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Controlled drug delivery to eye is one of the most challenging fields of pharmaceutical research. Low drug-contact time and poor ocular bioavailability due to drainage of solution, tear turnover and its dilution or lacrimation are the problems associated with conventional systems. In addition, anatomical barriers and physiological conditions of eye are also important parameters which control designing of drug delivery systems. Nanosized carriers like micro/nano-suspensions, liposome, niosome, dendrimer, nanoparticles, ocular inserts, implants, hydrogels and prodrug approaches have been developed for this purpose. These novel systems offer manifold advantages over conventional systems as they increase the efficiency of drug delivery by improving the release profile and also reduce drug toxicity. Conventional delivery systems get diluted with tear, washed away through the lacrimal gland and usually require administering at regular time intervals whereas nanocarriers release drug at constant rate for a prolonged period of time and thus enhance its absorption and site specific delivery. This review presents an overview of the various aspects of the ocular drug delivery, with special emphasis on nanocarrier based strategies, including structure of eye, its barriers, delivery routes and the challenges/limitations associated with development of novel nanocarriers. The recent progresses in therapy of ocular disease like gene therapy have also been included so that future options should also be considered from the delivery point of view. Recent progress in the delivery of proteins and peptides via ocular route has also been incorporated for reader benefit.

In clinical practices, solution of dorzolamide hydrochloride (DH) and timolol maléate (TM) is recommended for the treatment of glaucoma. However, low drug-contact time and poor ocular bioavailability of drugs due to drainage of solution, tear turnover and its dilution or lacrimation limits its uses. In addition, systemic absorption of TM may induce undesirable cardiovascular side effects. Chitosan (CS) is a polycationic biodegradable polymer which provides sustained and local delivery of drugs to the ocular sites. Hyaluronic acid (HA) also provides synergistic effect for mucoadhesion in association with chitosan. In the present study, hyaluronic acid modified chitosan nanoparticles (CS-HA-NPs) loaded with TM and DH were developed and characterized. The CS-HA-NPs were evaluated for size, shape, zeta potential, entrapment efficiency, and mucoadhesive strength. The in vitro release study was also performed in PBS pH 7.4. The ocular irritation potential of CS-HA-NPs was estimated using draize test on albino rabbits. A significant reduction in IOP level was obtained using CS-HA-NPs as compared to plain solution of drug and a comparable higher reduction in IOP level was observed as to CS-NPs. These results suggest that HA potentialy enhance the mucoadhesiveness and efficiency of CS-NPs and may be promising carrier for ocular drug delivery.

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Acne, a common skin disease in teenagers, is caused by Propionibacterium acnes (P. acnes). Isotretinoin (ITR) is though reported to have immense antiacne potential, yet there are hardly any reports vouching its antimicrobial activity. The present study, therefore, was undertaken to study the antimicrobial activity of ITR and evaluate the effect of its encasement in nanocarriers on its minimum inhibitory concentration (MIC). The nanocarriers were also evaluated for the skin transport characteristics. MICs of pure drug and entrapped drug in nanolipid carriers (ITR-NLCs) and in solid lipid nanoparticles (ITR-SLNs) were determined by broth dilution method against clindamycin phosphate as the reference antibiotic. It was observed that ITR possessed marked antimicrobial activity against anaerobic pathogen, P. acnes. Nanocarriers loaded with ITR, that is, SLNs and NLCs, enhanced the antimicrobial activity even at lower concentrations vis-à-vis the drug alone and improved drug transport potential vis-à-vis the commercial gel. The unique findings could be the result of effective adhesion of ITR-loaded nanocarriers to the bacterial membranes and release of drug directly to the target. Besides establishing ITR as an antimicrobial agent against acne-causing bacteria, the current work ratifies immense potential of nanocolloidal carriers like SLNs and NLCs to treat acne in a more efficient manner.

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