Drug treatments for tinnitus

Protective Effects of Deferoxamine on Vestibulotoxicity in Gentamicin-Induced Bilateral Vestibulopathy Rat Model

Introduction: Administration of aminoglycoside (AG) antibiotics is one of the most common causes of ototoxicity. This study aimed to determine the protective effects of deferoxamine, an iron-chelating agent, on vestibulotoxicity using an intratympanic gentamicin injection (ITGM)-induced bilateral vestibulopathy rat model.

Methods: Fifteen Sprague-Dawley rats were randomly assigned to the ITGM only (n = 5), the ITGM combined with intramuscular deferoxamine (DFO) injection (ITGM+DFO, n = 5), or the intratympanic normal saline (control, n = 5) group. The rats in the ITGM+DFO group received intramuscular injection of 150 mg/kg of deferoxamine at 30, 90, and 150 min after the ITGM. The vestibular function was evaluated using the rotarod and open field test every 3 days after the injection until Day 16 when the rats were subjected to histological changes.

Results: The rats in the ITGM only group began to show significantly impaired vestibular function 2 days after ITGM into both ears. In contrast, the vestibular function was maintained in the control and ITGM+DFO groups without a difference throughout the experiments. The rats in the ITGM only group showed a near-complete loss of the type I and II hair cells and a collapse of the sensory epithelium in both the saccule and utricle. In contrast, the rats in the ITGM+DFO and control groups showed a relatively well-preserved sensory epithelium including the hair cells, cilia, and otolith layer.

Conclusion: This study provides experimental evidence for preventive effects of iron-chelating agents on AG-induced vestibulotoxicity. Simultaneous administration of iron-chelating agents may be considered when using ototoxic agents, especially in those considered to be vulnerable to toxic damage of the inner ear.

Therapeutic Approaches to the Treatment of Tinnitus

Tinnitus is a highly prevalent condition that is associated with hearing loss in most cases. In the absence of external stimuli, phantom perceptions of sounds emerge from alterations in neuronal activity within central auditory and nonauditory structures. Pioneering studies using lidocaine revealed that tinnitus is susceptible to pharmacological interventions. However, lidocaine is not effective in all patients, and no other drug has been identified with clear efficacy for the long-term treatment of tinnitus. In this review, we present recent advances in tinnitus research, including more detailed knowledge of its pathophysiology and involved neurotransmitter systems. Moreover, we summarize results from animal and clinical treatment studies as well as from studies that identified tinnitus as a side effect of pharmacological treatments. Finally, we focus on challenges in the development of pharmacological compounds for the treatment of tinnitus, namely the limitations of available animal models and of standardized clinical research methodologies.

Efficacy of Chinese herb Cistanche Yishen granules in treatment of tinnitus for patients with chronic nephritis

OBJECTIVE

This study aimed to investigate the efficacy of Chinese herb Cistanche Yishen granules (CYG) in the treatment of tinnitus for patients with chronic nephritis.

METHODS

A total of 89 adult patients were diagnosed with chronic glomerulonephritis from January 2016 to December 2017. All the patients were randomly divided into two groups, such as the control group and the CYG group. The efficacy of tinnitus was determined using tinnitus handicap inventory (THI), Pittsburgh sleep quality index (PSQI), pure tone audiometry (PTA), speech reception threshold (SRT), and visual analog scale (VAS) for tinnitus loudness and annoyance.

RESULTS

In both these two groups of patients, values of THI, PSQI, PTA, SRT, and VAS for tinnitus loudness and annoyance were significantly decreased after the treatment compared with those before treatment. However, all values in CYG group after the treatment were significantly lower than those in the control group.

CONCLUSION

CYG could apparently release the tinnitus symptoms in the patients with chronic nephritis. This study might give more clinical evidence for Cistanche in the treatment of tinnitus and give a new treatment method for the patients with tinnitus.

Tinnitus Treatment Trends

OBJECTIVE

The American Academy of Otolaryngology-Head and Neck Surgery (AAO-HNS) recently published guidelines on the treatment of tinnitus. This paper examines the possible impact of those guidelines on otologic practice.

DESIGN

A survey was sent to the members of the American Neurotology Society before and after the publication of Clinical practice guideline: tinnitus. The goals of this study were to see if the guidelines changed attitudes of otologists, confirm what treatments and explanations are being used in the field before and after the guidelines were published.

MAIN OUTCOMES

Five hundred fifty-eight surveys were sent out and there were 216 responses. Otologists generally seemed to practice in accordance with the recommendations of the guidelines even before these were published. Drugs and sound therapies were not commonly used for primary tinnitus either before or after publication of the guidelines. One treatment that otologists seemed to have confidence in that was omitted from the guidelines was surgical treatment of hearing loss.

CONCLUSION

Opinions regarding the treatment of tinnitus vary considerably. The AAO-HNS clinical practice guideline: tinnitus has not significantly altered the practices of otologists, but the guidelines provide meaningful, important information for other clinicians who deal infrequently with tinnitus.

Efficacy of Trimetazidine Dihydrochloride for Relieving Chronic Tinnitus: A Randomized Double-Blind Study

Objectives.

To evaluate the efficacy of trimetazidine dihydrochloride as a treatment for chronic tinnitus.

Methods.

A total of 97 chronic tinnitus patients were evaluated in this randomized, prospective, double-blind, placebo-controlled trial. After assessing for eligibility, 82 patients were randomly assigned into placebo or trimetazidine groups according to the medication. The trimetazidine group received 20×3 mg/day per oral trimetazidine dihydrochloride and the placebo group received 20×3 mg/day per oral placebo for 3 months. Tinnitus handicap inventory (THI), visual analogue scale (VAS) questionnaires and audiometric results were used to determine the effectiveness of trimetazidine treatment.

Results.

The study group comprised 82 tinnitus subjects, 42 (51%) of whom received trimetazidine dihydrochloride and 40 (49%) who received placebo. There was no significant difference between placebo and trimetazidine groups in THI grade and VAS (both pre- and posttreatment scores) (P>0.05) and no significant improvement was observed in subjective loudness score in either group (P>0.05). Additionally there was no significant difference between groups in pre- and posttreatment pure tone hearing thresholds at all measured frequencies (P>0.05).

Conclusion.

Trimetazidine dihydrochloride therapy was ineffective for relieving chronic tinnitus.

The anti-inflammatory selective melanocortin receptor subtype 4 agonist, RO27-3225, fails to prevent acoustic trauma-induced tinnitus in rats

In preliminary studies we have observed a massive microglial activation in the cochlear nucleus following acoustic trauma-induced tinnitus in rats, which suggests that inflammatory responses within the central auditory system may be involved in the development and maintenance of tinnitus. Recently, the anti-inflammatory properties of melanocortins (MCs), have gained increasing interest in pharmacology due to their promising therapeutic potential in the treatment of inflammatory-mediated diseases. Among the five subtypes of the MC receptor, MC3 and MC4 receptors are the predominant brain receptors and are thought to play an important role in brain inflammation and neuroprotection. Importantly, MC4 receptors have been found in the mouse and rat central auditory systems. In this study we investigated whether the MC4 receptor agonist, RO27-3225, injected s.c at a dose of 90 or 180µg/kg, 30min before acoustic trauma and then every 12h for 10 days, could prevent the development of acoustic trauma-induced tinnitus in rats, using a conditioned behavioural suppression model. Although evidence of tinnitus developed in the exposed-vehicle group compared to the sham-vehicle group (P≤0.03), in response to a 32kHz tone, there were no significant drug effects from treatment with RO27-3225, indicating that it did not confer any protection against the development of tinnitus in this animal model. This result suggests that the anti-inflammatory effects of MC4 receptor agonists may not be sufficient to prevent tinnitus.

The use of benzodiazepines for tinnitus: systematic review

Objectives:

To investigate the effectiveness of benzodiazepine use for subjective tinnitus and to consider this in the context of the concomitant side effects.

Methods:

A systematic search of several databases using the terms ‘tinnitus’ and ‘benzodiazepines’ was conducted to find clinical trials of benzodiazepines and comparators in tinnitus patients. These studies were then assessed for risk of bias.

Results:

Six clinical trials were included. Clonazepam was found to be effective in three studies, but these studies had limitations regarding adequate blinding. The effectiveness of alprazolam was equivocal. Diazepam was not effective in two studies and oxazepam was effective in one study.

Conclusion:

Benzodiazepine use for subjective tinnitus does not have a robust evidence base. Clonazepam has the most evidence to support its use and is relatively less likely to lead to abuse because of its longer half-life, but caution is still needed given the other serious side effects.

Cannabinoid CB1 Receptor Agonists Do Not Decrease, but may Increase Acoustic Trauma-Induced Tinnitus in Rats

Tinnitus has been suggested to arise from neuronal hyperactivity in auditory areas of the brain, and anti-epileptic drugs are sometimes used to provide relief from tinnitus. Recently, the anti-epileptic properties of the cannabinoid drugs have gained increasing interest; however, the use of cannabinoids as a form of treatment for tinnitus is controversial. In this study, we tested whether a combination of delta-9-tetrahydrocannabinol (delta-9-THC) and cannabidiol (CBD), delivered in a 1:1 ratio, could affect tinnitus perception in a rat model of acoustic trauma-induced tinnitus. Following sham treatment or acoustic trauma, the animals were divided into the following groups: (1) sham (i.e., no acoustic trauma) with vehicle treatment; (2) sham with drug treatment (i.e., delta-9-THC + CBD); (3) acoustic trauma-exposed exhibiting tinnitus, with drug treatment; and (4) acoustic trauma-exposed exhibiting no tinnitus, with drug treatment. The animals received either the vehicle or the cannabinoid drugs every day, 30 min before the tinnitus behavioral testing. Acoustic trauma caused a significant increase in the auditory brainstem response (ABR) thresholds in the exposed animals, indicating hearing loss; however, there was a partial recovery over 6 months. Acoustic trauma did not always result in tinnitus; however, among those that did exhibit tinnitus, some of them had tinnitus at multiple frequencies while others had it only at a single frequency. The cannabinoids significantly increased the number of tinnitus animals in the exposed-tinnitus group, but not in the sham group. The results suggest that cannabinoids may promote the development of tinnitus, especially when there is pre-existing hearing damage.

Round window membrane intracochlear drug delivery enhanced by induced advection

Delivery of therapeutic compounds to the inner ear via absorption through the round window membrane (RWM) has advantages over direct intracochlear infusions; specifically, minimizing impact upon functional hearing measures. However, previous reports show that significant basal-to-apical concentration gradients occur, with the potential to impact treatment efficacy. Here we present a new approach to inner ear drug delivery with induced advection aiding distribution of compounds throughout the inner ear in the murine cochlea. Polyimide microtubing was placed near the RWM niche through a bullaostomy into the middle ear cavity allowing directed delivery of compounds to the RWM. We hypothesized that a posterior semicircular canalostomy would induce apical flow from the patent cochlear aqueduct to the canalostomy due to influx of cerebral spinal fluid. To test this hypothesis, young adult CBA/CaJ mice were divided into two groups: bullaostomy approach only (BA) and bullaostomy+canalostomy (B+C). Cochlear function was evaluated by distortion product otoacoustic emission (DPOAE) and auditory brainstem response (ABR) thresholds during and after middle ear infusion of salicylate in artificial perilymph (AP), applied near the RWM. The mice recovered for 1week, and were re-tested. The results demonstrate there was no significant impact on auditory function utilizing the RWM surgical procedure with or without the canalostomy, and DPOAE thresholds were elevated reversibly during the salicylate infusion. Comparing the threshold shifts for both methods, the B+C approach had more of a physiological effect than the BA approach, including at lower frequencies representing more apical cochlear locations. Unlike mouse cochleostomies, there was no deleterious auditory functional impact after 1week recovery from surgery. The B+C approach had more drug efficacy at lower frequencies, underscoring potential benefits for more precise control of delivery of inner ear therapeutic compounds.

Directing neural plasticity to understand and treat tinnitus

The functional organization of cortical and subcortical networks can be altered by sensory experience. Sensory deprivation destabilizes neural networks resulting in increased excitability, greater neural synchronization and increased spontaneous firing in cortical and subcortical neurons. This pathological activity is thought to generate the phantom percept of chronic tinnitus. While sound masking, pharmacotherapy and cortical stimulation can temporarily suppress tinnitus for some patients, these interventions do not eliminate the pathological activity that is responsible for tinnitus. A treatment that could reverse the underlying pathology would be expected to be effective in alleviating the symptoms, if not curative. Targeted neural plasticity can provide the specificity required to restore normal neural activity in dysfunctional neural circuits that are assumed to underlie many forms of tinnitus. The forebrain cholinergic system and the noradrenergic system play a significant role in modulating cortical plasticity. Stimulation of the vagus nerve is known to activate these neuromodulatory pathways. Our earlier studies have demonstrated that pairing sounds with either nucleus basalis of Meynert (NB) stimulation or vagus nerve stimulation (VNS) generates highly specific and long-lasting plasticity in auditory cortex neurons. Repeatedly pairing tones with brief pulses of VNS reversed the physiological and behavioral correlates of tinnitus in noise exposed rats. We also recently demonstrated that VNS modulates synchrony and excitability in the auditory cortex at least in part by activation of muscarinic acetylcholine receptors, suggesting that acetylcholine is involved in the mechanism of action of VNS. These results suggest that pairing sounds with VNS provides a new avenue of treatment for some forms of tinnitus. This paper discusses neuromodulation as treatment for tinnitus with a focus on the potential value of pairing VNS with sound stimulation as a treatment of chronic tinnitus.

Evidence that Memantine Reduces Chronic Tinnitus Caused by Acoustic Trauma in Rats

Subjective tinnitus is a chronic neurological disorder in which phantom sounds are perceived. Increasing evidence suggests that tinnitus is caused by neuronal hyperactivity in auditory brain regions, either due to a decrease in synaptic inhibition or an increase in synaptic excitation. One drug investigated for the treatment of tinnitus has been the uncompetitive N-methyl-d-aspartate (NMDA) receptor antagonist, memantine, although the evidence relating to it has been unconvincing to date. We re-investigated the effects of memantine on the behavioral manifestations of tinnitus induced by acoustic trauma (a 16-kHz, 110-dB pure tone presented unilaterally for 1 h) in rats. We used a conditioned lick suppression model in which lick suppression was associated with the perception of high frequency sound resembling tinnitus and a suppression ratio (SR) was calculated by comparing the number of licks in the 15-s period preceding the stimulus presentation (A) and the 15-s period during the stimulus presentation (B), i.e., SR = B/(A + B). Acoustic trauma resulted in a significant increase in the auditory brainstem-evoked response (ABR) threshold in the affected ear (P ≤ 0.0001) and a decrease in the SR compared to sham controls in response to 32 kHz tones in five out of eight acoustic trauma-exposed animals. A 5-mg/kg dose of memantine significantly reduced the proportion of these animals which exhibited tinnitus-like behavior (2/5 compared to 5/5; P ≤ 0.006), suggesting that the drug reduced tinnitus. These results suggest that memantine may reduce tinnitus caused by acoustic trauma.

An active loudness model suggesting tinnitus as increased central noise and hyperacusis as increased nonlinear gain

The present study uses a systems engineering approach to delineate the relationship between tinnitus and hyperacusis as a result of either hearing loss in the ear or an imbalanced state in the brain. Specifically examined is the input-output function, or loudness growth as a function of intensity in both normal and pathological conditions. Tinnitus reduces the output dynamic range by raising the floor, while hyperacusis reduces the input dynamic range by lowering the ceiling or sound tolerance level. Tinnitus does not necessarily steepen the loudness growth function but hyperacusis always does. An active loudness model that consists of an expansion stage following a compression stage can account for these key properties in tinnitus and hyperacusis loudness functions. The active loudness model suggests that tinnitus is a result of increased central noise, while hyperacusis is due to increased nonlinear gain. The active loudness model also generates specific predictions on loudness growth in tinnitus, hyperacusis, hearing loss or any combinations of the three conditions. These predictions need to be verified by experimental data and have explicit implications for treatment of tinnitus and hyperacusis.

A randomized, controlled study comparing the effects of vestipitant or vestipitant and paroxetine combination in subjects with tinnitus

OBJECTIVE

Tinnitus is a common symptom that demonstrates a significant comorbidity with anxiety and depression. The novel neurokinin-1 receptor antagonist, vestipitant, has anxiolytic properties and a good safety profile. Vestipitant was investigated for potential effect against chronic tinnitus as a stand-alone treatment and in conjunction with a selective serotonin reuptake inhibitor, paroxetine.

STUDY DESIGN

Randomized, double-blind, crossover study.

SETTING

Tertiary neurotologic and audiologic center with additional referrals from a secondary university hospital center.

PATIENTS

Twenty-four adult patients with tinnitus were randomized into the study.

MAIN OUTCOME MEASURES

Visual analogue scale (VAS) measurements of tinnitus loudness (intensity), pitch and distress, VAS measurements of arousal/anxiety, Tinnitus Handicap Inventory, Quick Inventory of Depressive Symptomatology, and plasma concentrations of trial drugs.

RESULTS

No statistically significant treatment benefit effect was detected for tinnitus (intensity, pitch, and distress) VAS scores, arousal-anxiety VAS scores, Tinnitus Handicap Inventory, or tinnitus aggravation scores assessed on Days 1 and 14. However, a statistically significant worsening of tinnitus intensity and distress scores was observed after vestipitant compared with placebo for the mean data collected over the treatment period. No relevant differences in vestipitant plasma concentrations were observed between the subjects given the combination with paroxetine and those receiving vestipitant alone. No specific relationships were observed between tinnitus intensity and vestipitant plasma concentrations.

CONCLUSION

Although well-tolerated vestipitant, alone or in combination with paroxetine, was not effective in ameliorating tinnitus in this patient group.

A dose-response analysis of the effects of L-baclofen on chronic tinnitus caused by acoustic trauma in rats

Subjective tinnitus is a chronic neurological disorder in which phantom sounds are perceived. Drugs that increase GABAergic neurotransmission in the CNS are sometimes used as a treatment. One such drug is the GABA(B) receptor agonist L-baclofen. The aim of this study was to investigate the effects of L-baclofen on the psychophysical attributes of tinnitus in rats.The effects of 1, 3 or 5 mg/kg L-baclofen (s.c.) on the psychophysical attributes of tinnitus were investigated using a conditioned lick suppression model, following acoustic trauma (a 16 kHz, 110 dB pure tone presented unilaterally for 1 h) in rats. In pre-drug testing, acoustic trauma resulted in a significant increase in the auditory brainstem-evoked response (ABR) threshold in the affected ear (P < 0.008) and a significant decrease in the suppression ratio (SR) compared to sham controls in response to the 20 kHz tones, but not the broadband noise or the 10 kHz tones (P < 0.002). The 3 and 5 mg/kg doses of L-baclofen significantly reversed the frequency-specific decrease in the SR in the acoustic trauma group, indicating that the drug reduced tinnitus. Following washout from the 3 mg/kg dose, but not the 5 mg/kg dose, the significant decrease in the SR for the acoustic trauma group returned, suggesting a return of the tinnitus. These results suggest that L-baclofen should be reconsidered as a drug treatment for tinnitus. This article is part of a Special Issue entitled 'Post-Traumatic Stress Disorder'.

Acoustic trauma that can cause tinnitus impairs impulsive control but not performance accuracy in the 5-choice serial reaction time task in rats

Although tinnitus is an auditory disorder, it is often associated with attentional and emotional problems. Functional neuroimaging studies in humans have revealed that the hippocampus, amygdala and anterior cingulate, areas of the brain involved in emotion, attention and spatial processing, are also involved in auditory memory and tinnitus perception. However, few studies of tinnitus-evoked emotional and cognitive changes have been reported using animal models of tinnitus. In the present study, we investigated whether acoustic trauma that could cause tinnitus would affect attention and impulsivity in rats. Eight male Wistar rats were exposed to unilateral acoustic trauma (110 dB, 16 kHz for 1 h under anaesthesia) and eight rats underwent the same anaesthesia without acoustic trauma. Tinnitus was tested in noise-exposed rats using a frequency-specific shift in a discrimination function with a conditioned lick suppression paradigm. At 4 months after the noise exposure, the rats were tested in a 5-choice serial reaction time task. The behavioural procedure involved training the rats to discriminate a brief visual stimulus presented randomly in one of the five spatial locations and responding by poking its nose through the illuminated hole and collecting a food pellet from the magazine. While all of the animals performed equally well in making correct responses, the animals exposed to acoustic trauma made significantly more premature responses. The results suggest that rats exposed to acoustic trauma and some of which have chronic tinnitus are impaired in impulsive control, but not performance accuracy.

Safety of intratympanic injection of AM-101 in patients with acute inner ear tinnitus

Effective pharmacological treatments for tinnitus have proven elusive. Emerging evidence suggests that dysregulation of cochlear N-methyl-D-aspartate (NMDA) receptors may underlie aberrant excitation of the auditory nerve, which in turn is perceived as tinnitus. The blocking of these receptors thus represents a promising therapeutic approach. In a recent phase I/II clinical trial, the safety and local tolerance of intratympanic injections of the NMDA receptor antagonist AM-101 was evaluated for the first time in humans. The results from the double-blind, randomized, placebo-controlled study show that intratympanically injected AM-101 was well tolerated by study participants, and provided the first indications of therapeutic efficacy.

‘‘Ringing in the Ears’’: Narrative Review of Tinnitus and Its Impact

About 10% of the population experiences tinnitus, a common and distressing symptom characterized by the perception of sound in the absence of external stimuli. There is, however, marked heterogeneity in etiology, perception, and extent of distress among those who experience tinnitus. Reactions to tinnitus vary from simple awareness to severe irritation; some people have difficulty in hearing because of the loudness of the noise. Severe tinnitus causes many, often psychological, symptoms (e.g., tension, frustration, impaired concentration, disrupted sleep). For some, tinnitus is temporary, for others it is longstanding. Although many people adjust successfully, others are disabled by tinnitus; approximately 5% experience persistent and severe symptoms affecting their lifestyle and significantly reducing their quality of life. Because tinnitus is poorly understood and no single therapeutic approach is effective for all patients, many patients are told that ‘‘nothing can be done’’ and they must ‘‘learn to live with it.’’ In spite of these challenges, there is remarkably little relevant nursing literature on tinnitus. This literature review was conducted to explore current knowledge of tinnitus, including prevalence, causes and diagnosis, and assessment. Its psychosocial effects and impact on individuals are considered. Implications for practice are discussed—demonstrating that understanding the full impact of the condition and identifying patients’ needs are essential to effective care.

Transcutaneous electrical nerve stimulation (TENS) of upper cervical nerve (C2) for the treatment of somatic tinnitus

Somatic tinnitus has been defined as tinnitus temporally associated to a somatic disorder involving the head and neck. Several studies have demonstrated the interactions between the somatosensory and auditory system at the dorsal cochlear nucleus (DCN), inferior colliculus, and parietal association areas. The objective is to verify the effect of transcutaneous electrical nerve stimulation of the upper cervical nerve (C2) in the treatment of somatic tinnitus. As electrical stimulation of C2 increases activation of the DCN through the somatosensory pathway and enlarges the inhibitory role of the DCN on the central nervous system, C2 TENS can be considered for tinnitus modulation. A total of 240 patients in whom tinnitus is modulated by somatosensory events (e.g., tinnitus change with rotation, retro- and antiflexion of neck) or modulated by pressure on head or face were included in this study. Both a real and a sham TENS treatment were applied for 30 min (10 min of 6 Hz, followed by 10 min of 40 Hz and 10 min of sham). Significant tinnitus suppression was found (P < 0.001). Only 17.9% (N = 43) of the patients with tinnitus responded to C2 TENS. They had an improvement of 42.92%, and six patients had a reduction of 100%.

The effects of the Chinese herbal medicine EMF01 on salicylate-induced tinnitus in rats

AIM OF THE STUDY

Traditional Chinese medicine (TCM) has been reported to successfully alleviate tinnitus, although well-controlled studies have not been conducted. In this study, we attempted to test a TCM, Er Ming Fang (EMF01) containing Rehmannia glutinosa, Cornus officinalis, Salvia mittiorrhiza, Pueraria, Schisandra chinensis, Poria cocos and Platycodon grandiflorum, on salicylate-induced tinnitus in rats, using a conditioned lick suppression paradigm.

MATERIALS AND METHODS

A pilot study examined the effect of 8.75 g/kg and 17.5 g/kg EMF01 (delivered by oral gavage for 20 days) and showed a slight decrease in the suppression ratio (SR) in the 8.75 g/kg group. In order to confirm the possible effect of EMF01 on tinnitus at 8.75 g/kg, a further study was carried out with a larger sample size.

RESULTS

While there were statistically significant differences between the treatment groups, post hoc tests revealed that EMF01 did not have any significant effect on salicylate-induced tinnitus.

CONCLUSIONS

While this study does not support the efficacy of EMF01 in the treatment of salicylate-induced tinnitus, further studies should be conducted to determine if it alleviates tinnitus associated with acoustic trauma.

State-of-the-art mechanisms of intracochlear drug delivery

PURPOSE OF REVIEW

Treatment of auditory and vestibular dysfunction has become increasingly dependent on inner ear drug delivery. Recent advances in molecular therapy and nanotechnology have pushed development of alternate delivery methodologies involving both transtympanic and direct intracochlear infusions. This review examines recent developments in the field relevant to both clinical and animal research environments.

RECENT FINDINGS

Transtympanic delivery of gentamicin and corticosteroids for the treatment of Meniere's disease and sudden sensorineural hearing loss continues to be clinically relevant, with understanding of pharmacokinetics becoming more closely studied. Stabilizing matrices placed on the round window membrane for sustained passive delivery of compounds offer more controlled dosing profiles than transtympanic injections. Nanoparticles are capable of traversing the round window membrane and cochlear membranous partitions, and may become useful gene delivery platforms. Cochlear and vestibular hair cell regeneration has been demonstrated by vector delivery to the inner ear, offering promise for future advanced therapies.

SUMMARY

Optimal methods of inner ear drug delivery will depend on toxicity, therapeutic dose range, and characteristics of the agent to be delivered. Advanced therapy development will likely require direct intracochlear delivery with detailed understanding of associated pharmacokinetics.

Localized cell and drug delivery for auditory prostheses

Localized cell and drug delivery to the cochlea and central auditory pathway can improve the safety and performance of implanted auditory prostheses (APs). While generally successful, these devices have a number of limitations and adverse effects including limited tonal and dynamic ranges, channel interactions, unwanted stimulation of non-auditory nerves, immune rejection, and infections including meningitis. Many of these limitations are associated with the tissue reactions to implanted auditory prosthetic devices and the gradual degeneration of the auditory system following deafness. Strategies to reduce the insertion trauma, degeneration of target neurons, fibrous and bony tissue encapsulation, and immune activation can improve the viability of tissue required for AP function as well as improve the resolution of stimulation for reduced channel interaction and improved place-pitch and level discrimination. Many pharmaceutical compounds have been identified that promote the viability of auditory tissue and prevent inflammation and infection. Cell delivery and gene therapy have provided promising results for treating hearing loss and reversing degeneration. Currently, many clinical and experimental methods can produce extremely localized and sustained drug delivery to address AP limitations. These methods provide better control over drug concentrations while eliminating the adverse effects of systemic delivery. Many of these drug delivery techniques can be integrated into modern auditory prosthetic devices to optimize the tissue response to the implanted device and reduce the risk of infection or rejection. Together, these methods and pharmaceutical agents can be used to optimize the tissue-device interface for improved AP safety and effectiveness.