Trans-scleral iontophoretic delivery of low molecular weight therapeutics

Multi-physics simulations for investigating the effect of electrode conditions on transscleral ocular iontophoresis for particulate drug delivery into ocular tissues

Purpose

Transscleral ocular iontophoresis has been proposed to deliver charged particulate drugs to ocular tissues effectively by transmitting a weak electrical current through the sclera. The electric fields formed are influenced by the electrode conditions, thus affecting the amount of particulate drugs delivered to the ocular tissues via iontophoresis. Computational simulation is widely used to simulate drug concentrations in the eye; therefore, reflecting the characteristics of the drugs in living tissues to the simulations is important for a more precise estimation of drug concentration. In this study, we investigated the effect of electrode conditions (location and size) on the efficacy of transscleral iontophoresis.

Methods

We first determined the simulation parameters based on the comparison of the amount of drug in the sclera in the simulation and in vivo experimental results. The injection of the negatively charged nanoparticles into the cul-de-sac of the lower eyelid was simulated. The active electrode (cathode) was attached to the skin immediately above the injection site, while the return electrode (anode) was placed over the eyebrow. The drug concentration distribution in the eye, based on either the location or size of each electrode, was evaluated using the finite element method with the estimated simulation parameters.

Results

Our results indicate that drug permeability varies depending on the location and the size of the electrodes.

Conclusion

Our findings demonstrate that the determination of optimal electrode conditions is necessary to enhance the effectiveness of transscleral iontophoresis.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13534-024-00359-2.

Application of iontophoresis in ophthalmic practice: an innovative strategy to deliver drugs into the eye

Delivery of drugs to special locations of ocular lesions, while minimizing systemic and local toxic effects, is recognized as a critical challenge in the ophthalmic practice. The special anatomy and physiology barriers within the eyeball entail effective drug delivery systems. Emerging attempts in drug delivery has led to developments in ocular iontophoresis, which acts as a noninvasive technology to enhance drug penetration using a small electric current. This technique offers greater flexibility to deliver desired drug dose in a controlled and tolerable manner. In previous studies, this technique has been testified to deliver antibiotics, corticoid, proteins and other gene drugs into the eye with the potency of treating or alleviating diverse ophthalmological diseases including uveitis, cataract, retinoblastoma, herpes simplex and cytomegalovirus retinitis (CMVR), etc. In this review, we will introduce the recent developments in iontophoresis device. We also summarize the latest progress in coulomb controlled iontophoresis (CCI), hydrogel ionic circuit (HIC) and EyeGate II delivery system (EGDS), as well as overview the potential toxicity of iontophoresis. We will discuss these factors that affect the efficacy of iontophoresis experiments, and focus on the latest progress in its clinical application in the treatment of eye diseases.

Innovative Strategies for Drug Delivery to the Ocular Posterior Segment

Innovative and new drug delivery systems (DDSs) have recently been developed to vehicle treatments and drugs to the ocular posterior segment and the retina. New formulations and technological developments, such as nanotechnology, novel matrices, and non-traditional treatment strategies, open new perspectives in this field. The aim of this mini-review is to highlight promising strategies reported in the current literature based on innovative routes to overcome the anatomical and physiological barriers of the vitreoretinal structures. The paper also describes the challenges in finding appropriate and pertinent treatments that provide safety and efficacy and the problems related to patient compliance, acceptability, effectiveness, and sustained drug delivery. The clinical application of these experimental approaches can help pave the way for standardizing the use of DDSs in developing enhanced treatment strategies and personalized therapeutic options for ocular pathologies.

Non-Invasive Iontophoretic Delivery of Cytochrome c to the Posterior Segment and Determination of Its Ocular Biodistribution

The intact porcine eye globe model was used to demonstrate that transscleral iontophoresis could deliver a small protein, cytochrome c (Cyt c), to the posterior segment and to investigate post-iontophoretic biodistribution in the different ocular compartments. The effects of Cyt c concentration (1, 5, and 10 mg/mL), current density (3.5 and 5.5 mA/cm²), and duration of the current application (10 min and 1, 2, and 4 h) were evaluated. The data confirmed that transscleral iontophoresis enhanced the intraocular delivery of Cyt c under all conditions as compared to passive controls (same setup but without the current application). Increasing the Cyt c concentration resulted in a proportional enhancement in the Cyt c delivery. Increasing the current density from 3.5 to 5.5 mA/cm² increased iontophoretic delivery at a Cyt c concentration of 10 mg/mL but did not appear to do so at 5 mg/mL; this was attributed in part to the effect of melanin binding. Short duration iontophoresis (10 min, 3.5 mA/cm²) of a 10 mg/mL Cyt c solution created a depot in the sclera. When this was followed by a 4 h incubation period, post-iontophoretic Cyt c diffusion from the sclera resulted in a different biodistribution, and Cyt c could be quantified in the posterior segment.

Peptidomimetics Therapeutics for Retinal Disease

Ocular disorders originating in the retina can result in a partial or total loss of vision, making drug delivery to the retina of vital importance. However, effectively delivering drugs to the retina remains a challenge for ophthalmologists due to various anatomical and physicochemical barriers in the eye. This review introduces diverse administration routes and the accordant pharmacokinetic profiles of ocular drugs to aid in the development of safe and efficient drug delivery systems to the retina with a focus on peptidomimetics as a growing class of retinal drugs, which have great therapeutic potential and a high degree of specificity. We also discuss the pharmacokinetic profiles of small molecule drugs due to their structural similarity to small peptidomimetics. Lastly, various formulation strategies are suggested to overcome pharmacokinetic hurdles such as solubility, retention time, enzymatic degradation, tissue targeting, and membrane permeability. This knowledge can be used to help design ocular delivery platforms for peptidomimetics, not only for the treatment of various retinal diseases, but also for the selection of potential peptidomimetic drug targets.

Iontophoretic Dexamethasone Phosphate Compared to Topical Prednisolone Acetate 1% for Noninfectious Anterior Segment Uveitis

PURPOSE

To evaluate the safety and efficacy of dexamethasone phosphate ophthalmic solution (EGP-437) delivered by a transscleral iontophoresis delivery system (EyeGate II) compared to that of topical prednisolone acetate 1% (PA 1%) in subjects with noninfectious anterior uveitis.

DESIGN

Prospective, randomized, double-masked, parallel group, noninferiority clinical trial.

METHODS

A total of 193 subjects with active noninfectious anterior uveitis (anterior chamber [AC] cell count ≥11 cells) were randomized to EGP-437 delivered by iontophoresis (days 0 and 7) or self-administered PA 1% daily (tapered schedule, days 0-28). Masking was maintained with placebo iontophoresis or eye drops. The primary efficacy endpoint was the proportion of subjects with an AC cell count of zero on day 14. Noninferiority of EGP-437 was defined if the lower limit of the confidence interval (CI) for the difference (EGP-437 minus PA 1%) was less than -10%.

RESULTS

At day 14, 32 of 96 EGP-437 subjects (33.3%) and 32 of 97 PA 1% subjects (33.0%) had an AC cell count of zero (difference, 0.34; 95% CI, -12.94 to 13.63; P = 0.064). Efficacy trended better with EGP-437 among patients with more severe baseline uveitis (AC cell count >25). Safety and tolerability were good with both treatments. EGP-437 subjects experienced fewer IOP elevations ≥6 mm Hg versus PA 1% subjects (13 vs 24 incidents, respectively, through day 28).

CONCLUSIONS

Despite clinically similar response rates, statistical noninferiority of EGP-437 versus a tapered regimen of PA 1% was not achieved. Numerical trends suggesting fewer IOP elevations with EGP-437, similar efficacy overall, and possibly better efficacy in more severe disease warrant further study.

Ophthalmic Drug Delivery Using Iontophoresis: Recent Clinical Applications

Background: Iontophoresis is a noninvasive delivery system designed to overcome barriers to ocular penetration of topical ophthalmic medications by employing a low-amplitude electrical current to promote the migration of a charged drug substance across biological membranes. Trans-scleral iontophoresis of dexamethasone phosphate has demonstrated dramatically increased intraocular concentrations of dexamethasone in rabbit ocular tissues compared with topical instillation, including 50- to 100-fold greater aqueous humor concentrations. Methods: This article reviews available data on recent clinical applications of iontophoretic ophthalmic drug delivery. Results: The EyeGate II delivery system (EGDS) is a trans-scleral iontophoresis system that has been used in conjunction with EGP-437, a proprietary-charged formulation of dexamethasone phosphate for iontophoretic delivery. In patients with noninfectious anterior uveitis, EGP-437, delivered through 2 iontophoretic treatments using the EGDS, demonstrated similar efficacy to topical prednisolone acetate 1% eye drops instilled 8 times daily over 28 days, suggesting the potential to decrease or eliminate the need for daily dosing of topical steroids in this patient population. Other applications for EGP-437 delivered through the EGDS that have been explored in clinical trials include treatment of dry eye, postsurgical inflammation and pain, and scleritis. In addition, transcorneal iontophoresis has been used outside of the United States to enhance riboflavin penetration in patients undergoing corneal cross-linking as therapy for progressive keratoconus. Conclusions: The reviewed studies demonstrate the feasibility of using iontophoresis to enhance drug delivery to ocular tissues and support the potential of this noninvasive technique across a range of ophthalmic indications.

Targeting drug delivery within the suprachoroidal space

The suprachoroidal space (SCS), a potential anatomical space between the sclera and choroid, is a novel route for drug delivery targeting the chorioretinal layers of the eye. The safety and efficacy of SCS drug delivery have been shown in multiple clinical trials. Recent studies have developed methods for more precise targeting within the SCS at sites of action at the posterior pole (e.g., macula), near the limbus (e.g., ciliary body), and throughout the SCS using iontophoresis, swollen hydrogels, high-density particle emulsions, highly viscous and non-Newtonian fluids, and microstents. Here, we review novel technologies targeting the posterior, anterior, or entire SCS.

Selected Medicines Used in Iontophoresis

Iontophoresis is a non-invasive method of systemic and local drug delivery using an electric field. Iontophoresis enables diffusion of the selected drug via skin, mucosa, enamel, dentin, and other tissues. The amount of delivered therapeutic molecules is about 10⁻2000 times greater than conventional forms of delivery. Among other fields, this method is used in dentistry, ophthalmology, otorhinolaryngology, and dermatology. According to related literature, the most important drugs studied or administered by iontophoresis are: Local anesthetics, opioids, steroids, non-steroidal anti-inflammatory drugs, antibacterial drugs, antifungal drugs, antiviral drugs, anticancer drugs, fluorides, and vitamins. The present review covers current available data regarding the selected medicines used in iontophoresis. Furthermore, indications and conditions of iontophoresis application are reviewed.

Ocular drug delivery targeted by iontophoresis in the suprachoroidal space using a microneedle

Treatment of many posterior-segment ocular indications would benefit from improved targeting of drug delivery to the back of the eye. Here, we propose the use of iontophoresis to direct delivery of negatively charged nanoparticles through the suprachoroidal space (SCS) toward the posterior pole of the eye. Injection of nanoparticles into the SCS of the rabbit eye ex vivo without iontophoresis led to a nanoparticle distribution mostly localized at the site of injection near the limbus and <15% of nanoparticles delivered to the most posterior region of SCS (>9 mm from the limbus). Iontophoresis using a novel microneedle-based device increased posterior targeting with >30% of nanoparticles in the most posterior region of SCS. Posterior targeting increased with increasing iontophoresis current and increasing application time up to 3 min, but further increasing to 5 min was not better, probably due to the observed collapse of the SCS within 5 min after injection ex vivo. Reversing the direction of iontophoretic flow inhibited posterior targeting, with just ~5% of nanoparticles reaching the most posterior region of SCS. In the rabbit eye in vivo, iontophoresis at 0.14 mA for 3 min after injection of a 100 μL suspension of nanoparticles resulted in ~30% of nanoparticles delivered to the most posterior region of the SCS, which was consistent with ex vivo findings. The procedure was well tolerated, with only mild, transient tissue effects at the site of injection. We conclude that iontophoresis in the SCS using a microneedle has promise as a method to target ocular drug delivery within the eye, especially toward the posterior pole.

Overcoming ocular drug delivery barriers through the use of physical forces

Overcoming the physiological barriers in the eye remains a key obstacle in the field of ocular drug delivery. While ocular barriers naturally have a protective function, they also limit drug entry into the eye. Various pharmaceutical strategies, such as novel formulations and physical force-based techniques, have been investigated to weaken these barriers and transport therapeutic agents effectively to both the anterior and the posterior segments of the eye. This review summarizes and discusses the recent research progress in the field of ocular drug delivery with a focus on the application of physical methods, including electrical fields, sonophoresis, and microneedles, which can enhance penetration efficiency by transiently disrupting the ocular barriers in a minimally or non-invasive manner.

Ocular Drug Distribution and Safety of a Noninvasive Ocular Drug Delivery System of Dexamethasone Sodium Phosphate in Rabbit

PURPOSE

To determine the ocular toxicity, systemic exposure, and amounts of dexamethasone sodium phosphate (DSP) in ocular tissues after administration of DSP with the Visulex system (DSP-Visulex).

METHODS

DSP-Visulex was applied onto healthy rabbit eyes. DSP concentrations (4%, 8%, 15%, and 25%) and treatment durations (5, 10, and 20 min) were evaluated for the amounts of DSP in the ocular tissues and in plasma after single administrations of DSP-Visulex. The drug in eye tissues and plasma was analyzed by high-performance liquid chromatography-UV/VIS and by liquid chromatography-mass spectrometry, respectively. The safety and tolerability were ascertained based on clinical observations and histopathological examinations from repeat weekly DSP-Visulex treatments (4%, 8%, 15%, and 25% for 20 min) for 12 weeks.

RESULTS

Significant amounts of DSP (ie, higher than 1 μg/g) were found in the anterior chamber, retina-choroid, cornea, vitreous, conjunctiva, and sclera after single applications of DSP-Visulex. The DSP concentrations in the ocular tissues and in plasma increased with increased DSP concentrations in the Visulex applicator and with increased application times. Systemic DSP was rapidly detected. The plasma half-life was 2-3 h. C_max was 148 and 1,844 ng/mL, and the area under the plasma drug concentration versus time curve (AUC) was 418 and 3,779 ng · h/mL for the low dose (4% DSP-Visulex for 5 min) and the high dose (15% DSP-Visulex for 20 min), respectively. Ocular findings over 12 weeks were mostly conjunctival injection and eye discharge. These were transient and mild. Histopathological examinations indicated the eyes to be normal.

CONCLUSIONS

DSP can be administered safely and effectively into the rabbit eye with the Visulex system. Treatment duration and DSP concentration are important factors in achieving therapeutic levels. Repeat applications of DSP-Visulex are safe and well tolerated for weekly administrations over 4-12 weeks. DSP-Visulex has clinical potential for the noninvasive treatment of ocular diseases.

Transscleral passive and iontophoretic transport: theory and analysis

INTRODUCTION

The sclera is considered the 'static barrier,' a main barrier for transscleral drug delivery. The characterization of passive and iontophoretic transport across the sclera in vitro is the first step toward our ability to predict transscleral drug delivery. Although previous studies have investigated this topic, the quantitative structure permeation relationships (QSPR) for passive and iontophoretic transscleral transport are not available.

AREAS COVERED

This review evaluated previous results of transscleral passive and iontophoretic transport in vitro and examined QSPR for transscleral permeation of small permeants and macromolecules. Passive permeation data in the literature were compared with respective to the animal species employed in the studies. Data variability was investigated. Electrotransport theory and the mechanisms of iontophoresis were reviewed and used to analyze the iontophoresis data.

EXPERT OPINION

QSPR was examined for passive transscleral permeation, showing correlations between logarithm of permeability coefficient and logarithm of molecular weight. Potential causes of data variability were proposed. QSPR were established for electroosmosis using the molecular weight of neutral permeants and for iontophoresis enhancement using the molecular weight and charge of ionic permeants. However, QSPR for charged macromolecules were empirical; iontophoretic flux enhancement was significantly smaller than Nernst-Planck model prediction due to complicating factors.

Principles of pharmacology in the eye

The eye is a highly specialized organ that is subject to a huge range of pathology. Both local and systemic disease may affect different anatomical regions of the eye. The least invasive routes for ocular drug administration are topical (e.g. eye drops) and systemic (e.g. tablets) formulations. Barriers that subserve as protection against pathogen entry also restrict drug permeation. Topically administered drugs often display limited bioavailability due to many physical and biochemical barriers including the pre-corneal tear film, the structure and biophysiological properties of the cornea, the limited volume that can be accommodated by the cul-de-sac, the lacrimal drainage system and reflex tearing. The tissue layers of the cornea and conjunctiva are further key factors that act to restrict drug delivery. Using carriers that enhance viscosity or bind to the ocular surface increases bioavailability. Matching the pH and polarity of drug molecules to the tissue layers allows greater penetration. Drug delivery to the posterior segment is a greater challenge and, currently, the standard route is via intravitreal injection, notwithstanding the risks of endophthalmitis and retinal detachment with frequent injections. Intraocular implants that allow sustained drug release are at different stages of development. Novel exciting therapeutic approaches include methods for promoting transscleral delivery, sustained release devices, nanotechnology and gene therapy.

Non-invasive strategies for targeting the posterior segment of eye

The safe and effective treatment of eye diseases has been remained a global myth. Several advancements have been done and various drug delivery and treatment techniques have been suggested. The Posterior segment disorders are the leading cause of visual impairments and blindness. Targeting the therapeutic agents to the anterior and posterior segments of the eye has attracted extensive attention from the scientific community. Significant key factors in the success of ocular therapy are the development of safe, effective, economic and non-invasive novel drug delivery systems. These specialized non-invasive ocular drug delivery systems revolutionized the drug delivery strategies by overcoming the limitations, provided targeted delivery to the ocular tissues by avoiding larger doses, and reducing the toxicity encountered by the conventional approaches. These non-invasive systems are fabricated by ingredients encompassing biodegradability, biocompatibility, mucoadhesion, solubility and permeability enhancement and stimuli responsiveness. The variety of routes are utilized to provide minimally invasive drug delivery to the patients without any discomfort and pain. This review is focused on the brief introduction, types, significance, preparation techniques, components and mechanism of drug release of non-invasive systems, including in situ gelling systems, microspheres, iontophoresis, nanoparticles, nanosuspensions and specialized novel emulsions.

Review on Usage of Vancomycin in Livestock and Humans: Maintaining Its Efficacy, Prevention of Resistance and Alternative Therapy

Vancomycin is one of the “last-line” classes of antibiotics used in the treatment of life-threatening infections caused by Gram-positive bacteria. Even though vancomycin was discovered in the 1950s, it was widely used after the 1980s for the treatment of infections caused by methicillin-resistant Staphylococci, as the prevalence of these strains were increased. However, it is currently evident that vancomycin-resistant Staphylococcus aureus and vancomycin-resistant Enterococci have developed for various reasons, including the use of avaparcin—an analog of vancomycin—as a feed additive in livestock. Therefore, prophylactic and empiric use of antibiotics and their analogues need to be minimized. Herein we discuss the rational use of vancomycin in treating humans, horses, farm animals, and pet animals such as dogs, cats, and rabbits. In present day context, more attention should be paid to the prevention of the emergence of resistance to antibiotics in order to maintain their efficacy. In order to prevent emergence of resistance, proper guidance for the responsible use of antimicrobials is indispensable. Therefore, almost all stakeholders who use antibiotics should have an in-depth understanding of the antibiotic that they use. As such, it is imperative to be aware of the important aspects of vancomycin. In the present review, efforts have been made to discuss the pharmacokinetics and pharmacodynamics, indications, emergence of resistance, control of resistance, adverse effects, and alternative therapy for vancomycin.

The Future of Dry Eye Treatment: A Glance into the Therapeutic Pipeline

Dry eye syndrome is both a primary disease and a secondary result of many pathological states of the eye. The symptoms range from mild to severe itching, burning, irritation, eye fatigue, and even vision loss that can lead to disability. Dry eye affects approximately 60 million people worldwide; as a result, medications to treat dry eye comprise approximately 15% of the ophthalmic pharmaceutical market. While doctors and patients eagerly await new treatments, pharmaceuticals in the pipeline are moving through the approval process with several promising drugs having completed phase 3 clinical testing. This review summarizes the findings of studies of the most promising, upcoming dry eye treatments in phase 2 and 3 clinical trials in the USA.

Transcorneal iontophoresis of dendrimers: PAMAM corneal penetration and dexamethasone delivery

Iontophoresis of nanocarriers in the eye has been proposed to sustain drug delivery and maintain therapeutic concentrations. Fourth generation polyamidoamine (PAMAM) dendrimers are semi-rigid nanoparticles with surface groups that are easily modified. These dendrimers are known to modulate tight junctions, increase paracellular transport of small molecules and be translocated across epithelial barriers, exhibiting high uptake by different cell lines. The first aim of this study was to investigate the effect of iontophoresis on PAMAM penetration and distribution into the cornea. The second aim was to evaluate, ex vivo and in vivo, the effect of these dendrimers in dexamethasone (Dex) transcorneal iontophoresis. Anionic (PAMAM G3.5) and cationic (PAMAM G4) dendrimers were labeled with fluorescein isothiocyanate (FITC), and their distribution in the cornea was investigated using confocal microscopy after ex vivo anodal and cathodal iontophoresis for various application times. The particle size distribution and zeta potential of the dendrimers in an isosmotic solution were determined using dynamic light scattering and Nanoparticle Tracking Analysis (NTA), where the movement of small particles and the formation of large aggregates, from 5 to 100 nm, could be observed. Transcorneal iontophoresis increased the intensity and depth of PAMAM-FITC fluorescence in the cornea, suggesting improved transport of the dendrimers across the epithelium toward the stroma. PAMAM complexes with Dex were characterized by (13)C-NMR, (1)H-NMR and DOSY. PAMAM G3.5 and PAMAM G4 increased the aqueous solubility of Dex by 10.3 and 3.9-fold, respectively; however, the particle size distribution and zeta potential remained unchanged. PAMAM G3.5 decreased the Dex diffusion coefficient 48-fold compared with PAMAM G4. The ex vivo studies showed that iontophoresis increased the amount of Dex that penetrated into the cornea by 2.9, 5.6 and 3.0-fold for Dex, Dex-PAMAM G4 and Dex-PAMAM G3.5, respectively. In vivo experiments, however, revealed that iontophoresis of Dex-PAMAM-G3.5 increased Dex concentration in the aqueous humor by 6.6-fold, while iontophoresis of Dex-PAMAM G4 and Dex increased it 2.5 and 2-fold, respectively. Therefore, iontophoresis targeted PAMAM to the cornea but it is the sustained delivery of the Dex from PAMAM that prevents its rapid elimination from the aqueous humor. In conclusion, iontophoresis of PAMAM complexes represents a promising strategy for targeted and sustained topical drug delivery to the eye.

[Development of a novel transdermal delivery system of peptide and protein drugs using microneedle arrays]

Transdermal delivery of peptide and protein drugs may be limited by the stratum corneum, which is a protective barrier against the entry of microorganisms and water. Many approaches have been utilized to promote peptide and protein drugs delivery across the stratum corneum, including chemical enhancer modification and physical disruption of barrier function. However, it has been difficult to achieve therapeutic levels of peptide and protein drugs via this route without any skin irritation. Recently, attention has been paid to the possibility of using microneedle arrays in delivering peptide and protein drugs into the skin. As a novel and minimally invasive approach, microneedle arrays are capable of creating superficial pathways across the skin for peptide and protein drugs to achieve enhanced transdermal drug delivery. This method combines the efficacy of conventional injection needles with the convenience of transdermal patches, while minimizing the disadvantages of these administration methods. Therefore, microneedle arrays are a very useful alternative method for delivering peptide and protein drugs from the skin into the systemic circulation without any serious damage to skin. In this review, recent challenges in the developments of microneedle arrays for the delivery of peptide and protein drugs are summarized. Then, future developments of microneedle arrays for the delivery of peptide and protein drugs are also discussed in order to improve their therapeutic efficacy and safety.

One-Year Feasibility Study of Replenish MicroPump for Intravitreal Drug Delivery: A Pilot Study

PURPOSE

To determine the feasibility of the surgical procedure and to collect some safety data regarding the bioelectronics of a novel micro drug pump for intravitreal drug delivery in a Beagle dog model for up to 1 year.

METHODS

Thirteen Beagle dogs were assigned to two groups. The experimental group (n = 11) underwent pars plana implantation of MicroPump; the body of which was sutured episclerally, while its catheter was secured at a pars plana sclerotomy. The control group (n = 2) underwent sham surgeries in the form of a temporary suturing of the MicroPump, including placement of the pars plana tube. Baseline and follow-up exams included ophthalmic examination and imaging. The experimental animals were euthanized and explanted at predetermined time points after surgery (1, 3, and 12 months), while the control animals were euthanized at 3 months. All operated eyes were submitted for histopathology.

RESULTS

Eyes were scored according to a modified McDonald-Shadduck system and ophthalmic imaging. Neither the implanted eyes nor the control eyes showed clinically significant pathological changes beyond the expected surgical changes. The operated eyes showed neither significant inflammatory reaction nor tissue ingrowth through the sclerotomy site compared with the fellow eyes.

CONCLUSION

This study shows that the Replenish Posterior MicroPump could be successfully implanted with good safety profile in this animal model.

TRANSLATIONAL RELEVANCE

The results of this study in a Beagle dog model are supportive of the biocompatibility of Replenish MicroPump and pave the way to the use of these devices for ocular automated drug delivery after further testing in larger animal models.

Evaluation of ocular and general safety following repeated dosing of dexamethasone phosphate delivered by transscleral iontophoresis in rabbits

PURPOSE

To evaluate the toxicokinetics and tolerability (local ocular and general toxicity) of the anti-inflammatory agent, dexamethasone phosphate (a prodrug of dexamethasone) delivered to the eye in rabbits by transscleral iontophoresis.

METHODS

Female rabbits (n=6/group) received dexamethasone phosphate (40 mg/mL ophthalmic solution, EGP-437) transsclerally to the right eye (OD) using the Eyegate(®) II ocular iontophoresis delivery system once biweekly for 24 consecutive weeks at current doses of 10, 14, and 20 mA-min and current levels up to, and including -4 mA for 3.5-5 min. The study included 2 control groups (n=6/group): (1) a noniontophoresis control [an ocular applicator-loaded citrate buffer (placebo) without current] and (2) an iontophoresis control (a citrate buffer plus cathode iontophoresis at 20 mA-min, -4 mA for 5 min). Recoverability was evaluated 4 weeks following the last dose in 2 animals per group. The left eye (OS) was untreated and served as an internal control for each animal. Ocular and general safety of dexamethasone phosphate and dexamethasone were assessed. Other evaluations included toxicokinetics, ophthalmic examinations, intraocular pressure (IOP) measurements, electroretinographs, clinical observations, body weight, hematology and serum chemistry, gross necropsy, organ weight, and microscopic histopathology.

RESULTS

The biweekly transscleral iontophoresis with either the citrate buffer or dexamethasone phosphate at cathodic doses up to, and including 20 mA-min and currents up to, and including -4 mA for 24 weeks was well-tolerated. Transient signs of conjunctival hyperemia and chemosis, mild corneal opacity, and fluorescein staining of the cornea were noted and attributed to expected ocular reactions to the temporary placement of the ocular applicator and application of iontophoresis. There were no dexamethasone phosphate-, dexamethasone-, or iontophoresis-related effects on IOP, electroretinography, or histopathology. Reductions in body weight gain, anemia, decreased leukocyte and lymphocyte counts, compromised liver function, enlarged liver, and reduced spleen weight were consistent with systemic corticosteroid-mediated pharmacology, repeated use of anesthesia, stress, and sedentariness, and unlikely to be related to iontophoresis application.

CONCLUSIONS

The results of this investigation suggest that repeated transscleral iontophoresis with dexamethasone phosphate may be safe for use as a treatment for inflammatory ocular disorders that require prolonged and/or repeated corticosteroid therapy.

Emerging drugs for the treatment of dry eye disease

INTRODUCTION

Dry eye disease (DED) is a common, age-related ocular condition that in its mildest forms causes bothersome symptoms of ocular discomfort, fatigue, and visual disturbance that interfere with quality of life and in its more severe forms causes chronic pain and fluctuating vision. Though it is highly prevalent and costs billions of dollars to manage, current treatments have largely been inadequate, making it a frustrating condition, both for physicians and patients alike.

AREAS COVERED

This article will cover the recently discovered pathophysiology of DED that has prompted investigators to explore new molecules that target the core mechanisms that drive DED. These include anti-inflammatory/immune-modulatory drugs, secretagogues, lubricant, hormones, and autologous serum. Their potential mechanism of action and data from recent trials on efficacy/safety will be reviewed.

EXPERT OPINION

The emerging drugs have a vast range of putative mechanisms of action that may not only provide symptomatic relief but may potentially break the vicious cycle of DED and provide long-lasting cure. Current and future research may change our perspective on DED and redefine its treatment algorithms.

Effect of iontophoresis on the in vitro trans-scleral transport of three single stranded oligonucleotides

Oligonucleotides represent a subject of clinical interest due to their potential ability to treat several diseases, including those affecting the posterior segment of the eye. Unfortunately, therapeutic oligonucleotides are currently administered by means of highly invasive approaches, such as intravitreal injections. The aim of the present work was to study in vitro, across isolated bovine sclera, the effect of iontophoresis on the transport of three single stranded oligonucleotides (ssDNA), 12-, 24- and 36-mer, selected as reference compounds in view of a non-invasive drug delivery to the back of the eye. All the three sequences were able to cross bovine sclera in vitro without iontophoresis. When anodal iontophoresis was applied, no change in flux was observed, while in the presence of cathodal iontophoresis the permeability coefficients increased four-fold compared to passive conditions. This behavior can be ascribed to the electrorepulsive mechanism, due to the negative charge of the nucleic acid backbone. It was also observed that the molecular weights of the three sequences did not affect trans-scleral transport, neither in passive, nor in current assisted permeation. Furthermore, increasing the current intensity from 1.75 mA to 3 mA, no effect on the trans-scleral transport of the 24-mer was noticed. Although preliminary, the results demonstrate that cathodal iontophoresis enhances trans-scleral transport of single stranded oligonucleotides and suggest its use as a novel non-invasive approach for the treatment of diseases affecting the posterior segment of the eye.

Sustained release micellar carrier systems for iontophoretic transport of dexamethasone across human sclera

A challenge in ocular drug delivery is to maintain the therapeutic concentration of a drug at the site of action in the eye. The objective of the present study was to investigate the feasibility of micellar carrier systems for sustained drug delivery in transscleral iontophoresis in vitro. Simple and mixed micelles prepared using sodium taurocholate (TA) alone or with egg lecithin (LE) were the carrier systems studied. Dexamethasone (DEX), a poorly water soluble corticosteroid, was the model drug. The micellar carrier systems were first characterized for their solubilization and encapsulation of the drug. Passive and 2-mA iontophoretic (both cathodal and anodal) transport experiments were conducted using these micellar carrier systems in side-by-side diffusion cells with excised human sclera in vitro. Drug release studies were performed after the transport experiments. Saturated DEX solution without the micellar carriers was used as a control. It was found that the solubilization capacity of the micellar carrier systems increased as the total lipid concentration of the systems increased. Drug release from the sclera was significantly prolonged with the micellar carrier systems as compared to the control after passive and iontophoretic delivery. Less than ~20% of DEX was released from the sclera in approximately 2h after cathodal iontophoretic delivery of the micellar carrier systems, whereas more than ~50% of DEX was released from the control in the same time period under the same condition. Micellar carrier systems can be a suitable transscleral drug delivery system for poorly water soluble drugs by enhancing their aqueous solubilities and providing sustained drug delivery. These micellar carrier systems can be efficiently delivered into and across the sclera by iontophoresis for drug delivery.

Iontophoretic drug delivery across the nail

INTRODUCTION

Topical drug delivery to treat nail diseases such as onychomycosis and psoriasis is receiving increasing attention. Topical nail delivery is challenged by the complicated structure of the nail and the low permeability of most drugs across the nail plate. Considerable effort has been directed at developing methods to promote drug permeation across the nail plate. Iontophoresis efficiently enhances molecular transport across the skin and the eye and is now being tested for its potential in ungual delivery.

AREAS COVERED

This review covers the basic mechanisms of transport (electro-osmosis and -migration) and their relative contribution to nail iontophoresis as well as the key factors governing nail permselectivity and ionic transport numbers. Methodological issues concerning research in this area are summarized. The data available in vivo on nail iontophoresis of terbinafine specifically are reviewed in separate sections.

EXPERT OPINION

Our understanding of nail iontophoresis has improved considerably since 2007; most decisively, the feasibility of nail iontophoresis in vivo has been clearly demonstrated. Future work is required to establish the adequate implementation of the technique so that its clinical efficacy to treat onychomycosis and nail psoriasis can be unequivocally determined.

Evaluation of dexamethasone phosphate delivered by ocular iontophoresis for treating noninfectious anterior uveitis

PURPOSE

Determine safe, effective, iontophoretic dose(s) of EGP-437 (dexamethasone phosphate formulated for iontophoresis) in patients with noninfectious anterior uveitis; evaluate systemic drug exposures.

DESIGN

Prospective, phase I/II, multicenter, double-masked, parallel group, randomized clinical trial.

PARTICIPANTS

Forty outpatients with anterior uveitis.

METHODS

Forty of 42 randomized patients received an iontophoresis treatment in 1 qualifying eye and completed the study. Patients were randomized into 1 of 4 iontophoresis dose groups (1.6, 4.8, 10.0, or 14.0 mA-min), treated with EGP-437 via the EyeGate II Delivery System (EGDS), and followed until day 28.

MAIN OUTCOME MEASURES

The main outcome measures were anterior chamber cell (ACC) scores at days 14 and 28; time to ACC score of zero; proportion of patients with an ACC score reduction from baseline of ≥ 0.5 at day 28; mean change from baseline in ACC score at day 28; and the systemic exposures of dexamethasone and dexamethasone phosphate after EGP-437 treatment with the EGDS.

RESULTS

After a single EGP-437 treatment, 19 of 40 patients (48%) achieved an ACC score of zero at day 14. By day 28, 24 of 40 patients (60%) achieved an ACC score of zero. A Kaplan-Meier analysis demonstrated that the 1.6 mA-min dose was the most effective and revealed an inverse dose response; median days to an ACC score of zero were 11.5 days in the 1.6 mA-min group versus 31 days in the 14.0 mA-min group. Twenty-six patients (65%) had an ACC score reduction from baseline of ≥ 0.5 at day 28. The mean change in ACC score from baseline to day 28 was -2.14 with a median of -2.00. Throughout the study, the mean intraocular pressure remained within normal range and mean best-corrected visual acuity at 4 meters remained relatively stable. Most adverse events were mild; no serious adverse events were reported. Pharmacokinetics results showed low short-term systemic exposure to dexamethasone after iontophoresis; no nonocular systemic corticosteroid-mediated effects were observed.

CONCLUSIONS

Approximately two thirds of the patients reached an ACC score of zero within 28 days, after only receiving 1 iontophoresis treatment. The lower doses seemed to be the most effective, and treatments were well-tolerated.

FINANCIAL DISCLOSURE(S)

Proprietary or commercial disclosure may be found after the references.

Trans-scleral delivery of macromolecules

Non-invasive drug delivery to the posterior segment of the eye represents an important unmet medical need, and trans-scleral delivery could be an interesting solution. This review analyses the possibility of trans-scleral drug delivery for high molecular weight compounds, such as proteins and genetic material, which currently represent the most innovative and efficacious molecules for the treatment of many diseases of the posterior segment of the eye. The paper reviews all the barriers, both static and dynamic, involved in trans-scleral administration of drugs, trying to elucidate the role of each of them in the specific case of macromolecules. Delivery systems to sustain drug release and enhancing strategies to improve trans-scleral penetration are also described. Finally, the review approaches the use of computational models as a screening tool to evaluate the feasibility of trans-scleral administration for macromolecules.

Ocular iontophoresis of EGP-437 (dexamethasone phosphate) in dry eye patients: results of a randomized clinical trial

PURPOSE

To assess safety and efficacy of EGP-437 (dexamethasone phosphate 40 mg/mL [DP]) in dry eye patients.

METHODS

The study employed a prospective, single-center, double-masked design utilizing a Controlled Adverse Environment (CAE). Patients (n = 103) with confirmed signs and symptoms of dry eye syndrome were randomized into 1 of 3 iontophoresis treatment groups: 7.5 mA-min at 2.5 mA (DP 7.5, n = 41); 10.5 mA-min at 3.5 mA (DP 10.5, n = 37); or 10.5 mA-min at 3.5 mA (placebo, n = 25). Three CAE visits and 4 follow-up visits occurred over 3 weeks. Patients meeting enrollment criteria received iontophoresis in both eyes after the second CAE exposure (visit 3) and before the third CAE exposure (visit 5). Primary efficacy endpoints were corneal staining and ocular discomfort. Secondary endpoints included tear film break-up time, ocular protection index (OPI), and symptomatology.

RESULTS

The DP 7.5 and DP 10.5 treatment groups showed statistically significant improvements in signs and symptoms of dry eye at various time points; however, the primary endpoints were not achieved. The DP 7.5 treatment group exhibited statistically significant improvements in corneal staining (when comparing the differences between study entry and exit, 3 weeks, P = 0.039), OPI (immediately following the second treatment, P = 0.048) and ocular discomfort at follow-up visits (a week after the first treatment, P = 0.032; 24 hours after the second treatment, P = 0.0032). Treatment-emergent adverse events (AEs) were experienced by 87% of patients and were consistent across all treatment groups. Most AEs were mild and no severe AEs were observed.

CONCLUSION

Ocular iontophoresis of EGP-437 demonstrated statistically and clinically significant improvements in signs and symptoms of dry eye syndrome within a CAE model.