Recent Advances in Topical Ocular Drug Delivery

Drug delivery to the anterior segment of the eye: A review of current and future treatment strategies

Research in the development of ophthalmic drug formulations and innovative technologies over the past few decades has been directed at improving the penetration of medications delivered to the eye. Currently, approximately 90% of all ophthalmic drug formulations (e.g. liposomes, micelles) are applied as eye drops. The major challenge of topical eye drops is low bioavailability, need for frequent instillation due to the short half-life, poor drug solubility, and potential side effects. Recent research has been focused on improving topical drug delivery devices by increasing ocular residence time, overcoming physiological and anatomical barriers, and developing medical devices and drug formulations to increase the duration of action of the active drugs. Researchers have developed innovative technologies and formulations ranging from sub-micron to macroscopic size such as prodrugs, enhancers, mucus-penetrating particles (MPPs), therapeutic contact lenses, and collagen corneal shields. Another approach towards the development of effective topical drug delivery is embedding therapeutic formulations in microdevices designed for sustained release of the active drugs. The goal is to optimize the delivery of ophthalmic medications by achieving high drug concentration with prolonged duration of action that is convenient for patients to administer.

Design, development, and characterization of an idebenone-loaded poly-ε-caprolactone intravitreal implant as a new therapeutic approach for LHON treatment

Leber's Hereditary Optic Neuropathy (LHON) is a hereditary mitochondrial neurodegenerative disease of unclear etiology and lack of available therapeutic alternatives. The main goal of the current pilot study was based on the evaluation of the feasibility and characteristics of prolonged and controlled idebenone release from a PCL intravitreal implant. The design, development, and characterization of idebenone-loaded PCL implants prepared by an homogenization/extrusion/solvent evaporation method allowed the obtention of high PY, EE and LC values. In vitro characterization was completed by the assessment of mechanical and instrumental properties. The in vitro release of idebenone from the PCL implants was assessed and the implant erosion was monitored by the mass loss and surface morphology changes. DSC was used to estimate stability and interaction among implant's components. The present work demonstrated the controlled and prolonged idebenone delivery from the PCL implants in an in vitro model. A consistent preclinical base was established, supporting the idea of idebenone-loaded PCL implants as a new strategy of long-term sustained intraocular delivery for the LHON treatment.

Cationic self-assembled peptide-based molecular hydrogels for extended ocular drug delivery

The physiological barriers and clearance mechanism of the eye challenge the therapeutic delivery for treating various ocular disorders effectively. Here, we show the use of a cationic peptide (i.e., Nap-FFKK) as the molecular hydrogelator for generating supramolecular hydrogels spontaneously in a pH value of 5-7 which allows it to function as a promising ocular drug vehicle. The cationic peptide-based hydrogel hardly exhibited the cytotoxicity against human corneal epithelial cell (i.e., HCEC) from the in vitro cytotoxicity assay. Moreover, the single topical instillation of the hydrogel resulted in high ocular tolerance and biocompatibility. In vivo corneal distribution of the cationic peptide-based hydrogel showed that it dramatically increased the retention and the adhesion on the surface of cornea, compared to the anionic peptide-based analogue, owing to the ionic interactions with mucin on the ocular surface. In addition, we also synthesized environment-sensitive fluorophore-conjugated analogues (i.e., NBD-FFKK and NBD-FFD) to visualize the uptake of hydrogels in HCEC cells, revealing that the cationic peptide-based hydrogel displayed the better in vitro cellular uptake than the anionic peptide-based hydrogel. More importantly, the resulting cationic Nap-FFKK supramolecular hydrogel displayed a superior ocular bioavailability over that of anionic Nap-FFD supramolecular hydrogel, as indicated by in vivo pharmacokinetics study. This work, as a systematic investigation of ionic peptide-based molecular hydrogels in the ocular application, illustrates a new and powerful supramolecular approach for antagonizing clinically difficult ocular drug delivery. STATEMENT OF SIGNIFICANCE: Here we show the use of a cationic peptide as the molecular hydrogelator for generating supramolecular hydrogels, which allows it to function as a promising ocular drug vehicle for antagonizing the therapeutic delivery difficulties associated with the physiological barriers and clearance mechanism of the eye. The in vitro and in vivo studies of the hydrogel both show high ocular tolerance and biocompatibility. Moreover, the in vivo corneal distribution of the hydrogel exhibits the increased retention and adhesion on the surface of cornea. This work, as an investigation of cationic peptide-based molecular hydrogels in the ocular application, illustrates a powerful supramolecular approach for overcoming clinically difficult ocular drug delivery.

Recent Advances in the Excipients Used for Modified Ocular Drug Delivery

In ocular drug delivery, maintaining an efficient concentration of the drug in the target area for a sufficient period of time is a challenging task. There is a pressing need for the development of effective strategies for drug delivery to the eye using recent advances in material sciences and novel approaches to drug delivery. This review summarizes the important aspects of ocular drug delivery and the factors affecting drug absorption in the eye including encapsulating excipients (chitosan, hyaluronic acid, poloxamer, PLGA, PVCL-PVA-PEG, cetalkonium chloride, and gelatin) for modified drug delivery.

Design and Development of Antibacterial/Anti-inflammatory Dual Drug-Loaded Nanofibrous Inserts for Ophthalmic Sustained Delivery of Gentamicin and Methylprednisolone: In Vitro Bioassay, Solvent, and Method Effects’ Evaluation

Purpose: To overcome the challenges caused by the use of conventional ophthalmic dosage forms such as the fast elimination of the drug from the surface of the eye, in this study, dual drug-loaded nanofibers were developed for sustained ophthalmic delivery of gentamicin (GNT) and methylprednisolone (MP). Moreover, the solvent effects, polymer mixtures, and method of preparation on the release profile of the prepared nanofibers, were evaluated.

Methods: The nanofibers were prepared using polycaprolactone (PCL), poly (lactic-co-glycolic acid) (PLGA), and polyvinyl alcohol (PVA) using electrospinning technique. Thereafter, seven optimized formulations were developed with different solvent mixtures and polymer concentrations using various electrospinning methods. The physicochemical and mechanical properties of nanofibers were also evaluated, and the morphology of formulations was observed. The antibacterial efficacy was investigated and the in vitro release amounts of GNT and MP from nanofibers were estimated using the bioassay and ultraviolet-visible (UV-Vis) spectroscopy.

Results: The developed G1, G4, G5, G6, and G7 had suitable mechanical properties and morphologies with diameter ranging between 70-350 nm. The 1:1 v/v ratio of DMF/DCM in the solvent mixture and using core-shell technique for the preparation, formed nanofibers with more favorable release profiles. The optimized formulations indicated sustained-release manner for both drugs during 3-9 days and the antibacterial efficacy against Staphylococcus aureus.

Conclusion: Among all the prepared formulations, the nanofiber with core-shell structure possessed the best sustained-release profiles of GNT and MP. The obtained results suggest that these nanofibers have a potential to be used as an insert in the eye for long-term release of the drug.

Phospho-Sulindac (OXT-328) Inhibits Dry Eye Disease in Rabbits: A Dose-, Formulation- and Structure-Dependent Effect

Purpose: Inflammation of the ocular surface is central to dry eye disease (DED). The anti-inflammatory agent phospho-sulindac (PS) at a high dose was efficacious against DED in a rabbit model. We assessed the dose, formulation and structure dependence of PS's effect. Methods: In rabbits with concanavalin A-induced DED we evaluated a range of PS concentrations (0.05%-1.6%) and dosing frequencies, assessed the duration of its effect with PS in 2 solution formulations and one emulsion formulation, and compared the efficacy of PS to that of sulindac, and of the structurally similar phospho-ibuprofen amide. We determined tear breakup time (TBUT) (tear stability), Schirmer's tear test (tear production), and by esthesiometry corneal sensitivity (symptoms). We also determined the biodistribution in the eye of topically applied PS. Results: PS in a solution formulation, given as eye drops q.i.d. was efficacious starting at a dose of 0.1%. The effect was apparent after 2 days of treatment and lasted at least 8 days after the last dose. Both signs (evidenced by TBUT and Schirmer's test) and symptoms (measured by corneal sensitivity) improved significantly. The best formulation was the solution formulation; a cyclodextrin-based formulation was also successful but the emulsion formulation was not. PS and its metabolites were essentially restricted to the anterior chamber of the eye. Sulindac and phospho-ibuprofen amide had no efficacy on DED. Conclusions: PS is efficacious against DED. Its effect, encompassing signs, and symptoms, are dose, formulation, and structure dependent. PS has therapeutic promise and merits further development.

Formulation of olopatadine hydrochloride viscous eye drops - physicochemical, biopharmaceutical and efficacy assessment using in vitro and in vivo approaches

The aim of this work was the formulation and the comprehensive evaluation of the viscous eye drops using vehicles containing medium chain chitosan (0.5% w/v), hydroxypropyl guar gum (0.25% w/v) and their combination as carriers for olopatadine (0.1% w/v). Physicochemical properties (appearance, clarity, pH, osmolality, viscosity and drug content) of the tested formulations were within acceptable ranges for the ophthalmic preparations, while DSC and FT-IR techniques demonstrated the compatibility between olopatadine and polymers. The drug permeability was successfully estimated in vitro using both HCE-T cell-based models (Model I and Model II) and the parallel artificial membrane permeability assay (PAMPA), considering the impact of chitosan as a permeation enhancer. The MTT cytotoxicity assay demonstrates that the tested formulations (diluted 10-fold in HBSS pH 5.5) were non-toxic and well tolerated. An ocular itch test on mice was carried out with the formulation containing the combination of polymers comparable with a commercially available olopatadine eye drops without viscosity enhancers. The tested eye drops produced a slightly higher anti-pruritic/analgesic-like effect than the commercial preparation. It could be assumed that the use of this viscous ophthalmic vehicle due to its advanced mucoadhesive properties and good safety profile is a feasible strategy to improve the efficacy of olopatadine.

A Review on Newer Ocular Drug Delivery Systems with an Emphasis on Glaucoma

Glaucoma is an irreversible condition resulting from the increase in intraocular pressure (IOP); which leads to permanent loss of vision with the destruction of retinal ganglion cells (RGCs). The IOP elevations are controlled in normal by the physiological flow of aqueous humour. A population with age above 40 is more susceptible to glaucoma. Other factors like gender, genetics, race etc. plays major roles in the development of the disease. Current treatment methods available for the disease includes drugs come under the classes of beta receptor blockers, carbonic anhydrase inhibitors, cholinergic agonists, prostaglandins etc. N-methyl-D-aspartate (NMDA) antagonists, inducible nitric oxide synthase (iNOS) inhibition, cytoskeletal agents, Rho-kinase inhibitors etc are few novel targets sites which are in research focus for the treatment of the disease. Developments in nanomedicine are also being evaluated for their potential in treating the growing glaucomatous population. Nanosystems are suggested to avoid the difficulties in tackling the various ocular barriers to a limit, help to decrease the instillation frequency of topical medication and can provide drug delivery in a sustained or controlled manner. This review focuses on the current and emerging treatment methods for glaucoma along with some of the nanoformulations for ocular drug delivery.

Gene therapy in the anterior eye segment

This review provides comprehensive information about the advances in gene therapy in the anterior segment of the eye including cornea, conjunctiva, lacrimal gland, and trabecular meshwork. We discuss gene delivery systems including viral and non-viral vectors as well as gene editing techniques, mainly CRISPR-Cas9, and epigenetic treatments including antisense and siRNA therapeutics. We also provide a detailed analysis of various anterior segment diseases where gene therapy has been tested with corresponding outcomes. Disease conditions include corneal and conjunctival fibrosis and scarring, corneal epithelial wound healing, corneal graft survival, corneal neovascularization, genetic corneal dystrophies, herpetic keratitis, glaucoma, dry eye disease, and other ocular surface diseases. Although most of the analyzed results on the use and validity of gene therapy at the ocular surface have been obtained in vitro or using animal models, we also discuss the available human studies. Gene therapy approaches are currently considered very promising as emerging future treatments of various diseases, and this field is rapidly expanding.

PLGA nanoparticles containing Lingzhi extracts rescue corneal epithelial cells from oxidative damage

Oxidative stress-related ocular surface epithelial damage can be initiated by ambient oxygen, UV radiation, and chemical burns. The oxidative damage to cornea can lead to inflammation and even vision loss. Lingzhi (Ganoderma lucidum) is a Chinese herbal drug and has been shown to prevent chronic diseases in clinical practices and has been proven to possess anti-oxidative and anti-inflammatory properties. In the study, we prepared poly (lactic-co-glycolic acid) (PLGA) nanoparticles (NPs) as a sustained drug release system of Lingzhi (LZH) to improve bioavailability. The particle size of developed NPs containing LZH (LZH-NPs) was ~184 nm with narrow size distribution. The results of cellular uptake revealed that using NPs as a drug delivery system could significantly increases the intracellular retention time. The results of the cell viability and chemiluminescence assay revealed that 5 μg/ml of LZH-NPs might be the threshold concentration for cultivation of corneal epithelial cells. After treating LZH-NPs in oxidative damaged cells, the results showed that the inflammation-related gene expression and DNA fragmentation level were both significantly decreased. Post-treatment of LZH-NPs in damaged corneal epithelial cells could increase the cell survival rate. In the rabbit corneal alkali burn model, topical instillation of LZH-NPs could promote corneal wound healing and decrease the inflammation. These results suggest that LZH-NPs may have the potential to treat ocular surface diseases caused by oxidative stress.

Treatment of Severe Acute Bacterial Keratitis in Rabbits Using Continuous Topical Ocular Instillation with Norvancomycin

Purpose

Efficacy of norvancomycin (NVCM) through continuous topical ocular instillation drug delivery (CTOIDD) system for treating severe acute bacterial keratitis infection with Staphylococcus aureus was investigated.

Methods

Rabbits with bacterial keratitis were treated using CTOIDD with NVCM (n=13), topical NVCM eye drops (n=11), and CTOIDD with saline (n=8). Clinical signs of keratitis in all groups were assessed consecutively for a week. Bacterial quantification of excised corneas was counted on the fourth and eighth days. Histopathologic examinations were performed to assess inflammatory cell infiltration on the eighth day.

Results

All signs of bacterial keratitis were alleviated in CTOIDD with NVCM according to criteria, and the CTOIDD-NVCM group had significantly less inflammation than CTOIDD-saline (p<0.05), and eye drop-NVCM (p<0.05). Two eyes in the eye drop-NVCM group, four eyes in the CTOIDD-saline group had corneal perforation (CP), while none of the rabbits showed CP in the CTOIDD-NVCM group. Bacterial counts were significantly less in the CTOIDD with NVCM group in comparison to the eye drop-NVCM (p<0.05), and CTOIDD-saline (p<0.05) groups. Severe inflammation and marked inflammatory cell infiltration were found in histopathologic examinations in the CTOIDD-saline and eye drop-NVCM groups, while significantly less inflammation was documented in the CTOIDD-NVCM (p<0.05) group.

Conclusion

CTOIDD with NVCM effectively reduced the severity and treated acute bacterial S. aureus keratitis infection in a rabbit model. The presented approach of CTOIDD with NVCM appears to be a promising therapeutic approach for severe acute bacterial keratitis.

New Approach in Ocular Drug Delivery: In vitro and ex vivo Investigation of Cyclodextrin-Containing, Mucoadhesive Eye Drop Formulations

Background

Optimal transcorneal penetration is necessary for ocular therapy; meanwhile, it is limited by the complex structure and defensive mechanisms of the eye. Antimicrobial stability of topical ophthalmic formulations is especially important. According to previous studies, the mostly used preservative, benzalkonium-chloride is irritative and toxic on corneal epithelial cells; therefore, novel non-toxic, antimicrobial agents are required. In this study, prednisolone-containing ophthalmic formulations were developed with expected optimal permeation without toxic or irritative effects.

Methods

The toxicity and permeability of prednisolone-containing eye drops were studied on a human corneal epithelial cell line (HCE-T) and ex vivo cornea model. The lipophilic drug is dissolved by the formation of cyclodextrin inclusion complex. Zinc-containing mucoadhesive biopolymer was applied as an alternative preservative agent, whose toxicity was compared with benzalkonium-chloride.

Results

As the results show, benzalkonium-chloride-containing samples were toxic on HCE-T cells. The biopolymer caused no cell damage after the treatment. This was confirmed by immunohistochemistry assay. The in vitro permeability was significantly higher in formulations with prednisolone-cyclodextrin complex compared with suspension formulation. According to the ex vivo permeability study, the biopolymer-containing samples had significantly lower permeability.

Conclusion

Considering the mucoadhesive attribute of target formulations, prolonged absorption is expected after application with less frequent administration. It can be stated that the compositions are innovative approaches as novel non-toxic ophthalmic formulations with optimal drug permeability.

A sustained release cysteamine microsphere/thermoresponsive gel eyedrop for corneal cystinosis improves drug stability

Cystinosis is a rare, metabolic, recessive genetic disease in which the intralysosomal accumulation of cystine leads to system wide organ and tissue damage. In the eye, cystine accumulates in the cornea as corneal cystine crystals and severely impacts vision. Corneal cystine crystals are treated with cysteamine eyedrops when administrated 6 to 12 times day and used within 1 week. The strict dosing regimen and poor stability are inconvenient and add to the burden of therapy. To reduce the dosing frequency and improve the stability, we present reformulation of cysteamine into a novel controlled release eyedrop. In this work, we characterize and evaluate a topical drug delivery system comprised of encapsulated cysteamine in polymer microspheres with a thermoresponsive gel carrier. Spray-dried encapsulation of cysteamine was performed. In vitro cysteamine release, stability, and ocular irritation and corneal permeation were evaluated. The data suggest that encapsulated cysteamine improves the stability to 7 weeks when compared with 1-week aqueous cysteamine eyedrops. Release studies from one drop of our system show that cysteamine release was present for 24 h and above the minimum cysteamine eyedrop amount (6 drops). Cysteamine from our system also resulted in negligible irritation and enhanced permeation when compared with traditional cysteamine eyedrops. In vivo studies were implemented to support ease of administration, tolerability, and retention for 24 h. These studies suggest that our controlled release delivery system may provide stable cysteamine from a safe, once daily gel eyedrop.

Topical drug delivery to the posterior segment of the eye: Thermodynamic considerations

Almost all studies on non-invasive topical drug delivery to the eye have emphasized the importance of biological barriers, static membrane barriers such as the cornea and the conjunctiva/sclera and dynamic barriers such as the lacrimal drainage. Hardly any have discussed the importance of the thermodynamic activity of the permeating drug molecules. Most drugs permeate from the eye surface into the eye by passive diffusion where, according to Fick's first law, the drug concentration gradient over the various permeation barriers (e.g., the tear fluid and the lipophilic membrane barriers) is the driving force. At the barrier interphases the dissolved drug molecules must partition from one barrier to another. For example, at the tear-cornea interphase the drug molecules must partition from the aqueous exterior into the lipophilic membrane. The drug partition coefficient between two phases is commonly defined as the equilibrium concentration ratio. However, these are only approximations. The actual driving force in Fick's first law is the gradient of the chemical potential and the equilibrium between two phases is attained when the chemical potential of the drug in one phase is equal to that in the other phase. Here the importance of thermodynamic considerations in topical drug delivery to the eye is reviewed.

Advancement on Sustained Antiviral Ocular Drug Delivery for Herpes Simplex Virus Keratitis: Recent Update on Potential Investigation

The eyes are the window to the world and the key to communication, but they are vulnerable to multitudes of ailments. More serious than is thought, corneal infection by herpes simplex viruses (HSVs) is a prevalent yet silent cause of blindness in both the paediatric and adult population, especially if immunodeficient. Globally, there are 1.5 million new cases and forty thousand visual impairment cases reported yearly. The Herpetic Eye Disease Study recommends topical antiviral as the front-line therapy for HSV keratitis. Ironically, topical eye solutions undergo rapid nasolacrimal clearance, which necessitates oral drugs but there is a catch of systemic toxicity. The hurdle of antiviral penetration to reach an effective concentration is further complicated by drugs’ poor permeability and complex layers of ocular barriers. In this current review, novel delivery approaches for ocular herpetic infection, including nanocarriers, prodrugs, and peptides are widely investigated, with special focus on advantages, challenges, and recent updates on in situ gelling systems of ocular HSV infections. In general congruence, the novel drug delivery systems play a vital role in prolonging the ocular drug residence time to achieve controlled release of therapeutic agents at the application site, thus allowing superior ocular bioavailability yet fewer systemic side effects. Moreover, in situ gel functions synergistically with nanocarriers, prodrugs, and peptides. The findings support that novel drug delivery systems have potential in ophthalmic drug delivery of antiviral agents, and improve patient convenience when prolonged and chronic topical ocular deliveries are intended.

Zoudani E, Daliri R, Aghamirsalim M, Raahemifar K. Biodegradable Nanoparticle for Cornea Drug Delivery: Focus Review

During recent decades, researchers all around the world have focused on the characteristic pros and cons of the different drug delivery systems for cornea tissue change for sense organs. The delivery of various drugs for cornea tissue is one of the most attractive and challenging activities for researchers in biomaterials, pharmacology, and ophthalmology. This method is so important for cornea wound healing because of the controllable release rate and enhancement in drug bioavailability. It should be noted that the delivery of various kinds of drugs into the different parts of the eye, especially the cornea, is so difficult because of the unique anatomy and various barriers in the eye. Nanoparticles are investigated to improve drug delivery systems for corneal disease. Biodegradable nanocarriers for repeated corneal drug delivery is one of the most attractive and challenging methods for corneal drug delivery because they have shown acceptable ability for this purpose. On the other hand, by using these kinds of nanoparticles, a drug could reside in various part of the cornea for longer. In this review, we summarized all approaches for corneal drug delivery with emphasis on the biodegradable nanoparticles, such as liposomes, dendrimers, polymeric nanoparticles, niosomes, microemulsions, nanosuspensions, and hydrogels. Moreover, we discuss the anatomy of the cornea at first and gene therapy at the end.

Ion Exchange Nanoparticles for Ophthalmic Drug Delivery

We report here on ion-exchange polymeric nanoparticles from a linear copolymer of maleic anhydride methyl vinyl ether esterified with 30% octadecanol. The side chains for the polymer structure were optimized through metadynamics simulations, which revealed the use of octadecanol esters generates ideal free energy surfaces for drug encapsulation and release. Nanoparticles were synthesized using a solvent evaporation-precipitation method by mixing the polymer solution in acetone into water; upon acetone evaporation, a nanodispersion with an average particle size of ∼150 nm was obtained. Gentamicin sulfate, possessing five amino groups, was spontaneously entrapped in the nanocarrier by ionic interactions. Encapsulation efficiency increases significantly with the increase in pH and ionic strength. In vivo results demonstrate high gentamicin (GM) content in the enteric chamber (AUC 8207 ± 1334 (μg min)/mL) compared to 3% GM solution (AUC 2024 ± 438 (μg min)/mL). The formulation was also able to significantly extend the release of gentamicin when applied to rabbit cornea. These anionic nanoparticles can be used for extended-release of other cationic drugs.

Glycol chitosan/oxidized hyaluronic acid hydrogel film for topical ocular delivery of dexamethasone and levofloxacin

In the present study, we fabricated a glycol chitosan/oxidized hyaluronic acid hydrogel film with promising potential for the dual ophthalmic delivery of dexamethasone (Dex) and levofloxacin (Lev). Utilizing different oxidation degrees of oxidized hyaluronic acid (OHA), several blank hydrogel films and Lev-loaded hydrogel films were successfully fabricated. With an increase in the oxidation degree of OHA, the swelling ratio of the hydrogel films decreased accordingly. The hydrogel films displayed a stepwise release of Lev and Dex, with Lev rapidly released from the hydrogel film, followed by a sustained release of Dex. Lev-loaded hydrogel films revealed a potent capacity to inhibit bacterial growth in different bacterial strains. In lipopolysaccharide-activated RAW264.7 macrophages, the formulated hydrogel films displayed potent in vitro anti-inflammatory activity by significantly downregulating various inflammatory cytokines. Overall, the fabricated hydrogel film acting as a dual drug delivery system might be a promising vehicle for the treatment of postoperative endophthalmitis.

HPLC-UV analytical validation of a method for quantification of progesterone in ex vivo trans-corneal and trans-scleral diffusion studies

Progesterone (PG) diminishes free radical damage and thus can afford protection against oxidative stress affecting the retina. The therapeutic use of PG is limited because it is a highly hydrophobic steroid hormone with very low solubility in water. This is the main drawback for the therapeutic application of PG at ocular level. The aims of this study were: (i) to analyze if PG causes ocular irritation (ii) to validate a HPLC method to determine PG in ex vivo studies and (iii) to evaluate PG permeation through cornea and sclera. A high performance liquid chromatographic method was developed and validated to detect PG incorporated to β-cyclodextrin using a Waters Sunfire C18 (150 × 4.6 mm) reverse-phase column packed with 5 μm silica particles using a mobile phase consisted of a mixture of acetonitrile (ACN) and pure water 80:20 (v/v), pH 7.4. The limit of detection and the limit of quantification for 50 μL injection of PG were found to be 0.42 and 1.26 μg/mL, respectively. The calibration curve showed excellent linearity over the concentration range (0.5 μg/mL to 100 μg/mL). As proof of concept, ex-vivo experiments to investigate PG permeation through cornea and sclera with vertical diffusion cells were carried out to quantify PG diffusion. Ex vivo experiments demonstrate its applicability to investigate permeation levels of PG from 6.57 ± 0.37 μg/cm² at cornea and 8.13 ± 0.85 μg/cm² sclera. In addition, at the end of diffusion studies the amount of PG retained in each tissue was also quantified, and it was 40.87 ± 9.84 μg/cm² (mean ± SD; n = 6) in cornea and 56.11 ± 16.67 μg/cm² (mean ± SD; n = 6) in sclera.

Evaluation of commercial soft contact lenses for ocular drug delivery: A review

Soft contact lenses have generated growing interest in ocular drug delivery due to their potential to enhance drug bioavailability in ocular tissues. Commercially available soft contact lenses offer several advantages for ocular drug delivery as they are manufactured on a large scale, which guarantees the availability of a consistent and reproducible product, and their favorable safety profile is well-established through broad clinical use. Here we review the rationale for using commercially available soft contact lenses for ocular drug delivery; summarize the evolution of the materials used in contact lens fabrication; and explore various methods used to improve the drug release characteristics and its tissue penetration. While significant progress has been made, several issues still require further attention for the commercial launch of a viable drug-eluting contact lens product, including control of initial burst release, shelf-life stability, and drug loss during processing or storage.

Nanoformulations for Ocular Delivery of Drugs - A Patent Perspective

Efficient delivery of ocular therapeutics with improved efficacy, enhanced bioavailability, and acceptable patient compliance presents unique challenges. This can be attributed to the presence of protective mechanisms, physicobiological barriers, and structural obstacles in the eye. Nanotherapeutic interventions have been explored extensively over the past few years to overcome these limitations. The present review focusses on the nanoformulations developed for the diagnosis and treatment of various ocular diseases besides providing an in-depth insight into the patents reported for the same.

Mucus-Penetrating Particles and the Role of Ocular Mucus as a Barrier to Micro- and Nanosuspensions

The ocular surface is naturally covered with a layer of mucus. Along with other functions, this mucus layer serves to trap and eliminate foreign substances, such as allergens, pathogens, and debris. In playing this pivotal role, mucus can also hinder topical delivery of therapeutics to the eye. Recent studies provide evidence that drugs formulated as traditional micro- or nanoparticles are susceptible to entrapment and rapid clearance by ocular mucus. Mucus-penetrating particles (MPPs) is a nanoparticle technology that emerged over the past decade. With a muco-inert surface and a particle size smaller than the mucus mesh size, MPPs can diffuse in ex vivo mucus essentially freely. Preclinical studies have shown that, compared with particles lacking the mucus-penetrating attributes, MPPs can improve the uniformity of drug particle distribution on mucosal surfaces and enhance drug delivery to ocular tissues.

The prominence of the dosage form design to treat ocular diseases

The eye is susceptible to various diseases commonly difficult to treat. To overcome the barriers imposed by this organ for required drugs penetration, technological strategies have been implemented to ocular formulations. Among them are the use of temperature or electric stimuli and the development of nanoparticles. The objective of this review is to present the main barriers to ocular drug delivery and to discuss strategies used in the development of ocular dosage forms, primarily for topical delivery, to increase the local bioavailability of drugs, target their delivery and increase patient compliance. Results obtained in the last years related to the topical administration of liposomes, dendrimers, iontophoresis, among other nanoparticulate systems focused on ophthalmic delivery, will be addressed. Finally, some clinical trials and marketed formulations that use nanotechnology to topically treat eye diseases will be presented.

Chitosan Derivatives with Mucoadhesive and Antimicrobial Properties for Simultaneous Nanoencapsulation and Extended Ocular Release Formulations of Dexamethasone and Chloramphenicol Drugs

The aim of this work was to evaluate the effectiveness of neat chitosan (CS) and its derivatives with 2-acrylamido-2-methyl-1-propanesulfonic acid (AAMPS) and [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide (MEDSP) as appropriate nanocarriers for the simultaneous ocular administration of dexamethasone sodium phosphate (DxP) and chloramphenicol (CHL). The derivatives CS-AAMPS and CS-MEDSP have been synthesized by free-radical polymerization and their structure has been proved by Fourier-Transformed Infrared Spectroscopy (FT-IR) spectroscopy. Both derivatives exhibited low cytotoxicity, enhanced mucoadhesive properties and antimicrobial activity against Staphylococcus aureus (S.aureus) and Escherichia coli (E. coli). Encapsulation was performed via ionic crosslinking gelation using sodium tripolyphosphate (TPP) as the crosslinking agent. Dynamic light scattering measurements (DLS) showed that the prepared nanoparticles had bimodal distribution and sizes ranging from 50-200 nm and 300-800 nm. Drugs were encapsulated in their crystalline (CHL) or amorphous (DexSP) form inside nanoparticles and their release rate was dependent on the used polymer. The CHL dissolution rate was substantially enhanced compared to the neat drug and the release time was extended up to 7 days. The release rate of DexSP was much faster than that of CHL and was prolonged up to 3 days. Drug release modeling unveiled that diffusion is the main release mechanism for both drugs. Both prepared derivatives and their drug-loaded nanoparticles could be used for extended and simultaneous ocular release formulations of DexSP and CHL drugs.

Recent Advances in the Design of Topical Ophthalmic Delivery Systems in the Treatment of Ocular Surface Inflammation and Their Biopharmaceutical Evaluation

Ocular inflammation is one of the most common symptom of eye disorders and diseases. The therapeutic management of this inflammation must be rapid and effective in order to avoid deleterious effects for the eye and the vision. Steroidal (SAID) and non-steroidal (NSAID) anti-inflammatory drugs and immunosuppressive agents have been shown to be effective in treating inflammation of the ocular surface of the eye by topical administration. However, it is well established that the anatomical and physiological ocular barriers are limiting factors for drug penetration. In addition, such drugs are generally characterized by a very low aqueous solubility, resulting in low bioavailability as only 1% to 5% of the applied drug permeates the cornea. The present review gives an updated insight on the conventional formulations used in the treatment of ocular inflammation, i.e., ointments, eye drops, solutions, suspensions, gels, and emulsions, based on the commercial products available on the US, European, and French markets. Additionally, sophisticated formulations and innovative ocular drug delivery systems will be discussed. Promising results are presented with micro- and nanoparticulated systems, or combined strategies with polymers and colloidal systems, which offer a synergy in bioavailability and sustained release. Finally, different tools allowing the physical characterization of all these delivery systems, as well as in vitro, ex vivo, and in vivo evaluations, will be considered with regards to the safety, the tolerance, and the efficiency of the drug products.

Hydrogel Biomaterials for Application in Ocular Drug Delivery

There are many challenges involved in ocular drug delivery. These are a result of the many tissue barriers and defense mechanisms that are present with the eye; such as the cornea, conjunctiva, the blinking reflex, and nasolacrimal drainage system. This leads to many of the conventional ophthalmic preparations, such as eye drops, having low bioavailability profiles, rapid removal from the administration site, and thus ineffective delivery of drugs. Hydrogels have been investigated as a delivery system which is able to overcome some of these challenges. These have been formulated as standalone systems or with the incorporation of other technologies such as nanoparticles. Hydrogels are able to be formulated in such a way that they are able to change from a liquid to gel as a response to a stimulus; known as "smart" or stimuli-responsive biotechnology platforms. Various different stimuli-responsive hydrogel systems are discussed in this article. Hydrogel drug delivery systems are able to be formulated from both synthetic and natural polymers, known as biopolymers. This review focuses on the formulations which incorporate biopolymers. These polymers have a number of benefits such as the fact that they are biodegradable, biocompatible, and non-cytotoxic. The biocompatibility of the polymers is essential for ocular drug delivery systems because the eye is an extremely sensitive organ which is known as an immune privileged site.

PEGylated microemulsion for dexamethasone delivery to posterior segment of eye

Dexamethasone (Dex) is one of the most commonly used anti-vascular endothelial growth factor (anti-VEGF) drugs being used in ocular diseases whether it is associated with anterior segment or posterior segment. For diseases of posterior segment of eye, Dex is delivered as intravitreal implant but the route used for the same is very invasive and poses several hazards on long term use. Thus, topical formulation with ability to outreach retina from ocular surface was intended. Thus, polyethylene glycolylated (PEGylated) microemulsion (ME) was attempted as it can cross the membranous barrier of eye (cornea, conjunctiva, and sclera) and remain afloat in fluidic barrier (aqueous humor, choroid, etc.) as well. Present investigation involved development of Dex-loaded PEGylated ME which was stable, non-toxic to ocular surface, capable to cross cornea and enhanced residence as well as availability of loaded drug in retina. The developed PEGylated ME had physicochemical properties like size (15.98 ± 3.05 nm), polydispersity index (0.25 ± 0.04), zeta potential (-0.04 ± 0.47 mV), percentage transmittance (99.84 ± 1.17%), and drug content (99.32 ± 3.21%). It showed sustained Dex release in in vitro conditions. It also displayed efficiency in enhancing retention of drugs in retina in in vivo pharmacokinetic study on Sprague-Dawley rats. PEGylated ME can retain the drug in retina of rats longer than simple eye drop solution via topical ocular route.

Potential application of liposomal nanodevices for non-cancer diseases: an update on design, characterization and biopharmaceutical evaluation

Liposomes, lipid-based vesicular systems, have attracted major interest as a means to improve drug delivery to various organs and tissues in the human body. Recent literature highlights the benefits of liposomes for use as drug delivery systems, including encapsulating of both hydrophobic and hydrophilic cargos, passive and active targeting, enhanced drug bioavailability and therapeutic effects, reduced systemic side effects, improved cargo penetration into the target tissue and triggered contents release. Pioneering work of liposomes researchers led to introduction of long-circulating, ligand-targeted and triggered release liposomes, as well as, liposomes containing nucleic acids and vesicles containing combination of cargos. Altogether, these findings have led to widespread application of liposomes in a plethora of areas from cancer to conditions such as cardiovascular, neurologic, respiratory, skin, autoimmune and eye disorders. There are numerous review articles on the application of liposomes in treatment of cancer, which seems the primary focus, whereas other diseases also benefit from liposome-mediated treatments. Therefore, this article provides an illustrated detailed overview of liposomal formulations, in vitro characterization and their applications in different disorders other than cancer. Challenges and future directions, which must be considered to obtain the most benefit from applications of liposomes in these disorders, are discussed.

Comparative Assessment of Distribution Characteristics and Ocular Pharmacokinetics of Norvancomycin Between Continuous Topical Ocular Instillation and Hourly Administration of Eye Drop

Background

The aim of this study was to compare the distribution characteristics and ocular pharmacokinetics of norvancomycin (NVCM) in ocular tissues of the anterior segment between continuous topical ocular instillation and hourly administration of eye drop in rabbits.

Methods

Sixty rabbits were randomly divided into two groups: continuous topical ocular instillation drug delivery (CTOIDD) group and eye drop (control) group. In the CTOIDD group, NVCM solution (50 mg/mL) was perfused to the ocular surface using the CTOIDD system at 2 mL/h up to 10 h and the same solution was administered at one drop (50 μL) per hour for 10 h in the control group. Animals (N=6 per time-point per group) were humanely killed at 2, 4, 6, 10, and 24 h to analyze their ocular tissues and plasma. The concentrations of NVCM in the conjunctiva, cornea, aqueous humour, iris, ciliary body and plasma were measured by HPLC with photodiode array detector. The pharmacokinetic parameters were calculated by Kinetica 5.1.

Results

The highest concentrations of NVCM for the CTOIDD group and control group were 2105.45±919.89 μg/g and 97.18±43.14 μg/g in cornea, 3033.92±1061.95 μg/g and 806.99±563.02 μg/g in conjunctiva, 1570.19±402.87 μg/g and 46.93±23.46 μg/g in iris, 181.94±47.11 μg/g and 15.38±4.00 μg/g in ciliary body, 29.78±4.90 μg/mL and 3.20±1.48 μg/mL in aqueous humour, and 26.89±5.57 μg/mL and 1.90±1.87 μg/mL in plasma, respectively. The mean NVCM levels significantly increased at all time-points in cornea, iris, and ciliary body (p<0.05) in the CTOIDD group. The AUC_0–24 values in the CTOIDD group were 27,543.70 μg·h/g in cornea, 32,514.48 μg·h/g in conjunctiva, 8631.05 μg·h/g in iris, 2194.36 μg·h/g in ciliary body and 343.9 μg·h/mL in aqueous humour, which were higher than for the eye drop group in all tissues.

Conclusion

Since continuous instillation of NVCM with CTOIDD could reach significantly higher concentrations and was sustained for a longer period compared with hourly administration of eye drop, CTOIDD administered NVCM could be a possible method to treat bacterial keratitis.

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Cytosine-functionalized bioinspired hydrogels for ocular delivery of antioxidant transferulic acid

Contact lenses (CLs) are being pointed out as feasible platforms for controlled delivery of ophthalmic drugs. Bioinspired strategies may endow CLs with affinity for a given drug by mimicking its physiological receptor using adequate functional monomers and tuning their conformation in the space through the molecular imprinting technology. However, there are some active substances, such as efficient antioxidant agents, that cannot be used as templates because they degrade during polymerization or even hinder the polymerization itself. Therefore, the development of CLs able to sustain the release of antioxidants for the prevention and/or treatment of several age-related and light-induced eye diseases has not been explored yet. Searching for an alternative bioinspired strategy, the present work relies on the fact that some drugs owe their therapeutic action to their ability to interact with nucleotides that build up DNA and RNA. Thus, the aim of this work was to design hydrogels functionalized with the nitrogenous base cytosine for the controlled uptake and release of transferulic acid (TA) having a complementary chemical structure in terms of hydrogen bonding and π-π stacking ability. Hydrogels were prepared from mixtures of 2-hydroxyethyl methacrylate (HEMA), glycidyl methacrylate (GMA) and ethyleneglycolphenylether methacrylate (EGPEM). GMA was used as a bridge to immobilize cytosine after hydrogel synthesis, while EGPEM was added to reinforce hydrophobic interactions with TA. The hydrogels were characterized in terms of suitability to be used as CLs (swelling, light transmission, mechanical properties, biocompatibility) and capability to host TA and sustain its release in lachrymal fluid while maintaining the antioxidant activity. Relevantly, the bioinspired CLs favored TA accumulation in cornea and sclera tissues.

Physiologically Based Pharmacokinetic Model to Support Ophthalmic Suspension Product Development

FDA's Orange Book lists 17 currently marketed active pharmaceutical ingredients (API) formulated within ophthalmic suspensions in which a majority has 90% or more of the API undissolved. We used an ocular physiologically based pharmacokinetic (O-PBPK) model to compare a suspension with a solution for ophthalmic products with dexamethasone (Dex) as the model drug. Simulations with a Dex suspension O-PBPK model previously verified in rabbit were used to characterize the consequences of drug clearance mechanism in the precorneal compartment on pharmacokinetic (PK) exposure and to assess the ocular and systemic PK characteristics of ophthalmic suspensions with different strengths or magnitudes of viscosity. O-PBPK-based simulations show that (1) Dex suspension 0.05% has a 2.5- and 5-fold higher AUC in aqueous humor and plasma, respectively, than the Dex saturated solution; (2) strength increase by 5- and 10-fold induces a respective 2.2- and 3.3-fold increase in aqueous humor and 4.4- and 8.6-fold increase in plasma C_max and AUC; and (3) increasing formulation viscosity (from 1.6 to 75 cP) causes an overall increase in API available for absorption in the cornea resulting in a higher ocular C_max and AUC with no significant impact on systemic exposure. This research demonstrates that solid particles present in a suspension can not only help to achieve a higher ocular exposure but also unfavorably raise systemic exposure. A model able to correlate formulation changes to both ocular and plasma exposure is a necessary tool to support ocular product development taking into consideration both local efficacy and systemic safety aspects.

Intraocular administration of tetramethylpyrazine hydrochloride to rats: a direct delivery pathway for brain targeting?

The purpose of this study was to compare the pharmacokinetic profile of tetramethylpyrazine hydrochloride (TMPH) in rat plasma and tissues following intravenous (iv), intragastric (ig) and intraocular (io) administration. After io, ig and iv administration of a single dose at 10 mg/kg, tissue and plasma samples drawn from the femoral artery were collected at timed intervals. The concentration of TMPH in the samples was analyzed using high-performance liquid chromatography (HPLC). The area under the concentration-time curve (AUC) and the drug targeting efficiency percentage (DTE(%)) were calculated to evaluate the targeting efficiency of the drug with the three different administration routes. After io administration, TMPH was rapidly absorbed to reach its peak plasma and brain concentration within 5 min. The systemic bioavailability obtained with io administration was greater than that obtained through the ig route (63.22% vs. 16.88%). The AUCt rank order of the iv administration group was AUCkidney >AUCheart >AUCliver >AUCbrain >AUCspleen >AUClung; that of the ig administration group as AUCkidney >AUCliver >AUCheart >AUCspleen >AUCbrain >AUClung; while that of the io administration group was AUCkidney >AUCbrain >AUCheart >AUCliver >AUCspleen >AUClung. The ratio of the AUCbrain value between the io route and iv injection was 1.05, which was greater than that obtained after ig administration (0.30). The DTE after io administration was calculated: brain (165.72%), heart (97.76%), liver (113.06%), spleen (105.31%), lung (163.40%) and kidney (135.31%). The io administration group showed obvious drug transport to the brain. These results indicate that TMPH is rapidly absorbed from the eye into the systemic circulation, and there may be a direct translocation pathway for TMPH from the eye to the brain. Therefore, io administration of TMPH could be a promising alternative to intravenous and oral approaches.

Ocular Drug Delivery: Present Innovations and Future Challenges

Ocular drug delivery has always been a challenge for ophthalmologists and drug-delivery scientists due to the presence of various anatomic and physiologic barriers. Inimitable static and dynamic ocular barriers not only exclude the entry of xenobiotics but also discourage the active absorption of therapeutic agents. Designing an ideal delivery scheme should include enhanced drug bioavailability and controlled release of drug at the site of action, which can overcome various ocular barriers. Conventional ophthalmic medications include the use of topical eye drops and intravitreal injections of anti-vascular endothelial growth factor agent for treatment of anterior and posterior segment disorders, respectively. Current inventions for anterior ocular segment disorders such as punctum plugs, ocular implants, drug-eluting contact lenses, and ocular iontophoresis represent state-of-the-art inventions for sustained and controlled drug release. Parallel efforts for ocular drug delivery technologies for back of the eye disorders have resulted in the approval of various intravitreal implants. Novel drug-delivery technologies, including nanoparticles, nanomicelles, dendrimers, microneedles, liposomes, and nanowafers, are increasingly studied for anterior and posterior disorders. To achieve patient compliance for back of the eye disorders, novel approaches for noninvasive delivery of potent therapeutic agents are on the rise. In this review article, we discuss past successes, present inventions, and future challenges in ocular drug-delivery technologies. This expert opinion also discusses the future challenges for ocular drug-delivery systems and the clinical translatable potential of nanotechnology from benchtop to bedside.

Effect of different doses of borneol on the pharmacokinetics of vinpocetine in rat plasma and brain after intraocular administration

The effect of different doses of borneol on the pharmacokinetics of vinpocetine after intraocular administration in the rat plasma and the brain was investigated.Intraocular administration of vinpocetine (3 mg/kg) was performed, in combination with different doses (0, 5, 10, and 20 mg/kg) of borneol. Intravenous administration of vinpocetine was used as a control (1 mg/kg). The concentrations of vinpocetine in the rat plasma and the brain were determined using a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method. Using the non-compartmental models with the DSA 2.0 software, the main pharmacokinetics parameters and the brain-targeting effect evaluated.In comparison with intravenous administration, after intraocular administration of vinpocetine alone, the absolute bioavailability (F) of vinpocetine was 43.82% for the plasma, and the drug target index (DTI) was 1.05 for the brain. After intraocular administration of vinpocetine combined with different doses of borneol, the relative bioavailability (Fr) of vinpocetine in the plasma was increased by 130.46-182.90%. The relative bioavailability (Fr) of vinpocetine in the brain was improved (147.19-225.36%). The DTI was 1.12, 1.18, and 1.21 for 5, 10, and 20 mg/kg of borneol, respectively.Compared with the intraocular administration of vinpocetine alone, the co-administration of different doses of borneol resulted in an obvious brain targeting effect.

Current Approaches to Use Cyclodextrins and Mucoadhesive Polymers in Ocular Drug Delivery—A Mini-Review

Ocular drug delivery provides a challenging opportunity to develop optimal formulations with proper therapeutic effects and acceptable patient compliance because there are many restricting factors involved, such as complex anatomical structures, defensive mechanisms, rapid drainage, and applicability issues. Fortunately, recent advances in the field mean that these problems can be overcome through the formulation of innovative ophthalmic products. Through the addition of solubility enhancer cyclodextrin derivatives and mucoadhesive polymers, the permeability of active ingredients is improved, and retention time is increased in the ocular surface. Therefore, preferable efficacy and bioavailability can be achieved. In this short review, the authors describe the theoretical background, technological possibilities, and the current approaches in the field of ophthalmology.

Ocular Biodistribution Studies using Molecular Imaging

Classical methodologies used in ocular pharmacokinetics studies have difficulties to obtain information about topical and intraocular distribution and clearance of drugs and formulations. This is associated with multiple factors related to ophthalmic physiology, as well as the complexity and invasiveness intrinsic to the sampling. Molecular imaging is a new diagnostic discipline for in vivo imaging, which is emerging and spreading rapidly. Recent developments in molecular imaging techniques, such as positron emission tomography (PET), single-photon emission computed tomography (SPECT) and magnetic resonance imaging (MRI), allow obtaining reliable pharmacokinetic data, which can be translated into improving the permanence of the ophthalmic drugs in its action site, leading to dosage optimisation. They can be used to study either topical or intraocular administration. With these techniques it is possible to obtain real-time visualisation, localisation, characterisation and quantification of the compounds after their administration, all in a reliable, safe and non-invasive way. None of these novel techniques presents simultaneously high sensitivity and specificity, but it is possible to study biological procedures with the information provided when the techniques are combined. With the results obtained, it is possible to assume that molecular imaging techniques are postulated as a resource with great potential for the research and development of new drugs and ophthalmic delivery systems.

Posterior segment drug delivery for the treatment of exudative age-related macular degeneration and diabetic macular oedema

Inhibitors of vascular endothelial growth factors are used to treat a myriad of retinal conditions, including exudative age-related macular degeneration (AMD), diabetic macular oedema (DME) and diabetic retinopathy. Although effective, long-term efficacy is limited by the need for frequent and invasive intravitreal injections. The quest for sustained action therapeutics that can be delivered to target tissue in the least invasive manner is an arduous endeavour that has ended in premature failure for several technologies in Phase II or III trials. Nevertheless, there have been promising preclinical studies, and more are on the horizon: port delivery systems for the treatment of exudative AMD have entered Phase III trials and a wide array of preclinical studies have demonstrated the potential for nanoparticles, such as liposomes, dendrimers and cell penetrating peptides to deliver therapeutics into the posterior segment via minimally invasive routes. In this review, we discuss the challenges posed by ocular barriers for drug penetration and present the recent advancements of the most pertinent drug delivery platforms with a focus on the treatment of exudative AMD and DME.

Natamycin solid lipid nanoparticles - sustained ocular delivery system of higher corneal penetration against deep fungal keratitis: preparation and optimization

Background

Fungal keratitis (FK) is a serious pathogenic condition usually associated with significant ocular morbidity. Natamycin (NAT) is the first-line and only medication approved by the Food and Drug Administration for the treatment of FK. However, NAT suffers from poor corneal penetration, which limits its efficacy for treating deep keratitis.

Purpose

The objective of this work was to prepare NAT solid lipid nanoparticles (NAT-SLNs) to achieve sustained drug release and increased corneal penetration.

Methods

NAT-SLNs were prepared using the emulsification-ultrasonication technique. Box– Behnken experimental design was applied to optimize the effects of independent processing variables (lipid concentration [X₁], surfactant concentration [X₂], and sonication frequency [X₃]) on particle size (R₁), zeta potential (ZP; R₂), and drug entrapment efficiency (EE%) (R₃) as responses. Drug release profile, ex vivo corneal permeation, antifungal susceptibility, and cytotoxicity of the optimized formula were evaluated.

Results

The optimized formula had a mean particle size of 42 r.nm (radius in nanometers), ZP of 26 mV, and EE% reached ~85%. NAT-SLNs showed an extended drug release profile of 10 hours, with enhanced corneal permeation in which the apparent permeability coefficient (P_app) and steady-state flux (J_ss) reached 11.59×10⁻² cm h⁻¹ and 3.94 mol h⁻¹, respectively, in comparison with 7.28×10⁻² cm h⁻¹ and 2.48 mol h⁻¹ for the unformulated drug, respectively. Antifungal activity was significantly improved, as indicated by increases in the inhibition zone of 8 and 6 mm against Aspergillus fumigatus ATCC 1022 and a Candida albicans clinical isolate, respectively, and minimum inhibitory concentration values that were decreased 2.5-times against both of these pathogenic strains. NAT-SLNs were found to be non-irritating to corneal tissue. NAT-SLNs had a prolonged drug release rate^, that improved corneal penetration, and increased antifungal activity without cytotoxic effects on corneal tissues.

Conclusion

Thus, NAT-SLNs represent a promising ocular delivery system for treatment of deep corneal keratitis.

Drug delivery systems and novel formulations to improve treatment of rare corneal disease

As the field of ocular drug delivery grows so does the potential for novel drug discovery or reformulation in lesser-known diseases of the eye. In particular, rare corneal diseases are an interesting area of research because drug delivery is limited to the outermost tissue of the eye. This review will highlight the opportunities and challenges of drug reformulation and alternative treatment approaches for rare corneal diseases. The barriers to effective drug delivery and proposed solutions in development will be discussed along with an overview of corneal rare disease resources, their current treatments and ophthalmic drug delivery systems that could benefit such cases. The regulatory considerations for effective translation of orphan-designated products will also be discussed.