympanic injection provides an effective approach to manage severe vertigo in Ménière's disease. Although there are several medications available, that which is the most effective is still subject to debate.

OBJECTIVE

To assess the effectiveness and safety of the different medications used in the treatment of Ménière's disease by intratympanic injection using a network meta-analysis.

METHODS

PubMed, EMBASE, CINAHL and CENTRAL were searched. Only randomised controlled trials that compared the effectiveness of medications used for intratympanic injection to treat Ménière's disease with each other or a placebo were included. The primary outcome assessed was the effectiveness of medication in the management of vertigo symptoms. The effectiveness was expressed in terms of risk ratio (RR) with a 95% credible interval (CrI) for individual studies analysed. Network meta-analyses were performed by Stata version 15.0 using the network package.

RESULTS

Nine studies involving 314 patients treated with five different medications were included in the present analysis. A number of injections given varied from 1 to 10 and the follow-up time from 3 to 28 months. When compared to each other or to a placebo, Gentamicin was found to be the most efficacious medication, followed by Methylprednisolone, Latanoprost, Dexamethasone and Ganciclovir in order of effectiveness. However, no significant difference in efficacy was found between Gentamicin and Methylprednisolone when outcomes from studies with a follow-up time equal to or more than 24 months were analysed. It was not possible to conduct subgroup and sensitivity analysis because of the limited number of studies that were included.

CONCLUSION

All medications are more effective than a placebo in the treatment of Ménière's disease by intratympanic injection. According to the SUCRA, Gentamicin ranked the most effective, with Gentamicin and Methylprednisolone equally effective in the long-term effect. When the potential risk of hearing loss induced by Gentamicin is taken into consideration, Methylprednisolone may be the best choice for the treatment of Ménière's disease by intratympanic injection.

Partial Aminoglycoside Lesions in Vestibular Epithelia Reveal Broad Sensory Dysfunction Associated with Modest Hair Cell Loss and Afferent Calyx Retraction

Although the effects of aminoglycoside antibiotics on hair cells have been investigated for decades, their influences on the dendrites of primary afferent neurons have not been widely studied. This is undoubtedly due to the difficulty in disassociating pathology to dendritic processes from that resulting from loss of the presynaptic hair cell. This was overcome in the present investigation through development of a preparation using Chinchilla laniger that enabled direct perilymphatic infusion. Through this strategy we unmasked gentamicin's potential effects on afferent calyces. The pathophysiology of the vestibular neuroepithelia after post-administration durations of 0.5 through 6 months was assessed using single-neuron electrophysiology, immunohistochemistry, and confocal microscopy. Hair cell densities within cristae central zones (0.5-, 1-, 2-, and 6-months) and utricle peri- and extrastriola (6-months) regions were determined, and damage to calretinin-immunoreactive calyces was quantified. Gentamicin-induced hair cell loss exhibited a profile that reflected elimination of a most-sensitive group by 0.5-months post-administration (18.2%), followed by loss of a second group (20.6%) over the subsequent 5.5 months. The total hair cell loss with this gentamicin dose (approximately 38.8%) was less than the estimated fraction of type I hair cells in the chinchilla's crista central zone (approximately 60%), indicating that viable type I hair cells remained. Extensive lesions to afferent calyces were observed at 0.5-months, though stimulus-evoked modulation was intact at this post-administration time. Widespread compromise to calyx morphology and severe attenuation of stimulus-evoked afferent discharge modulation was found at 1 month post-administration, a condition that persisted in preparations examined through the 6-month post-administration interval. Spontaneous discharge was robust at all post-administration intervals. All calretinin-positive calyces had retracted at 2 and 6 months post-administration. We found no evidence of morphologic or physiologic recovery. These results indicate that gentamicin-induced partial lesions to vestibular epithelia include hair cell loss (ostensibly reflecting an apoptotic effect) that is far less extensive than the compromise to stimulus-evoked afferent discharge modulation and retraction of afferent calyces (reflecting non-apoptotic effects). Additionally, calyx retraction cannot be completely accounted for by loss of type I hair cells, supporting the possibility for direct action of gentamicin on the afferent dendrite.

Protective role of intratympanic nigella sativa oil against gentamicin induced hearing loss

OBJECTIVE

Aminoglycosides, used to combat with life-threatening infections, have a substantial risk of hearing loss. Nigella sativa is an annual herbaceous plant and used for treatment of many diseases for ages. We aimed to investigate the protective role of intratympanic nigella sativa oil against gentamicin induced hearing loss in an animal model.

METHODS AND MATERIALS

Twenty eight guinea pigs were randomly divided into four groups: i-control, ii- Intratympanic nigella sativa oil (IT-NSO), iii- Intraperitoneal gentamicin (IP-G) and iv- Intraperitoneal gentamicin and intratympanic nigella sativa oil (IP-G + IT-NSO). Preoperative and postoperative hearing thresholds were determined with auditory brainstem response with click and 8 kHz tone-burst stimuli. Histological analysis of the cochlea specimens were performed under light microscope. Semiquantitative grading of the histological findings was carried out and compared between the groups.

RESULTS

Highest posttreatment hearing thresholds were detected in IP-G group. Posttreatment mean hearing threshold of the IP-G group with click stimulus was significantly higher than the IP-G + IT-NSO group (p = 0.004). whereas the difference was not significant with 8 kHz tone-burst stimulus (p = 0.137). Both IP-G and IP-G + IT-NSO groups had significantly higher hearing thresholds compared to control and IT-NSO groups (p > 0.05). Histological examination of the control and IT-NSO groups demonstrated normal appearance of cochlear nerve, stria vascularis and organ of Corti. IP-G group showed the most severe histological alterations including hydropic and vacuolar degenerations, hair cell damage and deformation of the basilar mambrane. Histological evidence of damage was significantly reduced in IP-G + IT-NSO group compared to IP-G group.

CONCLUSION

Addition of intratympanic NSO to systemic gentamicin was demonstrated to have beneficial effects in hearing thresholds which was supported by histological findings.

Intratympanic (IT) Therapies for Menière's Disease: Some Consensus Among the Confusion

Purpose of Review

Aminoglycosides and corticosteroids are commonly used to treat Menière's disease. Intratympanic (IT) administration of these medications allows high inner ear concentrations without significant adverse systemic effects. As a direct result, IT therapy has grown in popularity. Recent studies have compared patient outcomes between IT aminoglycosides and corticosteroids. This review summarizes these findings.

Recent Findings

Trials comparing IT corticosteroids to IT placebo or oral therapy have had conflicting results. Most recently, Lambert et al. investigated the effect of IT dexamethasone in a sustained-release formulation compared to placebo. Their findings demonstrated improvement in some secondary measures of vertigo with the sustained-release formulation.IT gentamicin is known to be effective in controlling vertigo in Menière's disease. In a recent study from 2016, Patel et al compared IT gentamicin and IT methylprednisolone in a double-blind, randomized controlled trial and identified no significant differences between the two in vertigo control.

Summary

IT injections of aminoglycosides and corticosteroids can improve vertigo control. Hearing and vestibular loss however may result with IT aminoglycosides. Corticosteroids demonstrate limited hearing loss but may not have the same efficacy in controlling vertigo. Further investigation in the etiology of Menière's disease is needed to tailor the proposed treatment to suit the disease mechanism.

Sustained and Transient Vestibular Systems: A Physiological Basis for Interpreting Vestibular Function

Otolithic afferents with regular resting discharge respond to gravity or low-frequency linear accelerations, and we term these the static or sustained otolithic system. However, in the otolithic sense organs, there is anatomical differentiation across the maculae and corresponding physiological differentiation. A specialized band of receptors called the striola consists of mainly type I receptors whose hair bundles are weakly tethered to the overlying otolithic membrane. The afferent neurons, which form calyx synapses on type I striolar receptors, have irregular resting discharge and have low thresholds to high frequency (e.g., 500 Hz) bone-conducted vibration and air-conducted sound. High-frequency sound and vibration likely causes fluid displacement which deflects the weakly tethered hair bundles of the very fast type I receptors. Irregular vestibular afferents show phase locking, similar to cochlear afferents, up to stimulus frequencies of kilohertz. We term these irregular afferents the transient system signaling dynamic otolithic stimulation. A 500-Hz vibration preferentially activates the otolith irregular afferents, since regular afferents are not activated at intensities used in clinical testing, whereas irregular afferents have low thresholds. We show how this sustained and transient distinction applies at the vestibular nuclei. The two systems have differential responses to vibration and sound, to ototoxic antibiotics, to galvanic stimulation, and to natural linear acceleration, and such differential sensitivity allows probing of the two systems. A 500-Hz vibration that selectively activates irregular otolithic afferents results in stimulus-locked eye movements in animals and humans. The preparatory myogenic potentials for these eye movements are measured in the new clinical test of otolith function—ocular vestibular-evoked myogenic potentials. We suggest 500-Hz vibration may identify the contribution of the transient system to vestibular controlled responses, such as vestibulo-ocular, vestibulo-spinal, and vestibulo-sympathetic responses. The prospect of particular treatments targeting one or the other of the transient or sustained systems is now being realized in the clinic by the use of intratympanic gentamicin which preferentially attacks type I receptors. We suggest that it is valuable to view vestibular responses by this sustained-transient distinction.

Intratympanal gentamicin in Meniere's disease: Effects on individual semicircular canals

OBJECTIVE

In this retrospective study the aim of the authors was to examine the effect of gentamicin on the individual semicircular canals after low dose, single injection intratympanal gentamicin therapy in Meniere's disease.

METHODS

Data of 32 patients treated between 2011 and 2015 were collected. The high frequency, high acceleration vestibuloocular reflex (VOR) gain was measured in the individual semicircular canals using video head impulse test immediately before the first intratympanal gentamicin instillation and approximately two months later.

RESULTS

In all cases 'AAO-HNS Class A' vertigo control could be attained at least for several months. In 13 cases only one instillation was necessary. In the other 19 cases the attacks returned after a few months. In 11 cases the injection had to be repeated a second time, in 4 cases 3 injections, in 2 cases 4, in 1 case 5 injections and in another 6 injections were necessary. The initial VOR gain was normal in all cases and two months after one injection it decreased in average by 40% in a highly significant manner. However, there were cases in which, although the patients became free of attacks, the gain values remained normal.

CONCLUSION

It was possible to demonstrate a significant correlation between the gain decrease of the individual canals. There was no prognostic correlation between the initial gain decrease after the first injection and the necessity of further injections. Gain values also decreased slightly but significantly in the lateral and posteriors canals on the contralateral, untreated side, possibly because of the missing disfacilitation from the treated side.

Gentamicin Applied to the Oval Window Suppresses Vestibular Function in Guinea Pigs

Intratympanic gentamicin therapy is widely used clinically to treat the debilitating symptoms of Ménière's disease. Cochleotoxicity is an undesirable potential side effect of the treatment and the risk of hearing loss increases proportionately with gentamicin concentration in the cochlea. It has recently been shown that gentamicin is readily absorbed through the oval window in guinea pigs. The present study uses quantitative functional measures of vestibular and cochlea function to investigate the efficacy of treating the vestibule by applying a small volume of gentamicin onto the stapes footplate in guinea pigs. Vestibular and cochlea function were assessed by recording short latency vestibular evoked potentials in response to linear head acceleration and changes in hearing threshold, respectively, 1 and 2 weeks following treatment. Histopathology was analyzed in the crista ampullaris of the posterior semi-circular canal and utricular macula in the vestibule, and in the basal and second turns of the cochlea. In animals receiving gentamicin on the stapes footplate, vestibular responses were significantly suppressed by 72.7 % 2 weeks after treatment with no significant loss of hearing. This suggests that the vestibule can be treated directly by applying gentamicin onto the stapes footplate.

Intratympanic methylprednisolone versus gentamicin in patients with unilateral Ménière's disease: a randomised, double-blind, comparative effectiveness trial

BACKGROUND

Ménière's disease is characterised by severe vertigo attacks and hearing loss. Intratympanic gentamicin, the standard treatment for refractory Ménière's disease, reduces vertigo, but damages vestibular function and can worsen hearing. We aimed to assess whether intratympanic administration of the corticosteroid methylprednisolone reduces vertigo compared with gentamicin.

METHODS

In this double-blind comparative effectiveness trial, patients aged 18-70 years with refractory unilateral Ménière's disease were enrolled at Charing Cross Hospital (London, UK) and Leicester Royal Infirmary (Leicester, UK). Patients were randomly assigned (1:1) by a block design to two intratympanic methylprednisolone (62·5 mg/mL) or gentamicin (40 mg/mL) injections given 2 weeks apart, and were followed up for 2 years. All investigators and patients were masked to treatment allocation. The primary outcome was vertigo frequency over the final 6 months (18-24 months after injection) compared with the 6 months before the first injection. Analyses were done in the intention-to-treat population, and then per protocol. This trial is registered with ClinicalTrials.gov, number NCT00802529.

FINDINGS

Between June 19, 2009, and April 15, 2013, 256 patients with Ménière's disease were screened, 60 of whom were enrolled and randomly assigned: 30 to gentamicin and 30 to methylprednisolone. In the intention-to-treat analysis (ie, all 60 patients), the mean number of vertigo attacks in the final 6 months compared with the 6 months before the first injection (primary outcome) decreased from 19·9 (SD 16·7) to 2·5 (5·8) in the gentamicin group (87% reduction) and from 16·4 (12·5) to 1·6 (3·4) in the methylprednisolone group (90% reduction; mean difference -0·9, 95% CI -3·4 to 1·6). Patients whose vertigo did not improve after injection (ie, non-responders) after being assessed by an unmasked clinician were eligible for additional injections given by a masked clinician (eight patients in the gentamicin group vs 15 in the methylprednisolone group). Two non-responders switched from methylprednisolone to gentamicin. Both drugs were well tolerated with no safety concerns. Six patients reported one adverse event each: three in the gentamicin group and three in the methylprednisolone group. The most common adverse event was minor ear infections, which was experienced by one patient in the gentamicin group and two in the methylprednisolone group.

INTERPRETATION

Methylprednisolone injections are a non-ablative, effective treatment for refractory Ménière's disease. The choice between methylprednisolone and gentamicin should be made based on clinical knowledge and patient circumstances.

FUNDING

Ménière's Society and National Institute for Health Research Imperial Biomedical Research Centre.

Intratympanic therapy in Meniere's syndrome or disease: up to date evidence for clinical practice

BACKGROUND

Meniere's syndrome or disease (MS/D) is typically characterised by episodic vertigo, aural fullness, tinnitus and fluctuating hearing loss. There are multiple options available for treatment with variation in consensus on the best intervention.

OBJECTIVE

To evaluate the evidence on the efficacy of intratympanic therapies [steroids, gentamicin, antivirals and other therapies] on the frequency and severity of vertigo and other symptoms of MS/D.

SEARCH STRATEGY

A literature search was performed on AMED, EMBASE, HMIC, MEDLINE, PsycINFO, BNI, CINAHL, HEALTH BUSINESS ELITE, CENTRAL and Cochrane Ear, Nose and Throat disorders group trials register using various MeSH. The search was restricted to English and human subjects, and the last date of search was December 2014.

SELECTION CRITERIA

Randomised controlled trials of intratympanic therapies [steroids, gentamicin antivirals and latanoprost] versus a placebo or another treatment.

RESULTS

We analysed 8 RCT's comparing intratympanic steroids, gentamicin, ganciclovir (antiviral) and latanoprost versus another form of intratympanic treatment or placebo.

CONCLUSIONS

On the basis of 6 RCT's (n = 242), there is evidence to support the effectiveness of intratympanic steroids and gentamicin to control symptoms of vertigo in MS/D albeit with a risk of hearing loss with gentamicin. However, there was no consensus found on doses or treatment protocols. There was no evidence to support the use of other forms of intratympanic therapy (antivirals and latanoprost) in MS/D.

Ménière's Syndrome or Disease: Time Trends in Management and Quality of Evidence Over the Last Two Decades

OBJECTIVE

To evaluate the evidence and trends in published literature on the treatment of Ménière's syndrome or disease (MS/D) by comparing studies published in the last two decades.

DATA SOURCES

A literature search was performed on AMED, EMBASE, HMIC, MEDLINE, PsycINFO, BNI, CINAHL, HEALTH BUSINESS ELITE, CENTRAL and Cochrane Ear, Nose and Throat disorders groups trials register using a combination of MeSH. The date of last search was October 2014.

STUDY SELECTION AND DATA EXTRACTION

Two hundred five studies (104 in decade I and 101 in decade II) were evaluated to report trends in the management of this condition, the differing levels of evidence published for each treatment modality, evaluate whether the guidelines published by the AAOHNS-Committee on Hearing and Equilibrium had been correctly employed, and whether the randomized controlled trials (RCTs) were compliant with the CONSORT guidelines.

RESULTS

The number of published RCTs almost tripled from decade I (1994-2003) to decade II (2004-2103). There was a significant decline in the use of surgical intervention (p = 0.013); however, the number of studies involving the use of intratympanic injection remained largely unchanged. There was a shift in the level of evidence in published studies; studies with level 1 evidence tripled from decade I to II (4.8 to 17.8%, respectively) (p = 0.03); however, compliance with the AAOHNS-CHE criteria for reporting treatment outcomes and the CONSORT checklist was still poor.

CONCLUSION

Although the evidence base on published literature on MS/D has improved over the last decade with an increase in emphasis on RCTs and quality of life (QoL) studies, a significant number of studies failed to follow AAOHNS-CHE criteria for reporting treatment outcome and the CONSORT criteria for reporting RCTs.

Is low-dose intratympanic gentamicin an effective treatment for Ménière's disease: the Birmingham experience

BACKGROUND

Since the development of intratympanic aminoglycoside in the 1950s, otologists have been able to chemically ablate the vestibule. We present the results of using low-dose intratympanic gentamicin to treat Ménière's disease.

METHOD

A retrospective review was performed of all patients who underwent low-dose intratympanic gentamicin therapy over seven years. Data on gender, age, number of procedures, pure tone audiometry and symptom control were analysed.

RESULTS

In all, 38 patients underwent low-dose intratympanic gentamicin therapy. These comprised 25 females and 13 males, with an average age of 58.4 years. Hearing was preserved in 87.5 per cent of patients, with no significant difference before and after treatment (p = 0.744). In all, 85.7 per cent of patients had complete or substantial symptom control (classes A and B, respectively).

CONCLUSION

Low-dose intratympanic gentamicin therapy was effective in controlling the symptoms of Ménière's disease patients, while preserving hearing.

Histopathologic Changes of the Inner ear in Rhesus Monkeys After Intratympanic Gentamicin Injection and Vestibular Prosthesis Electrode Array Implantation

Bilateral vestibular deficiency (BVD) due to gentamicin ototoxicity can significantly impact quality of life and result in large socioeconomic burdens. Restoring sensation of head rotation using an implantable multichannel vestibular prosthesis (MVP) is a promising treatment approach that has been tested in animals and humans. However, uncertainty remains regarding the histopathologic effects of gentamicin ototoxicity alone or in combination with electrode implantation. Understanding these histological changes is important because selective MVP-driven stimulation of semicircular canals (SCCs) depends on persistence of primary afferent innervation in each SCC crista despite both the primary cause of BVD (e.g., ototoxic injury) and surgical trauma associated with MVP implantation. Retraction of primary afferents out of the cristae and back toward Scarpa's ganglion would render spatially selective stimulation difficult to achieve and could limit utility of an MVP that relies on electrodes implanted in the lumen of each ampulla. We investigated histopathologic changes of the inner ear associated with intratympanic gentamicin (ITG) injection and/or MVP electrode array implantation in 11 temporal bones from six rhesus macaque monkeys. Hematoxylin and eosin-stained 10-μm temporal bone sections were examined under light microscopy for four treatment groups: normal (three ears), ITG-only (two ears), MVP-only (two ears), and ITG + MVP (four ears). We estimated vestibular hair cell (HC) surface densities for each sensory neuroepithelium and compared findings across end organs and treatment groups. In ITG-only, MVP-only, and ITG + MVP ears, we observed decreased but persistent ampullary nerve fibers of SCC cristae despite ITG treatment and/or MVP electrode implantation. ITG-only and ITG + MVP ears exhibited neuroepithelial thinning and loss of type I HCs in the cristae but little effect on the maculae. MVP-only and ITG + MVP ears exhibited no signs of trauma to the cochlea or otolith end organs except in a single case of saccular injury due to over-insertion of the posterior SCC electrode. While implanted electrodes reached to within 50-760 μm of the target cristae and were usually ensheathed in a thin fibrotic capsule, dense fibrotic reaction and osteoneogenesis were each observed in only one of six electrode tracts examined. Consistent with physiologic studies that have demonstrated directionally appropriate vestibulo-ocular reflex responses to MVP electrical stimulation years after implantation in these animals, histologic findings in the present study indicate that although intralabyrinthine MVP implantation causes some inner ear trauma, it can be accomplished without destroying the distal afferent fibers an MVP is designed to excite.

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.

Ototoxicity of Polymyxin B, Neomycin, and Hydrocortisone Suspension in Tympanoplasty Surgery

Objectives

(1) To determine the safety of using a commercially available suspension of polymyxin B, neomycin, and hydrocortisone (PNH) in tympanoplasty surgery. (2) To apply evidence-based medicine to tympanoplasty surgery when considering potential ototoxicity.

Study Design

Case series with chart review.

Setting

Tertiary otology practice, single surgeon.

Methods

Approval for this study was obtained from the St. Dominic–Jackson Memorial Hospital Institutional Review Board. Data were gathered on 272 consecutive type 1, underlay tympanoplasties for which both pre- and postoperative audiometric data were available over a 10-year period. In each surgery, gelatin sponge saturated in a commercially available PNH suspension was placed in the middle ear to support the graft. Patients ranged in age from 3 years to 79 years. Preoperative and postoperative bone conduction thresholds were measured at 500, 1000, 2000, 3000, and 4000 Hz.

Results

The average change in sensorineural hearing as measured by bone conduction thresholds was negligible, with a slight improvement in all frequencies tested except 4000 Hz. The changes by frequencies were as follows: 500 Hz (–1.624 dB), 1000 Hz (–1.399 dB), 2000 Hz (–0.975 dB), 3000 Hz (–0.596 dB), and 4000 Hz (+0.560 dB). The 5-frequency average change was −0.545 dB.

Conclusions

The commonly used otic solution containing polymyxin B, neomycin, and hydrocortisone demonstrates no ototoxicity in tympanoplasty surgery and is safe to use in this setting.

Meniere's disease: an evidence based approach to assessment and management

Menière's disease (MD) is frequently over-diagnosed in both primary and secondary care. This is unfortunate given the significant medical and social implications of such a diagnosis. Difficulties may arise in differentiating the patient with true MD from those individuals with less clearly defined disorders of cochleo-vestibular function. In this review, we suggest a practical evidence based approach to assessment and management of the patient with MD.

Cochlear function in Ménière's disease

OBJECTIVE

The authors assessed the effectiveness of therapy, common features of pure-tone audiograms, and results of non-invasive electrocochleography before and after mild inhibition of peripheral vestibular function by infrequent administration of single intratympanic gentamicin injections (ITPG) in patients with Ménière's disease (MD).

STUDY SAMPLE

Sixty-two patients with Ménière's disease.

DESIGN

Retrospective study.

RESULTS

Out of 62 patients 65% received one injection, 24% two, 6% three, 3% five, and 2% six injections. Between injections, class A vertigo control was obtained after two weeks in all cases. Before ITPG, out of 62 pure-tone threshold audiograms 37 were 'flat'. Average hearing threshold at 2 kHz was significantly better than that of 250, 500, and 0.75 kHz on the affected side.

CONCLUSIONS

Hearing threshold in advanced MD is often flat with a characteristic small peak in the high frequency range, most frequently around 2-3 kHz. Should the complaints be intolerable, single injection ITPG-therapy may be safe and effective.

Calcium imaging in gentamicin ototoxicity: increased intracellular calcium relates to oxidative stress and late apoptosis

OBJECTIVES

To estimate intracellular calcium changes in gentamicin (GM) ototoxicity using calcium imaging. To investigate GM-induced physiologic changes in auditory cells including cell viability, apoptosis, and oxidative stress.

METHODS

Varying concentrations of GM were applied to the HEI-OC1 cochlear cell line. Calcium imaging tracked changes in intracellular calcium concentration during GM cytotoxicity. Cell viability and intracellular reactive oxygen species (ROS) levels also were measured.

RESULTS

Little change in calcium levels occurred in HEI-OC1 cells exposed to less than 35 mM GM. However, calcium rose continuously in cells exposed to more than 60 mM GM. With administration of intermediate concentrations of 40 or 50 mM GM, calcium increased variably in different cells, returning to baseline in some cases, or rising continuously in others. Upon increase of GM concentration, intracellular calcium concentration and ROS were increased, and cell viability was decreased due to late apoptosis.

CONCLUSION

This study shows that GM increased intracellular calcium, ROS, and late apoptosis of HEI-OC1 cells derived from cochlear tissue. Increase of intracellular calcium is related to GM-induced apoptosis and oxidative stress. Calcium imaging can be used to determine change of intracellular calcium concentrations and apoptosis in GM ototoxicity.

Intratympanic gentamicin for Ménière's disease or syndrome

BACKGROUND

Ménière's disease is characterised by three major symptoms: vertigo, deafness and tinnitus, which may be accompanied by aural fullness, all of which are discontinuous and variable in intensity. While discontinuous, these symptoms are synchronous. Intratympanic application of gentamicin, an ototoxic aminoglycoside, is a relatively new ablative treatment for vertigo in Ménière's disease with promising results.

OBJECTIVES

To assess the effectiveness of intratympanic gentamicin in the treatment of vertigo in Ménière's disease.

SEARCH STRATEGY

We searched the Cochrane Ear, Nose and Throat Disorders Group Trials Register; the Cochrane Central Register of Controlled Trials (CENTRAL); PubMed; EMBASE; CINAHL; Web of Science; BIOSIS Previews; Cambridge Scientific Abstracts; ISRCTN and additional sources for published and unpublished trials. The date of the most recent search was 30 June 2010.

SELECTION CRITERIA

All randomised or quasi-randomised controlled trials of intratympanic gentamicin versus placebo, or versus another treatment for Ménière's disease.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed trial quality and extracted data. We contacted study authors for further information.

MAIN RESULTS

We identified two trials, involving 50 participants, which fulfilled the inclusion criteria. Both of these trials are prospective, double-blind, placebo-controlled randomised clinical trials on the effect of intratympanic gentamicin on vertigo complaints. Both of these trials found a significant reduction in vertigo complaints in the gentamicin group when compared to the placebo group. Due to clinical heterogeneity we could not perform a meta-analysis.

AUTHORS' CONCLUSIONS

Based on the results of the two included studies, intratympanic gentamicin seems to be an effective treatment for vertigo complaints in Ménière's disease, but carries a risk of hearing loss.

Intratympanic gentamicin in Ménière's disease: our experience

Aims:

To analyse intratympanic gentamicin injection as a treatment option in patients with monolateral Ménière's disease resistant to medical treatment.

Material and methods:

Longitudinal, prospective, descriptive study of response to gentamicin treatment in 71 patients diagnosed with Ménière's disease and treated medically for more than a year, unsuccessfully. American Academy of Otolaryngology-Head and Neck Surgery criteria were used for diagnosis and follow up.

Results:

Complete vertigo control was obtained in 65.6 per cent of patients, and complete or substantial control in 84.37 per cent. Thirteen patients (18.3 per cent) suffered significant hearing loss.

Conclusion:

This intratympanic gentamicin injection protocol enabled effective vertigo control in most patients, and represents a good alternative to more aggressive techniques for the treatment of Ménière's disease which does not respond to medical treatment.

Principles of local drug delivery to the inner ear

As more and more substances have been shown in preclinical studies to be capable of preventing damage to the inner ear from exposure to noise, ototoxic drugs, ischemia, infection, inflammation, mechanical trauma and other insults, it is becoming very important to develop feasible and safe methods for the targeted delivery of drugs to specific regions in the inner ear. Recently developed methods for sampling perilymph from the cochlea have overcome major technical problems that have distorted previous pharmacokinetic studies of the ear. These measurements show that drug distribution in perilymph is dominated by passive diffusion, resulting in large gradients along the cochlea when drugs are applied intratympanically. Therefore, in order to direct drugs to specific regions of the ear, a variety of delivery strategies are required. To target drugs to the basal cochlear turn and vestibular system while minimizing exposure of the apical cochlear turns, single one-shot intratympanic applications are effective. To increase the amount of drug reaching the apical cochlear turns, repeated intratympanic injections or controlled-release drug delivery systems, such as biodegradable biopolymers or catheters and pumps, are more effective. However, if the applied substance does not easily pass through the round window membrane, or if a more widespread distribution of drug in the ear is required, then intralabyrinthine injections of the substance may be required. Intralabyrinthine injection procedures, which are currently in development in animals, have not yet been proven safe enough for human use.

Middle ear exploration in patients with Ménière's disease who have failed outpatient intratympanic gentamicin therapy

OBJECTIVE

Treatment of medically refractory Ménière's disease (MD) with intratympanic (IT) gentamicin has now become a standard therapy. This procedure is effective in controlling vertigo attacks, but approximately 10% of patients do not have an adequate response. The objective of the current study was to evaluate the option of middle ear exploration with direct application of gentamicin to the round window (MEE-G) in patients with persistent MD after transtympanic injection of gentamicin.

STUDY DESIGN

A retrospective chart review of 191 patients with MD treated with IT gentamicin revealed 16 who failed to have symptomatic relief after transtympanic injection. Options discussed with these patients included labyrinthectomy, vestibular nerve section, and MEE-G.

SETTING

Tertiary referral center.

PATIENTS

Eight patients opted for MEE-G.

INTERVENTION

Patients were taken to the operating room for MEE-G. After removal of the round window obstruction, gentamicin-soaked pledgets were placed for at least 30 minutes.

MAIN OUTCOME MEASURES

Control of MD-related vertigo and need for additional therapy.

RESULTS

At the time of MEE-G, all 8 patients were found to have adhesions, bone dust blocking the round window, or a thickened round window membrane. In 6 of these patients, vertigo symptoms due to MD either resolved with no further therapy (4 patients) or with subsequent IT gentamicin injections in clinic (2 patients). The remaining 2 patients underwent a vestibular nerve section, which resolved MD symptoms in each case.

CONCLUSION

Anatomic barriers to the round window membrane may be a significant cause of IT gentamicin failure, and MEE-G can be considered before ablative therapy in this subset of patients with Ménière's disease.

Vestibular evoked myogenic potentials: an overview

The vestibular evoked myogenic potential (VEMP) test is a relatively new diagnostic tool that is in the process of being investigated in patients with specific vestibular disorders. Briefly, the VEMP is a biphasic response elicited by loud clicks or tone bursts recorded from the tonically contracted sternocleidomastoid muscle, being the only resource available to assess the function of the saccule and the lower portion of the vestibular nerve.

Aim

In this review, we shall highlight the history, methods, current VEMP status, and discuss its specific application in the diagnosis of the Ménière's Syndrome.

Contemporary Role of Endolymphatic Mastoid Shunt Surgery in the Era of Transtympanic Perfusion Strategies

Objectives:

Although there exist undisputed methods to permanently silence the aberrant end organ, controversy surrounds the durable efficacy of non-ablative interventions. This study provides a contemporary review of our institution's clinical experience in performing endolymphatic mastoid shunt surgery (EMSS) in patients with medically refractory endolymphatic hydrops, or Meniere's disease.

Methods:

Between 1984 and 2002, 1,612 patients were referred to our institution with a diagnosis of Meniere's disease. Of these referrals, 1,172 patients met the criteria for Meniere's disease. Although 553 patients responded to medical management, 486 patients underwent EMSS and 133 patients had refractory disease that required chemical or surgical obliterative interventions. The retrospective study utilizes data collected on 226 patients who were followed for a minimum of 5 years.

Results:

Overall, 78% patients responded favorably to EMSS, according to the functional level scale and class categories delineated by the American Academy of Otolaryngology-Head and Neck Surgery 1995 guidelines for control of vertigo. According to the Arenberg anatomic classification for endolymphatic sac location, EMSS achieved adequate control of vertigo in 86% of type I cases, 90% of type II cases, and 82% of type III cases.

Conclusions:

Endolymphatic mastoid shunt surgery is a relatively safe, effective procedure for the long-term control of vertigo in patients with medically refractory Meniere's disease.

Meniere's disease

Meniere's disease is a chronic illness that affects a substantial number of patients every year worldwide. The disease is characterised by intermittent episodes of vertigo lasting from minutes to hours, with fluctuating sensorineural hearing loss, tinnitus, and aural pressure. Although there is currently no cure, more than 85% of patients with Meniere's disease are helped by either changes in lifestyle and medical treatment, or minimally invasive surgical procedures such as intratympanic steroid therapy, intratympanic gentamicin therapy, and endolymphatic sac surgery. Vestibular neurectomy has a very high rate of vertigo control and is available for patients with good hearing who have failed all other treatments. Labyrinthectomy is undertaken as a last resort and is best reserved for patients with unilateral disease and deafness.

Concentration gradient along the scala tympani after local application of gentamicin to the round window membrane

OBJECTIVES

The distribution of gentamicin along the fluid spaces of the cochlea after local applications has never previously been demonstrated. Computer simulations have predicted that significant basal-apical concentration gradients might be expected, and histologic studies indicate that hair cell damage is greater at the base than at the apex after local gentamicin application. In the present study, gradients of gentamicin along the cochlea were measured.

METHODS

A recently developed method of sampling perilymph from the cochlear apex of guinea pigs was used in which the samples represent fluid originating from different regions along the scala tympani. Gentamicin concentration was determined in sequential apical samples that were taken after up to 3 hours of local application to the round window niche.

RESULTS

Substantial gradients of gentamicin along the length of the scala tympani were demonstrated and quantified, averaging more than 4,000 times greater concentration at the base compared with the apex at the time of sampling. Peak concentrations and gradients for gentamicin varied considerably between animals, likely resulting from variations in round window membrane permeability and rates of perilymph flow.

CONCLUSIONS

The large gradients for gentamicin demonstrated here in guinea pigs account for how it is possible to suppress vestibular function in some patients with a local application of gentamicin without damaging auditory function. Variations in round window membrane permeability and in perilymph flow could account for why hearing losses are observed in some patients.

Long-Term Disability of Class A Patients With M??ni??re???s Disease After Treatment With Intratympanic Gentamicin

OBJECTIVE

The main objective of this study was to characterize the residual vestibular symptoms and disability in patients with Ménière's disease who had achieved complete control of vertigo through intratympanic gentamicin treatment. Furthermore, we assessed whether the Functional Level Score prior to treatment reflected the posttreatment symptoms and disability.

STUDY DESIGN

Prospective.

SETTING

Tertiary medical center.

PATIENTS

This study involved 103 patients with Ménière's disease treated with intratympanic gentamicin who, after a long-term follow up, have not suffered new vertigo spells and were not subject to any major modification in their treatment.

METHODS

At inclusion and at the last follow-up visit after a minimum of 3 years of ending the treatment, the clinical status (number of vertigo spells), the unsteadiness as well as the disability produced by the disease, symptoms of anxiety, and compensation were asked using specific questionnaires. The results before and after treatment were analyzed using nonparametric tests.

RESULTS

After a 5-year follow-up, complete control of vertigo was obtained in 81% of the patients with Ménière's disease who were treated with intratympanic gentamicin. Of them, 15.5% still complained of unsteadiness. A functional level of 6 or unsteadiness after treatment are related with a nonreduction in disability after long-term control of vertigo spells.

CONCLUSIONS

The efficacy of gentamicin administered intratympanically is high after long-term follow-up as shown by the disappearance of vertigo spells and by the reduction in disability, increase in perception of quality of life, and reduction in anxiety related to vestibular symptoms. Unsteadiness, although an infrequent complaint, determines a level of almost similar severity in those issues. Special care must be taken with patients with a Functional Level Scale score of 6 at the time of beginning treatment.

Current Management of Ménière's Disease in an Only Hearing Ear

OBJECTIVE

Ménière's disease in an only hearing ear is rare. Our objective is to define the current practice patterns for this problem.

SUBJECTS

Clinically active members of the American Otological Society and the American Neurotology Society.

MAIN OUTCOME MEASURE

Survey responses.

RESULTS

Three hundred fifty-four surveys were sent out, and 165 were returned (48%). Ninety-nine percent recommended dietary modification as first line. Only 39% recommended oral corticosteroids. Second-line treatments were, in order of significance, the Meniett device (Medtronic ENT, Jacksonville, FL, USA), intratympanic corticosteroids, endolymphatic mastoid shunt, intratympanic gentamicin, and endolymphatic sac vein decompression. Interestingly, 71.5% of respondents would operate on an only hearing ear provided the appropriate circumstances.

CONCLUSION

We have documented current practice patterns for treatment. Second-line treatments vary, but the Meniett is recommended most frequently, and further recommendations may not logically progress from least to most invasive. Many respondents eventually offer surgery.

Perilymph sampling from the cochlear apex: a reliable method to obtain higher purity perilymph samples from scala tympani

Measurements of drug levels in the fluids of the inner ear are required to establish kinetic parameters and to determine the influence of specific local delivery protocols. For most substances, this requires cochlear fluids samples to be obtained for analysis. When auditory function is of primary interest, the drug level in the perilymph of scala tympani (ST) is most relevant, since drug in this scala has ready access to the auditory sensory cells. In many prior studies, ST perilymph samples have been obtained from the basal turn, either by aspiration through the round window membrane (RWM) or through an opening in the bony wall. A number of studies have demonstrated that such samples are likely to be contaminated with cerebrospinal fluid (CSF). CSF enters the basal turn of ST through the cochlear aqueduct when the bony capsule is perforated or when fluid is aspirated. The degree of sample contamination has, however, not been widely appreciated. Recent studies have shown that perilymph samples taken through the round window membrane are highly contaminated with CSF, with samples greater than 2microL in volume containing more CSF than perilymph. In spite of this knowledge, many groups continue to sample from the base of the cochlea, as it is a well-established method. We have developed an alternative, technically simple method to increase the proportion of ST perilymph in a fluid sample. The sample is taken from the apex of the cochlea, a site that is distant from the cochlear aqueduct. A previous problem with sampling through a perforation in the bone was that the native perilymph rapidly leaked out driven by CSF pressure and was lost to the middle ear space. We therefore developed a procedure to collect all the fluid that emerged from the perforated apex after perforation. We evaluated the method using a marker ion trimethylphenylammonium (TMPA). TMPA was applied to the perilymph of guinea pigs either by RW irrigation or by microinjection into the apical turn. The TMPA concentration of the fluid sample was compared with that measured in perilymph prior to taking the sample using a TMPA-selective microelectrode sealed into ST. Data were interpreted with a finite element model of the cochlear fluids that was used to simulate each aspect of the experiment. The correction of sample concentration back to the perilymph concentration prior to sampling can be performed based on the known ST volume (4.7microL in the guinea pig) and the sample volume. A more precise correction requires some knowledge of the profile of drug distribution along the cochlear prior to sampling. This method of sampling from the apex is technically simple and provides a larger sample volume with a greater proportion of perilymph compared to sampling through the RW.

Local inner-ear drug delivery and pharmacokinetics

Several drugs that are applied directly to the inner ear are in widespread clinical use for the treatment of inner-ear disorders. Many new substances and drug delivery systems specific to the inner ear are under development and in some cases are being evaluated in animal experiments and in clinical studies. However, the pharmacokinetics of drugs in the inner ear is not well defined and the field is plagued by technical problems in obtaining pure samples of the inner-ear fluids for analysis. Nevertheless, a basic understanding of the mechanisms of drug dispersal in the inner ear has emerged, which facilitates the design and interpretation of future pharmacokinetic studies.