Sustained reduction of intraocular pressure by supraciliary delivery of brimonidine-loaded poly(lactic acid) microspheres for the treatment of glaucoma

Hollow microneedles for ocular drug delivery

Microneedles (MNs) are micron-sized needles, typically <2 mm in length, arranged either as an array or as single needle. These MNs offer a minimally invasive approach to ocular drug delivery due to their micron size (reducing tissue damage compared to that of hypodermic needles) and overcoming significant barriers in drug administration. While various types of MNs have been extensively researched, significant progress has been made in the use of hollow MNs (HMNs) for ocular drug delivery, specifically through suprachoroidal injections. The suprachoroidal space, situated between the sclera and choroid, has been targeted using optical coherence tomography-guided injections of HMNs for the treatment of uveitis. Unlike other MNs, HMNs can deliver larger volumes of formulations to the eye. This review primarily focuses on the use of HMNs in ocular drug delivery and explores their ocular anatomy and the distribution of formulations following potential HMN administration routes. Additionally, this review focuses on the influence of formulation characteristics (e.g., solution viscosity, particle size), HMN properties (e.g., bore or lumen diameter, MN length), and routes of administration (e.g., periocular transscleral, suprachoroidal, intravitreal) on the ocular distribution of drugs. Overall, this paper highlights the distinctive properties of HMNs, which make them a promising technology for improving drug delivery efficiency, precision, and patient outcomes in the treatment of ocular diseases.

Copolyester toughened poly(lactic acid) biodegradable material prepared by in situ formation of polyethylene glycol and citric acid

Polylactic acid (PLA) is a high-modulus, high-strength bio-based thermoplastic polyester with good biodegradability, which is currently a promising environmentally friendly material. However, its inherent brittleness has hindered its widespread use. In this study, we reported a simple and non-toxic strategy for toughening PLA, using biodegradable materials such as polyethylene glycol (PEG) and citric acid (CA) as precursors. Through reactive melt blending with PLA, PEG and CA form PEGCA copolyesters in situ during blending. At the same time, CA can react with PLA and PEG, forming a copolyester structure at the interface of the two phases, improving the interfacial compatibility between PEG and PEGCA with PLA. Fourier transform infrared spectroscopy confirms this. Experimental results show that when the content of PEG/CA reaches 15% (PLA/PEG/CA-15%) in the blends, the impact strength of the blend was 4.47 kJ m-2, and the maximum elongation at break was as high as 360.1%, which were about 2 and 44 times higher than those of pure PLA, respectively. Moreover, the tensile strength was still maintained at the level of 70%. This work can expand the application of PLA in food packaging and medical supplies.

Polymeric microneedles for the eye: An overview of advances and ocular applications for minimally invasive drug delivery

Ocular drug delivery is challenging due to the presence of tissue barriers and clearance mechanisms. Most widely used topical formulations need frequent application because of poor permeability, short retention, and low bioavailability. Invasive intraocular injections and implants that deliver drugs at the target site are associated with infections, inflammation, and even vision loss post-use. These gaps can be addressed by a delivery platform that can efficiently deliver drug with minimal tissue damage. Microneedles were introduced as a delivery platform for overcoming dermal barriers with minimal tissue damage. After the successful clinical transition of microneedles in the transdermal drug delivery, they are now being extensively studied for ocular applications. The attributes of minimally invasive application and the capability to deliver a wide range of therapeutics make microneedles an attractive candidate for ocular drug delivery. The current manuscript provides a detailed overview of the recent advancements in the field of microneedles for ocular use. This paper reviews research focusing on polymeric microneedles and their pharmaceutical and biopharmaceutical properties. A brief discussion about their clinical translation and regulatory concerns is also covered. The multitude of research articles supports the fact that microneedles are a potential, minimally invasive drug delivery platform for ophthalmic use.

Design and ex vivo development of a suprachoroidal spacer implant to treat glaucoma

Glaucoma is a leading cause of visual impairment and blindness in the United States and worldwide. Elevated intraocular pressure (IOP) has been identified as the only modifiable risk factor in glaucoma, and there exists a need for a glaucoma procedure that is safe, efficacious, and can be performed in the outpatient clinic setting. Suprachoroidal expansion has been explored as a method to lower IOP previously. The purpose of this work was to design a monolithic hydrogel implant that would not clear or degrade to potentially achieve long term (possibly permanent) IOP reduction. Here, we developed and showed ex vivo testing of a novel photo-crosslinked polyethylene glycol (PEG) suprachoroidal spacer implant delivered via a custom-designed injector system. We optimized the composition, shape, and mechanics of the implant to be suitable for implantation with the suprachoroidal space. We developed a microneedle injector system to deliver this implant. We showed precise control over implant location and volume occupied within the suprachoroidal space. Further preclinical testing is needed to demonstrate efficacy.

Mechanism and application of β-adrenoceptor blockers in soft tissue wound healing

Soft tissue damage stimulates sympathetic nerves to release large amounts of catecholamine hormones which bind to β-adrenergic receptors (β-ARs) on the cell membrane surface. It activates the downstream effector molecules and impairs soft tissue wound healing. β-blockers specifically inhibit β-ARs activation in acute/chronic skin lesions and ulcerative hemangiomas. They also accelerate soft tissue wound healing by shortening the duration of inflammation, speeding keratinocyte migration and reepithelialization, promoting wound contraction and angiogenesis, and inhibiting bacterial virulence effects. In addition, β-blockers shorten wound healing periods in patients with severe thermal damage by reducing the hypermetabolic response. While β-blockers promote/inhibit corneal epithelial cell regeneration and restores limbal stem/progenitor cells function, it could well accelerate/delay corneal wound healing. Given these meaningful effects, a growing number of studies are focused on examining the efficacy and safety of β-blockers in soft tissue wound repair, including acute and chronic wounds, severe thermal damage, ulcerated infantile hemangioma, corneal wounds, and other soft tissue disorders. However, an intensive investigation on their acting mechanisms is imperatively needed. The purpose of this article is to summerize the roles of β-blockers in soft tissue wound healing and explore their clinical applications.

Stimulus-Responsive Hydrogels as Drug Delivery Systems for Inflammation Targeted Therapy

Deregulated inflammations induced by various factors are one of the most common diseases in people's daily life, while severe inflammation can even lead to death. Thus, the efficient treatment of inflammation has always been the hot topic in the research of medicine. In the past decades, as a potential biomaterial, stimuli-responsive hydrogels have been a focus of attention for the inflammation treatment due to their excellent biocompatibility and design flexibility. Recently, thanks to the rapid development of nanotechnology and material science, more and more efforts have been made to develop safer, more personal and more effective hydrogels for the therapy of some frequent but tough inflammations such as sepsis, rheumatoid arthritis, osteoarthritis, periodontitis, and ulcerative colitis. Herein, from recent studies and articles, the conventional and emerging hydrogels in the delivery of anti-inflammatory drugs and the therapy for various inflammations are summarized. And their prospects of clinical translation and future development are also discussed in further detail.

Microneedles for advanced ocular drug delivery

In the field of ocular drug delivery, topical delivery remains the most common treatment option for managing anterior segment diseases, whileintraocular injectionsare the current gold standard treatment option for treating posterior segment diseases. Nonetheless, topical eye drops are associated with low bioavailability (<5%), and theintravitreal administration procedure is highly invasive, yielding poor patient acceptability. In both cases, frequent administration is currently required. As a result, there is a clear unmet need for sustained drug delivery to the eye, particularly in a manner that can be localised. Microneedles, which are patches containing an array of micron-scale needles (<1 mm), have the potential to meet this need. These platforms can enable localised drug delivery to the eye while enhancing penetration of drug molecules through key ocular barriers, thereby improving overall therapeutic outcomes. Moreover, the minimally invasive manner in which microneedles are applied could provide significant advantages over traditional intravitreal injections regarding patient acceptability. Considering the benefitsofthis novel ocular delivery system, this review provides an in-depth overviewofthe microneedle systems for ocular drug delivery, including the types of microneedles used and therapeutics delivered. Notably, we outline and discuss the current challenges associated with the clinical translation of these platforms and offer opinions on factors which should be considered to improve such transition from lab to clinic.

Suprachoroidal Injection: A Novel Approach for Targeted Drug Delivery

Treating posterior segment and retinal diseases poses challenges due to the complex structures in the eye that act as robust barriers, limiting medication delivery and bioavailability. This necessitates frequent dosing, typically via eye drops or intravitreal injections, to manage diseases, often leading to side effects with long-term use. Suprachoroidal injection is a novel approach for targeted drug delivery to the posterior segment. The suprachoroidal space is the region between the sclera and the choroid and provides a potential route for minimally invasive medication delivery. Through a more targeted delivery to the posterior segment, this method offers advantages over other routes of administration, such as higher drug concentrations, increased bioavailability, and prolonged duration of action. Additionally, this approach minimizes the risk of corticosteroid-related adverse events such as cataracts and intraocular pressure elevation via compartmentalization. This review focuses on preclinical and clinical studies published between 2019 and 2023, highlighting the potential of suprachoroidal injection in treating a variety of posterior segment diseases. However, to fully harness its potential, more research is needed to address current challenges and limitations, such as the need for technological advancements, refinement of injection techniques, and consideration of cost and accessibility factors. Future studies exploring its use in conjunction with biotech products, gene therapies, and cell-based therapies can lead to personalized treatments that can revolutionize the field of ophthalmology.

Recent Advances of Ocular Drug Delivery Systems: Prominence of Ocular Implants for Chronic Eye Diseases

Chronic ocular diseases can seriously impact the eyes and could potentially result in blindness or serious vision loss. According to the most recent data from the WHO, there are more than 2 billion visually impaired people in the world. Therefore, it is pivotal to develop more sophisticated, long-acting drug delivery systems/devices to treat chronic eye conditions. This review covers several drug delivery nanocarriers that can control chronic eye disorders non-invasively. However, most of the developed nanocarriers are still in preclinical or clinical stages. Long-acting drug delivery systems, such as inserts and implants, constitute the majority of the clinically used methods for the treatment of chronic eye diseases due to their steady state release, persistent therapeutic activity, and ability to bypass most ocular barriers. However, implants are considered invasive drug delivery technologies, especially those that are nonbiodegradable. Furthermore, in vitro characterization approaches, although useful, are limited in mimicking or truly representing the in vivo environment. This review focuses on long-acting drug delivery systems (LADDS), particularly implantable drug delivery systems (IDDS), their formulation, methods of characterization, and clinical application for the treatment of eye diseases.

Intraocular nano-microscale drug delivery systems for glaucoma treatment: design strategies and recent progress

Glaucoma is a leading cause of irreversible visual impairment and blindness, affecting over 76.0 million people worldwide in 2020, with a predicted increase to 111.8 million by 2040. Hypotensive eye drops remain the gold standard for glaucoma treatment, while inadequate patient adherence to medication regimens and poor bioavailability of drugs to target tissues are major obstacles to effective treatment outcomes. Nano/micro-pharmaceuticals, with diverse spectra and abilities, may represent a hope of removing these obstacles. This review describes a set of intraocular nano/micro drug delivery systems involved in glaucoma treatment. Particularly, it investigates the structures, properties, and preclinical evidence supporting the use of these systems in glaucoma, followed by discussing the route of administration, the design of systems, and factors affecting in vivo performance. Finally, it concludes by highlighting the emerging notion as an attractive approach to address the unmet needs for managing glaucoma.

Preparation and Characterization of Ion-Sensitive Brimonidine Tartrate In Situ Gel for Ocular Delivery

Brimonidine tartrate (BRT) is a highly selective α2 adrenergic receptor agonist as treatment for patients with open angle glaucoma and high intraocular pressure. The objective of this study was to formulate an ophthalmic ion-sensitive in situ gel (ISG) of BRT to increase the retention time of the drug and its bioavailability. The optimum formulation of 2 mg/mL BRT-ISG was obtained with 0.45% gellan gum as the gel matrix. In vitro release results showed that the water-soluble drug bromonidine tartrate in ocular in situ gels exhibited a high burst effect and fast release in solution. The results of dialysis membrane permeation showed that there was a significant difference between the commercially available and BRT-ISG groups after 45 min. The results of the pre-corneal retention study indicated that gellan gum can effectively prolong ocular surface retention. Preliminary stability results showed that it should be stored in a cool and dark place, and the formulation under long-term preservation can be basically stable. The pharmacokinetic study of the BRT-ISG in the anterior chamber of the rabbit eye was studied by microdialysis technique, and microdialysis samples were analyzed by LC-MS/MS. The pharmacokinetic study showed that the BRT-ISG reached Cmax (8.16 mg/L) at 93 min after administration, which was 2.7 times that of the BRT eye drops, and the AUC(0-t) (1397.08 mg·min/L) was 3.4 times that of the BRT eye drops. The optimal prescription can prolong the retention time of BRT in front of the cornea and significantly improve the bioavailability of BRT in the eye. Combined with the results of in vitro release, permeation and pre-corneal retention studies, the improvement of BRT-ISG bioavailability in rabbit eyes was found to be mainly due to the retention effect after the mixture of ISG and tears.

Sustained release glaucoma therapies: Novel modalities for overcoming key treatment barriers associated with topical medications

Glaucoma is a progressive optic neuropathy and a leading cause of irreversible blindness. The disease has conventionally been characterized by an elevated intraocular pressure (IOP); however, recent research has built the consensus that glaucoma is not only dependent on IOP but rather represents a multifactorial optic neuropathy. Although many risk factors have been identified ranging from demographics to co-morbidities to ocular structural predispositions, IOP is currently the only modifiable risk factor, most often treated by topical IOP-lowering medications. However, topical hypotensive regimens are prone to non-adherence and are largely inefficient, leading to disease progression in spite of treatment. As a result, several companies are developing sustained release (SR) drug delivery systems as alternatives to topical delivery to potentially overcome these barriers. Currently, Bimatoprost SR (Durysta^TM) from Allergan plc is the only FDA-approved SR therapy for POAG. Other SR therapies under investigation include: bimatoprost ocular ring (Allergan) (ClinicalTrials.gov identifier: NCT01915940), iDose^® (Glaukos Corporation) (NCT03519386), ENV515 (Envisia Therapeutics) (NCT02371746), OTX-TP (Ocular Therapeutix) (NCT02914509), OTX-TIC (Ocular Therapeutix) (NCT04060144), and latanoprost free acid SR (PolyActiva) (NCT04060758). Additionally, a wide variety of technologies for SR therapeutics are under investigation including ocular surface drug delivery systems such as contact lenses and nanotechnology. While challenges remain for SR drug delivery technology in POAG management, this technology may shift treatment paradigms and dramatically improve outcomes.

Six-month sustained delivery of anti-VEGF from in-situ forming hydrogel in the suprachoroidal space

Patients with wet age-related macular degeneration (AMD) require intravitreal injections of bevacizumab (Bev) or other drugs, often on a monthly basis, which is a burden on the healthcare system. Here, we developed an in-situ forming hydrogel comprised of Bev and hyaluronic acid (HA) crosslinked with poly(ethylene glycol) diacrylate for slow release of Bev after injection into the suprachoroidal space (SCS) of the eye using a microneedle. Liquid Bev formulations were cleared from SCS within 5 days, even when formulated with high viscosity, unless Bev was conjugated to a high molecular-weight HA (2.6 MDa), which delayed clearance until 1 month. To extend release to 6 months, we synthesized in-situ forming Bev-HA hydrogel initially as a low-viscosity mixture suitable for injection and flow in the SCS to cover a large area extending to the posterior pole of the eye where the macula is located in humans. Within 1 h after injection, Bev and HA were crosslinked, which retained Bev for slow release as the hydrogel biodegraded. In vivo studies in the rabbit eye reported Bev release for >6 months, depending on gel formulation and Bev assay. The in-situ forming Bev-HA hydrogel was well tolerated, as assessed by clinical exam, fundus imaging, histological analysis, and intraocular pressure measurement. We conclude that Bev released from an in-situ forming hydrogel may enable long-acting treatments of AMD and other posterior ocular indications.

Suprachoroidal delivery enables targeting, localization and durability of small molecule suspensions

Drug delivery to the suprachoroidal space (SCS®) has become a clinical reality after the 2021 FDA approval of CLS-TA, a triamcinolone acetonide injectable suspension for suprachoroidal use (XIPERE®), administered via a microneedle-based device, the SCS Microinjector®. Suprachoroidal (SC) delivery facilitates targeting, compartmentalization, and durability of small molecule suspensions, thereby potentially addressing some of the efficacy, safety, and treatment burden limitations of current retinal therapies. Herein, the design features of the SCS Microinjector are reviewed, along with the biomechanics of SC drug delivery. Also presented are preclinical evaluations of SC small molecule suspensions from 4 different therapeutic classes (plasma kallikrein inhibitor, receptor tyrosine kinase inhibitor, corticosteroid, complement factor D inhibitor), highlighting their potential for durability, targeted compartmentalization, and acceptable safety profiles following microinjector-based SC delivery. The clinical evaluations of the safety, tolerability and efficacy of SC delivered triamcinolone further supports potential of SC small molecule suspensions as a clinically viable strategy for the treatment of chorioretinal diseases. Also highlighted are current limitations, key pharmacological considerations, and future opportunities to optimize the SC microinjector platform for safe, effective, and potentially long-acting drug delivery for the treatment of chorioretinal disorders.

Iontophoretic ocular delivery of latanoprost-loaded nanoparticles via skin-attached electrodes

Prolonged drug efficacy to reduce the number of administrations is a key factor in the successful treatment of glaucoma through topical drug delivery to the eye. Therefore, we propose a new strategy for iontophoretic ocular delivery of drug-loaded nanoparticles. Considering safety and convenience, our strategy is involved with topical administration of the drug-loaded nanoparticles followed by their permeation into the eye tissues via noninvasive iontophoresis, using the skin-attached electrodes. Thus, those nanoparticles stayed longer in the eye, and during this period, the drug was released in a sustained manner, thereby prolonging drug exposure even with one-time treatment. The nanoparticles were made of poly(lactic-co-glycolic acid) (PLGA), which were loaded with a glaucoma drug, latanoprost. We varied the size of the nanoparticles at 100, 200, 300, and 500 nm and sought to find the optimum size under the fixed conditions for iontophoresis proposed in this work (4 mA; 30 min). Even with iontophoresis through the skin-attached electrodes, the nanoparticles were indeed deposited in the eye tissues, where with an increase in particle size, drug release was more sustained, but fewer particles could permeate into the eye tissues. Because of these two competing factors, iontophoretic delivery of the 300-nm particles exhibited the most prolonged drug efficacy in vivo for more than 7 days, and showed an approximately 23-fold increase in drug efficacy compared with that of Xalatan®, a commercially available eye drop of latanoprost developed for once-a-day administration every day. STATEMENT OF SIGNIFICANCE: To treat glaucoma, conventional eye drops are often prescribed; however, they often require multiple daily administrations due to rapid preocular clearance. To resolve this, we suggest a noninvasive iontophoretic ocular delivery of latanoprost-loaded PLGA nanoparticles using the skin-attached electrodes. Even with iontophoresis via the skin-attached electrodes, the nanoparticles can indeed be deposited into the eye tissues. However, with an increase in particle size, fewer particles can permeate into the eye tissues, although drug release is more sustained. Therefore, the particles with a size of 300 nm show the optimal in vivo delivery profile in this work, where the drug efficacy can be extended for more than 7 days with a single administration.

Sustained release of brimonidine from BRI@SR@TPU implant for treatment of glaucoma

Glaucoma is the leading cause of irreversible vision loss worldwide, and reduction of intraocular pressure (IOP) is the only factor that can be interfered to delay disease progression. As the first line and preferred method to treat glaucoma, eye drops have many shortcomings, such as low bioavailability, poor patient compliance, and unsustainable therapeutic effect. In this study, a highly efficient brimonidine (BRI) silicone rubber implant (BRI@SR@TPU implant) has been designed, prepared, characterized, and administrated for sustained relief of IOP to treat glaucoma. The in vitro BRI release from BRI@SR@TPU implants shows a sustainable release profile for up to 35 d, with decreased burst release and increased immediate drug concentration. The carrier materials are not cytotoxic to human corneal epithelial cells and conjunctival epithelial cells, and show good biocompatibility, which can be safely administrated into rabbit’s conjunctival sac. The BRI@SR@TPU implant sustainably released BRI and effectively reduced IOP for 18 d (72 times) compared to the commercial BRI eye drops (6 h). The BRI@SR@TPU implant is thus a promising noninvasive platform product for long-term IOP-reducing in patients with glaucoma and ocular hypertension.

Extraocular, periocular, and intraocular routes for sustained drug delivery for glaucoma

Although once daily anti-glaucoma drug therapy is a current clinical reality, most therapies require multiple dosing and there is an unmet need to develop convenient, safe, and effective sustained release drug delivery systems for long-term treatment to improve patient adherence and outcomes. One of the first sustained release drug delivery systems was approved for the reduction of intraocular pressure in glaucoma patients. It is a polymeric reservoir-type insert delivery system, Ocusert™, placed under the eyelid and on the ocular surface for zero-order drug release over one week. The insert, marketed in two strengths, released pilocarpine on the eye surface. While many clinicians appreciated this drug product, it was eventually discontinued. No similar sustained release non-invasive drug delivery system has made it to the market to date for treating glaucoma. Drug delivery systems under development include punctal plugs, ring-type systems, contact lenses, implants, microspheres, nanospheres, gels, and other depot systems placed in the extraocular, periocular, or intraocular regions including intracameral, supraciliary, and intravitreal spaces. This article discusses the advantages and disadvantages of the various routes of administration and delivery systems for sustained glaucoma therapy. It also provides the reader with some examples and discussion of drug delivery systems that could potentially be applied for glaucoma treatment. Interestingly, one intracamerally injected implant, Durysta™, was approved recently for sustained intraocular pressure reduction. However, long-term acceptance of such devices has yet to be established. The ultimate success of the delivery system will depend on efficacy relative to eye drop dosing, safety, reimbursement options, and patient acceptance. Cautious development efforts are warranted considering prior failed approaches for sustained glaucoma drug delivery. Neuroprotective approaches for glaucoma therapy including cell, gene, protein, and drug-combination therapies, mostly administered intravitreally, are also rapidly progressing towards assessment in humans.

Suprachoroidal Delivery of Small Molecules, Nanoparticles, Gene and Cell Therapies for Ocular Diseases

Suprachoroidal drug delivery technology has advanced rapidly and emerged as a promising administration route for a variety of therapeutic candidates, in order to target multiple ocular diseases, ranging from neovascular age-related macular degeneration to choroidal melanoma. This review summarizes the latest preclinical and clinical progress in suprachoroidal delivery of therapeutic agents, including small molecule suspensions, polymeric entrapped small molecules, gene therapy (viral and nonviral nanoparticles), viral nanoparticle conjugates (VNCs), and cell therapy. Formulation customization is critical in achieving favorable pharmacokinetics, and sustained drug release profiles have been repeatedly observed for multiple small molecule suspensions and polymeric formulations. Novel therapeutic agents such as viral and nonviral gene therapy, as well as VNCs, have demonstrated promise in animal studies. Several of these suprachoroidally-administered therapies have been assessed in clinical trials, including small molecule suspensions of triamcinolone acetonide and axitinib, viral vector RGX-314 for gene therapy, and VNC AU-011. With continued drug delivery research and optimization, coupled with customized drug formulations, suprachoroidal drug delivery may address large unmet therapeutic needs in ophthalmology, targeting affected tissues with novel therapies for efficacy benefits, compartmentalizing therapies away from unaffected tissues for safety benefits, and achieving durability to relieve the treatment burden noted with current agents.

Drug-Free, Nonsurgical Reduction of Intraocular Pressure for Four Months after Suprachoroidal Injection of Hyaluronic Acid Hydrogel

Glaucoma is the leading cause of irreversible blindness. Current treatments use drugs or surgery to reduce intraocular pressure (IOP). In this study, a drug-free, nonsurgical method is developed that lowers IOP for 4 months without requiring daily patient adherence. The approach involves expanding the suprachoroidal space (SCS) of the eye with an in situ-forming hydrogel injected using a microneedle. This study tests the hypothesis that SCS expansion increases the drainage of aqueous humor from the eye via the unconventional pathway, which thereby lowers IOP. SCS injection of a commercial hyaluronic acid (HA) hydrogel reduces the IOP of normotensive rabbits for more than 1 month and an optimized HA hydrogel formulation enables IOP reduction for 4 months. Safety assessment by clinical ophthalmic examinations indicate the treatment is well tolerated. Histopathology shows minor hemorrhage and fibrosis at the site of injection. Further analysis by ultrasound biomicroscopy demonstrates a strong correlation of IOP reduction with SCS expansion. Outflow facility measurements show no difference in pressure-dependent outflow by the conventional pathway between treated and untreated eyes, supporting the hypothesis. In conclusion, SCS expansion with an in situ-forming hydrogel can enable extended IOP reduction for treating ocular hypertension and glaucoma without drugs or surgery.

Novel Drug Delivery Systems Fighting Glaucoma: Formulation Obstacles and Solutions

Glaucoma is considered to be one of the biggest health problems in the world. It is the main cause of preventable blindness due to its asymptomatic nature in the early stages on the one hand and patients' non-adherence on the other. There are several approaches in glaucoma treatment, whereby this has to be individually designed for each patient. The first-line treatment is medication therapy. However, taking into account numerous disadvantages of conventional ophthalmic dosage forms, intensive work has been carried out on the development of novel drug delivery systems for glaucoma. This review aims to provide an overview of formulation solutions and strategies in the development of in situ gel systems, nanosystems, ocular inserts, contact lenses, collagen corneal shields, ocular implants, microneedles, and iontophoretic devices. The results of studies confirming the effectiveness of the aforementioned drug delivery systems were also briefly presented.

Brimonidine-LAPONITE® intravitreal formulation has an ocular hypotensive and neuroprotective effect throughout 6 months of follow-up in a glaucoma animal model

Intravitreal administration is widely used in ophthalmological practice to maintain therapeutic drug levels near the neuroretina and because drug delivery systems are necessary to avoid reinjections and sight-threatening side effects. However, currently there is no intravitreal treatment for glaucoma. The brimonidine-LAPONITE® formulation was created with the aim of treating glaucoma for extended periods with a single intravitreal injection. Glaucoma was induced by producing ocular hypertension in two rat cohorts: [BRI-LAP] and [non-bri], with and without treatment, respectively. Eyes treated with brimonidine-LAPONITE® showed lower ocular pressure levels up to week 8 (p < 0.001), functional neuroprotection explored by scotopic and photopic negative response electroretinography (p = 0.042), and structural protection of the retina, retinal nerve fibre layer and ganglion cell layer (p = 0.038), especially on the superior-inferior axis explored by optical coherence tomography, which was corroborated by a higher retinal ganglion cell count (p = 0.040) using immunohistochemistry (Brn3a antibody) up to the end of the study (week 24). Furthermore, delayed neuroprotection was detected in the contralateral eye. Brimonidine was detected in treated rat eyes for up to 6 months. Brimonidine-LAPONITE® seems to be a potential sustained-delivery intravitreal drug for glaucoma treatment.

Micro-interaction of mucin tear film interface with particles: The inconsistency of pharmacodynamics and precorneal retention of ion-exchange, functionalized, Mt-embedded nano- and microparticles

Physiological reflexes and anatomical barriers render traditional eye drop delivery inefficient. We previously reported that drug-loaded nanoparticles and microspheres prepared from montmorillonite and Eudragit polymers exhibited good sustained-release and lowered intraocular pressure. Here, we compared the performance of optimized formulations to select the most suitable formulation for glaucoma therapy. We found that the microspheres had much higher encapsulation efficiency and drug loading than nanoparticles. Moreover, cytocompatibility experiments demonstrated that nanoparticles showed more severe cytotoxicity than microspheres, probably due to their smaller particles, enhanced cell uptake, and intracellular solubility. Interestingly, the pre-corneal retention time of nanoparticles reflected a clear advantage over microspheres, while the duration of the pharmacological effect of nanoparticles was not as good as that of microspheres: compared with the nanoparticle depressurization duration of only 8 h, the microspheres continuously depressurized for 12 h. The slower release of the microspheres and its micro-interaction mechanism with the discontinuous mucin layer of the tear film led to the inconsistency between duration of pharmacodynamics and fluorescence ocular retention time. In summary, the lower cytotoxicity and longer pharmacological effect of microspheres indicate their potential advantages for glaucoma applications.

Current and new pharmacotherapeutic approaches for glaucoma

INTRODUCTION

Glaucoma is the leading cause of irreversible blindness worldwide. Medical therapy is the main line of treatment of open-angle glaucoma (OAG) and ocular hypertension. Despite the expansion of the glaucoma lineup with the newly approved medication classes, many barriers and issues still exist with topical therapy. Novel non-topical drug delivery may address such issues, adding more options to glaucoma pharmacotherapy.

AREAS COVERED

This review outlines current topical therapies for glaucoma, in addition to new medications under trials. The issues with topical therapy, in general, are discussed, as well as the new non-topical drug delivery systems. The authors performed a comprehensive search for published studies on glaucoma medical therapy using the electronic database of PubMed and manual search for each medication and non-topical delivery options. The extra- and intraocular delivery methods and the new topical glaucoma medications under research are covered.

EXPERT OPINION

Medical management of glaucoma represents a challenge for both patients and clinicians. Noncompliance (e.g. difficulty with administering the eye drops), cost, side effects, and intraocular pressure fluctuation are the major problems with topical therapy. To overcome such barriers, research should continue in developing new medications and innovation of non-topical drug delivery systems.

512-Channel Geometric Droplet-Splitting Microfluidic Device by Injection of Premixed Emulsion for Microsphere Production

We present a 512-channel geometric droplet-splitting microfluidic device that involves the injection of a premixed emulsion for microsphere production. The presented microfluidic device was fabricated using conventional photolithography and polydimethylsiloxane casting. The fabricated microfluidic device consisted of 512 channels with 256 T-junctions in the last branch. Five hundred and twelve microdroplets with a narrow size distribution were produced from a single liquid droplet. The diameter and size distribution of prepared micro water droplets were 35.29 µm and 8.8% at 10 mL/h, respectively. Moreover, we attempted to prepare biocompatible microspheres for demonstrating the presented approach. The diameter and size distribution of the prepared poly (lactic-co-glycolic acid) microspheres were 6.56 µm and 8.66% at 10 mL/h, respectively. To improve the monodispersity of the microspheres, we designed an additional post array part in the 512-channel geometric droplet-splitting microfluidic device. The monodispersity of the microdroplets prepared with the microfluidic device combined with the post array part exhibited a significant improvement.

Nanotechnology for Medical and Surgical Glaucoma Therapy-A Review

Glaucoma is the second leading cause of blindness worldwide. Even though significant advances have been made in its management, currently available antiglaucoma therapies suffer from considerable drawbacks. Typically, the success and efficacy of glaucoma medications are undermined by their limited bioavailability to target tissues and the inadequate adherence demonstrated by patients with glaucoma. The latter is due to a gradual decrease in tolerability of lifelong topical therapies and the significant burden to patients of prescribed stepwise antiglaucoma regimens with frequent dosing which impact quality of life. On the other hand, glaucoma surgery is restricted by the inability of antifibrotic agents to efficiently control the wound healing process without causing severe collateral damage and long-term complications. Evolution of the treatment paradigm for patients with glaucoma will ideally include prevention of retinal ganglion cell degeneration by the successful delivery of neurotrophic factors, anti-inflammatory drugs, and gene therapies. Nanotechnology-based treatments may surpass the limitations of currently available glaucoma therapies through optimized targeted drug delivery, increased bioavailability, and controlled release. This review addresses the recent advances in glaucoma treatment strategies employing nanotechnology, including medical and surgical management, neuroregeneration, and neuroprotection.

Promising therapeutic drug delivery systems for glaucoma: a comprehensive review

The delivery of ophthalmic drugs is challenging despite easy accessibility via the ocular surface. Topical instillation of eye drops is a relatively easy and most commonly used as a conduit for drug delivery for treating a myriad of ocular morbidities, particularly involving the anterior segment, and has an additional benefit of avoiding the first-pass metabolism while passing through the systemic circulation. The primary challenges of drug administration through traditional methods include-inadequate patient education for proper drug instillation technique, compliance, adherence, and persistence. Various dynamic (choroidal and conjunctival blood flow, lymphatic clearance, and tear dilution) and static (namely, different layers of cornea, sclera, and retina including blood aqueous and blood-retinal barriers) ocular barriers limit drug delivery to the target ocular tissues. The maintenance of the therapeutic drug levels on the ocular surface for a prolonged duration is an added challenge, thus preventing persistent delivery for longer durations. These factors result in inadequate management, leading to poor prognosis in vision loss in as many as 27% of the patients diagnosed with glaucoma. We have reviewed the research and advancements in the development of novel and well-tolerated drug delivery systems with the common goal of overcoming the factors limiting adequate drug delivery to the target tissues in glaucomatous patients with traditional techniques. In the recent past, multiple research groups have successfully designed noninvasive, sustained drug delivery systems, promoting the efficacy as well as the feasibility of delivering topical drugs to the anterior segment.

Promising Approach in the Treatment of Glaucoma Using Nanotechnology and Nanomedicine-Based Systems

Glaucoma is considered a leading cause of blindness with the human eye being one of the body's most delicate organs. Ocular diseases encompass diverse diseases affecting the anterior and posterior ocular sections, respectively. The human eye's peculiar and exclusive anatomy and physiology continue to pose a significant obstacle to researchers and pharmacologists in the provision of efficient drug delivery. Though several traditional invasive and noninvasive eye therapies exist, including implants, eye drops, and injections, there are still significant complications that arise which may either be their low bioavailability or the grave ocular adverse effects experienced thereafter. On the other hand, new nanoscience technology and nanotechnology serve as a novel approach in ocular disease treatment. In order to interact specifically with ocular tissues and overcome ocular challenges, numerous active molecules have been modified to react with nanocarriers. In the general population of glaucoma patients, disease growth and advancement cannot be contained by decreasing intraocular pressure (IOP), hence a spiking in future research for novel drug delivery systems and target therapeutics. This review focuses on nanotechnology and its therapeutic and diagnostic prospects in ophthalmology, specifically glaucoma. Nanotechnology and nanomedicine history, the human eye anatomy, research frontiers in nanomedicine and nanotechnology, its imaging modal quality, diagnostic and surgical approach, and its possible application in glaucoma will all be further explored below. Particular focus will be on the efficiency and safety of this new therapy and its advances.

Collagenase injection into the suprachoroidal space of the eye to expand drug delivery coverage and increase posterior drug targeting

Injection into the suprachoroidal space (SCS) allows drug delivery targeted to sclera, choroid, and retina. Here, we studied SCS injection formulated with collagenase to expand drug delivery coverage and increase posterior drug targeting within SCS by breaking down collagen fibrils that link sclera and choroid in the SCS. When 1 μm latex microparticles were injected with a collagenase formulation using microneedles into the SCS of rabbit eyes ex vivo and incubated at 37 °C for 4 h, microparticle delivery coverage increased from 20% to 45% and enhanced posterior drug targeting. Collagenase concentration was optimized to 0.5 mg/mL to maximize expanded posterior delivery and minimize tissue damage. Effects of collagenase injection within SCS increased and then plateaued 4 h after injection. Simultaneous injection of collagenase and microparticles had a greater effect on expanded delivery in the SCS compared to sequential injection. Collagenase injection into the SCS of rabbit eyes in vivo was also effective to expand delivery and was generally well-tolerated, showing transiently lowered IOP, but no apparent lasting adverse effects on ocular tissues such as sclera, choroid, and retina, as determined by analyzing histology, sclera tensile strength, and fundus imaging. We conclude that addition of collagenase during SCS injection can expand drug delivery coverage and increase posterior drug targeting.

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.

Suprachoroidally injected pharmacological agents for the treatment of chorio-retinal diseases: a targeted approach

Delivery of pharmaceuticals to the posterior segment presents challenges that arise from the anatomy and clearance pharmacokinetics of the eye. Systemic and several local administration options [topical, periocular, intravitreal (IVT) and subretinal] are in clinical use, each with a unique benefit to risk profile shaped by factors including the administered agent, frequency of dosing, achievable pharmaceutical concentrations within posterior segment structures versus elsewhere in the eye or the body, invasiveness of the procedure and the inherent challenges with some administration methods. The use of the suprachoroidal space (SCS), which is the region between the sclera and the choroid, is being explored as a potential approach to target pharmacotherapies to the posterior segment via a minimally invasive injection procedure. Preclinical data on agents such as vascular endothelial growth factor inhibitors and triamcinolone acetonide (TA) indicate that administration via suprachoroidal injection results in more posterior distribution of the pharmacologic agent, with higher exposure to the sclera, choroid, retinal pigment epithelium cells and retina, and lesser exposure to the anterior segment, than observed with IVT administration. Based in part on these findings, clinical trials have explored the efficacy and safety of suprachoroidal administration of pharmacologic therapies in conditions affecting the posterior segment. Data on a proprietary formulation of TA administered by suprachoroidal injection show improvement in anatomic and visual outcomes in subjects with noninfectious uveitis, with the potential to mitigate the known risks of cataract and increased intraocular pressure (IOP) associated with the use of intraocular corticosteroids. Suprachoroidal administration appears to be a promising treatment modality and is also in the early stages of investigation for other possible applications, such as injection of antiglaucoma agents into the anterior SCS for long-lasting control of elevated IOP, and as a mode of delivery for gene- or cell-based therapies for retinal disorders.

Targeted Drug Delivery in the Suprachoroidal Space by Swollen Hydrogel Pushing

Purpose

The purpose is to target model drug particles to the posterior region of the suprachoroidal space (SCS) of the eye controlled via pushing by hydrogel swelling.

Methods

A particle formulation containing 1% hyaluronic acid (HA) with fluorescent polymer particles and a hydrogel formulation containing 4% HA were introduced in a single syringe as two layers without mixing, and injected sequentially into the SCS of the rabbit eye ex vivo and in vivo using a microneedle. Distribution of particles in the eye was determined by microscopy.

Results

During injection, the particle formulation was pushed toward the middle of the SCS by the viscous hydrogel formulation, but less than 12% of particles reached the posterior SCS. After injection, the particle formulation was pushed further toward the macula and optic nerve in the posterior SCS by hydrogel swelling and spreading. Heating the eye to 37°C, or injecting in vivo decreased viscosity and mechanical strength of the hydrogel, thereby allowing it to swell and flow further in the SCS. A high salt concentration (9% NaCl) in the hydrogel formulation further increased hydrogel swelling due to osmotic flow into the hydrogel. In this way, up to 76% of particles were delivered to the posterior SCS from an injection made near the limbus.

Conclusions

This study shows that model drug particles can be targeted to the posterior SCS by HA hydrogel swelling and pushing without particle functionalization or administering external driving forces.

Metal-Organic Frameworks as Drug Delivery Platforms for Ocular Therapeutics

Metal-organic frameworks (MOFs) have been evaluated as potential nanocarriers for intraocular incorporation of brimonidine tartrate to treat chronic glaucoma. Experimental results show that UiO-67 and MIL-100 (Fe) exhibit the highest loading capacity with values up to 50-60 wt %, whereas the performance is quite limited for MOFs with narrow cavities (below 0.8 nm, for example, UiO-66 and HKUST-1). The large loading capacity in UiO-67 is accompanied by an irreversible structural amorphization in aqueous and physiological media that promotes extended release kinetics above 12 days. Compared to the traditional drawbacks associated with the sudden release of the commercial drugs (e.g., ALPHAGAN), these results anticipate UiO-67 as a potential nanocarrier for drug delivery in intraocular therapeutics. These promising results are further supported by cytotoxicity tests using retinal photoreceptor cells (661W). Toxicity of these structures (including the metal nodes and organic ligands) for retinal cells is rather low for all samples evaluated, except for HKUST-1.

Medical and Surgical Applications for the Suprachoroidal Space

In recent years, advances in ocular imaging, drug delivery, and ophthalmic surgery have allowed for better visualization and access to the suprachoroidal space. Although previously considered as only a potential space, the suprachoroidal space may serve as a route for drug delivery to the posterior pole, an egress for glaucoma drainage devices, a location for temporary buckling, and a site for prosthesis implantation. Drugs delivered to the suprachoroidal space may achieve higher concentrations in the retina while minimizing exposure to anterior segment tissues, potentially reducing risks of glaucoma or cataracts. Finally, advanced multimodal imaging now allows not only a better understanding of the physiology of the suprachoroid, but also in vivo monitoring of pathologies and drug delivery to the suprachoroidal space. Here, we discuss the newest developments in the medical and surgical applications of this space with potential.

The Effect of an Educational Intervention on Adherence to Intraocular Pressure-Lowering Medications in a Large Cohort of Older Adults with Glaucoma

BACKGROUND

Glaucoma is a progressive, irreversible disease that can lead to vision loss and lower quality of life if treatment is not optimized. Effective glaucoma therapies are available to lower intraocular pressure (IOP) and minimize or delay disease progression. Nonetheless, adherence to treatment remains suboptimal for many patients.

OBJECTIVE

To identify potentially nonadherent patients and evaluate the effect of patient- and physician-centric educational interventions on adherence by using a validated predictive model of nonadherence to glaucoma medication.

METHODS

This prospective, randomized, controlled, and interventional study included Humana Medicare Advantage Prescription Drug plan patients with a glaucoma diagnosis between May and October 2014, ≥ 1 pharmacy claim for glaucoma medication, and ≥ 50% likelihood of nonadherence. Patients and physicians were randomized to cohorts A (no interventions), B (physician intervention), or C (patient and physician interventions). Physicians in cohorts B and C received information on the model, adherence, and patient profiles at baseline and months 3, 6, and 9. Patients in cohort C received educational materials on glaucoma and adherence (same schedule). The primary outcome was the proportion of days covered (PDC) with medication over 12 months. Adherence was defined as PDC ≥ 0.80.

RESULTS

Overall, 23,306 patients and 2,955 physicians were eligible. After excluding physicians with < 3 nonadherent patients, each cohort included 200 physicians and 600 patients. Mean PDC was 0.54-0.56 across cohorts. At 12 months, ≥ 90.5% of physicians and ≥ 75.5% of patients remained in the study; mean PDC was 0.53-0.54 across cohorts. No statistically significant between-cohort differences in PDC and adherence were observed.

CONCLUSIONS

Intensive educational mailings to patients and their physicians did not improve PDC or adherence in this large population of potentially nonadherent patients with glaucoma. Findings highlight the difficulty of improving adherence in a disease that requires lifelong therapy despite being largely asymptomatic and can inform development of future interventions aimed at improving adherence to glaucoma therapy.

DISCLOSURES

This study was sponsored by Allergan plc (Dublin, Ireland). Fiscella and Chandwani are employees of Allergan plc. Caplan, Kamble, Bunniran, and Uribe are employees of Comprehensive Health Insights, a Humana company. The authors did not receive honoraria or other payments for authorship.

Recent advance of nanoparticle-based topical drug delivery to the posterior segment of the eye

INTRODUCTION

Considering that the number of patients afflicted by posterior eye diseases is increasing, effective drug delivery is currently in high clinical demand. Topical administration has been identified as the preferred option, while sufferingfrom multiple barriers. The development of nanoparticle-based drug delivery system provides an option, which would enhance the drug permeability across the barriers and achieve the desired drug level in the targeted tissue.

AREAS COVERED

This review highlights the barrier to the posterior segment of the eye via topical administration. The up-to-date development of lipid nanoparticles, liposomes, emulsions, spanlastics, micelles, polymeric nanoparticles, layered double hydroxides (LDH), dendrimers, cyclodextrins(CDs), and prodrugs are summarized. Moreover, nanocarriers currently in clinical trials for posterior segment diseases have been discussed.

EXPERT OPINION

Topical nanoparticle-based drug delivery systems have demonstrated significant progress. An ideal formulation should prolong retention time on the surface, enhance drug permeability through the ocular tissues, and efficiently deliver drugs to the targeted site. To design the rational targeting nanoparticle-based drug delivery system, a better understanding of the distribution of transporters and receptors on the eye is required. Ultimately, there is an urgent need to develop targeting hybrid drug delivery systems with the combination of the advantages of several nanocarriers.

Sustained Dorzolamide Release Prevents Axonal and Retinal Ganglion Cell Loss in a Rat Model of IOP-Glaucoma

Purpose

To determine if one injection of a sustained release formulation of dorzolamide in biodegradable microparticles (DPP) reduces retinal ganglion cell (RGC) loss in a rat model of glaucoma.

Methods

We injected either DPP or control microparticles intravitreally in rats. Two days later, unilateral ocular hypertension was induced by translimbal, diode laser treatment by a surgeon masked to treatment group. IOP and clinical exams were performed until sacrifice 6 weeks after laser treatment. RGC loss was measured by masked observers in both optic nerve cross-sections and RGC layer counts from retinal whole mounts.

Results

Cumulative IOP exposure was significantly reduced by DPP injection (49 ± 48 mm Hg × days in treated versus 227 ± 191 mm Hg × days in control microparticle eyes; P = 0.012, t-test). While control-injected eyes increased in axial length by 2.4 ± 1.7%, DPP eyes did not significantly enlarge (0.3 ± 2.2%, difference from control, P = 0.03, t-test). RGC loss was significantly less in DPP eyes compared with control microparticle injection alone (RGC axon count reduction: 21% vs. 52%; RGC body reduction: 25% vs. 50% [beta tubulin labeling]; P = 0.02, t-test).

Conclusions

A single injection of sustained release DPP protected against RGC loss and axial elongation in a rat model of IOP glaucoma.

Translational Relevance

Sustained release IOP-lowering medications have the potential to stop glaucoma progression.

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.

The suprachoroidal space as a route of administration to the posterior segment of the eye

The suprachoroidal space (SCS) is a potential space between the sclera and choroid that traverses the circumference of the posterior segment of the eye. The SCS is an attractive site for drug delivery because it targets the choroid, retinal pigment epithelium, and retina with high bioavailability, while maintaining low levels elsewhere in the eye. Indeed, phase III clinical trials are investigating the safety and efficacy of SCS drug delivery. Here, we review the anatomy and physiology of the SCS; methods to access the SCS; kinetics of SCS drug delivery; strategies to target within the SCS; current and potential clinical indications; and the safety and efficacy of this approach in preclinical animal studies and clinical trials.

Long-term intraocular pressure reduction with intracameral polycaprolactone glaucoma devices that deliver a novel anti-glaucoma agent

Long-term treatment of glaucoma, a major leading cause of blindness, is challenging due to poor patient compliance. Therefore, a drug delivery device that can achieve drug release over several months can be highly beneficial for glaucoma management. Here, we evaluate the long-term pharmacokinetics and therapeutic efficacy of polycaprolactone intracameral drug delivery devices in rabbit eyes. Our study showed that a single drug delivery device loaded with a proprietary hypotensive agent, DE-117, reduced intraocular pressure in normotensive rabbits significantly for 23weeks. In addition, we demonstrated that concentration of DE-117 and its hydrolyzed active form (hDE-117) was maintained in the aqueous humor and the target tissue (iris-ciliary body) up to 24weeks. Our proof-of-concept glaucoma implant shows potential as a long-term treatment that circumvents patient compliance barriers compared to current treatment via eye drops.

New pharmacotherapy for the treatment of glaucoma

INTRODUCTION

Glaucoma is the second leading cause of blindness in the world and current pharmacotherapies for glaucoma have remained relatively unchanged (with the exception of fixed combinations of previously available medications) since the mid-1990s with the development of prostaglandin analogues. Now, with both new formulations and new classes of medications with novel mechanisms of action, the medical therapy of glaucoma may be heralding a new dawn in medical management. Areas covered: This review outlines new topical therapies for intraocular pressure (IOP) lowering treatment, in addition to new formulations, preservative-free options, and advances in glaucoma medical therapy delivery. We performed a comprehensive search for published studies for glaucoma medical therapy using the electronic database PubMed. A manual search for each therapy or delivery system was also performed. Expert commentary: These advances in glaucoma therapy have the potential to overcome many barriers to glaucoma's medical care, particularly in terms of adherence. However, both time and research are needed to prove the relative efficacy and safety of these new pharmacotherapies and products, helping us decide their role in the treatment of elevated intraocular pressure. We are hopeful that these new developments in therapy may bring more options for glaucoma medical therapy.

Co-instillation of nano-solid magnesium hydroxide enhances corneal permeability of dissolved timolol

We prepared magnesium hydroxide (MH) nanoparticles by a bead mill method, and investigated whether the co-instillation of MH nanoparticles improves the low transcorneal penetration of water-soluble drugs, such as the anti-glaucoma eye drug timolol maleate (TM). MH particle size was decreased by the bead mill treatment to a mean particle size of 71 nm. In addition, the MH nanoparticles were highly stable. Next, we demonstrated the effect of MH nanoparticles on the corneal surface. MH shows only slight solubility in lacrimal fluid, and the instillation of MH nanoparticles for 14 days did not affect the behavior (balance of secretion and excretion) of the lacrimal fluid in rabbit corneas. Moreover, there was no observable corneal toxicity of MH nanoparticles, and treatment with MH nanoparticles enhanced the intercellular space ratio in the eyes of rats. MH alone did not permeate into the cornea; however, the co-instillation of MH nanoparticles and dissolved TM (nMTFC) enhanced the corneal penetration of TM. In addition, the intraocular pressure (IOP)-reducing effect of nMTFC was significantly higher than those of the TM solution or the co-instillation of MH microparticles and TM. In conclusion, we found that MH nanoparticles enhance the corneal penetration of dissolved TM with no observable corneal stimulation or obstruction of the nasolacrimal duct by the MH nanoparticles. It is possible that the co-instillation of MH nanoparticles may provide a useful way to improve the bioavailability of water-soluble drugs in the ophthalmic field. These findings provide significant information that can be used to design further studies aimed at developing anti-glaucoma eye drugs.