Polycarboxylic acid nanoparticles for ophthalmic drug delivery: an ex vivo evaluation with human cornea

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.

Ocular drug delivery to the anterior segment using nanocarriers: A mucoadhesive/mucopenetrative perspective

There is a growing demand for effective treatments for ocular conditions that improve patient compliance and reduce side-effects. While methods such as implants and injections have proven effective, topical administration remains the method of choice for the delivery of therapeutics to the anterior segment of the eye. However, topical administration suffers from multiple drawbacks including low bioavailability of the target therapeutic, systemic toxicity, and the requirement for high therapeutic doses due to the effective clearance mechanisms that exist in the eye. Nanoparticles that have tunable mucoadhesion and/or mucopenetration offer outstanding potential to overcome the anatomical and physiological barriers present to improve ocular bioavailability, reduce toxicity, and increase ocular retention, among other benefits. The current review highlights recent advances in the field of developing nanocarriers with tunable mucoadhesion and mucopenetration for drug delivery to the eye.

Nanocarriers for ocular drug delivery: current status and translational opportunity

Ocular diseases have a significant effect on vision and quality of life. Drug delivery to ocular tissues is a challenge to formulation scientists. The major barriers to delivering drugs to the anterior and posterior segments include physiological barriers (nasolacrimal drainage, blinking), anatomical barriers (static and dynamic), efflux pumps and metabolic barriers. The static barriers comprise the different layers of the cornea, sclera, and blood–aqueous barriers whereas dynamic barriers involve conjunctival blood flow, lymphatic clearance and tear drainage. The tight junctions of the blood–retinal barrier (BRB) restrict systemically administered drugs from entering the retina. Nanocarriers have been found to be effective at overcoming the issues associated with conventional ophthalmic dosage forms. Various nanocarriers, including nanodispersion systems, nanomicelles, lipidic nanocarriers, polymeric nanoparticles, liposomes, niosomes, and dendrimers, have been investigated for improved permeation and effective targeted drug delivery to various ophthalmic sites. In this review, various nanomedicines and their application for ophthalmic delivery of therapeutics are discussed. Additionally, scale-up and clinical status are also addressed to understand the current scenario for ophthalmic drug delivery.

Ocular diseases have a significant effect on vision and quality of life.

Ocular Drug Delivery Barriers-Role of Nanocarriers in the Treatment of Anterior Segment Ocular Diseases

Ocular drug delivery is challenging due to the presence of anatomical and physiological barriers. These barriers can affect drug entry into the eye following multiple routes of administration (e.g., topical, systemic, and injectable). Topical administration in the form of eye drops is preferred for treating anterior segment diseases, as it is convenient and provides local delivery of drugs. Major concerns with topical delivery include poor drug absorption and low bioavailability. To improve the bioavailability of topically administered drugs, novel drug delivery systems are being investigated. Nanocarrier delivery systems demonstrate enhanced drug permeation and prolonged drug release. This review provides an overview of ocular barriers to anterior segment delivery, along with ways to overcome these barriers using nanocarrier systems. The disposition of nanocarriers following topical administration, their safety, toxicity and clinical trials involving nanocarrier systems are also discussed.

Brimonidine tartrate-eudragit long-acting nanoparticles: formulation, optimization, in vitro and in vivo evaluation

In the present study, an effort was made to design prolonged release Eudragit nanoparticles of brimonidine tartrate by double emulsion-solvent evaporation technique for the treatment of open-angle glaucoma. The effect of various formulation variables like initial drug amount, lecithin proportion, phase volume and pH, secondary emulsifier and polymer proportion were studied. Various process variables like energy and duration of emulsification, lyophilization on the characteristics of nanoparticles and in vitro drug release profile were studied. The selected formulations were subjected to in vivo intraocular pressure-lowering efficacy studies by administering aqueous dispersion of nanoparticles into the lower cul de sac of glaucomatous rabbits. The prepared Eudragit-based nanoparticles were found to have narrow particle size range and improved drug loading. The investigated process and formulation variables found to have significant effect on the particle size, drug loading and entrapment efficiency, and in vitro drug release profile of nanoparticles. The selected formulations upon in vivo ocular irritability and tolerability tests were found to be well tolerated with no signs of irritation. In vivo pharmacodynamic efficacy studies revealed that the selected nanoparticle formulations significantly improved the therapy as area under the ∆IOP vs. time curve [AUC((∆IOP vs. t))] showed several fold increase in intensity and duration of intraocular pressure (IOP) decrease. All the selected nanoparticle formulations were found to prolong the drug release in vitro and prolong IOP reduction efficacy in vivo, thus rendering them as a potential carrier in developing improved drug delivery systems for the treatment of glaucoma.

Bioadhesive sulfacetamide sodium microspheres: evaluation of their effectiveness in the treatment of bacterial keratitis caused by Staphylococcus aureus and Pseudomonas aeruginosa in a rabbit model

The aim of this study was to prepare bioadhesive sulfacetamide sodium (SA) microspheres to increase their residence time on the ocular surface and to enhance their treatment efficacy on ocular keratitis. Microspheres were fabricated by spray drying method using mixture of polymers such as pectin, polycarbophil and hydroxypropylmethyl cellulose (HPMC) at different ratios. The particle size and distribution, morphological characteristics, thermal behavior, encapsulation efficiency, mucoadhesion and in vitro drug release studies on formulations have been investigated. After optimisation studies, SA-loaded polycarbophil microsphere formulation with polymer:drug ratio of 2:1 was found to be the most suitable for ocular application and used in in vivo studies. In vivo studies were carried out on New Zealand male rabbit eyes with keratitis caused by Pseudomonas aeruginosa and Staphylococcus aureus. Sterile microsphere suspension in light mineral oil was applied to infected eyes twice a day. Plain SA suspension was used as a positive control. On 3rd and 6th days of the antimicrobial therapy, the eyes were examined in respect to clinical signs of infection (blepharitis, conjunctivitis, iritis, corneal oedema and corneal infiltrates) which are the main symptoms of bacterial keratitis and then cornea samples were counted microbiologically. The rabbit eyes treated with microspheres demonstrated significantly lower clinical scores than those treated with SA alone. A significant decrease in the number of viable bacteria in eyes treated with microspheres was observed in both infection models when compared to those treated with SA alone. In conclusion, in vitro and in vivo studies showed that SA-loaded microspheres were proven to be highly effective in the treatment of ocular keratitis.

Ocular drug delivery: nanomedicine applications

Nanocarriers, such as nanoparticles, liposomes and dendrimers, are used to enhance ocular drug delivery. Easily administered as eye drops, these systems provide a prolonged residence time at the ocular surface after instillation, thus avoiding the clearance mechanisms of the eye. In combination with a controlled drug delivery, it should be possible to develop ocular formulations that provide therapeutic concentrations for a long period of time at the site of action, thereby reducing the dose administered as well as the instillation frequency. In intraocular drug delivery, the same systems can be used to protect and release the drug in a controlled way, reducing the number of injections required. Another potential advantage is the targeting of the drug to the site of action, leading to a decrease in the dose required and a decrease in side effects.

Drug release from pH-responsive thermogelling pentablock copolymers

A novel pH-dependent injectable sustained delivery system was developed by utilizing a cationic pentablock copolymer that exhibits a thermoreversible sol-gel transition. Aqueous solutions of the pentablock copolymer, consisting of poly(2-diethylaminoethyl-methyl methacrylate)-poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide)-poly(2-diethylaminoethyl-methyl methacrylate) (PDEAEM(25)-PEO(100)-PPO(65)-PEO(100)-PDEAEM(25)) exhibit temperature and pH dependent micellization due to the lower critical solution temperature of the PPO blocks and the polyelectrolyte character of the PDEAEM blocks, respectively. Aqueous solutions of the copolymers above 12 wt % are free flowing liquids at room temperature and form elastic physical hydrogels reversibly above 37 degrees C. Hydrophobic probe absorbance studies indicate that pentablock copolymer micelles increase the solubility of sparingly soluble drugs. Solutions of the pentablock copolymer that form gels at body temperature exhibit sustained zero-order release in in vitro experiments. The release rates of model drugs and proteins were significantly influenced by the pH of the release media, thereby making these polymers ideal candidates for modulated drug delivery.