Ocular Drug Delivery System: Challenges and Approaches

Abstract

The ocular drug delivery deviates through a number of anatomical and physiological barriers, which have been a bottleneck for the ophthalmologists. The ocular barriers, static and dynamic, decrease the absorption of the therapeutic agents and the entry of the xenobiotics. Thus, a conventional ocular dosage form has various disadvantages of its use in ocular diseases. Hence, an ideal ocular delivery system has always been aimed, where the bioavailability of a drug is maintained for a longer period of time. The present review aims to focus on the drawbacks of the conventional ocular therapy and the advantages of designing novel delivery systems, with their certain specific advantages in ocular pharmacokinetics and the enhancement of bioavailability. These novel approaches emphasize on the benefits of various ocular drug delivery systems, like eye ointments, gels and use of viscosity enhancers, prodrugs, penetration enhancers, microparticles, liposomes, niosomes, ocular inserts, implants, intravitreal injections, nanoparticles, nanosuspension, microemulsion, dendrimers, in situ gels, iontophoresis and periocular injections. The compiled data presented in this review will act as a good information resource and reference point for further researches in the field of ocular drug delivery aiming non-invasive sustained release of drugs in the anterior and posterior segments of the eye.

Microemulsion Based Nanostructures for Drug Delivery

“…These authors suggested that the dendrimer improved the drug efficacy by enhancing cellular delivery compared to pure ibuprofen. In ocular drug delivery, dendrimers are an ideal carrier system due to nonirritating, biocompatible, sterile, isotonic, and biodegradable properties (Raj et al, 2020). Viewed in this way, Vandamme and Brobeck (2005) improved the bioavailability of the pilocarpine increasing the resident time in the eye of the drug by using PAMAM dendrimers.…”

Nanotechnology-based formulations to amplify intraocular bioavailability

“…Nanotechnology-based ophthalmic formulations fall into two broad categories: organic nanoparticles (liposomes, niosomes/discosomes, dendrimers, nanoemulsions, nanosuspensions, and nanospheres) and inorganic nanoparticles (metallic, carbonous, and silica nanoparticles and quantum dots). 5 , 27 , 29 Organic nanoparticles are essential carriers of pharmaceutical compounds, while inorganic nanoparticles have garnered significant attention for their theranostic properties. Despite, mesoporous silica inorganic nanoparticles are capable of absorbing exceptionally copious amounts of active substance inside their pores.…”

“…The active substance is released in a sustained manner which leads to enhanced bioavailability. 5 , 46 A natural polymer, chitosan, is often supplemented in ophthalmic formulations due to its endogenous mucoadhesive nature. Its positively charged amino groups interact with the negatively charged layer of the tear-film mucinous layer.…”

“…Although safe and well-tolerated by the eye, ointments inflict blurring of vision. 5 Gels lead to a prolonged precorneal residence time, which depends on their viscosity properties, their ability to diffuse on the ocular surface, and their water retention capacity. Gels, however, achieve only a limited improvement in bioavailability, and the dosing frequency can be decreased to once a day at most.…”

Discosomes: A Futuristic Upheaval in Vesicular Drug Delivery

“…Discosomes were shown entrapping water-soluble solutes. Discosomes of 5(6)-carboxy-fluorescein were developed and started in retaining 50% of entrapped CF over a 24 h period at room temperature [52,53]. Discosomes are voluminous discoidal structures that subsist under definite conditions of this phase of non-ionic surfactant vesicle formation.…”