Development of topical ophthalmic In Situ gel-forming estradiol delivery system intended for the prevention of age-related cataracts

Applications and Recent Developments of Hydrogels in Ophthalmology

Hydrogels are a type of functional polymer material with a three-dimensional network structure composed of physically or chemically cross-linked polymers. All hydrogels have two common features: first, their structure contains a large number of hydrophilic groups; therefore, they have a high water content and can swell in water. Second, they have good regulation, and the physical and chemical properties of their cross-linked network can be changed by environmental factors and deliberate modification methods. In recent years, the application of hydrogels in ophthalmology has gradually attracted attention. By selecting an appropriate composition and cross-linking mode, hydrogels can be used in different fields for various applications, such as gel eye drops, in situ gel preparation, intravitreal injection, and corneal contact lenses. This Review provides a detailed introduction to the classification of hydrogels and their applications in glaucoma, vitreous substitutes, fundus diseases, corneal contact lenses, corneal diseases, and cataract surgery.

Hydrogels for Mucosal Drug Delivery

Mucosal tissues are often a desirable site of drug action to treat disease and engage the immune system. However, systemically administered drugs suffer from limited bioavailability in mucosal tissues where technologies to enable direct, local delivery to these sites would prove useful. In this Spotlight on Applications article, we discuss hydrogels as an attractive means for local delivery of therapeutics to address a range of conditions affecting the eye, nose, oral cavity, gastrointestinal, urinary bladder, and vaginal tracts. Considering the barriers to effective mucosal delivery, we provide an overview of the key parameters in the use of hydrogels for these applications. Finally, we highlight recent work demonstrating their use for inflammatory and infectious diseases affecting these tissues.

Cationic Nano-Lipidic Carrier Mediated Ocular Delivery of Triamcinolone Acetonide: A Preclinical Investigation in the Management of Uveitis

The current study was undertaken to evaluate the efficacy of a novel nano-lipoidal eye drop formulation of triamcinolone acetonide (TA) for the topical treatment of uveitis. The triamcinolone acetonide-loaded nanostructured lipid carriers (cTA-NLC) were developed by employing 'hot microemulsion method' using biocompatible lipids, which exhibited a sustained release nature and enhanced efficacy when evaluated in vitro. The in vivo efficacy of this developed formulation was tested on Wistar rats, and a single-dose pharmacokinetic study was conducted in rabbits. The eyes of animals were examined for any signs of inflammation using the 'Slit-lamp microscopic' method. The aqueous humor collected from the sacrificed rats was tested for total protein count and cell count. The total protein count was determined using BSA assay method, while the total cell count was determined by Neubaur's hemocytometer method. The results showed that the cTA-NLC formulation had negligible signs of inflammation, with a clinical score of uveitis 0.82 ± 0.166, which is much less than control/untreated (3.80 ± 0.3) and free drug suspension (2.66 ± 0.405). The total cell count was also found to be significantly low for cTA-NLC (8.73 ± 1.79 × 10⁵) as compared to control (52.4 ± 7.71 × 10⁵) and free drug suspension (30.13 ± 3.021 × 10⁵). Conclusively, the animal studies conducted showed that our developed formulation holds the potential for effective management of uveitis.

Caspofungin-Loaded Formulations for Treating Ocular Infections Caused by Candida spp

Fungal keratitis causes corneal blindness worldwide. The treatment includes antibiotics, with Natamycin being the most commonly used; however, fungal keratitis is difficult to treat, so alternative therapies are needed. In situ gelling formulations are a promising alternative; this type of formulation has the advantages of eye drops combined with the advantages of ointments. This study was designed to develop and characterize three formulations containing 0.5% CSP: CSP-O1, CSP-O2, and CSP-O3. CSP is an antifungal drug that acts against a diverse variety of fungi, and Poloxamer 407 (P407) is a polymer of synthetic origin that is able to produce biocompatible, biodegradable, highly permeable gels and is known to be thermoreversible. Short-term stability showed that formulations are best stored at 4 °C, and rheological analysis showed that the only formulation able to gel in situ was CSP-O3. In vitro release studies indicated that CSP-O1 releases CSP most rapidly, while in vitro permeation studies showed that CSP-O3 permeated the most. The ocular tolerance study showed that none of the formulations caused eye irritation. However, CSP-O1 decreased the cornea's transparency. Histological results indicate that the formulations are suitable for use, with the exception of CSP-O3, which induced slight structural changes in the scleral structure. All formulations were shown to have antifungal activity. In view of the results obtained, these formulations could be promising candidates for use in the treatment of fungal keratitis.

Optically Clear Silk Fibroin Films with Tunable Properties for Potential Corneal Tissue Engineering Applications: A Process-Property-Function Relationship Study

Owing to the shortage of donor corneas and issues associated with conventional corneal transplantation, corneal tissue engineering has emerged as a promising therapeutic alternative. Biocompatibility and other attractive features make silk fibroin a biomaterial of choice for corneal tissue engineering applications. The current study presents three modes of silk fibroin film fabrication by solvent casting with popular solvents, viz. aqueous (aq), formic acid (FA), and hexafluoroisopropanol (HFIP), followed by three standard modes of postfabrication annealing with water vapor, methanol vapor, and steam, and systematic characterization studies including corneal cell culture in vitro. The results indicated that silk fibroin films made from aq, FA, and HFIP solvents had surface roughness (Rq) of 1.39, 0.32, and 0.13, contact angles of 73°, 85°, and 89°, water uptake% of 58, 29, and 27%, swelling ratios of 1.58, 1.3, and 1.28, and water vapor transmission% of 39, 26, and 22%, respectively. The degradation rate was in the order of aq > HF > FA, whereas the tensile strength was in the order of aq < HF < FA. Further, the results of the annealing process indicated notable changes in morpho-topographical, physical, degradation, and tensile properties. However, the films showed no detectable changes in chemical composition and remained optically clear with >90% transmission in the visible range, irrespective of fabrication and postfabrication processing conditions. The films were noncytotoxic against L929 cells and were cytocompatible with rabbit cornea-derived SIRC cells in vitro. The study demonstrated the potential of fine-tuning various properties of silk fibroin films by varying the fabrication and postfabrication processing conditions.

Nanoparticles Loaded Thermoresponsive In Situ Gel for Ocular Antibiotic Delivery against Bacterial Keratitis

Antibiotics delivered through conventional dosage against ophthalmic infections show lower therapeutic efficacy due to their low residence time. Therefore, there is a great need to design and develop novel dosage forms that would increase the ocular residence time of antibiotics at the site of infection. This study describes the development of nanoparticles laden in situ gelling solution, intended to sustain antibiotic release for improved therapeutic efficiency. Oxytetracycline-loaded gelatin-polyacrylic acid nanoparticles were prepared and incorporated in poloxamer-N407 solution. The rheological properties of the system were studied concerning time and temperature. Moreover, in vivo biocompatibility of the system was ascertained using the Draize test and histological studies. Finally, the optimized formulation was evaluated for in vitro antibacterial activity against one of the most common keratitis causing bacteria, Pseudomonas aeruginosa. Additionally, the in vivo efficacy was evaluated on the rabbit’s eye conjunctivitis model. The formulation showed a sustained effect against keratitis; furthermore, the antibacterial activity was comparable with the commercial product.

New Preservative-Free Formulation for the Enhanced Ocular Bioavailability of Prostaglandin Analogues in Glaucoma

Glaucoma is a wide-spread eye disease caused by elevated intraocular pressure. Uncontrolled, this pressure may lead to damages to the optic nerve. Prostaglandin analogues, such as latanoprost and travoprost (which are water-insoluble active substances), are the most used class of active pharmaceutical ingredient. To administer them as eye drops, preservatives, such as benzalkonium chloride, are used as solubilizers. The latter is known to cause a local inflammation when used chronically and is not recommended for patients with ocular surface disorders. In this work, we sought to use polysorbate 80 (PS80) as a solubilizing agent simultaneously with sodium hyaluronate (NaHA) as a thickener and cytoprotective agent for the corneal surface. The first part of this study assessed the compatibility of the excipients with the active substance, using physicochemical methods such as spectra fluorescence and differential scanning calorimetry (DSC), as well as the solubilization mechanism of PS80 regarding prostaglandin analogues using nuclear magnetic resonance (NMR). The second part evaluated the stability of a formula candidate, its viscosity upon instillation, and its pharmacokinetic profile in rabbits as compared to the commercially approved medicine Travatan®. The results show that sodium hyaluronate is inert with respect to travoprost, while PS80 successfully solubilizes it, meaning that benzalkonium chloride is no longer required. Moreover, the pharmacokinetic profiles of the rabbits showed that the original formula described in the present study enhanced the ocular bioavailability of the drug, making it a promising product to control intraocular pressure with a potential reduced dosage of travoprost, therefore minimizing its related side effects.

Gellan gum-based in situ gelling ophthalmic nanosuspension of Posaconazole

The formulation and delivery of highly hydrophobic drugs in an optimized dosage form is challenging to formulation scientists. Posaconazole has shown promising action in case studies against fungal keratitis. Biological macromolecules like gellan gum would aid in enhancing the availability of such drugs by increasing the contact time of the formulation. Herein, we propose a transmucosal ocular delivery system of Posaconazole by developing a gellan gum-based in situ gelling nanosuspension. The HPLC method for Posaconazole was developed and validated as per ICH guidelines. The nanosuspension was prepared by microfluidization and optimized by Quality by Design. The gellan gum concentration selected was 0.4% w/v based on the viscosity and mucoadhesion measurements. A greater zone of inhibition of ~ 15 mm was observed for the prepared nanosuspension as compared to ~ 11 mm for the marketed itraconazole nanosuspension. A potential irritancy score of 0.85, considered to be non-irritant, was observed for the developed nanosuspension. Higher drug release of ~ 35% was noted for the nanosuspension compared to about ~ 10% for the coarse suspension. Ex vivo corneal retention studies on excised goat cornea demonstrated ~ 70% drug retention in the tissue. Graphical abstract depicting the central hypothesis of the work.

Gel-Based Materials for Ophthalmic Drug Delivery

The most common route of administration of ophthalmic drugs is the topical route because it is convenient, non-invasive, and accessible to all patients. Unfortunately, drugs administered topically are not able to reach effective concentrations. Moreover, their bioavailability must be improved to decrease the frequency of administrations and their side effects, and to increase their therapeutic efficiency. For this purpose, in recent decades, particular attention has been given to the possibility of developing prolonged-release forms that are able to increase the precorneal residence time and decrease the loss of the drug due to tearing. Among these forms, gel-based materials have been studied as an ideal delivery system because they are an extremely versatile class with numerous prospective applications in ophthalmology. These materials are used in gel eye drops, in situ gelling formulations, intravitreal injections, and therapeutic contact lenses. This review is intended to describe gel-based materials and their main applications in ophthalmology.

Repurposing of nifedipine loaded in situ ophthalmic gel as a novel approach for glaucoma treatment

Glaucoma is a chronic eye disease characterized by elevated intraocular pressure (IOP) which causes severe complications to the eyes and may lead to vision loss. The effective treatment of such diseases motivated the search for novel and unique drugs and delivery systems. It has been reported that, nifedipine (NF) is effective in reducing the elevated IOP due to vasodilatation of eye vascular smooth muscles. NF loaded thermo-sensitive in situ gels were prepared by the cold method using poloxamer 407 (P407) and hydroxypropyl methyl cellulose (HPMC) polymers adopting Box-Behnken experimental design. All the prepared formulae were tested for homogeneity, clarity, pH, isotonicity, gelling capacity, rheological behavior, in vitro drug release and were tested in vivo on rabbits. The prepared in situ gels were homogenous, transparent, having a pH ranged from 5 to 5.5 and undergo sol-gel transition within few seconds physiological temperature. The in situ gels showed sustained in vitro release of NF where about 76% of the loaded drug was released over 12 h. NF loaded in situ gels showed a 45.83 ± 2.91% reduction in the IOP, with no sign of toxicity or irritation to the eye in rabbits. The current investigations clarified the efficiency of this novel and unique NF loaded in situ gel for the control of the IOP compared to the conventional ophthalmic dosage forms.

Ion-Triggered In Situ Gelling Nanoemulgel as a Platform for Nose-to-Brain Delivery of Small Lipophilic Molecules

Background: Intranasal route offers a direct nose-to-brain delivery via olfactory and trigeminal nerves and minimizes the systemic exposure of the drug. Although reliable and non-invasive, intranasal administration of lipophilic neuroprotective agents for brain targeting is still challenging. Literature focuses on naturally-derived compounds as a promising therapeutics for chronic brain diseases. Naringin, a natural flavonoid obtained from citrus fruits possesses neuroprotective effects. By regulating multiple crucial cellular signaling pathways, naringin acts on several therapeutic targets that make it suitable for the treatment of neurodegenerative diseases like Alzheimer’s disease and making it a suitable candidate for nasal administration. However, the hydrophobicity of naringin is the primary challenge to formulate it in an aqueous system for nasal administration. Method: We designed a lipid-based nanoemulsifying drug delivery system of naringin using Acrysol K140 as an oil, Tween 80 as a surfactant and Transcutol HP as a cosolvent, to improve solubility and harness the benefits of nanosizing like improved cellular penetration. Intranasal instillations of therapeutic agents have limited efficacy due to drug washout and inadequate adherence to the nasal mucosa. Therefore, we reconstituted the naringin self-emulsifying system in a smart, biodegradable, ion-triggered in situ gelling hydrogel and optimized for desirable gel characteristics. The naringin-loaded composition was optimized and characterized for various physicochemical and rheological properties. Results: The formulation showed a mean droplet size 152.03 ± 4.6 nm with a polydispersity index <0.23. Ex vivo transmucosal permeation kinetics of the developed formulation through sheep nasal mucosa showed sustained diffusion and enhanced steady-state flux and permeability coefficient. Scanning and transmission electron microscopy revealed the spherical shape of emulsion droplets and entrapment of droplets in a gel structure. The formulation showed excellent biocompatibility as analyzed from the viability of L929 fibroblast cells and nasal mucosa histopathology after treatment. In vivo biodistribution studies revealed significantly higher drug transport and brain targeting efficiency. Conclusion: In situ gelling system with nanoemulsified naringin demonstrated a safe nasal delivery providing a new dimension to the treatment of chronic neurodegenerative diseases using small hydrophobic phytoconstituents with minimization of dose and related systemic adverse effects.

Experimental design, formulation and in vivo evaluation of a novel topical in situ gel system to treat ocular infections

In situ gels have been extensively explored as ocular drug delivery system to enhance bioavailability and efficacy. The objective of present study was to design, formulate and evaluate ion-activated in situ gel to enhance the ocular penetration and therapeutic performance of moxifloxacin in ophthalmic delivery. A simplex lattice design was utilized to examine the effect of various factors on experimental outcomes of the in situ gel system. The influence of polymers (independent variables) such as gellan gum (X₁), sodium alginate (X₂), and HPMC (X₃) on gel strength, adhesive force, viscosity and drug release after 10 h (Q₁₀) were assessed. Selected formulation (MH7) was studied for ex vivo permeation, in vivo irritation and pharmacokinetics in rabbits. Data revealed that increase in concentration of polymers led to higher gel strength, adhesive force and viscosity, however, decreases the drug release. MH7 exhibited all physicochemical properties within acceptable limits and was stable for 6 months. Release profile of moxifloxacin from MH7 was comparable to the check point batches and followed Korsmeyer-Peppas matrix diffusion-controlled mechanism. Ocular irritation study signifies that selected formulation is safe and non-irritant for ophthalmic administration. In vivo pharmacokinetics data indicates significant improvement of moxifloxacin bioavailability (p < 0.0001) from MH7, as evidenced by higher C_max (727 ± 56 ng/ml) and greater AUC (2881 ± 108 ng h/ml), when compared with commercial eye drops (C_max; 503 ± 85 ng/ml and AUC; 978 ± 86 ng h/ml). In conclusion, developed in situ gel system (MH7) could offers a more effective and extended ophthalmic therapy of moxifloxacin in ocular infections when compared to conventional eye drops.

Development, Optimization, and Antifungal Assessment of Ocular Gel Loaded With Ketoconazole Cubic Liquid Crystalline Nanoparticles

Ketoconazole is a drug that belongs to azole antifungal group. The current available marketed products of ketoconazole are accompanied with potential drawbacks such as short retention time at the eye surface and eye irritation. The aim of this research is to find a solution for the previously mentioned limitations through loading of ketoconazole within cubosomes (KZ-Cub) to be used as ophthalmic drug delivery systems. Cubosomes properties will help to keep the encapsulated drug in the solubilized form. Further incorporation of cubosomes into biodegradable polymer based gel could prolong the ocular retention time of the drug. Three studied independent variables included glyceryl-mono-oleate, Pluronic-F127 and Polyvinyl alcohol percentage with respect to the dispersion media, while particle size, entrapment efficiency and stability index were the dependent variables that have been evaluated. The optimized cubosomes was assessed for its in-vitro and in-vivo antifungal activity. The prepared gel loaded with KZ-Cub formula had an enhanced permeability, ocular availability, antifungal activity and significant decrease in MIC values compared to commercial one, which reflected the strong impact on the activity of KZ in the management of eye infection.

Combination of Nanomicellar Technology and In Situ Gelling Polymer as Ocular Drug Delivery System (ODDS) for Cyclosporine-A

A combination of in situ gelling systems and a loaded drug self-assembling nanomicellar carrier was chosen in this study as a new potential Ocular Drug Delivery System (ODDS) for Cyclosporine-A (CyA), a poorly water-soluble drug. Two non-ionic surfactants (d-α-tocopherol polyethylene glycol succinate, VitE-TPGS and polyoxyl 40 hydrogenated castor oil, RH-40) were used to produce the nanomicelles. The physical-chemical characterization of the nanomicelles in terms of CyA entrapment (EE%) and loading efficiency (LE%), cloud point (CP), regeneration time (RT), size and polydispersity index (PI) allowed us to select the best combination of surfactant mixture, which showed appropriate stability, high CyA-EE (99.07%), very small and homogeneous dimensions and favored the solubilization of an amount of CyA (0.144% w/w) comparable to that contained in marketed emulsion Ikervis^®. The selected nanomicellar formulation incorporated into optimized ion-sensitive polymeric dispersions of gellan gum (GG-LA: 0.10, 0.15 and 0.20% w/w) able to trigger the sol-gel transition after instillation was characterized from technological (osmolality, pH, gelling capacity, rheological behavior, wettability, TEM and storage stability at 4 and 20 °C) and biopharmaceutical points of view. This new combined approach allowed us to obtain clear aqueous dispersions that were easy to instill and able to form a viscous gel when in contact with the tear fluid, improving CyA ocular bioavailability. Furthermore, this new ODDS prevented CyA transcorneal permeation, exhibited low cytotoxicity and prolonged the CyA resident time in the precorneal area compared to Ikervis^®.

Ciprofloxacin self-dissolvable Soluplus based polymeric films: a novel proposal to improve the management of eye infections

Infections of the eye are among the leading causes of vision impairment and vision loss worldwide. The ability of a drug to access the anterior parts of the eye is negligible after systemic administration. Effective drug delivery to the eye is a major challenge due to the presence of protective mechanisms and physiological barriers that result in low ocular availability after topical application. The main purpose of this work was the improvement of the corneal and conjunctival permeation of the antibiotic Ciprofloxacin, a wide spectrum antibiotic used for the most common eye infection, using a self-dissolving polymeric film. Films were prepared by the solvent casting technique, using polyvinyl caprolactam-polyvinyl acetate-polyethylene glycol graft co-polymer (Soluplus), polyvynyl alcohol, and propylene glycol. Films were homogeneous in drug content and thickness, as demonstrated by adapting the Swiss Roll technique followed by microscopy observation. These films proved in vitro to control the release of the Ciprofloxacin. Ex vivo permeability studies using Franz diffusion cells and porcine cornea and sclera showed an effective permeability of the drug without inducing irritation of the tissues. Films swelled in contact with artificial tears forming an in situ gel over 20 min, which will improve drug contact and reduce the need of multiple dosing. The antibiotic activity was also tested in vitro in five types of bacterial cultures, assuring the pharmacological efficacy of the films. The developed films are a promising drug delivery system to topically treat or prevent ocular infections.

Evaluation of in-situ gel-forming eye drop containing bacteriophage against Pseudomonas aeruginosa keratoconjunctivitis in vivo

Introduction: Eradication of Pseudomonas aeruginosa has become increasingly difficult due to its remarkable capacity to resist antibiotics. Bacteriophages have been suggested as an alternative treatment for bacterial infections. Methods: In-situ gel-forming eye drop containing phage against P. aeruginosa keratoconjunctivitis was prepared. The Cystoviridae phage was formulated as in-situ gel-forming formulation which is a solution formulation but turns into gel when it contacts the eye. Therapeutic effectiveness of the in-situ gel forming formulation was evaluated by histological examination on day 12 post-infection. Results: The viscosity of selected formulation increased when it was instilled into the eye. The histological results showed edema, abscesses, and destruction of the stromal structure of cornea in groups where no in-situ gel-forming formulation was used. In the group where in-situ gel forming formulation was used, re-epithelialization and normal corneal structure were observed. Conclusion: In-situ gel-forming ophthalmic formulation containing phage can be effective in the treatment of P. aeruginosa keratoconjunctivitis.

In situ ophthalmic gel forming systems of poloxamer 407 and hydroxypropyl methyl cellulose mixtures for sustained ocular delivery of chloramphenicole: optimization study by factorial design

Background

Conventional drug delivery systems have some major drawbacks such as low bioavailability, short residence time and rapid precorneal drainage. An in situ gel drug delivery system provides several benefits, such as prolonged pharmacological duration of action, simpler production techniques, and low cost of manufacturing. This research aims to get the optimum formula of chloramphenicol in situ gel based on the physical evaluation.

Methods

The effects of independent variables (poloxamer 407 and hydroxypropyl methyl cellulose (HPMC) concentration) on various dependent variables (gelling capacity, pH and viscosity) were investigated by using 3² factorial design and organoleptic evaluation was done with descriptive analysis.

Results

The optimized formula of chloramphenicol in situ gel yielded 9 variations of poloxamer 407 and HPMC bases composition in % w/v as follows, F1 (5; 0.45), F2 (7.5; 0.45), F3 (10; 0.45), F4 (5; 0.725), F5 (7.5; 0.725), F6 (10; 0.725), F7 (5; 1), F8 (7.5; 1), F9 (10; 1). The results indicated that the organoleptic, pH, and gelling capacity parameters matched all formulas (F1–F9), however, the viscosity parameter only matched F3, F6, F8, and F9. Based on factorial design, F6 had the best formula with desirability value of 0.54, but the design recommended that formula with the composition bases of poloxamer 407 and HPMC at the ratio of 8.16 % w/v and 0.77 % w/v, respectively, was the optimum formula with a desirability value of 0.69.

Conclusion

All formulas have met the Indonesian pharmacopoeia requirements based on the physical evaluation, especially formula 6 (F6), which was supported by the result of factorial design analysis.

The gamut of perspectives, challenges, and recent trends for in situ hydrogels: a smart ophthalmic drug delivery vehicle

Polymers have a major role in the controlled delivery of pharmaceutical compounds to a targeted portion of the body. In this quest, a high priority research area is the targeted delivery of ophthalmic drugs to the interior regions of the eyes. Due to their complex anatomical/biochemical nature. This necessitates an advanced drug delivery cargo that could administer a therapeutic agent to the targeted location by evading various obstacles. The ongoing focus is to design an ophthalmic formulation by coupling it with a smart in situ forming polymeric hydrogel. These smart macromolecules have an array of unique theranostic properties and can utilize the in vivo biological parameters as a stimulus to change their macromolecular state from liquid to gel. The fast gelling hydrogel improves the corneal contact time, facilitates sustained drug release, resists the burst-out effect, and assists drug permeability to anterior regions. This review summarizes the rationale, scientific objectives, properties, and classification of the biologically important in situ hydrogels in the niche of ophthalmic drug delivery. The current trends and prospectives of the array of stimulus-responsive polymers, copolymers, and nanomaterials are discussed broadly. The crucial biointerfacial attributes with pros and cons are reviewed by investigating the effect of the nature of polymers as well as the ratio/percentage of additives and copolymers that influence the overall performance.

Triamcinolone acetonide loaded-cationic nano-lipoidal formulation for uveitis: Evidences of improved biopharmaceutical performance and anti-inflammatory activity

Topical administration of corticosteroids is the cornerstone treatment of anterior uveitis, but poor corneal penetration and retention cause hindrance in their therapeutic utility. The conventional eye drops are less valuable in conditions where inflammation reaches deeper regions of the eye. Therefore, there is a clear need for an effective drug delivery system, which can increase corticosteroid penetration after topical application. To address this, cationic nanostructured lipid carriers of the drug triamcinolone acetonide (cTA-NLC) were prepared. The cTA-NLC were prepared by a hot microemulsion method and evaluated for drug release, permeation, cell uptake, cytotoxicity, anti-inflammatory activity and ocular irritancy. The cTA-NLC are nanometric in size (< 200 nm), with a zeta potential of about +35 mv and % drug EE of 88 %. The nanocarriers exhibited slow and sustained release of around 84 % in 24 h and transcorneal drug permeation of 51 % in 8 h. The nanocarriers exhibited no cytotoxicity (% cell viability of>90 %). The cell uptake study showed that nanocarriers could retain inside the cells for 24 h. The developed formulation could significantly reduce the TNF-α level in LPS induced inflamed cells. The studies indicated that cTA-NLC could be a promising option for the topical treatment of uveitis.

Brinzolamide Dimethyl Sulfoxide In Situ Gelling Ophthalmic Solution: Formulation Optimisation and In Vitro and In Vivo Evaluation

In the present work, a cost-effective, stable and sustained release ophthalmic solution formulation of brinzolamide (BRZ) was developed for the treatment of glaucoma. The prototype formulation undergoes 'in situ gelling' when administered in the eye, thereby providing longer residence (16-24 h). As a result, the same therapeutic endpoint is achieved with once daily dosing vis-à-vis the commercially available product Azopt® (brinzolamide 1.0% w/v, Alcon Laboratories, USA) that requires 3-4 times instillations per day. The prototype formulations were prepared using dimethyl sulfoxide, polyoxyl 35 castor oil and polysorbate 80. Gellan gum was used as the in situ gelling agent. Formulation variables like (i) concentration of the drug, dimethyl sulfoxide and in situ gelling agent and (ii) type and concentration of solubiliser showed a significant effect on the solubility of brinzolamide, in vitro gelling time, in vitro drug release and in situ gel stability. Prototype formulations were evaluated in New Zealand white rabbits for ocular toxicity and efficacy study. The tested formulations were well tolerated and reduced intraocular pressure (IOP) from 25-28 to 12-14 mmHg compared to saline and placebo control samples. Additionally, a significant increase in the area under change in IOP from baseline (ΔIOP) vs. time curve and a longer mean residence time (MRT) were also observed for the test formulations (7.4 to 17.7 h) compared to the commercially available suspension of Azopt® (4.9 h) (p < 0.0001). Thus, 'in situ gelling' formulation strategy described in this work can work as a viable option for ocular delivery of brinzolamide for the treatment of glaucoma.

Advancing the stimuli response of polymer-based drug delivery systems for ocular disease treatment

Recent exploitations of stimuli-responsive polymers as ophthalmic drug delivery systems for the treatment of eye diseases are summarized and discussed.

Novel in situ gelling ophthalmic drug delivery system based on gellan gum and hydroxyethylcellulose: Innovative rheological characterization, in vitro and in vivo evidence of a sustained precorneal retention time

Achieving drug delivery at the ocular level encounters many challenges and obstacles. In situ gelling delivery systems are now widely used for topical ocular administration and recognized as a promising strategy to improve the treatment of a wide range of ocular diseases. The present work describes the formulation and evaluation of a mucoadhesive and ion-activated in situ gelling delivery system based on gellan gum and hydroxyethylcellulose for the delivery of phenylephrine and tropicamide. First, physico-chemical characteristics were assessed to ensure suitable properties regarding ocular administration. Then, rheological properties such as viscosity and gelation capacity were determined. Gelation capacity of the formulations and the effect of hydroxyethylcellulose on viscosity were demonstrated. A new rheological method was developed to assess the gel resistance under simulated eye blinking. Afterward, mucoadhesion was evaluated using tensile strength test and rheological synergism method in both rotational and oscillatory mode allowing mucoadhesive properties of hydroxyethylcellulose to be point out. Finally, residence time on the ocular surface was investigated in vivo, using cyanine 5.5 dye as a fluorescent marker entrapped in the in situ gelling delivery systems. Residence performance was studied by non-invasive optical imaging on vigilant rabbits, allowing eye blinking and nasolacrimal drainage to occur physiologically. Fluorescence intensity profiles pointed out a prolonged residence time on the ocular surface region for the developed formulations compared to conventional eye drops, suggesting in vitro / in vivo correlations between rheological properties and in vivo residence performances.

Levofloxacin Hemihydrate In Situ Gelling Ophthalmic Solution: Formulation Optimization and In Vitro and In Vivo Evaluation

Bacterial conjunctivitis is a leading cause of ocular infections requiring short-term therapeutic treatment with frequent administration of drugs on daily basis. Topical dosage forms available in the market for the treatment of bacterial conjunctivitis such as simple drug solutions and suspensions are rapidly eliminated from the precorneal space upon instillation due to tear turn over and nasolacrimal drainage, limiting intraocular bioavailability of drug to less than 10% of the administered dose. To overcome issues related to conventional drop, an effort was made to design and evaluate prolong release ophthalmic solution of levofloxacin hemihydrate (LFH) using ion-sensitive in situ gelling polymer. Gellan gum was used as the in situ gelling agent. Formulations were screened based on in vitro gelation time, in vitro drug release, and stability towards sol to gel conversion upon storage. The prototype formulations exhibiting quick in vitro gelling time (< 15 s), prolonged in vitro drug release (18-24 h), and stability for at least 6 months at 25°C/40% relative humidity (RH) and 40°C/25% RH were evaluated for pharmacokinetic studies using healthy New Zealand white rabbits. Tested formulations were found to be well-tolerated and showed significant increase in AUC_0-24 (22,660.39 h ng/mL) and mean residence time (MRT 12 h) as compared with commercially available solution Levotop PF® (Ajanta Pharma Ltd., India)(AUC_0-24 6414.63 h ng/mL and MRT 4 h). Thus, solution formulations containing in situ gelling polymer may serve as improved drug delivery system providing superior therapeutic efficacy and better patient compliance for the treatment of bacterial conjunctivitis.

Design of l-Lysine-Based Organogelators and Their Applications in Drug Release Processes

This work reports on the synthesis of three new l-lysine-based organogelators bis(N²-alkanoyl-N⁶-l-lysyl ethylester)oxalylamides, where alkanoyls are lauroyl, myristoyl, and palmitoyl. The gels of these gelators were prepared with high yields in eco-friendly solvents commonly used in cosmetics such as ethyl and isopropyl esters of lauric and myristic acids, liquid paraffin, 1-decanol, and 1,2-propanediol. Fourier transform infrared measurements revealed the involvement of intermolecular hydrogen bonds in the gelation. Scanning electron microscopy images of xerogels indicated different morphologic patterns with regard to the alkanoyl chain length and the solvent employed in their preparation. The gel formation was supported by rheological measurements. Three gels prepared in liquid paraffin were loaded with naproxen (Npx) with a quite high loading capacity (up to 166.6% as percentage of gelator) without gel disruption. The release of Npx from the gel matrix into the buffered solution at physiologic pH was evaluated using UV-vis spectroscopy. The results revealed that the release rate of Npx from the organogels significantly retarded with increasing organogelator concentration, whereas it enhanced with increasing Npx concentration. The rate was also found to be pH-dependent; the lower the pH, the lower the rate. Furthermore, molecular dynamic calculations performed on the octamer of myristoyl-bearing gelator (N ² M/N ⁶ Lys) in 1,2-propanediol provided useful information regarding the structural properties of the gels, which may be of interest to interpret the structure of the gel matrix. Altogether, this work provided valuable outcomes, which may be relevant to the pharmaceutical industry. It may be suggested that l-lysine-based gels have potentials in the delivery of nonsteroidal anti-inflammatory drug molecules. Besides, the release of the drug can be fine-tuned by the correct choice of gelator-solvent combination.

Plasma-based fast-gelling biohybrid gels for biomedical applications

Blood based biomaterials are widely researched and used in different biomedical applications including cell therapy, drug delivery, sealants etc. due to their biocompatibility and biodegradability. Blood derived gels are successfully used in clinical studies due to the presence of fibrinogen and several platelet growth factors. In spite of their wide applications, it is challenging to use blood-based biomaterials due to their low mechanical stability, poor adhesive property and contamination risk. In this study, we used porcine plasma to form gel in presence of biodegradable synthetic crosslinkers. Mechanical strength of this plasma gel could be tailored by altering the amount of crosslinkers for any desired biomedical applications. These plasma gels, formed by the synthetic crosslinkers, were utilized as a drug delivery platform for wound healing due to their low cytotoxicity. A model drug release study with these plasma gels indicated slow and sustained release of the drugs.

Vancomycin-loaded niosomes integrated within pH-sensitive in-situ forming gel for treatment of ocular infections while minimizing drug irritation

Objectives

The aim of the current study was to minimize ocular irritation and prolong the pharmacological action of vancomycin via formulation into nanosized spherical niosomes loaded into pH-sensitive in-situ forming gel.

Methods

Stability and rheological behaviour of the various gelling systems were evaluated. The ability of the selected system to eradicate methicillin-resistant Staphylococcus aureus (MRSA) infections was examined in vitro and in vivo. Draize technique was also used to assess ocular irritation in rabbits.

Key findings

Nanosized spherical niosomes loaded with vancomycin at high entrapment efficiency were prepared and integrated into polymeric solution that forms gel in situ upon instillation into the eye, to allow for a further increase in the ocular residence time. In MRSA-infected rabbits, there were 180- and 2.5-fold increases in the antibacterial efficacy after treatment with the vancomycin niosomal gels in comparison with the untreated animals and the animals treated with the vancomycin free drug solution, respectively.

Conclusions

The developed formulations demonstrated promising in-vivo biocompatibility and antibacterial efficacy, signifying their potential application as ophthalmic preparation to overcome ocular infections induced by resistant bacterial strains while minimizing drug irritation and improving patient compliance.

A potential nanoparticle-loaded in situ gel for enhanced and sustained ophthalmic delivery of dexamethasone

Increasing the permeability of drugs across the cornea is key to improving drug absorption by the eye. This study presents a newly developed in situ gel loaded with nanoparticles, which could achieve controlled drug release and high ocular drug bioavailability by avoiding rapid precorneal clearance. The physicochemical parameters of the formulation were investigated and showed uniform size, physical stability, and favorable rheological and gelling properties. Ex vivo permeation studies revealed significantly higher drug release from the in situ gel loaded with nanoparticles compared to the conventional poloxamer in situ gel and the drug solution. When compared with a marketed formulation, the in situ gel loaded with nanoparticles provided slower controlled release and higher ocular bioavailability of dexamethasone. In conclusion, the developed nanoparticle-loaded in situ gel can successfully increase drug ocular bioavailability by enhancing contact time with the ocular surface and permeation through the cornea.

Chitosan-Based In Situ Gels for Ocular Delivery of Therapeutics: A State-of-the-Art Review

Ocular in situ gels are a promising alternative to overcome drawbacks of conventional eye drops because they associate the advantages of solutions such as accuracy and reproducibility of dosing, or ease of administration with prolonged contact time of ointments. Chitosan is a natural polymer suitable for use in ophthalmic formulations due to its biocompatibility, biodegradability, mucoadhesive character, antibacterial and antifungal properties, permeation enhancement and corneal wound healing effects. The combination of chitosan, pH-sensitive polymer, with other stimuli-responsive polymers leads to increased mechanical strength of formulations and an improved therapeutic effect due to prolonged ocular contact time. This review describes in situ gelling systems resulting from the association of chitosan with various stimuli-responsive polymers with emphasis on the mechanism of gel formation and application in ophthalmology. It also comprises the main techniques for evaluation of chitosan in situ gels, along with requirements of safety and ocular tolerability.

Research progress of in-situ gelling ophthalmic drug delivery system

Blindness and vision impairment are the most devastating global health problems resulting in a substantial economic and social burden. Delivery of drug to particular parts of the anterior or posterior segment has been a major challenge due to various protective barriers and elimination mechanisms associated with the unique anatomical and physiological nature of the ocular system. Drug administration to the eye by conventional delivery systems results in poor ocular bioavailability (<5%). The designing of a novel approach for a safe, simple, and effective ocular drug delivery is a major concern and requires innovative strategies to combat the problem. Over the past decades, several novel approaches involving different strategies have been developed to improve the ocular delivery system. Among these, the ophthalmic in-situ gel has attained a great attention over the past few years. This review discussed and summarized the recent and the promising research progress of in-situ gelling in ocular drug delivery system.

Delivery of therapeutics for deep-seated ocular conditions - status quo

OBJECTIVES

There is a need for research into designing effective pharmaceutical systems for delivering therapeutic drugs to the posterior of the eye for glaucoma-related pathology, macular degeneration, diabetic retinopathy, macular oedema, retinitis and choroiditis. Conventionally, eye drops have been extensively utilised for topical drug delivery to the anterior segment of the eye, but are less effective for delivery of therapeutics to the back of the eye due to significant barriers hampering drug penetration into the target intraocular tissue. This review explores some of the current and novel delivery systems employed to deliver therapeutics to the back of the eye such as those using liposomes, ocular implants, in situ gels, and nanoparticles, and how they can overcome some of these limitations.

KEY FINDINGS

Issues such as blinking, precorneal fluid drainage, tear dilution and turnover, conjunctiva and nasal drug absorption, the corneal epithelium, vitreous drug clearance, and the blood-ocular barriers are reviewed and discussed.

SUMMARY

Further studies are needed to address their shortcomings such as drug compatibility and stability, economic viability and patient compliance.

A novel thermo-sensitive hydrogel-based on poly(N-isopropylacrylamide)/hyaluronic acid of ketoconazole for ophthalmic delivery

The aim of this study is to develop thermo-sensitive in situ gelling formulation of KCL based on poly(N-isopropylacrylamide)/hyaluronic acid. The prepared preparations were characterized for in vitro gelation, drug release and antifungal activity. In this study, drug content of prepared gels was found to be in the range of 91-96%. The pH value was in the range of 6.0-7.5. By measuring the gelation temperature of the prepared PN-HA thermogelling solutions, it was 33 °C. In vitro release showed that the release of KCL from in situ gels was moderate without burst effects. The KCL PN-HA in situ gels were well-tolerated by the rabbits, and no macroscopic signs of irritation, redness, or other toxic effects were observed. From in vivo antimicrobial study, KCL PN-HA in situ gels may be concluded to have a better cure percent in clinical profile and negative growth of Candida albicans in microbiological test. Therefore, this new formulation could prove to be a novel ocular dosage form able to prolong the residence time and to control the release of drug when administered into the eye.

Development of topical ophthalmic In Situ gel-forming estradiol delivery system intended for the prevention of age-related cataracts

The goal of this study was to develop and characterize an ion-activated in situ gel-forming estradiol (E2) solution eye drops intended for the prevention of age-related cataracts. Accordingly, in situ gelling eye drops were made using gellan gum as an ion-activated gel-forming polymer, polysorbate-80 as drug solubilizing agent, mannitol as tonicity agent, and combination of potassium sorbate and edetate disodium dihydrate (EDTA) as preservatives. The formulations were tested for the following characteristics: pH, clarity, osmolality, antimicrobial efficacy, rheological behavior, and in vitro drug release. Stability of the formulation was also monitored for 6 months at multiple storage conditions per ICH Q1A (R2) guidelines. The solution eye drops resulted in an in-situ phase change to gel-state when mixed with simulated tear fluid (STF). The gel structure formation was confirmed by viscoelastic measurements. Drug release from the gel followed non-fickian mechanism with 80% of drug released in 8 hr. The formulations were found to be clear, isotonic with suitable pH and viscoelastic behavior and stable at accelerated and long-term storage conditions for 6 months. In vitro results suggest that the developed formulation is suitable for further investigation in animal models to elucidate the ability of estrogen to prevent and delay cataracts.