Transcorneal permeation in a corneal device of non-steroidal anti-inflammatory drugs in drug delivery systems

Fostering the unleashing potential of nanocarriers-mediated delivery of ocular therapeutics

Ocular delivery is the most challenging aspect in the field of pharmaceutical research. The major hurdle for the controlled delivery of drugs to the eye includes the physiological static barriers such as the complex layers of the cornea, sclera and retina which restrict the drug from permeating into the anterior and posterior segments of the eye. Recent years have witnessed inventions in the field of conventional and nanocarrier drug delivery which have shown considerable enhancement in delivering small to large molecules across the eye. The dynamic challenges associated with conventional systems include limited drug contact time and inadequate ocular bioavailability resulting from solution drainage, tear turnover, and dilution or lacrimation. To this end, various bioactive-based nanosized carriers including liposomes, ethosomes, niosomes, dendrimer, nanogel, nanofibers, contact lenses, nanoprobes, selenium nanobells, nanosponge, polymeric micelles, silver nanoparticles, and gold nanoparticles among others have been developed to circumvent the limitations associated with the conventional dosage forms. These nanocarriers have been shown to achieve enhanced drug permeation or retention and prolong drug release in the ocular tissue due to their better tissue adherence. The surface charge and the size of nanocarriers (10-1000 nm) are the important key factors to overcome ocular barriers. Various nanocarriers have been shown to deliver active therapeutic molecules including timolol maleate, ampicillin, natamycin, voriconazole, cyclosporine A, dexamethasone, moxifloxacin, and fluconazole among others for the treatment of anterior and posterior eye diseases. Taken together, in a nutshell, this extensive review provides a comprehensive perspective on the numerous facets of ocular drug delivery with a special focus on bioactive nanocarrier-based approaches, including the difficulties and constraints involved in the fabrication of nanocarriers. This also provides the detailed invention, applications, biodistribution and safety-toxicity of nanocarriers-based therapeutcis for the ophthalmic delivery.

Preparation and Evaluation of Modified Chitosan Nanoparticles Using Anionic Sodium Alginate Polymer for Treatment of Ocular Disease

Mucoadhesive nanoparticles offer prolonged drug residence time at the corneal epithelium by adhering to the mucous layer of the eye. Here, in this research investigation, voriconazole-loaded chitosan mucoadhesive nanoparticles (VCZ-MA-NPs) were modified to mucous-penetrating nanoparticles (VCZ-MP-NPs) by coating them with anionic polymer sodium alginate. The ionic gelation method was utilized to prepare mucoadhesive chitosan nanoparticles, which were further coated with sodium alginate to obtain the surface properties essential for mucous penetration. The developed VCZ-MA-NPs and VCZ-MP-NPs were evaluated extensively for physicochemical delineation, as well as in vitro and ex vivo studies. The particle size, polydispersity index, and ζ potential of the VCZ-MA-NPs were discovered to be 116 ± 2 nm, 0.23 ± 0.004, and +16.3 ± 0.9 mV, while the equivalent values for VCZ-MP-NPs were 185 ± 1 nm, 0.20 ± 0.01, and -24 ± 0.9 mV, respectively. The entrapment efficiency and drug loading were obtained as 88.06%±1.29% and 7.27% ± 0.95% for VCZ-MA-NPs and 91.31% ± 1.05% and 10.38% ± 0.87% for VCZ-MP-NPs, respectively. The formulations were found to be stable under different conditions (4 °C, 25 °C, and 40 °C). Chitosan nanoparticles and modified nanoparticles showed a spherical and smooth morphology under electron microscopic imaging. An excised caprine cornea was used for the ex vivo permeation study, exhibiting 58.98% ± 0.54% and 70.02% ± 0.61% drug permeation for VCZ-MA-NPs and VCZ-MP-NPs, respectively. The findings revealed that the mucous-penetrating nanoparticles could effectively pass through the corneal epithelium, thus overcoming the mucous barrier and fungal layer of the eye, which highlights their potential in the treatment of fungal keratitis.

The effects of addition of functional monomers and molecular imprinting on dual drug release from intraocular lens material

Although cataract surgery is considered a safe procedure, post-surgery complications such as endophthalmitis and ocular inflammation, may occur. To prevent this, antibiotics and anti-inflammatories are prescribed in the form of eye drops during the post-operatory period, but they lead to a low drug bioavailability in target tissues. The objective of this work is to develop an intraocular lens (IOL) material to deliver simultaneously one antibiotic, moxifloxacin (MXF), and one anti-inflammatory, diclofenac (DFN), in therapeutic concentrations to prevent both complications. The IOL material was modified through the incorporation of functional monomers, as well as molecular imprinting with both drugs using the same functional monomers, namely acrylic acid (AA), methacrylic acid (MAA), 4-vinylpiridine (4-VP) and a combination of MAA + 4-VP. The best results were obtained with MAA. Molecular imprinting did not influence the drug release, except with AA. Application of a mathematical model predicted that the released MXF and DFN concentrations would stay above the pre-determined MIC of S. aureus and S. epidermidis and the minimum values of IC50 of COX-1 and COX-2, for 9 and 14 days, respectively. Antibacterial tests showed that the released antibiotic remained active. The physical properties of the drug-loaded MAA-hydrogel remained adequate. The developed system proved to be non-irritant and non-cytotoxic.

Advanced nanodelivery platforms for topical ophthalmic drug delivery

Conventional eye drops have several limitations, including the need for multiple applications per dose, hourly based dosage regiments, and suboptimal ocular bioavailability (<5%). The efficacy of topical ophthalmic medications can be significantly improved by controlling their contact time with the adherent mucin layer and by inducing sustained release properties, thus allowing for a prolonged contact time of the drug with the ocular tissues, which eventually will lead to improved drug bioavailability and a significant decrease in the frequency of eyedrop instillation. In this review, we critically highlight recent and innovative nanodrug delivery platforms, with a primary focus on the integration of nanotechnology, biomaterials, and polymer chemistry to facilitate precise spatial and temporal control over sustained drug release to the cornea.

Distribution of polymeric nanoparticles in the eye: implications in ocular disease therapy

Advantages of polymeric nanoparticles as drug delivery systems include controlled release, enhanced drug stability and bioavailability, and specific tissue targeting. Nanoparticle properties such as hydrophobicity, size, and charge, mucoadhesion, and surface ligands, as well as administration route and suspension media affect their ability to overcome ocular barriers and distribute in the eye, and must be carefully designed for specific target tissues and ocular diseases. This review seeks to discuss the available literature on the biodistribution of polymeric nanoparticles and discuss the effects of nanoparticle composition and administration method on their ocular penetration, distribution, elimination, toxicity, and efficacy, with potential impact on clinical applications.

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.

Ocular Drug Delivery

Although the eye is an accessible organ for direct drug application, ocular drug delivery remains a major challenge due to multiple barriers within the eye. Key barriers include static barriers imposed by the cornea, conjunctiva, and retinal pigment epithelium and dynamic barriers including tear turnover and blood and lymphatic clearance mechanisms. Systemic administration by oral and parenteral routes is limited by static blood-tissue barriers that include epithelial and endothelial layers, in addition to rapid vascular clearance mechanisms. Together, the static and dynamic barriers limit the rate and extent of drug delivery to the eye. Thus, there is an ongoing need to identify novel delivery systems and approaches to enhance and sustain ocular drug delivery. This chapter summarizes current and recent experimental approaches for drug delivery to the anterior and posterior segments of the eye.

Topical nanodelivery system of lutein for the prevention of selenite-induced cataract

Cataracts are responsible for half of the world blindness, surgery being the only viable treatment. Lutein, a naturally occurring carotenoid in the eye, has the potential to reduce cataract progression by protecting the eye from photo-oxidative stress. To restore the eye's natural line of defense against photo-oxidative stress, a formulation was developed using zein and poly(lactic-co-glycolic acid) nanoparticles (NPs) embedded in an optimized bioadhesive thermosensitive gel for the delivery of lutein via topical application. Cataracts were induced in Crl:WI rats via selenite injection at 13 days post-partum, followed by 7 days of treatment with free lutein or lutein-loaded NPs administered orally or topically. Cataract severity was significantly reduced in rats treated with topical applications of lutein-loaded NPs compared to the positive control, while no significant differences were observed in rats treated with other lutein formulations including oral and topically applied free lutein.

Drug delivery to the eye anterior chamber by intraocular lenses: An in vivo concentration estimation model

Drug loaded intraocular lenses have been proposed as an alternative to the conventional post-cataract removal prophylaxis through topical drug administration, since the drug or combination of drugs released from the lenses are delivered directly to the target site. In this work, a mathematical model to estimate the concentration of drug released from such lenses in the eye aqueous humor was developed. To attain these estimated concentration profiles, partition and effective diffusivity coefficients for the specific lens material were obtained from standard in vitro release experiments. The model was validated by comparing the predicted aqueous humor concentrations with those obtained in in vivo studies where hydrophilic acrylic intraocular lens loaded with an antibiotic (moxifloxacin) were implanted in rabbits. Subsequently, other partition and effective diffusivity values were determined for levofloxacin, diclofenac and ketorolac in the same hydrophilic acrylic and in a second material, a silicone hydrogel. Predicted drug concentrations in the aqueous humor allowed an initial screening and evaluation of the most promising system for post-cataract removal prophylaxis, with the hydrophilic acrylic material presenting promising results, especially for moxifloxacin and diclofenac controlled release.

In vitro and ex vivo correlation of drug release from ophthalmic ointments

In vitro drug release testing and ex vivo transcorneal drug permeation can provide valuable information on the performance of the Q1/Q2 equivalent ointments prior to any animal studies. Good correlation between in vitro and ex vivo drug release may be indicative of good in vitro and in vivo correlation. Accordingly, it is important to investigate in vitro as well as ex vivo drug release from Q1/Q2 equivalent ophthalmic ointments and evaluate whether a correlation between these release profiles can be established. Four Q1/Q2 equivalent loteprednol etabonate ointments were prepared using different processing methods and excipient sources. The rheological parameters (crossover modulus and K value) of the four formulations were determined. The in vitro drug release testing of the four ointment formulations were performed using three different apparati (Franz diffusion cells, USP apparatus 2 with enhancer cells and USP apparatus 4 with semisolid adapters). Three models (zero order, logarithmic and the Higuchi model) were used to study the release kinetics of the ointment formulations. The transcorneal (rabbit corneas) permeation studies were performed using spherical joint Franz diffusion cells. The USP apparatus 4 method demonstrated better discriminatory ability compared to the USP apparatus 2 and the Franz diffusion cell methods. The in vitro release profiles of the four Q1/Q2 equivalent ointments with manufacturing differences showed a better fit using the Higuchi model (R² > 0.98) for all three release testing methods, compared to the other two models. Ex vivo drug release through the rabbit corneas displayed zero order release kinetics. A logarithmic correlation between rheological parameters (crossover and K value) and transcorneal flux were established. In addition, a plot of the in vitro release rate against the ex vivo release flux of the four ointment formulations, yielded a straight line (R² > 0.98) for all three release methods. Accordingly, the rheological parameters may be useful in predicting in vitro as well as ex vivo release properties.

Cyclodextrin Enhances Corneal Tolerability and Reduces Ocular Toxicity Caused by Diclofenac

With advances in refractive surgery and demand for cataract removal and lens replacement, the ocular use of nonsteroidal anti-inflammatory drugs (NSAIDs) has increased. One of the most commonly used NSAIDs is diclofenac (Diclo). In this study, cyclodextrins (CDs), α-, β-, γ-, and HP-β-CDs, were investigated with in vitro irritation and in vivo ulceration models in rabbits to reduce Diclo toxicity. Diclo-, α-, β-, γ-, and HP-β-CD inclusion complexes were prepared and characterized and Diclo-CD complexes were evaluated for corneal permeation, red blood cell (RBCs) haemolysis, corneal opacity/permeability, and toxicity. Guest- (Diclo-) host (CD) solid inclusion complexes were formed only with β-, γ-, and HP-β-CDs. Amphipathic properties for Diclo were recorded and this surfactant-like functionality might contribute to the unwanted effects of Diclo on the surface of the eye. Contact angle and spreading coefficients were used to assess Diclo-CDs in solution. Reduction of ocular toxicity 3-fold to16-fold and comparable corneal permeability to free Diclo were recorded only with Diclo-γ-CD and Diclo-HP-β-CD complexes. These two complexes showed faster healing rates without scar formation compared with exposure to the Diclo solution and to untreated groups. This study also highlighted that Diclo-γ-CD and Diclo-HP-β-CD demonstrated fast healing without scar formation.

Nanotherapies for the treatment of ocular diseases

The topical route is the most frequent and preferred way to deliver drugs to the eye. Unfortunately, the very low ocular drug bioavailability (less than 5%) associated with this modality of administration, makes the efficient treatment of several ocular diseases a significant challenge. In the last decades, it has been shown that specific nanocarriers can interact with the ocular mucosa, thereby increasing the retention time of the associated drug onto the eye, as well as its permeability across the corneal and conjunctival epithelium. In this review, we comparatively analyze the mechanism of action and specific potential of the most studied nano-drug delivery carriers. In addition, we present the success achieved until now using a number of nanotherapies for the treatment of the most prevalent ocular pathologies, such as infections, inflammation, dry eye, glaucoma, and retinopathies.

Design and Evaluation of Ocular Controlled Delivery System for Diclofenac Sodium

Diclofenac sodium as ophthalmic dosage form is used for the treatment of the pain, swelling and redness of patients' eyes recovering from cataract surgery; however, it faces the bioavailability limitation of eye drops due to effective protective mechanisms and corneal barrier functions in the eyes. Therefore, this investigation was aimed to develop ocular film formulations to achieve controlled drug release. Drug films were prepared using polymers, namely hydroxypropyl methylcellulose (HPMC) and polyvinyl pyrrolidone (PVP), Eudragit RL PO, and Eudragit RS PO by solvent casting method considering parameters such as drug: polymer ratio, different polymer combinations as well as plasticizer effect. Ocular films were evaluated for various physicochemical parameters such as physical characters, film thickness, uniformity of weight, drug content, swelling index, mucoadhesion time and in-vitro release study. Ocular films complied with all physicochemical parameters underwent in-vitro release study. Finally, the film formulation with HPMC: Eudragit RS PO 1:1 ratio, Drug: Polymer ratio 1:45 and glycerin as plasticizer showed controlled and prolonged release following the zero order and non-Fickian transport.

Novel strategies for anterior segment ocular drug delivery

Research advancements in pharmaceutical sciences have led to the development of new strategies in drug delivery to anterior segment. Designing a new delivery system that can efficiently target the diseased anterior ocular tissue, generate high drug levels, and maintain prolonged and effective concentrations with no or minimal side effects is the major focus of current research. Drug delivery by traditional method of administration via topical dosing is impeded by ocular static and dynamic barriers. Various products have been introduced into the market that prolong drug retention in the precorneal pocket and to improve bioavailability. However, there is a need of a delivery system that can provide controlled release to treat chronic ocular diseases with a reduced dosing frequency without causing any visual disturbances. This review provides an overview of anterior ocular barriers along with strategies to overcome these ocular barriers and deliver therapeutic agents to the affected anterior ocular tissue with a special emphasis on nanotechnology-based drug delivery approaches.

Hydroxypropylmethylcellulose films for the ophthalmic delivery of diclofenac sodium

OBJECTIVES

The aim of this study was to prepare diclofenac/hydroxypropylmethylcellulose (HPMC) and diclofenac-loaded nanoparticles/HPMC films as potential systems for ocular delivery.

METHODS

Two different concentration of the polymer were used: 1.5 and 2.0% w/v. Chitosan-hyaluronic acid nanoparticles were prepared by the ionotropic gelation technique. Nanoparticles were characterized by transmission electron microscopy, dynamic light scattering, drug encapsulation efficiency and rheological studies. In-vitro drug studies and corneal penetration release studies were carried out. Drug release mechanism was finally evaluated by fitting the Ritger and Peppas equation to data. In addition corneal hydration level was calculated to determine whether films could damage the corneas.

KEY FINDINGS

Diclofenac HPMC films presented a faster drug release and a higher drug penetration than nanoparticles; on the contrary nanoparticles containing films were able to give a more sustained release of the drug and thus a slower diclofenac permeation through the cornea than HPMC films.

CONCLUSIONS

Nanoparticles loaded with diclofenac sodium in HPMC films may be a valuable alternative for the treatment of ocular inflammatory diseases, since these formulations offer the benefit of sustained releasing directly to the site of action.

Zn-Al-NO(3)-layered double hydroxides with intercalated diclofenac for ocular delivery

This study was aimed to evaluate the potential use of a drug delivery system, drug-layered double hydroxide (LDH) nanocomposites for ocular delivery. Diclofenac was successfully intercalated into Zn-Al-NO(3)-LDH by coprecipitation method. The nanocomposites were characterized by particle size, elemental chemical analysis, thermogravimetric analysis, etc. A tilt bilayer of diclofenac molecules formed in the interlayer with the gallery height of 1.868 nm. In vivo precorneal retention studies were conducted with diclofenac sodium (DS) saline, diclofenac-LDH nanocomposite dispersion, 2% polyvinylpyrrolidone (PVP) K30-diclofenac-LDH nanohybrid dispersion and 10% PVP K30-diclofenac-LDH nanohybrid dispersion, separately. Compared with DS saline, all the dispersions have extended the detectable time of DS from 3h to 6h; C(max) and AUC(0-t) of diclofenac-LDH nanocomposite dispersion showed 3.1-fold and 4.0-fold increase, respectively; C(max) and AUC(0-t) of 2% PVP K30-LDH nanohybrid dispersion were about 5.3-fold and 6.0-fold enhancement, respectively. Results of the Draize test showed that no eye irritation was demonstrated in rabbits after single and repeated administration. These results suggest that this novel ocular drug delivery system appears to offer promise as a means to improving the bioavailability of drugs after ophthalmic applications.

Ocular drug delivery

Ocular drug delivery has been a major challenge to pharmacologists and drug delivery scientists due to its unique anatomy and physiology. Static barriers (different layers of cornea, sclera, and retina including blood aqueous and blood-retinal barriers), dynamic barriers (choroidal and conjunctival blood flow, lymphatic clearance, and tear dilution), and efflux pumps in conjunction pose a significant challenge for delivery of a drug alone or in a dosage form, especially to the posterior segment. Identification of influx transporters on various ocular tissues and designing a transporter-targeted delivery of a parent drug has gathered momentum in recent years. Parallelly, colloidal dosage forms such as nanoparticles, nanomicelles, liposomes, and microemulsions have been widely explored to overcome various static and dynamic barriers. Novel drug delivery strategies such as bioadhesive gels and fibrin sealant-based approaches were developed to sustain drug levels at the target site. Designing noninvasive sustained drug delivery systems and exploring the feasibility of topical application to deliver drugs to the posterior segment may drastically improve drug delivery in the years to come. Current developments in the field of ophthalmic drug delivery promise a significant improvement in overcoming the challenges posed by various anterior and posterior segment diseases.