Ocular drug delivery

The eye is one of the most delicate organs in our body. The eye is a complex organ characterized by its low permeability, short precorneal residence time, and small area for absorption, which pose significant barriers to drug delivery. Typically, less than 10% of a drug administered penetrates the eye. Traditional ocular delivery systems are also constrained, with significant drug loss due to tears and blinking, leading to blurred vision and untimed release events without sustained action, resulting in suboptimal outcomes in ocular therapy. To overcome such challenges, in situ ophthalmic gels have been developed. These gels' ability to transition from a liquid to a gel state allows for sustained drug release at the target site. In situ gel systems are in solution form before administration and then convert to a gel under physiological conditions (pH, temperature, or ionic concentration). This review discusses the anatomy and physiology of the eye, the challenges of ocular drug delivery, types of in situ gelling systems, mechanisms of gel formation, types of smart polymers, and methods for evaluating polymeric in situ gels.   

The ocular drug delivery is one of the most challenging & interesting endeavors facingthe pharmaceutical companies in the market.  To circumvent the protective barriers of the eye without causing permanent tissue damage is the challenge to the formulator. Hence to improve the bioavailability of ocular drug considerable amount of research has been focused in developing the controlled drug delivery systems. The main aim of preparing the ocular insert is to increase the bioavailability of ocular drug. The Ocular inserts maintain the concentration of drug within the desired range. The Ideal ophthalmic drug delivery must be able to sustain the release of drug & to remain in the vicinity of front of the eye for the prolong period of time. In this review, we have focused on the Barriers for Ocular drug delivery system, mechanism of action, classification of ocular insert.

Eye is a window to the outside world and hence it becomes an important part of our body. Various diseases occurring in the eye cavity are difficult to treat. Some diseases require continuous use of medicine and other requires surgery. Lacrisert, Vitrasert, Mydriasert, Prosert etc. are patented technologies useful in the treatment of eye disorders. In this article brief description of various patented technologies such as Eyegiene kit, Ophtha coils, Versidoser, Microneedle, Implantable MEMS ocular drug delivery system, Ocuseal liquid bandage, Filter paper strips is given.

To increase the bioavailability and short ocular residence time of Norfloxacin eye drops, aqueous solutions of drug in chitosan/ Pluronic (poloxamer) were prepared. Mixtures of solutions of Pluronic (5-17.5% w/w) with chitosan (0.1-0.6% w/w) were prepared.  The formulations so prepared were in the liquid state at 4°C while turned into a gel at the temperature of the Cul-de-sac. Naturals polymers i.e., Poloxamer was used as the polymer which exhibited the phase transition behavior and chitosan was used to improve residence time. Norfloxacin release was determined using a membrane less dissolution model in artificial tear solution up to 8 hours and the samples were analyzed spectrophotometrically at 277nm. The rheological behavior of solutions in response to dilution or temperature changes and also the phase change temperature (PCT) were determined. Antimicrobial effect of the solutions was studied in nutrient agar in comparison to all formulations of Norfloxacin using Pseudomonas aueroginosa, Staphylococcus aureus and E.coli by the agar diffusion test using the cup-plate technique. The formulation consisted of 15% Pluronic and 0.5% chitosan, with the highest release efficiency (73.46 ± 0.876%) and an acceptable mean release time, is suggested as a suitable ophthalmic preparation for sustained release of Norfloxacin.

Ophthalmic products are formulated using essentially the same scientific principles and technology as dosage forms developed for other target organs. Despite numerous scientific efforts, efficient ocular drug delivery remains a challenge for pharmaceutical scientists.  Most ocular diseases are treated by topical drug application in the form of solutions, suspensions and ointment. These conventional dosage forms suffer from the problems of poor ocular bioavailability. The major diseases affecting the eye are age-related macular degeneration, diabetic macular edema, cataract, proliferative vitreoretinopathy, uveitis, cytomegalovirus, and glaucoma. A myriad of advances have been made to overcome these physiological barriers for the targeted ocular delivery of drugs. Various approaches that have been attempted to increase the bioavailability and the duration of therapeutic action of ocular drugs can be divided into two categories. The first is based on use of the drug delivery systems, which provide the controlled and continuous delivery of ophthalmic drugs. The second involves, maximizing corneal drug absorption and minimizing precorneal drug loss. This review provides an insight into various noval techniques employed in prolonging the ocular residence time and therefore bioavailability of drugs like mucoadhesive systems, Insitu gelling systems, microemulsions, lipid based nanocarriers, Nanosuspensions, Ocular iontopherosis.