Abstract
Topical drug delivery is one of the most challenging aspects of eye therapy. Eye drops are the most prevalent drug form, especially for widely distributed anterior segment eye diseases (cataracts, glaucoma, dry eye syndrome, inflammatory diseases, etc.), because they are convenient and easy to apply by patients. However, conventional drug formulations are usually characterized by short retention time in the tear film, insufficient contact with epithelium, fast elimination, and difficulties in overcoming ocular tissue barriers. Not more than 5% of the total drug dose administered in eye drops reaches the interior ocular tissues. To overcome the ocular drug delivery barriers and improve drug bioavailability, various conventional and novel drug delivery systems have been developed. Among these, nanosize carriers are the most attractive. The review is focused on the different drug carriers, such as synthetic and natural polymers, as well as inorganic carriers, with special attention to nanoparticles and nanomicelles. Studies in vitro and in vivo have demonstrated that new formulations could help to improve the bioavailability of the drugs, provide sustained drug release, enhance and prolong their therapeutic action. Promising results were obtained with drug-loaded nanoparticles included in in situ gel.
Highlights
According to the World Health Organization data, about 300 million people are living with serious vision disorders worldwide
The results showed that the chitosan coating increases the bioavailability of the particles and slows down the drug release from PLGA nanoparticles
Microparticles composed from PLGA and polyethylene glycol (PEG) and containing anti-glaucomatous dorzolamide showed a 35% greater intraocular pressure (IOP) decrease and >2-fold prolongation of this effect after topical instillation of particles suspension to the eye, as compared to Trusopt®, the commercial eye drops of dorzolamide [73]
Summary
According to the World Health Organization data, about 300 million people are living with serious vision disorders worldwide. The bioavailability of the ophthalmic drugs after systemic administration is strongly restricted by the bloodocular barrier system formed by two main barriers: the blood-aqueous barrier for the anterior segment and the blood-retinal barrier for the posterior eye segment (Figure 1) The former consists of the tight junctions of the non-pigmented epithelium of the ciliary body, iris tissues, and the iris blood vessels. The tear film on the cornea and conjunctiva covering the rest eye surface and the interior surface of the eyelids is the first permeability barrier limiting intraocular drug delivery. It is highly vascularized, and drugs penetrating the conjunctiva may be absorbed systematically directly from the conjunctival sac or the nasal cavity and reach general blood circulation rather than intraocular segments [8,16] It may cause significant drug loss into the systemic circulation thereby lowering its ocular bioavailability. Eye pathologies involving the anterior segment are widely distributed and include cataracts, dry eye syndrome, inflammatory diseases, infectious diseases, glaucoma, tumors, trauma (including eye burns), congenital and acquired abnormalities, and ocular manifestations of systemic diseases
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