Predictability of drug release from cochlear implants

High-Precision 3D Printing of Microporous Cochlear Implants for Personalized Local Drug Delivery

Hearing loss is a highly prevalent multifactorial disorder affecting 20% of the global population. Current treatments using the systemic administration of drugs are therapeutically ineffective due to the anatomy of the cochlea and the existing blood-labyrinth barrier. Local drug delivery systems can ensure therapeutic drug concentrations locally while preventing adverse effects caused by high dosages of systemically administered drugs. Here, we aimed to design, fabricate, and characterize a local drug delivery system for the human cochlea. The design was relevant to the size of the human ear, included two different shapes, and incorporated two different microporous structures acting as reservoirs for drug loading and release. The four cochlear implant designs were printed using the two-photon polymerization (2PP) technique and the IP-Q photoresist. The optimized 2PP process enabled the fabrication of the cochlear implants with great reproducibility and shape fidelity. Rectangular and cylindrical implants featuring cylindrical and tapered tips, respectively, were successfully printed. Their outer dimensions were 0.6 × 0.6 × 2.4 mm3 (L × W × H). They incorporated internal porous networks that were printed with high accuracy, yielding pore sizes of 17.88 ± 0.95 μm and 58.15 ± 1.62 μm for the designed values of 20 μm and 60 μm, respectively. The average surface roughness was 1.67 ± 0.24 μm, and the water contact angle was 72.3 ± 3.0°. A high degree of polymerization (~90%) of the IP-Q was identified after printing, and the printed material was cytocompatible with murine macrophages. The cochlear implants designed and 3D printed in this study, featuring relevant sizes for the human ear and tunable internal microporosity, represent a novel approach for personalized treatment of hearing loss through local drug delivery.

Release Kinetics of Metronidazole from 3D Printed Silicone Scaffolds for Sustained Application to the Female Reproductive Tract

Sustained vaginal administration of antibiotics or probiotics has been proposed to improve treatment efficacy for bacterial vaginosis. 3D printing has shown promise for development of systems for local agent delivery. In contrast to oral ingestion, agent release kinetics can be fine-tuned by the 3D printing of specialized scaffold designs tailored for particular treatments while enhancing dosage effectiveness via localized sustained release. It has been challenging to establish scaffold properties as a function of fabrication parameters to obtain sustained release. In particular, the relationships between scaffold curing conditions, compressive strength, and drug release kinetics remain poorly understood. This study evaluates 3D printed scaffold formulation and feasibility to sustain the release of metronidazole, a commonly used antibiotic for BV. Cylindrical silicone scaffolds were printed and cured using three different conditions relevant to potential future incorporation of temperature-sensitive labile biologics. Compressive strength and drug release were monitored for 14d in simulated vaginal fluid to assess long-term effects of fabrication conditions on mechanical integrity and release kinetics. Scaffolds were mechanically evaluated to determine compressive and tensile strength, and elastic modulus. Release profiles were fitted to previous kinetic models to differentiate potential release mechanisms. The Higuchi, Korsmeyer-Peppas, and Peppas-Sahlin models best described the release, indicating similarity to release from insoluble or polymeric matrices. This study shows the feasibility of 3D printed silicone scaffolds to provide sustained metronidazole release over 14d, with compressive strength and drug release kinetics tuned by the fabrication parameters.

Current Concepts and Future Trends in Increasing the Benefits of Cochlear Implantation: A Narrative Review

Hearing loss is the most common neurosensory disorder, and with the constant increase in etiological factors, combined with early detection protocols, numbers will continue to rise. Cochlear implantation has become the gold standard for patients with severe hearing loss, and interest has shifted from implantation principles to the preservation of residual hearing following the procedure itself. As the audiological criteria for cochlear implant eligibility have expanded to include patients with good residual hearing, more attention is focused on complementary development of otoprotective agents, electrode design, and surgical approaches. The focus of this review is current aspects of preserving residual hearing through a summary of recent trends regarding surgical and pharmacological fundamentals. Subsequently, the assessment of new pharmacological options, novel bioactive molecules (neurotrophins, growth factors, etc.), nanoparticles, stem cells, and gene therapy are discussed.

Inner Ear Pharmacotherapy for Residual Hearing Preservation in Cochlear Implant Surgery: A Systematic Review

Cochlear implantation initiates an inflammatory cascade in which both acute insertion trauma and chronic foreign body reaction lead to intracochlear fibrosis and loss of residual hearing. Several strategies have been proposed to attenuate the local reactive process after implantation, including intracochlear drug delivery. The present study gives an overview of what is being investigated in the field of inner ear therapeutics and cochlear implant surgery. The aim is to evaluate its potential benefit in clinical practice. A systematic search was conducted in PubMed, Embase, and Cochrane Library databases identifying comparative prospective studies examining the effect of direct inner ear drug application on mechanical cochlear trauma. Both animal and human studies were considered and all studies were assessed for quality according to the validated risk of bias tools. Intracochlear administration of drugs is a feasible method to reduce the local inflammatory reaction following cochlear implantation. In animal studies, corticosteroid use had a significant effect on outcome measures including auditory brainstem response, impedance, and histological changes. This effect was, however, only durable with prolonged drug delivery. Significant differences in outcome were predominantly seen in studies where the cochlear damage was extensive. Six additional reports assessing non-steroidal agents were found. Overall, evidence of anti-inflammatory effects in humans is still scarce.

Microimaging of a novel intracochlear drug delivery device in combination with cochlear implants in the human inner ear

The effective delivery of drugs to the inner ear is still an unmet medical need. Local controlled drug delivery to this sensory organ is challenging due to its location in the petrous bone, small volume, tight barriers, and high vulnerability. Local intracochlear delivery of drugs would overcome the limitations of intratympanic (extracochlear) and systemic drug application. The requirements for such a delivery system include small size, appropriate flexibility, and biodegradability. We have developed biodegradable PLGA-based implants for controlled intracochlear drug release that can also be used in combination with cochlear implants (CIs), which are implantable neurosensory prosthesis for hearing rehabilitation. The drug carrier system was tested for implantation in the human inner ear in 11 human temporal bones. In five of the temporal bones, CI arrays from different manufacturers were implanted before insertion of the biodegradable PLGA implants. The drug carrier system and CI arrays were implanted into the scala tympani through the round window. Implanted temporal bones were evaluated by ultra-high-resolution computed tomography (µ-CT) to illustrate the position of implanted electrode carriers and the drug carrier system. The µ-CT measurements revealed the feasibility of implanting the PLGA implants into the scala tympani of the human inner ear and co-administration of the biodegradable PLGA implant with a CI array.

Dexamethasone-loaded cochlear implants: How to provide a desired "burst release"

Cochlear implants containing iridium platinum electrodes are used to transmit electrical signals into the inner ear of patients suffering from severe or profound deafness without valuable benefit from conventional hearing aids. However, their placement is invasive and can cause trauma as well as local inflammation, harming remaining hair cells or other inner ear cells. As foreign bodies, the implants also induce fibrosis, resulting in a less efficient conduction of the electrical signals and, thus, potentially decreased system performance. To overcome these obstacles, dexamethasone has recently been embedded in this type of implants: into the silicone matrices separating the metal electrodes (to avoid short circuits). It has been shown that the resulting drug release can be controlled over several years. Importantly, the dexamethasone does not only act against the immediate consequences of trauma, inflammation and fibrosis, it can also be expected to be beneficial for remaining hair cells in the long term. However, the reported amounts of drug released at “early” time points (during the first days/weeks) are relatively low and the in vivo efficacy in animal models was reported to be non-optimal. The aim of this study was to increase the initial “burst release” from the implants, adding a freely water-soluble salt of a phosphate ester of dexamethasone. The idea was to facilitate water penetration into the highly hydrophobic system and, thus, to promote drug dissolution and diffusion. This approach was efficient: Adding up to 10% dexamethasone sodium phosphate to the silicone matrices substantially increased the resulting drug release rate at early time points. This can be expected to improve drug action and implant functionality. But at elevated dexamethasone sodium phosphate loadings device swelling became important. Since the cochlea is a tiny and sensitive organ, a potential increase in implant dimensions over time must be limited. Hence, a balance has to be found between drug release and implant swelling.

Novel biodegradable Round Window Disks for inner ear delivery of dexamethasone

Drug delivery to the inner ear is an important and very challenging field. The cochlea is protected by several barriers that need to be overcome in the drug delivery process. Local drug delivery can avoid undesirable side effects arising from systemic drug delivery. We developed a biodegradable dexamethasone-loaded Round Window (RW) Disk based on poly(D,L-lactic-co-glycolic acid) (PLGA) for local drug therapy to the inner ear by RW membrane administration by a film-casting method. The optimal drying time was characterized by thermogravimetric analysis and differential scanning calorimetry. In addition, the mass and polymer degradation over time of drug release was measured in vitro showing a total mass loss of 70% after 3 weeks. Dexamethasone release was determined by a RW model setup using a polyethylene terephthalate membrane. We achieved a controlled release over 52 days. Ex vivo implantation of a RW Disk onto a guinea pig RW membrane indicated well-fitting properties of the drug delivery device leading to a close surface contact with the membrane and the successful proof of concept. The developed RW Disks could be new and promising drug delivery device to achieve effective local drug delivery to the inner ear for an extended time.

Intracochlear PLGA based implants for dexamethasone release: Challenges and solutions

The effective treatment of diseases of the inner ear is currently an unmet medical need. Local controlled drug delivery to the cochlea is challenging due to the hidden location, small volume and high sensitivity of this organ. A local intracochlear delivery of drugs would avoid the problems of intratympanic (extracochlear) drug application, but is more invasive. The requirements for such a delivery system include a small size and appropriate flexibility. The delivery device must be rigid enough for surgical handling but also flexible to avoid traumatizing cochlear structures. We developed biodegradable dexamethasone loaded PLGA extrudates for the controlled intracochlear release. In order to achieve the desired flexibility, Polyethylene glycol (PEG) was used as a plasticizer. In addition to the drug release, the extrudates were characterized in vitro by differential scanning calorimetry (DSC) and texture analysis. Simulation of the pharmacokinetics of the inner ear support the expectation that a constant perilymph drug level is obtained after few hours and retained over several weeks. Ex vivo implantation of the extrudates into a guinea pig cochlea indicate that PEG containing extrudates have the desired balance between mechanical strength and flexibility for direct implantation into the cochlea. The location of the implant was visualized by computer tomography. In summary, we postulate that intracochlear administration of drug releasing biodegradable implants is a new and promising approach to achieve local drug delivery to the cochlea for an extended time.

Hybrid Ear Cubes for local controlled dexamethasone delivery to the inner ear

A new type of miniaturized implants for local controlled drug delivery to the inner ear is proposed: Hybrid Ear Cubes. They are composed of two main parts: (i) a cylinder, which is placed into a tiny hole (<0.4 mm) drilled into (or close to) the oval (or round) window, and (ii) a cuboid, which is placed into the middle ear. The drug is released at a pre-programmed rate into the perilymph: (i) via the cylindrical part of the implant, which is in direct contact with this liquid, and (ii) via diffusion from the cuboid through the oval/round window. Importantly, the cylindrical part assures a reliable fixation of the drug delivery system at the site of administration. Furthermore, the cuboid provides a relatively "large" drug reservoir, without expulsing perilymph from the cochlea. The required surgery is minimized compared to the placement of an intracochlear implant. In contrast to previously proposed Ear Cubes, which are mono-block systems, Hybrid Ear Cubes consist of two halves, which can: (i) be loaded with different drugs, (ii) be loaded with the same drug at different concentrations, and/or (iii) be based on two different matrix formers. This offers a substantially increased formulation flexibility. Different types of silicone-based Hybrid Ear Cubes were prepared, loaded with 10% dexamethasone in one half and 0-60% dexamethasone in the other half. Importantly, tiny drug crystals were homogeneously distributed throughout the respective implant halves. The observed drug release rates were very low (e.g., <0.5% after 2 months), which can be attributed to the type of drug and silicone as well as to the very small surface area exposed to the release medium. Importantly, no noteworthy implant swelling was observed.

Controlled drug release to the inner ear: Concepts, materials, mechanisms, and performance

Progress in drug delivery to the ear has been achieved over the last few years. This review illustrates the main mechanisms of controlled drug release and the resulting geometry- and size-dependent release kinetics. The potency, physicochemical properties, and stability of the drug molecules are key parameters for designing the most suitable drug delivery system. The most important drug delivery systems for the inner ear include solid foams, hydrogels, and different nanoscale drug delivery systems (e.g., nanoparticles, liposomes, lipid nanocapsules, polymersomes). Their main characteristics (i.e., general structure and materials) are discussed, with special attention given to underlining the link between the physicochemical properties (e.g., surface areas, glass transition temperature, microviscosity, size, and shape) and release kinetics. An appropriate characterization of the drug, the excipients used, and the formulated drug delivery systems is necessary to achieve a deeper understanding of the release process and decrease variability originating from the drug delivery system. This task cannot be solved by otologists alone. The interdisciplinary cooperation between otology/neurotology, pharmaceutics, physics, and other disciplines will result in improved drug delivery systems for the inner ear.

Intracochlear drug delivery in combination with cochlear implants : Current aspects

Local drug application to the inner ear offers a number of advantages over systemic delivery. Local drug therapy currently encompasses extracochlear administration (i. e., through intratympanic injection), intracochlear administration (particularly for gene and stem cell therapy), as well as various combinations with auditory neurosensory prostheses, either evaluated in preclinical or clinical studies, or off-label. To improve rehabilitation with cochlear implants (CI), one focus is the development of drug-releasing electrode carriers, e. g., for delivery of glucocorticosteroids, antiapoptotic substances, or neurotrophins to the inner ear. The performance of cochlear implants may thus be improved by protecting neuronal structures from insertion trauma, reducing fibrosis in the inner ear, and by stimulating growth of neuronal structures in the direction of the electrodes. Controlled drug release after extracochlear or intracochlear application in conjunction with a CI can also be achieved by use of a biocompatible, resorbable controlled-release drug-delivery system. Two case reports for intracochlear controlled release drug delivery in combination with cochlear implants are presented. In order to treat progressive reduction in speech discrimination and increased impedance, two cochlear implant patients successfully underwent intracochlear placement of a biocompatible, resorbable drug-delivery system for controlled release of dexamethasone. The drug levels reached in inner ear fluids after different types of local drug application strategies can be calculated using a computer model. The intracochlear drug concentrations calculated in this way were compared for different dexamethasone application strategies.

[Implants for drug substance delivery]

Implants for controlled drug delivery can be very helpful to improve the therapeutic efficacy of a medical treatment, and at the same time reduce the risk of toxic side effects. In this article, four different strategies are exemplarily presented: hybrid bone substitutes combining hydroxyapatite and chitosan hydrogels; vascular stents coated with a bio-inspired polymer; cochlear implants for local dexamethasone delivery; and in-situ forming implants for periodontitis treatment. But this is only a restricted selection, and numerous other approaches and applications based on implants releasing a drug (or a combination of drugs) exist. Compared to conventional implants or pharmaceutical dosage forms, they might offer decisive advantages.

Trans-Oval-Window Implants, A New Approach for Drug Delivery to the Inner Ear: Extended Dexamethasone Release From Silicone-based Implants

HYPOTHESIS

The purpose of this study was to develop a new strategy to deliver drugs to the inner ear from dexamethasone (DXM)-loaded silicone implants and to evaluate the distribution of the drug in the cochlea with confocal microscopy.

BACKGROUND

Systemic drug administration for the treatment of inner ear disorders is tricky because of the blood-cochlear barrier, a difficult anatomical access, the small size of the cochlea, and can cause significant adverse effects. An effective way to overcome these obstacles is to administer drugs locally.

METHODS

In vitro, the drug release from DXM-loaded silicone-based thin films and tiny implants into artificial perilymph was thoroughly analyzed by high-performance liquid chromatography. In vivo, a silicone implant loaded with 10% DXM and 5% polyethylene glycol 400 was implanted next to the stapes's footplate of gerbils. Delivery of DXM into the inner ear was proved by confocal microscopy imaging of the whole cochlea and the organ of Corti.

RESULTS

The study showed a continuous and prolonged release during 90 days in vitro. This was confirmed by confocal microscopy that allowed detection of DXM by fluorescence labeling in the cell body of the hair cells for at least 30 days. Interestingly, fluorescence was already observed after 20 minutes of implantation, reached a climax at day 7, and could still be detected 30 days after implantation.

CONCLUSIONS

Thus, we developed a new device for local corticosteroids delivery into the oval window with an extended drug release of DXM to the inner ear.

How to adjust dexamethasone mobility in silicone matrices: A quantitative treatment

Silicone-based drug delivery systems offer a great potential to improve the therapeutic efficacy and safety of a large variety of medical treatments, e.g. allowing for local long-term delivery of active agents to the inner ear. Different formulation parameters can be varied to adjust desired drug release kinetics. However, often only qualitative information is available on their effects, and product optimization is cumbersome. The aim of this study was to provide a quantitative analysis, allowing also for theoretical predictions of the impact of the device design on system performance. Dexamethasone was incorporated into thin films based on different types of silicones (e.g. varying in the type of side chains and contents of amorphous silica), optionally containing different types and amounts of poly(ethylene glycol) (PEG) (5% or 10%). Furthermore, the initial drug content was altered (from 10% to 50%). In most cases, an analytical solution of Fick's second law could be used to describe the resulting drug release kinetics from the films and to determine the respective "apparent" diffusion coefficient of the drug (which varied from 2×10(-14) to 2×10(-12)cm(2)/s, depending on the system's composition). Thus, the impact of the investigated formulation parameters on drug mobility in the polymeric matrices could be quantitatively described. Importantly, the knowledge of the "apparent" drug diffusivity can be used to theoretically predict the resulting release kinetics from dosage forms of arbitrary size and shape. For instance, dexamethasone release was theoretically predicted from cylindrical extrudates based on a selection of different silicone types. Interestingly, these predictions could be confirmed by independent experiments. Hence, this type of quantitative analysis can replace time-consuming and cost-intensive series of trial-and-error experiments during product optimization. This is particularly helpful, if long-term drug release (e.g., during several weeks, months or years) is targeted.

In vitro and in vivo pharmacokinetic study of a dexamethasone-releasing silicone for cochlear implants

Cochlear implants have been widely used for patients with profound hearing loss and partial deafness. Residual low-frequency hearing, however, may deteriorate due to insertion trauma and tissue response around the electrode array. The present study investigated in vitro and in vivo release of dexamethasone from silicone used for cochlear implant electrode carriers. The in vitro experiment involved an apparatus simulating the inner ear fluid environment in humans. Release from two sizes of silicone films (200 µm × 1 mm × 10 mm and 500 µm × 1 mm × 10 mm), each loaded with 2 % dexamethasone, and was measured for 24 weeks. In the in vivo experiment, silicone rods loaded with 2 or 10 % dexamethasone, respectively, were implanted into the scala tympani of guinea pigs. Perilymph concentrations were measured during the first week after implantation. The results showed that dexamethasone was released from the silicone in a sustained manner. After a burst release, perilymph concentration was similar for silicone incorporated with 2 and 10 % dexamethasone, respectively. The similar pharmacokinetic profile was found in the in vitro experiment. The period of sustained drug delivery was maintained for 20 weeks in vitro and for 1 week in vivo. The results of the present study suggest that drugs like dexamethasone are released in a controlled manner from silicon electrode carriers of cochlear implants. Further studies will identify optimal release profiles for the use with cochlear implants to improve their safety and long-term performance.

Recent advances in local drug delivery to the inner ear

Inner ear diseases are not adequately treated by systemic drug administration mainly because of the blood-perilymph barrier that reduces exchanges between plasma and inner ear fluids. Local drug delivery methods including intratympanic and intracochlear administrations are currently developed to treat inner ear disorders more efficiently. Intratympanic administration is minimally invasive but relies on diffusion through middle ear barriers for drug entry into the cochlea, whereas intracochlear administration offers direct access to the colchlea but is rather invasive. A wide range of drug delivery systems or devices were evaluated in research and clinic over the last decade for inner ear applications. In this review, different strategies including medical devices, hydrogels and nanoparticulate systems for intratympanic administration, and cochlear implant coating or advanced medical devices for intracoclear administration were explored with special attention to in vivo studies. This review highlights the promising systems for future clinical applications as well as the current hurdles that remain to be overcome for efficient inner ear therapy.

Dexamethasone eluting electrodes for cochlear implantation: Effect on residual hearing

OBJECTIVE

The aim of this study was to compare a cochlear implant electrode array loaded with dexamethasone (DXM) with a conventional passive electrode array for the preservation of residual hearing in gerbils.

METHODS

Thirty Mongolian gerbils (Meriones unguiculatus) were implanted with an eluting electrode loaded with DXM (1 and 10%) on one side and a conventional passive electrode on the other side. Hearing thresholds were determined by tone bursts auditory brainstem responses at 4-6 weeks post-implantation and 1-year post-implantation for older gerbils.

RESULTS

After 4-6 weeks post-implantation, residual hearing was statistically more preserved with electrode arrays loaded with DXM, regardless of concentration, for the frequencies 16 000 Hz (P = 0.0008), 4000 Hz (P = 0.0038), 1000 Hz (P = 0.0349), and 500 Hz (P = 0.0030). After 1 year, the difference in favor of the DXM+ electrode array was found statistically significant only for the frequency 16 000 Hz (P = 0.0103) but against it for the frequencies 1000 Hz (P = 0.0368) and 500 Hz (P = 0.0010).

CONCLUSION

Electrode array with prolonged release of DXM improved short-term preservation of residual hearing after implantation for the frequencies 500, 1000, 4000, and 16 000 Hz in gerbils. The long-term results at 1 year confirmed these data for higher frequencies, but must be verified for the lower frequencies of 500 and 1000 Hz.

Combinatorial approach in the design of multifunctional polymeric nano-delivery systems for cancer therapy

This update summarizes the recent advances in combinatorial design of polymeric material for developing multifunctional nanovectors to deliver nucleic acids and chemodrugs for cancer therapy.

Artificial neural networks for bilateral prediction of formulation parameters and drug release profiles from cochlear implant coatings fabricated as porous monolithic devices based on silicone rubber

Objectives

The coating of cochlear implants for topical delivery of drugs, for example, corticosteroids, or antibiotics is a novel approach to manage post-surgical complications associated with cochlear implantation surgery like inflammation or infections. Many variables, including formulation parameters, can be changed to modulate the amount and duration of drug release from these devices. Mathematical modeling of drug release profile from a delivery system may be helpful to accelerate formulations in a more cost-efficient way. To attain specific in vitro drug release characteristics, a model should be capable to provide good estimates on the initial formulation parameters, for example, composition, geometry and drug loading vice versa. Here, artificial neural networks (ANNs) are used to predict dexamethasone (DEX) release profile and formulation parameters, bilaterally, from cochlear implant coatings designed as porous, monolithic silicone rubber-based matrices.

Methods

The devices were fabricated as monolithic dispersions of DEX in a silicone rubber matrix containing porogens. A newly developed mathematical function was fitted on the experimental DEX release curves, and the function coefficients were fed into the network as input variables to simulate drug release profile from the porous devices. Formulation variables consisted of drug loading percentage (0.05–0.5% w/w), porogen type (dextran (dext) or sodium chloride particles) and porogen content (5–40% w/w). The ANN was also examined to determine optimal levels of the formulation parameters to provide a specifically desired drug release profile.

Key findings

The results showed that DEX release profile from porous cochlear implant devices can be modelled accurately and precisely using ANN in order to predict optimal levels for the formulation parameters to provide a specific drug release profile vice versa.

Conclusions

The developed ANNs were used to achieve shorter formulation development process, and to provide tailor-made drug delivery regimens. ANNs were also successfully simulated non-linear relationships present between the initial formulation variable(s) and predict the subsequent drug release patterns.

Dexamethasone-releasing cochlear implant coatings: application of artificial neural networks for modelling of formulation parameters and drug release profile

Objectives

Over the past few decades, mathematical modelling and simulation of drug delivery systems has been steadily gained interest as a focus for academic and industrial attention. Here, simulation of dexamethasone (DEX, a corticosteroid anti-inflammatory agent) release profile from drug-eluting cochlear implant coatings is reported using artificial neural networks.

Methods

The devices were fabricated as monolithic dispersions of the pharmaceutically active ingredient in a silicone rubber matrix. A two-phase exponential model was fitted on the experimentally obtained DEX release profiles. An artificial neural network (ANN) was trained to determine formulation parameters (i.e. DEX loading percentage, the devices surface area and their geometry) for a specific experimentally obtained drug release profile. In a reverse strategy, an ANN was trained for determining expected drug release profiles for the same set of formulation parameters.

Key findings

An algorithm was developed by combining the two previously developed ANNs in a serial manner, and this was successfully used for simulating the developed drug-eluting cochlear implant coatings. The models were validated by a leave-one-out method and performing new experiments.

Conclusions

The developed ANN algorithms were capable to bilaterally predict drug release profile for a known set of formulation parameters or find out the levels for input formulation parameters to obtain a desired DEX release profile.

Developments in delivery of medications for inner ear disease

INTRODUCTION

Hearing loss, tinnitus and balance disturbance represent common diseases that have tremendous impact on quality of life. Despite the high incidence of inner ear disease in the general population, there are currently no dedicated pharmacologic interventions available to treat these problems.

AREAS COVERED

This review will focus on how treatment of inner ear disease is moving toward local delivery at the end organ level. The authors will discuss current practice, ongoing clinical trials and potential areas of development such as hair cell regeneration and neurotrophin therapy.

EXPERT OPINION

The inner ear is accessible through the middle ear via the oval and round windows allowing diffusion of drugs into the perilymph. With a better understanding of the physiology of the inner ear and the underlying molecular causes of inner ear disease there is great potential for the development of novel therapeutics that can be locally administered. At present, there is a rapid development of drugs to target diverse inner ear diseases that cause sensorineural hearing loss and balance dysfunction.