New Approach in Ocular Drug Delivery: In vitro and ex vivo Investigation of Cyclodextrin-Containing, Mucoadhesive Eye Drop Formulations

The effect of mucoadhesive polymers on ocular permeation of thermoresponsive in situ gel containing dexamethasone-cyclodextrin complex

Dexamethasone (DXM) is a commonly used corticosteroid in the treatment of ocular inflammatory conditions that affect more and more people. The aim of this study was to evaluate the effect of the combination of hydroxypropyl-β-cyclodextrin (HPBCD), in situ gelling formulations, and other mucoadhesive polymers, i.e., hydroxypropyl methylcellulose (HPMC) and zinc-hyaluronate (ZnHA), on permeation by applying in vitro and ex vivo ophthalmic permeation models. Additionally, gelling properties, in vitro drug release, and mucoadhesion were measured to determine the impact of these factors on permeation and ultimately on bioavailability. The results showed that GEL1 and GEL2 had an optimal gelling temperature, 36.3 ℃ and 34.6 ℃, respectively. Moreover, the combination of Poloxamer 407 (P407) with other polymers improved the mucoadhesion (GEL1: 1333.7 mN) compared with formulations containing only P407 (P12: 721.8 mN). Both HPBCD and the gel matrix had a considerable influence on the drug release and permeability of DXM, and the combination could facilitate the permeation into the aqueous humor. After 30 min of treatment, the DXM concentration in the aqueous humor was 1.16-1.37 µg∕mL in case of the gels, whereas DXM could not be detected when treated with the DXM suspension. The results of the experiments using an in vitro cell line indicated that the formulations could be considered safe for topical treatment of the eye. In conclusion, with application of a small amount of HPMC (0.2 % w∕w), the concentration of P407 could be reduced to 12 % w/w while maintaining the ideal gelling properties and gel structure without negatively affecting permeability compared with the formulation containing a higher amount of P407. Furthermore, the gel matrix may also provide programmed and elongated drug release.

From Preformulative Design to in Vivo Tests: A Complex Path of Requisites and Studies for Nanoparticle Ocular Application. Part 2: In Vitro, Ex Vivo, and In Vivo Studies

The incidence of ocular pathologies is constantly increasing, as is the interest of the researchers in developing new strategies to ameliorate the treatment of these conditions. Nowadays, drug delivery systems are considered among the most relevant approaches due to their applicability in the treatment of a great variety of inner and outer eye pathologies through painless topical administrations. The design of such nanocarriers requires a deep study of many aspects related to the administration route but also a consideration of the authorities and pharmacopeial requirements, in order to achieve a clinical outcome. On such bases, the scope of this review is to describe the path of the analyses that could be performed on nanoparticles, along with the assessment of their applicability for ophthalmic treatments. Preformulation studies, physicochemical and technological characterization, and preliminary noncellular in vitro studies have been described in part 1 of this review. Herein, first the in vitro cellular assays are described; subsequently, nonocular organotypic tests and ex vivo studies are reported, as to present the various analyses to which the formulations can be subjected before in vivo studies, described in the last part. In each step, the models that could be used are presented and compared, highlighting the pros and cons. Moreover, their reliability and eventual acceptance by regulatory agencies are discussed. Hence, this review provides an overview of the most relevant assays applicable for nanocarriers intended for ophthalmic administration to guide researchers in the experimental decision process.

Development of Carvedilol Nanoformulation-Loaded Poloxamer-Based In Situ Gel for the Management of Glaucoma

The objective of the current study was to fabricate a thermosensitive in situ gelling system for the ocular delivery of carvedilol-loaded spanlastics (CRV-SPLs). In situ gel formulations were prepared using poloxamer analogs by a cold method and was further laden with carvedilol-loaded spanlastics to boost the precorneal retention of the drug. The gelation capacity, rheological characteristics, muco-adhesion force and in vitro release of various in situ gel formulations (CS-ISGs) were studied. The optimized formula (F2) obtained at 22% w/v poloxamer 407 and 5% w/v poloxamer 188 was found to have good gelation capacity at body temperature with acceptable muco-adhesion properties, appropriate viscosity at 25 °C that would ease its ocular application, and relatively higher viscosity at 37 °C that promoted prolonged ocular residence of the formulation post eye instillation and displayed a sustained in vitro drug release pattern. Ex vivo transcorneal penetration studies through excised rabbit cornea revealed that F2 elicited a remarkable (p ˂ 0.05) improvement in CRV apparent permeation coefficient (Papp = 6.39 × 10-6 cm/s) compared to plain carvedilol-loaded in situ gel (CRV-ISG; Papp = 2.67 × 10-6 cm/s). Most importantly, in normal rabbits, the optimized formula (F2) resulted in a sustained intraocular pressure reduction and a significant enhancement in the ocular bioavailability of carvedilol, as manifested by a 2-fold increase in the AUC0-6h of CRV in the aqueous humor, compared to plain CRV-ISG formulation. To sum up, the developed thermosensitive in situ gelling system might represent a plausible carrier for ophthalmic drug delivery for better management of glaucoma.

Cyclodextrin-enabled nepafenac eye drops with improved absorption open a new therapeutic window

Nepafenac is a highly effective NSAID used for treating postoperative ocular inflammation and pain after cataract surgery and its advantage over conventional topical NSAIDs has been proved many times. However, Nevanac® is a suspension eye drop, which clearly lacks patient compliance causing irritation, blurred vision, foreign body sensation along with problematic dosage due to its sticky, inhomogeneous consistence. In this study, nepafenac containing eye drops were prepared using hydroxypropyl-β-cyclodextrin to ensure complete dissolution of nepafenac, sodium hyaluronate to provide mucoadhesion and adequate viscosity and a preservative-free officinal formula, Oculogutta Carbomerae containing carbomer (just like Nevanac®), therefore providing a similar base for the new formulations. According to an experimental design, 11 formulations were tested in vitro including two reference formulations by measuring their viscosity, mucoadhesion, drug release and corneal permeability. Finally, two formulations were found promising and investigated further on porcine eyes ex vivo and corneal distribution of nepafenac was determined by RAMAN mapping. The results showed that one formulation possessed better bioavailability ex vivo than Nevanac® 0.1 % suspension, while the other formulation containing only 60 % of the original dose were ex vivo equivalent with Nevanac® opening the way to nepafenac-containing eye drops with better patient compliance in the future.

In Vitro and Ex Vivo Models for Assessing Drug Permeation across the Cornea

Drug permeation across the cornea remains a major challenge due to its unique and complex anatomy and physiology. Static barriers such as the different layers of the cornea, as well as dynamic aspects such as the constant renewal of the tear film and the presence of the mucin layer together with efflux pumps, all present unique challenges for effective ophthalmic drug delivery. To overcome some of the current ophthalmic drug limitations, the identification and testing of novel drug formulations such as liposomes, nanoemulsions, and nanoparticles began to be considered and widely explored. In the early stages of corneal drug development reliable in vitro and ex vivo alternatives, are required, to be in line with the principles of the 3Rs (Replacement, Reduction, and Refinement), with such methods being in addition faster and more ethical alternatives to in vivo studies. The ocular field remains limited to a handful of predictive models for ophthalmic drug permeation. In vitro cell culture models are increasingly used when it comes to transcorneal permeation studies. Ex vivo models using excised animal tissue such as porcine eyes are the model of choice to study corneal permeation and promising advancements have been reported over the years. Interspecies characteristics must be considered in detail when using such models. This review updates the current knowledge about in vitro and ex vivo corneal permeability models and evaluates their advantages and limitations.

Design and Optimization of In Situ Gelling Mucoadhesive Eye Drops Containing Dexamethasone

Poor bioavailability of eye drops is a well-known issue, which can be improved by increasing the residence time on the eye surface and the penetration of the active pharmaceutical ingredient (API). This study aims to formulate in situ gelling mucoadhesive ophthalmic preparations. To increase the residence time, the formulations were based on a thermosensitive polymer (Poloxamer 407 (P407)) and were combined with two types of mucoadhesive polymers. Dexamethasone (DXM) was solubilized by complexation with cyclodextrins (CD). The effect of the composition on the gel structure, mucoadhesion, dissolution, and permeability was investigated with 3³ full factorial design. These parameters of the gels were measured by rheological studies, tensile test, dialysis membrane diffusion, and in vitro permeability assay. The dissolution and permeability of the gels were also compared with DXM suspension and CD-DXM solution. The gelation is strongly determined by P407; however, the mucoadhesive polymers also influenced it. Mucoadhesion increased with the polymer concentration. The first phase of drug release was similar to that of the CD-DXM solution, then it became prolonged. The permeability of DXM was significantly improved. The factorial design helped to identify the most important factors, thereby facilitating the formulation of a suitable carrier for the CD-DXM complex.