Current Approaches to Use Cyclodextrins and Mucoadhesive Polymers in Ocular Drug Delivery—A Mini-Review

A Clinical, Pharmacological, and Formulation Evaluation of Melatonin in the Treatment of Ocular Disorders-A Systematic Review

Melatonin's cytoprotective properties may have therapeutic implications in treating ocular diseases like glaucoma and age-related macular degeneration. Literature data suggest that melatonin could potentially protect ocular tissues by decreasing the production of free radicals and pro-inflammatory mediators. This study aims to summarize the screened articles on melatonin's clinical, pharmacological, and formulation evaluation in treating ocular disorders. The identification of relevant studies on the topic in focus was performed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA 2020) guidelines. The studies were searched in the following databases and web search engines: Pubmed, Scopus, Science Direct, Web of Science, Reaxys, Google Scholar, Google Patents, Espacenet, and Patentscope. The search time interval was 2013-2023, with the following keywords: melatonin AND ocular OR ophthalmic AND formulation OR insert AND disease. Our key conclusion was that using melatonin-loaded nano-delivery systems enabled the improved permeation of the molecule into intraocular tissues and assured controlled release profiles. Although preclinical studies have demonstrated the efficacy of developed formulations, a considerable gap has been observed in the clinical translation of the results. To overcome this failure, revising the preclinical experimental phase might be useful by selecting endpoints close to clinical ones.

Chitosan-poly(lactide-co-glycolide)/poloxamer mixed micelles as a mucoadhesive thermo-responsive moxifloxacin eye drop to improve treatment efficacy in bacterial keratitis

A mucoadhesive self-assembling polymeric system was developed to carry moxifloxacin (M) for treating bacterial keratitis (BK). Chitosan-PLGA (C) conjugate was synthesized, and poloxamers (F68/127) were mixed in different proportions (1: 5/10) to prepare moxifloxacin (M)-encapsulated mixed micelles (M@CF68/127(5/10)Ms), including M@CF68(5)Ms, M@CF68(10)Ms, M@CF127(5)Ms, and M@CF127(10)Ms. The corneal penetration and mucoadhesiveness were determined biochemically, in vitro using human corneal epithelial (HCE) cells in monolayers and spheroids, ex vivo using goat cornea, and in vivo via live-animal imaging. The antibacterial efficacy was studied on planktonic biofilms of P. aeruginosa and S. aureus (in vitro) and Bk-induced mice (in vivo). Both M@CF68(10)Ms and M@CF127(10)Ms demonstrated high cellular uptake, corneal retention, muco-adhesiveness, and antibacterial effect, with M@CF127(10)Ms exhibiting superior therapeutic effects in P. aeruginosa and S. aureus-infected BK mouse model by reducing the corneal bacterial load and preventing corneal damage. Therefore, the newly developed nanomedicine is promising for clinical translation in treating BK.

Enhanced Solubility and Stability of Aripiprazole in Binary and Ternary Inclusion Complexes Using Hydroxy Propyl Beta Cyclodextrin (HPβCD) and L-Arginine

The low water solubility of an active pharmaceutical ingredient (aripiprazole) is one of the most critical challenges in pharmaceutical research and development. This antipsychotic drug has an inadequate therapeutic impact because of its minimal and idiosyncratic oral bioavailability to treat schizophrenia. The main objective of this study was to improve the solubility and stability of the antipsychotic drug aripiprazole (ARP) via forming binary as well as ternary inclusion complexes with hydroxypropyl-β-cyclodextrin (HPβCD) and L-Arginine (LA) as solubility enhancers. Physical mixing and lyophilization were used in different molar ratios. The developed formulations were analyzed by saturation solubility analysis, and dissolution studies were performed using the pedal method. The formulations were characterized by FTIR, XRD, DSC, SEM, and TGA. The results showcased that the addition of HPβCD and LA inclusion complexes enhanced the stability, in contrast to the binary formulations and ternary formulations prepared by physical mixing and solvent evaporation. Ternary formulation HLY47 improved dissolution rates by six times in simulated gastric fluid (SGF). However, the effect of LA on the solubility enhancement was concentration-dependent and showed optimal enhancement at the ratio of 1:1:0.27. FTIR spectra showed the bond shifting, which confirmed the formation of new complexes. The surface morphology of complexes in SEM studies showed the rough surface of lyophilization and solvent evaporation products, while physical mixing revealed a comparatively crystalline surface. The exothermic peaks in DSC diffractograms showed diminished peaks previously observed in the diffractogram of pure drug and LA. Lyophilized ternary complexes displayed significantly enhanced thermal stability, as observed from the thermograms of TGA. In conclusion, it was observed that the preparation method and a specific drug-to-polymer and amino acid ratio are critical for achieving high drug solubility and stability. These complexes seem to be promising candidates for novel drug delivery systems development.

Conjugates of Chitosan with β-Cyclodextrins as Promising Carriers for the Delivery of Levofloxacin: Spectral and Microbiological Studies

In this work, we synthesized chitosan 5 kDa conjugates with β-cyclodextrins with various substituents as promising mucoadhesive carriers for the delivery of fluoroquinolones using the example of levofloxacin. The obtained conjugates were comprehensively characterized by spectral methods (UV-Vis, ATR-FTIR, 1H NMR, SEM). The physico-chemical properties of the complex formations were studied by IR, UV, and fluorescence spectroscopy. The dissociation constants of complexes with levofloxacin were determined. Complexation with conjugates provided four times slower drug release in comparison with plain CD and more than 20 times in comparison with the free drug. The antibacterial activity of the complexes was tested on model microorganisms Gram-negative bacteria Escherichia coli ATCC 25922 and Gram-positive Bacillus subtilis ATCC 6633. The complex with the conjugate demonstrated the same initial levofloxacin antibacterial activity but provided significant benefits, e.g., prolonged release.

Cellulosic Polymers for Enhancing Drug Bioavailability in Ocular Drug Delivery Systems

One of the major impediments to drug development is low aqueous solubility and thus poor bioavailability, which leads to insufficient clinical utility. Around 70–80% of drugs in the discovery pipeline are suffering from poor aqueous solubility and poor bioavailability, which is a major challenge when one has to develop an ocular drug delivery system. The outer lipid layer, pre-corneal, dynamic, and static ocular barriers limit drug availability to the targeted ocular tissues. Biopharmaceutical Classification System (BCS) class II drugs with adequate permeability and limited or no aqueous solubility have been extensively studied for various polymer-based solubility enhancement approaches. The hydrophilic nature of cellulosic polymers and their tunable properties make them the polymers of choice in various solubility-enhancement techniques. This review focuses on various cellulose derivatives, specifically, their role, current status and novel modified cellulosic polymers for enhancing the bioavailability of BCS class II drugs in ocular drug delivery systems.

A review of controlled release from cyclodextrins: release methods, release systems and application

The controlled release of guest molecules from cyclodextrin (CD) inclusion complexes is very important for specific industrial applications in foods, medicine, cosmetics, textiles, agriculture, environmental protection, and chemical materials. The term "controlled release" encompasses several related methods, including those referred to as immediate release, sustained release and targeted release. Many different CD-based controlled release systems are currently used in practical applications. CD inclusion complexes, CD coupling, supramolecular hydrogels, and supramolecular micelles are among the most common. This review systematically introduces the principles and applications of CD-based controlled release systems, providing a theoretical basis for improving the bioavailability of effective substances and broadening their range of application.

A hybrid ocular delivery system of cyclosporine-A comprising nanomicelle-laden polymeric inserts with improved efficacy and tolerability

We report on hybrid nanomicelle-polymer inserts for improved delivery of cyclosporine A (CyA) to the surface of the eye. Hybrid inserts containing a nanomicellar formulation were prepared by the solvent casting method; their characteristics, in vitro release of CyA, eye irritation potential, nanomicelle distribution inside the insert, and in vivo pharmacokinetics of the most promising solid formulation (F3) were investigated. Nanomicelles capable of accommodating a therapeutically relevant amount of CyA (57.22 ± 5.90-68.52 ± 1.4 μg) were incorporated into five different polymeric formulations (F1-F5). The developed inserts displayed promising characteristics (size, weight, surface pH, and contact angle) that fulfill ocular tolerability requirements. Considering the technological properties and CyA in vitro release, F3 and F5 were the most promising formulations. SEM analysis suggested the F3 formulation as the potential prototype for CyA ocular delivery. The F3 formulation (CyA: 60.08 ± 2.85 μg) did not induce conjunctival irritation when HET-CAM assay was performed and was hence considered suitable for further study in a rabbit eye. The AUC value for CyA loaded in the F3 insert was about 2-fold greater than that obtained with the Ikervis® used as a control formulation. F3 produced a significant reduction (of about 7-folds) in the rate of CyA elimination from the tear fluid relative to Ikervis® and about 4-fold greater reduction than Nano-CyA (p = 0.0187). The ability of F3 to delay the elimination of the drug from the precorneal area is particularly desirable when treating dry eye syndrome. Furthermore, F3 did not induce ocular discomfort, a typical characteristic of solid ocular inserts, including commercially available ones.

Chitosan-Coated PLGA Nanoparticles Encapsulating Triamcinolone Acetonide as a Potential Candidate for Sustained Ocular Drug Delivery

The current treatment for the acquired retinal vasculopathies involves lifelong repeated intravitreal injections of either anti-vascular endothelial growth factor (VEGF) therapy or modulation of inflammation with steroids. Consequently, any treatment modification that decreases this treatment burden for patients and doctors alike would be a welcome intervention. To that end, this research aims to develop a topically applied nanoparticulate system encapsulating a corticosteroid for extended drug release. Poly (lactic-co-glycolic acid) (PLGA) nanoparticles (NPs) supports the controlled release of the encapsulated drug, while surface modification of these NPs with chitosan might prolong the mucoadhesion ability leading to improved bioavailability of the drug. Triamcinolone acetonide (TA)-loaded chitosan-coated PLGA NPs were fabricated using the oil-in-water emulsion technique. The optimized surface-modified NPs obtained using Box-Behnken response surface statistical design were reproducible with a particle diameter of 334 ± 67.95 to 386 ± 15.14 nm and PDI between 0.09 and 0.15. These NPs encapsulated 55-57% of TA and displayed a controlled release of the drug reaching a plateau in 27 h. Fourier-transform infrared spectroscopic (FTIR) analysis demonstrated characteristic peaks for chitosan (C-H, CONH2 and C-O at 2935, 1631 and 1087 cm-1, respectively) in chitosan-coated PLGA NPs. This result data, coupled with positive zeta potential values (ranged between +26 and +33 mV), suggests the successful coating of chitosan onto PLGA NPs. Upon coating of the NPs, the thermal stability of the drug, polymer, surfactant and PLGA NPs have been enhanced. The characteristics of the surface-modified NPs supports their use as potential candidates for topical ocular drug delivery for acquired retinal vasculopathies.

Cyclodextrins Allow the Combination of Incompatible Vancomycin and Ceftazidime into an Ophthalmic Formulation for the Treatment of Bacterial Keratitis

Ceftazidime (CZ) and vancomycin (VA) are two antibiotics used to treat bacterial keratitis. Due to their physical incompatibility (formation of a precipitate), it is not currently possible to associate both molecules in a single container for ophthalmic administration. We firstly characterized the incompatibility then investigated if 2-hydroxypropyl-beta (HPβCD) and 2-hydroxypropyl-gamma cyclodextrins (HPγCD) could prevent this incompatibility. The impact of pH on the precipitation phenomena was investigated by analysing the supernatant solution of the mixture using high performance liquid chromatography. A characterization of the inclusion of CZ with HPγCD using ¹H nuclear magnetic resonance (NMR), and VA with HPβCD using ¹H-NMR and a solubility diagram was performed. A design of experiment was built to determine the optimal conditions to obtain a formulation that had the lowest turbidity and particle count. Our results showed that VA and CZ form an equimolar precipitate below pH 7.3. The best formulation obtained underwent an in-vitro evaluation of its antibacterial activity. The impact of HPCDs on incompatibility has been demonstrated through the inclusion of antibiotics and especially VA. The formulation has been shown to be able to inhibit the incompatibility for pH higher than 7.3 and to possess unaltered antibacterial activity.

HP-β-CD for the formulation of IgG and Ig-based biotherapeutics

The main challenge to develop HCF for IgG and Ig-based therapeutics is to achieve essential solubility, viscosity and stability of these molecules in order to maintain product quality and meet regulatory requirement during manufacturing, production, storage, shipment and administration processes. The commonly used and FDA approved excipients for IgG and Ig -based therapeutics may no longer fulfil the challenge of HCF development for these molecules to certain extent, especially for some complex Ig-based platforms. 2-Hydroxypropyl beta-cyclodextrin (HP-β-CD) is one of the promising excipients applied recently for HCF development of IgG and Ig-based therapeutics although it has been used for formulation of small synthesized chemical drugs for more than thirty years. This review describes essential aspects about application of HP-β-CD as excipient in pharmaceutical formulation, including physico-chemical properties of HP-β-CD, supply chain, regulatory, patent landscape, marketed drugs with HP-β-CD, analytics and analytical challenges, stability and control strategies, and safety concerns. It also provides an overview of different studies, and outcomes thereof, regarding formulation development for IgGs and Ig-based molecules in liquid and solid (lyophilized) dosage forms with HP-β-CD. The review specifically highlights the challenges for formulation manufacturing of IgG and Ig-based therapeutics with HP-β-CD and identifies areas for future work in pharmaceutical and formulation development.

Advanced nanodelivery platforms for topical ophthalmic drug delivery

Conventional eye drops have several limitations, including the need for multiple applications per dose, hourly based dosage regiments, and suboptimal ocular bioavailability (<5%). The efficacy of topical ophthalmic medications can be significantly improved by controlling their contact time with the adherent mucin layer and by inducing sustained release properties, thus allowing for a prolonged contact time of the drug with the ocular tissues, which eventually will lead to improved drug bioavailability and a significant decrease in the frequency of eyedrop instillation. In this review, we critically highlight recent and innovative nanodrug delivery platforms, with a primary focus on the integration of nanotechnology, biomaterials, and polymer chemistry to facilitate precise spatial and temporal control over sustained drug release to the cornea.

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

Background

Optimal transcorneal penetration is necessary for ocular therapy; meanwhile, it is limited by the complex structure and defensive mechanisms of the eye. Antimicrobial stability of topical ophthalmic formulations is especially important. According to previous studies, the mostly used preservative, benzalkonium-chloride is irritative and toxic on corneal epithelial cells; therefore, novel non-toxic, antimicrobial agents are required. In this study, prednisolone-containing ophthalmic formulations were developed with expected optimal permeation without toxic or irritative effects.

Methods

The toxicity and permeability of prednisolone-containing eye drops were studied on a human corneal epithelial cell line (HCE-T) and ex vivo cornea model. The lipophilic drug is dissolved by the formation of cyclodextrin inclusion complex. Zinc-containing mucoadhesive biopolymer was applied as an alternative preservative agent, whose toxicity was compared with benzalkonium-chloride.

Results

As the results show, benzalkonium-chloride-containing samples were toxic on HCE-T cells. The biopolymer caused no cell damage after the treatment. This was confirmed by immunohistochemistry assay. The in vitro permeability was significantly higher in formulations with prednisolone-cyclodextrin complex compared with suspension formulation. According to the ex vivo permeability study, the biopolymer-containing samples had significantly lower permeability.

Conclusion

Considering the mucoadhesive attribute of target formulations, prolonged absorption is expected after application with less frequent administration. It can be stated that the compositions are innovative approaches as novel non-toxic ophthalmic formulations with optimal drug permeability.

Why chitosan could be apt candidate for glaucoma drug delivery - An overview

Most of the people in the world are affected by glaucoma, which leads to irreversible blindness. Several patient friendly treatments are available, nevertheless medications lack an easy and efficient way of sustained delivery. To make the delivery with enhanced bioavailability, biodegradable and non-biodegradable polymers-based drug carriers are explored. However, ocular drug delivery issues have not been resolved yet due to less adhesiveness, poor penetration ability, pH, and temperature dependent burst releases. Chitosan is found to be effective for ocular drug delivery due to excellent physio-chemical properties in terms of overcoming the existing issues. In this review, we aim to highlight why it has been chosen and the holy grail for ocular drug delivery. Besides, we have comprehensively reviewed recent patents on chitosan as a platform for ocular drug delivery and future perspectives on factors, lacunae and challenges that need to be addressed for better ocular delivery methods for glaucoma management.

New Insights into Advanced Drug Delivery and Absorption Systems

The therapeutic effect of a drug depends on the method of effective delivery of the active ingredient to the site(s) of the pharmacological target area [...]

Hydrogel Biomaterials for Application in Ocular Drug Delivery

There are many challenges involved in ocular drug delivery. These are a result of the many tissue barriers and defense mechanisms that are present with the eye; such as the cornea, conjunctiva, the blinking reflex, and nasolacrimal drainage system. This leads to many of the conventional ophthalmic preparations, such as eye drops, having low bioavailability profiles, rapid removal from the administration site, and thus ineffective delivery of drugs. Hydrogels have been investigated as a delivery system which is able to overcome some of these challenges. These have been formulated as standalone systems or with the incorporation of other technologies such as nanoparticles. Hydrogels are able to be formulated in such a way that they are able to change from a liquid to gel as a response to a stimulus; known as "smart" or stimuli-responsive biotechnology platforms. Various different stimuli-responsive hydrogel systems are discussed in this article. Hydrogel drug delivery systems are able to be formulated from both synthetic and natural polymers, known as biopolymers. This review focuses on the formulations which incorporate biopolymers. These polymers have a number of benefits such as the fact that they are biodegradable, biocompatible, and non-cytotoxic. The biocompatibility of the polymers is essential for ocular drug delivery systems because the eye is an extremely sensitive organ which is known as an immune privileged site.