Preparation and evaluation of a Carbopol/HPMC-based in situ gelling ophthalmic system for puerarin

Chitosan/carbomer nanoparticles- laden in situ gel for improved ocular delivery of timolol: in vitro, in vivo, and ex vivo study

Due to the small capacity of the eye cavity and the rapid drainage of liquid into the nasolacrimal duct, patients must frequently administer the drops. Nanoparticles (NPs) and in situ gel systems have each proven their ability to achieve eye retention independently. In this study, timolol-loaded chitosan-carbomer NPs were prepared using the polyelectrolyte complexation method, and incorporated into a pH-responsive in situ gel system made of carbomer. The rheological behavior of NPs-laden in situ gel was examined at room and physiological conditions. Characteristics such as zeta potential, surface tension, refractive index, mucoadhesive properties, drug release, transcorneal permeability, and intra-ocular pressure (IOP) lowering activity were investigated on NPS and NPs-laden in situ gel formulations. The optimum gained NPs system had an encapsulation efficiency of about 69% with a particle size of 196 nm. The zeta potential of the NP and NPs-laden in situ gel were - 16 and + 11 mV respectively. NPs-laden in situ gel presented enhanced viscosity at physiological pH. All physicochemical properties were acceptable for both formulations. NPs and NPs-laden in situ gel systems proved to sustain drug release. They showed mucoadhesive properties which were greater for NPs-laden in situ gel. IOP reduction by NPs-laden in situ gel was significantly higher and more long-lasting than the timolol solution and NPs. In conclusion, the developed NPs-laden in situ gel is a promising carrier for ocular drug delivery due to the slow release of drug from nanoparticles, its mucoadhesive properties, and high viscosity acquisition in contact with precorneal film, which lead to improved therapeutic efficacy.

Seeing the Future: A Review of Ocular Therapy

Ocular diseases present a unique challenge and opportunity for therapeutic development. The eye has distinct advantages as a therapy target given its accessibility, compartmentalization, immune privilege, and size. Various methodologies for therapeutic delivery in ocular diseases are under investigation that impact long-term efficacy, toxicity, invasiveness, and delivery range. While gene, cell, and antibody therapy and nanoparticle delivery directly treat regions that have been damaged by disease, they can be limited in the duration of the therapeutic delivery and have a focal effect. In contrast, contact lenses and ocular implants can more effectively achieve sustained and widespread delivery of therapies; however, they can increase dilution of therapeutics, which may result in reduced effectiveness. Current therapies either offer a sustained release or a broad therapeutic effect, and future directions should aim toward achieving both. This review discusses current ocular therapy delivery systems and their applications, mechanisms for delivering therapeutic products to ocular tissues, advantages and challenges associated with each delivery system, current approved therapies, and clinical trials. Future directions for the improvement in existing ocular therapies include combination therapies, such as combined cell and gene therapies, as well as AI-driven devices, such as cortical implants that directly transmit visual information to the cortex.

The potential benefits of polyphenols for corneal diseases

The cornea functions as the primary barrier of the ocular surface, regulating temperature and humidity while providing protection against oxidative stress, harmful stimuli and pathogenic microorganisms. Corneal diseases can affect the biomechanical and optical properties of the eye, resulting in visual impairment or even blindness. Due to their diverse origins and potent biological activities, plant secondary metabolites known as polyphenols offer potential advantages for treating corneal diseases owing to their anti-inflammatory, antioxidant, and antibacterial properties. Various polyphenols and their derivatives have demonstrated diverse mechanisms of action in vitro and in vivo, exhibiting efficacy against a range of corneal diseases including repair of tissue damage, treatment of keratitis, inhibition of neovascularization, alleviation of dry eye syndrome, among others. Therefore, this article presents a concise overview of corneal and related diseases, along with an update on the research progress of natural polyphenols in safeguarding corneal health. A more comprehensive understanding of natural polyphenols provides a novel perspective for secure treatment of corneal diseases.

Effect of Egg-Coating Material Properties by Blending Cassava Starch with Methyl Celluloses and Waxes on Egg Quality

An egg-coating material was developed to extend the shelf-life and freshness of eggs by blending cassava starch (CS) with gelling agents and waxes. The effects of the properties of this egg coating on egg quality were investigated. Hydroxypropyl methylcellulose (HPMC), carboxymethyl cellulose (CMC), beeswax, and paraffin wax were used. CS blended with low-molecular-weight paraffin (Paraffin(L)) and CMC coating material displayed a tensile strength of 4 MPa, 34% elongation at break, 0.0039 g day⁻¹ m⁻² water vapor permeability, and a water contact angle of 89° at 3 min. Eggs coated with CS/CMC/Paraffin(L) solutions had a Haugh unit value of 72 (AA grade) and exhibited a weight loss of 2.4% in 4 weeks. CMC improved the compatibility of CS and Paraffin(L). This improvement and the hydrophobicity of Paraffin(L) provided suitable mechanical and water-resistance properties to the coating material that helped to maintain the quality of the coated AA-grade eggs with low weight loss for 4 weeks.

Progress in drug formulation design and delivery of medicinal substances used in ophthalmology

Due to the very low bioavailability of drugs administered to the surface of the eyeball, issues related to the formulation of an ophthalmic drug pose a technological challenge. The essence of an ophthalmic drug is the selection of an appropriate active substance (API), but also auxiliary substances that determine the desired drug quality and API availability. The ophthalmic drug is not only classic eye drops. Therefore, on the basis of the literature data, the properties and application of auxiliary substances increasing the pharmaceutical availability of API, improving the penetration of API into the eye structures and modifying the viscosity of eye drops were characterized. The possibility of chemical modification of API and the use of prodrugs in ophthalmic drug forms was also noted. Taking into account the progress in the field of ophthalmic drug formulation, the use of multi-compartment systems (lipid particles, nanoparticles, microparticles, liposomes, niosomes, dendrimers) and modern ophthalmic drug delivery systems (inserts, implants, microneedles, contact lenses, ionophoretic systems) have been indicated. Examples of solutions already used by manufacturers, as well as those in the phase of laboratory or clinical trials, were indicated.

Optimization and Characterization of Brimonidine Tartrate Nanoparticles-loaded In Situ Gel for the Treatment of Glaucoma

Purposes: The present study aimed to develop brimonidine tartrate loaded poly(lactic-co-glycolic acid) acid vitamin E-tocopheryl polyethylene glycol 1000 succinate (BRT-PLGA-TPGS) nanoparticles in thermosensitivein situ gel to improve mucoadhensive properties and drug holding capacity for the better management of glaucoma.Methods: Nanoparticles was optimized by means of Box-Behnken Design (BBD). The formulations were prepared using various concentration of PLGA (0.1-0.4% w/v) and TPGS (0.3-0.5% w/v). The analytical data of fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC) and transmission electron microscopy (TEM) depicted the drug excipients compatibility and confirmed the nanoparticles. Nanoparticles incorporated gel was evaluated for transcorneal permeability, gelation time, gelling temperature, and rheological studies. In addition, in vitro, transcorneal permeation drug release studies and intraocular pressure (IOP) for optimized gel was also performed. Biocompatibility of formulations was investigated in rabbit model.Results: The drug loaded nanoparticles exhibited 115.72 ± 4.18 nm, 0.190 ± 0.02, -11.80 ± 2.24 mV and 74.85 ± 6.54% of mean size, polydispersity index (PDI), zeta potential and entrapment efficiency (% EE), respectively. As compared to marketed eye drop, the sustained and continuous release BRT release from Poloxamer-based in situ gel was 85.31 ± 3.51% till 24 h. The transcorneal steady-state flux (136.32 μg cm^-2 h^-1) of optimized in situ gel was approximately 3.5 times higher than marketed formulation (38.60 μg cm^-2 h^-1) flux at 4 h. The optimized formulation produces 3 fold greater influences on percentage reduction of IOP (34.46 ± 4.21%) than the marketed formulation (12.24 ± 2.90%) till 8 h.Conclusion: The incorporation of optimized BRT-PLGA-TPGS nanoparticles into a thermosensitivein situ gel matrix to improve precorneal residence time without causing eye irritation and also serve the sustained release of BRT through cornea for effective management of glaucoma.

A New Approach for Dry Eye Management By Mucoadhesive In situ Gel of Vitamin B12: Formulation, In vitro and In vivo Assessment

The commitment of the existent study was to develop a mucoadhesive in situ gel systems of vitamin B12 for the management of dry eye disease. The gels were prepared using pluronic F-127 and either of chitosan, carbapol 971P, sodium alginate, or hydroxy propyl methyl cellulose. Drug-excipients compatibility was investigated by means of differential scanning calorimetry and Fourier transform infrared spectroscopy. The gels were characterized for pH, clarity, gelling capacity, viscosity, and adhesion. In vitro release of vitamin B12 from the selected gels was investigated. In vivo effectiveness of the selected gel was determined in rabbit models using Schirmer's and fluorescein tests. The compatibility studies revealed the possibility of incidence of drug/polymer interaction in some formulations. F2-containing pluronic F127 and hydroxypropyl methyl cellulose showed the most appropriate physical characterization and in vitro release profile. The prepared gels showed prolonged drug release with drug release mechanism of combined diffusion and erosion. The in vivo study revealed good effectiveness of the prepared mucoadhesive in situ gel system of vitamin B12 in the treatment of dry eye disease that was comparable to that of the marketed drops.

Pharmacokinetics and Pharmacodynamics of 3 Doses of Oral-Mucosal Dexmedetomidine Gel for Sedative Premedication in Women Undergoing Modified Radical Mastectomy for Breast Cancer

BACKGROUND

Buccal dexmedetomidine (DEX) produces adequate preoperative sedation and anxiolysis when used as a premedication. Formulating the drug as a gel decreases oral losses and improves the absorption of buccal DEX. We compared pharmacokinetic and pharmacodynamic properties of 3 doses of buccal DEX gel formulated in our pharmaceutical laboratory for sedative premedication in women undergoing modified radical mastectomy for breast cancer.

METHODS

Thirty-six patients enrolled in 3 groups (n = 12) to receive buccal DEX gel 30 minutes before surgery at 0.5 µg/kg (DEX 0.5 group), 0.75 µg/kg (DEX 0.75 group), or 1 µg/kg (DEX 1 group). Assessments included plasma concentrations of DEX, and pharmacokinetic variables calculated with noncompartmental methods, sedative, hemodynamic and analgesic effects, and adverse effects.

RESULTS

The median time to reach peak serum concentration of DEX (Tmax) was significantly shorter in patients who received 1 µg/kg (60 minutes) compared with those who received 0.5 µg/kg (120 minutes; P = .003) and 0.75 µg/kg (120 minutes; P = .004). The median (first quartile-third quartile) peak concentration of DEX (maximum plasma concentration [Cmax]) in plasma was 0.35 ng/mL (0.31-0.49), 0.37 ng/mL (0.34-0.40), and 0.54 ng/mL (0.45-0.61) in DEX 0.5, DEX 0.75, and DEX 1 groups (P = .082). The 3 doses did not produce preoperative sedation. The 1 µg/kg buccal DEX gel produced early postoperative sedation and lower intraoperative and postoperative heart rate values. Postoperative analgesia was evident in the 3 doses in a dose-dependent manner with no adverse effects.

CONCLUSIONS

Provided that it is administered 60-120 minutes before surgery, sublingual administration of DEX formulated as an oral-mucosal gel may provide a safe and practical means of sedative premedication in adults.

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.

Design, Characterization, and Application of a pH-Triggered In Situ Gel for Ocular Delivery of Vinpocetine

We developed a pH-triggered in situ gel (ISG) for ocular delivery of vinpocetine to achieve systemic absorption and a brain-targeting effect in rats. Carbopol acted as a gelling agent combined with hydroxypropyl methylcellulose (HPMC) as a viscosity-enhancing agent. The concentration of Carbopol (0.2%, w/v) and HPMC (1.5%, w/v) was optimized for the ISG system. The optimized formulation was evaluated for studies on release in vitro, rheology, differential scanning calorimetry, ocular irritation, residence time, and in vivo pharmacokinetics. The vinpocetine ISG stayed longer in rabbit eyes than vinpocetine ointment. In vivo pharmacokinetics showed that compared with vinpocetine ointment, vinpocetine ISG attained a peak plasma concentration and area under the curve that was 1-2 folds greater in rat plasma. The Drug Targeting Index (DTI) was 1.06 and 1.26 for vinpocetine ointment and vinpocetine ISG, respectively, after ocular administration, showing that vinpocetine ISG had better distribution in rat brain. These results revealed that a pH-triggered ISG system via ocular administration could be an alternative approach compared with traditional ophthalmic formulations.

Comparative Pharmacokinetic Profiles of Puerarin in Rat Plasma by UHPLC-MS/MS after Oral Administration of Pueraria lobata Extract and Pure Puerarin

Puerarin is the main biologically active isoflavone in Pueraria lobata and has a wide range of biological activities. However, due to its poor water solubility and low oral bioavailability, its clinical applications are restricted. Compared with puerarin, the Pueraria lobata extract (PLE) has better water solubility, lower toxicity, and less side effects. In this study, the pharmacokinetics of orally administered puerarin (100 mg/kg) and PLE (763 mg/kg, equivalent to 100.0 mg/kg of puerarin) to rats was investigated by the UHPLC-MS/MS method. Results showed that when the rats were administered PLE, the area under the concentration-time curve from zero to infinity (AUC _0-inf ) dramatically increased from 219.83 ± 64.37 μg h/L to 462.62 ± 51.74 μg h/L (p < 0.01). The elimination half-time (t _1/2 ) also increased from 1.60 ± 0.38 h to 12.04 ± 5.10 h (p < 0.01). The maximum concentration (C _max) of puerarin decreased from 101.64 ± 41.82 ng/mL to 48.64 ± 21.47 ng/mL (p < 0.01), and time to reach the maximum plasma concentration (T _max) of puerarin decreased from 1.46 ± 1.08 h to 0.54 ± 0.30 h (p < 0.01). Results indicated that the pharmacokinetics of puerarin in Pueraria lobata may be dramatically different from pure puerarin in the plasma of rat, and oral bioavailability of puerarin may be increased when PLE was administrated to rats.

Advances and limitations of drug delivery systems formulated as eye drops

Topical instillation of eye drops remains the most common and easiest route of ocular drug administration, representing the treatment of choice for many ocular diseases. Nevertheless, low ocular bioavailability of topically applied drug molecules can considerably limit their efficacy. Over the last several decades, numerous drug delivery systems (DDS) have been developed in order to improve drug bioavailability on the ocular surfaces. This review systematically covers the most recent advances of DDS applicable by topical instillation, that have shown better performance in in vivo models compared to standard eye drop formulations. These delivery systems are based on in situ forming gels, nanoparticles and combinations of both. Most of the DDS have been developed using natural or synthetic polymers. Polymers offer many advantageous properties for designing advanced DDS including biocompatibility, gelation properties and/or mucoadhesiveness. However, despite the high number of studies published over the last decade, there are several limitations for clinical translation of DDS. This review article focuses on the recent advances for the development of ocular drug delivery systems. In addtion, the potential challenges for commercialization of new DDS are presented.

Pharmacokinetics and drug delivery systems for puerarin, a bioactive flavone from traditional Chinese medicine

Pueraria lobata (Willd.) Ohwi is a medicinal and edible homologous plant with a long history in China. Puerarin, the main component isolated from the root of Pueraria lobata, possesses a wide range of pharmacological properties. Daidzein and glucuronides are the main metabolites of puerarin and are excreted in the urine and feces. As active substrates of P-gp, multidrug resistance-associated protein and multiple metabolic enzymes, the pharmacokinetics of puerarin can be influenced by different pathological conditions and drug-drug interactions. Due to the poor water-solubility and liposolubility, the applications of puerarin are limited. So far, only puerarin injections and eye drops are on the market. Recent years, researches on improving the bioavailability of puerarin are developing rapidly, various nanotechnologies and preparation technologies including microemulsions and SMEDDS, dendrimers, nanoparticles and nanocrystals have been researched to improve the bioavailability of puerarin. In order to achieve biocompatibility and desired activity, more effective quality evaluations of nanocarriers are required. In this review, we summarize the pharmacokinetics and drug delivery systems of puerarin up to date.

Designing of a pH-Triggered Carbopol®/HPMC In Situ Gel for Ocular Delivery of Dorzolamide HCl: In Vitro, In Vivo, and Ex Vivo Evaluation

Dorzolamide HCl (DRZ) ophthalmic drop is one of the most common glaucoma medications which rapidly eliminates after instillation leading to short residence time of the drug on cornea. The purpose of the present study is to develop a pH-triggered in situ gel system for ophthalmic delivery of DRZ for treatment of ocular hypertension. In this study, a 3² full factorial design was used for preparation of in situ gel formulations using different levels of Carbopol® and hydroxyl propyl methyl cellulose (HPMC). Rheological behavior, in vitro drug release, ex vivo corneal permeability, and IOP-lowering activity were investigated. DRZ solution (2% w/v) containing of 0.1% (w/v) Carbopol® and 0.1% (w/v) HPMC was selected as the optimal formulation considering its free flow under non-physiological conditions (initial pH and 25 ± 2°C) and transition to appropriate gel form under physiological circumstance (pH 7.4 and 34°C). This in situ gel presented the mucoadhesive property. Ex vivo corneal permeability of this combined solution was similar to those of DRZ solution. The developed formulation compared to the marketed drop (Biosopt®) and DRZ 2% solution had a better performance in intraocular pressure activity. The efficiency and long duration of IOP reduction could be due to the prolonged residence time of the in situ gel. The presence of Carbopol® as a pH triggered and mucoadhesive polymer causes to attach to the ocular mucosal surface for a long term.

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.

Novel hydrogel-based ocular drug delivery system for the treatment of conjunctivitis

PURPOSE

Conventional dosage form like eye drops showed poor therapeutic response and also require frequent dosing. Therefore, developing the dosage form to deliver the drug to the target site without much loss of drug or without causing any systemic side effects is the challenging job for the researchers in pharmaceutical industries.

OBJECTIVE

The main aim of the present work was to formulate and evaluate hydrogel-based drug delivery containing combination of neomycin sulphate and betamethasone sodium phosphate in order to provide prolonged release and also better bioavailability of drugs for the treatment of eye infections.

METHODS

In this study, poloxamer 407 and chitosan at different concentrations were used as the gelling agents. The prepared formulations were evaluated for clarity, pH, drug content, gelling capacity, gelling temperature and in vitro drug release study.

RESULTS

From the preliminary studies, F5 formulation was selected as an optimized formulation. The optimized formulation was further evaluated for ex vivo permeation study, sterility test, HET-CAM and ocular irritation testing using rabbits. Ocular irritation by HET-CAM assay showed that the formulated gel does not cause any irritation to the blood vessels. Draize irritation test was performed using rabbits and results showed that formulation was non-irritant to the eye.

CONCLUSION

The formulated hydrogel formulation can be used as an alternative to conventional ophthalmic eye drop formulation of drugs neomycin and betamethasone for the purpose of providing prolonged therapy for the treatment of conjunctivitis.

Ophthalmic gels: Past, present and future

Aqueous gels formulated using hydrophilic polymers (hydrogels) along with those based on stimuli responsive polymers (in situ gelling or gel forming systems) continue to attract increasing interest for various eye health-related applications. They allow the incorporation of a variety of ophthalmic pharmaceuticals to achieve therapeutic levels of drugs and bioactives at target ocular sites. The integration of sophisticated drug delivery technologies such as nanotechnology-based ones with intelligent and environment responsive systems can extend current treatment duration to provide more clinically relevant time courses (weeks and months instead of hours and days) which will inevitably reduce dose frequency, increase patient compliance and improve clinical outcomes. Novel applications and design of contact lenses and intracanalicular delivery devices along with the move towards integrating gels into various drug delivery devices like intraocular pumps, injections and implants has the potential to reduce comorbidities caused by glaucoma, corneal keratopathy, cataract, diabetic retinopathies and age-related macular degeneration. This review describes ophthalmic gelling systems with emphasis on mechanism of gel formation and application in ophthalmology. It provides a critical appraisal of the techniques and methods used in the characterization of ophthalmic preformed gels and in situ gelling systems along with a thorough insight into the safety and biocompatibility of these systems. Newly developed ophthalmic gels, hydrogels, preformed gels and in situ gelling systems including the latest in the area of stimuli responsive gels, molecularly imprinted gels, nanogels, 3D printed hydrogels; 3D printed devices comprising ophthalmic gels are covered. Finally, new applications of gels in the production of artificial corneas, corneal wound healing and hydrogel contact lenses are described.

Formulation and ex vivo-in vivo evaluation of pH-triggered brimonidine tartrate in situ gel for the glaucoma treatment using application of 32 factorial design

CONTEXT

Short residence time, poor bioavailability and poor permeability are the major problems for conventional eye drops treatment.

OBJECTIVE

The aim of this article is to develop, optimize and ex vivo-in vivo investigation of brimonidine tartrate in situ gel as compared to marketed eye drops for the treatment of glaucoma.

MATERIALS AND METHODS

The effect of independent variables, namely concentrations of polymers, on various dependent variables like viscosity at physiological pH and in vitro drug release were studied by using 3² factorial design. Further the optimized formulation was characterized for ex vivo and in vivo study.

RESULTS AND DISCUSSION

Experimental data demonstrated that optimized in situ gel formulation (F8) showed in vitro-ex vivo sustained release profile with polymer composites carbopol 974P and HPMC K4M. After 5 h of ex vivo transcorneal permeation study, the amount recovered from the corneal surface on the donor chamber 12.40% (124 ug) and the amount collected from the receptor chamber 76.8% (760 ug) of the initial dose 1 mg. The total amount recovered from the permeation experiment was 89.2%. Bioadhesive carbopol 974P and viscosity HPMC K4M composites optimized formulation (F 8) produce greater influence on the duration of drug action and improved intraocular pressure reduction activity as compared to marketed eye drop solution in in vivo study.

CONCLUSION

The developed in situ gelling system as a promising ophthalmic formulation to prolong the drug lowering effect on the intraocular pressure.

Chitosan-based polymer hybrids for thermo-responsive nanogel delivery of curcumin

The purpose of this study is to design and develop thermoresponsive nano-sized hydrogel particles from a natural polymer, chitosan, as smart material platforms for curcumin delivery. Chitosan was used as the backbone material to be grafted with poly-(N-isopropylacrylamide) (pNIPAM) using an EDC/NHS coupling reaction. The conjugated products were characterized by ¹H NMR and TGA. Chitosan-grafted pNIPAM (CS-g-pN) nanogels were prepared by a sonication method. The loading of curcumin into the CS-g-pN nanogels was achieved using an incubation method. Size, morphology of nanogels, amounts of curcumin loaded to the nanogels and cellular uptake were investigated by DLS, TEM, fluorescent spectroscopy and confocal microscopy techniques, respectively. A CellTiter-Blue^® cell viability assay was performed in NIH-3T3 and HeLa cells to assess the safety while MTT assay was carried out in MDA-231, Caco-2, HepG2, and HT-29 cells for determining cytotoxic effects. Results showed that CS-g-pN with 3-60% degree of modification were simply assembled into spherical nanogel particles with submicron sizes, in which curcumin was encapsulated. The thermoresponsive behavior of each CS-g-pN nanogel formulation differed due to the grafted pNIPAM length and density. The CS-g-pN nanogel formulations were non-toxic towards NIH-3T3 and HeLa cells. Each curcumin-loaded CS-g-pN nanogel formulation could be up taken into NIH-3T3 cell lines and showed the dose-dependent cytotoxicity against tested cell lines. Successful development of this curcumin-loaded nanogel will lead to advanced materials that can be functionalized and optimized for targeted therapy and controlled delivery of small molecules and/or biomolecules for biomedical applications.

Embedding Well-Defined Responsive Hydrogels with Nanocontainers: Tunable Materials from Telechelic Polymers and Cyclodextrins

Design, synthesis, and application of cyclodextrin (CD) containing thermoresponsive hydrogels fabricated from thiol-reactive telechelic polymers are reported. Hydrophilic polymers containing 2-hydroxyethyl methacrylate and/or di(ethylene glycol)methylether methacrylate monomers as side chains and thiol-reactive groups at chain ends were synthesized. A series of hydrogels was fabricated using thiol-ene conjugation of these thiol-reactive polymers with multivalent thiol-containing CDs as crosslinkers. Clear and transparent hydrogels were obtained with good conversion (79-89%) by utilizing the "nucleophilic" and "radical" thiol-ene "click" reactions. Analysis of the amount of residual thiol groups in these hydrogels using Ellman's reagent suggested that gels with a moderately well-defined network structure were obtained. Hydrogels fabricated using different telechelic polymers were examined for their properties such as morphology, equilibrium water uptake, and rheological characteristics. Cytocompatibility of these hydrogels was ascertained by a cell viability assay that demonstrated low toxicity toward fibroblast cells. Thereafter, the CD-containing hydrogels were evaluated for the loading and controlled release of puerarin, an antiglaucoma drug. Utilization of thermoresponsive polymers as the matrix for these hydrogels allows use of temperature as a stimulus to modulate the drug release. A slower and more sustained drug release was observed at physiological temperatures compared to ambient conditions. The effect of temperature on the elasticity of the hydrogel was investigated rheologically to demonstrate that the collapse of the network structure occurs near physiological temperatures. The increased hydrophobicity and compactness of the gel matrix at higher temperatures results in a slower drug release. The strategy employed here demonstrates that tuning the matrix composition of hydrogels with well-defined network structures through appropriate choice of responsive copolymers allows design of materials with control of their physical properties and drug-release behavior.

Preparation and evaluation of HPMC-based pirfenidone solution in vivo

CONTEXT

Pirfenidone (PFD) has exhibited therapeutic potential in the treatment of cell proliferative disorders. The previously developed 0.5% water-based PFD eye drops by our team exhibited antiscarring effectiveness and ocular safety but with a limit of short half-life and poor bioavailability.

OBJECTIVE

To increase bioavailability of the water-based PFD eye drops, we prepared a viscous solution by adding hydroxypropyl methylcellulose (HPMC, F4M), which acted as a viscosity-enhancer. Subsequently, we compared the HPMC-based PFD solution with the water-based PFD eye drops.

MATERIALS AND METHODS

PFD solution with 1% HPMC (w/v) was prepared, and the viscosities at different shear rates were measured to investigate its rheology. PFD concentrations in the tear, aqueous humor, conjunctiva, cornea, and sclerae of New Zealand rabbits were detected at different time points with high-performance liquid chromatography (HPLC) following single instillation of the 0.5% PFD (w/v) water-based eye drops or HPMC-based solution.

RESULTS

Compared with the 0.5% water-based PFD eye drops, the HPMC-based solution increased the PFD levels in tears and prolonged the residence time from 10 to more than 20 min (p < .01). Consequently, the concentrations of PFD in aqueous humor, conjunctiva, cornea, and sclera were elevated to varying degrees until 90 min after topical administration.

CONCLUSIONS

The developed formulation possesses a same readily administration and simple preparation as the PFD eye drops; however, the HPMC-based solution exhibited the higher bioavailability.

Stimuli-Responsive Polymeric Systems for Controlled Protein and Peptide Delivery: Future Implications for Ocular Delivery

Therapeutic proteins and peptides have become notable in the drug delivery arena for their compatibility with the human body as well as their high potency. However, their biocompatibility and high potency does not negate the existence of challenges resulting from physicochemical properties of proteins and peptides, including large size, short half-life, capability to provoke immune responses and susceptibility to degradation. Various delivery routes and delivery systems have been utilized to improve bioavailability, patient acceptability and reduce biodegradation. The ocular route remains of great interest, particularly for responsive delivery of macromolecules due to the anatomy and physiology of the eye that makes it a sensitive and complex environment. Research in this field is slowly gaining attention as this could be the breakthrough in ocular drug delivery of macromolecules. This work reviews stimuli-responsive polymeric delivery systems, their use in the delivery of therapeutic proteins and peptides as well as examples of proteins and peptides used in the treatment of ocular disorders. Stimuli reviewed include pH, temperature, enzymes, light, ultrasound and magnetic field. In addition, it discusses the current progress in responsive ocular drug delivery. Furthermore, it explores future prospects in the use of stimuli-responsive polymers for ocular delivery of proteins and peptides. Stimuli-responsive polymers offer great potential in improving the delivery of ocular therapeutics, therefore there is a need to consider them in order to guarantee a local, sustained and ideal delivery of ocular proteins and peptides, evading tissue invasion and systemic side-effects.

Design and Evaluation of Voriconazole Loaded Solid Lipid Nanoparticles for Ophthalmic Application

Voriconazole is a second-generation antifungal agent with excellent broad spectrum of antifungal activity commercially available for oral and intravenous administration. Systemic administration of voriconazole is associated with side effects including visual and hepatic abnormalities. This study assessed the feasibility of using solid lipid nanoparticles for ocular delivery of voriconazole adopting stearic acid as lipidic material, tween 80 as a stabilizer, and Carbopol 934 as controlled release agent and for increasing the precorneal residence time in eye. The systems were prepared using two different methods, that is, ultrasonication method and microemulsion technique. The results indicated that the larger particle size of SLNs was found with microemulsion technique (308 ± 3.52 nm to 343 ± 3.51) compared to SLN prepared with ultrasonication method (234 ± 3.52 nm to 288 ± 4.58 nm). The polydispersity index values were less than 0.3 for all formulations and zeta potential of the prepared formulations by these two methods varied from −22.71 ± 0.63 mV to −28.86 ± 0.58 mV. Powder X-ray diffraction and differential scanning calorimetry indicated decrease in crystallinity of drug. The in vitro release study and the SLN formulations prepared with ultrasonication method demonstrated sustained release up to 12 hours. This study demonstrated that SLN prepared by ultrasonication method is more suitable than microemulsion technique without causing any significant effect on corneal hydration level.

Development and Evaluation of Diclofenac Sodium Loaded-N-Trimethyl Chitosan Nanoparticles for Ophthalmic Use

The ophthalmic preparation of diclofenac sodium (DC) for relieving ocular inflammation is presently available in the market only as an eye drop solution. Due to its low occular bioavailability, it requires frequent application leading to low patients' compliance and quality of life. This study was conducted to develop formulations of DC loaded-N-trimethyl chitosan nanoparticles (DC-TMCNs) for ophthalmic use to improve ocular biavailabiltiy of DC. DC-TMCNs varied in formulation compositions were prepared using ionic gelation technique and evaluated for their physicochemical properties, drug release, eye irritation potential, and ophthalmic absorption of diclofenac sodium. N-Trimethyl chitosan (TMC) with a 49.8% degree of quaternization was synthesized and used for DC-TMCNs production. The obtained DC-TMCNs had particle size in a range of 130-190 nm with zeta potential values of +4 to +9 mV and drug entrapment efficiencies of more than 70% depending on the content of TMC and sodium tripolyphosphate (TPP). The optimized DC-TMCNs formulation contained TMC, DC, and TPP at a weight ratio of TMC/DC/TPP = 3:1:1. Their lyophilized product reconstituted with phosphate buffer solution pH 5.5 possessed a drug release pattern that fitted within the zero-order model. The eye irritation tests showed that DC-TMCNs were safe for ophthalmic use. The in vivo ophthalmic drug absorption study performed on rabbits indicated that DC-TMCNs could improve ophthalmic bioavailability of DC. Results of this study suggested that DC-TMCNs had potential for use as an alternative to conventional DC eye drops for ophthalmic inflammation treatment.

Ocular pharmacokinetics of naringenin eye drops following topical administration to rabbits

PURPOSE

To investigate the ocular pharmacokinetics of 1% naringenin eye drops following topical administration to rabbits.

METHODS

One drop (50 μL) of 1% naringenin eye drops was instilled into both eyes of each rabbit. The animals were sacrificed at predetermined intervals after dosing, and ocular tissues and plasma were then collected. Concentrations of naringenin were analyzed using specific electrospray ionization liquid chromatography-tandem mass spectrometry method, which is proved to be sensitive, specific, precise, and suitable for determination of naringenin in ocular tissues and plasma of rabbits.

RESULTS

Ocular exposure to naringenin, based on AUC(0-t), was highest in cornea, followed by aqueous humor, retina, and vitreous body. The Cmax of naringenin in cornea, aqueous humor, vitreous body, and retina were 67945.30 ± 4109.34 ng/g, 1325.69 ± 239.34, 160.52 ± 38.78 ng/mL, and 1927.08 ± 660.77 ng/g at 0.083, 0.75, 0.083, and 0.083 h after topical administration, respectively. The half-lives for these tissues were 9.37, 0.65, 1.17, and 4.62 h, respectively. There was no significant difference between free naringenin and total naringenin in plasma based on Cmax and Tmax. Cmax of total naringenin in plasma at 0.083 h was 35.12 ± 0.54 ng/mL.

CONCLUSIONS

Measurable concentrations of naringenin were achieved in ocular tissues after topical application in rabbits. Topical instillation of naringenin may be an effective approach in the treatment of posterior section diseases.

Enhanced and sustained topical ocular delivery of cyclosporine A in thermosensitive hyaluronic acid-based in situ forming microgels

For nearly a decade, thermoresponsive ophthalmic in situ gels have been recognized as an interesting and promising ocular topical delivery vehicle for lipophilic drugs. In this study, a series of thermosensitive copolymers, hyaluronic acid-g-poly(N-isopropylacrylamide) (HA-g-PNIPAAm), was synthesized, by coupling carboxylic end-capped PNIPAAm to aminated hyaluronic acid through amide bond linkages, and was used as a potential carrier for the topical ocular administration of cyclosporine A (CyA). The lower critical solution temperature of HA-g-PNIPAAm₅₉ in aqueous solutions was measured as 32.7°C, which was not significantly affected by the polymer concentration. Moreover, HA-g-PNIPAAm₅₉ microgels showed a high drug loading efficiency (73.92%) and a controlled release profile that are necessary for biomedical application. Transmission electron microscopy (TEM) and atomic force microscopy (AFM) observations showed that HA-g-PNIPAAm microgels were spherical in shape with homogeneous size. Based on the result of the eye irritation test, the HA-g-PNIPAAm microgels formulation was shown to be safe and nonirritant for rabbit eyes. In addition, HA-g-PNIPAAm microgels achieved significantly higher CyA concentration levels in rabbit corneas (1455.8 ng/g of tissue) than both castor oil formulation and commercial CyA eye drops. Therefore, these newly described thermoresponsive HA-g-PNIPAAm microgels demonstrated attractive properties to serve as pharmaceutical delivery vehicles for a variety of ophthalmic applications.

Topical delivery of ocular therapeutics: carrier systems and physical methods

OBJECTIVE

The basic concepts, major mechanisms, technological developments and advantages of the topical application of lipid-based systems (microemulsions, nanoemulsions, liposomes and solid lipid nanoparticles), polymeric systems (hydrogels, contact lenses, polymeric nanoparticles and dendrimers) and physical methods (iontophoresis and sonophoresis) will be reviewed.

KEY FINDINGS

Although very convenient for patients, topical administration of conventional drug formulations for the treatment of eye diseases requires high drug doses, frequent administration and rarely provides high drug bioavailability. Thus, strategies to improve the efficacy of topical treatments have been extensively investigated. In general, the majority of the successful delivery systems are present on the ocular surface over an extended period of time, and these systems typically improve drug bioavailability in the anterior chamber whereas the physical methods facilitate drug penetration over a very short period of time through ocular barriers, such as the cornea and sclera.

SUMMARY

Although in the early stages, the combination of these delivery systems with physical methods would appear to be a promising tool to decrease the dose and frequency of administration; thereby, patient compliance and treatment efficacy will be improved.

In situ gel systems as 'smart' carriers for sustained ocular drug delivery

INTRODUCTION

In situ gel systems refer to a class of novel delivery vehicles, composed of natural, semisynthetic or synthetic polymers, which present the unique property of sol-gel conversion on receipt of biological stimulus.

AREAS COVERED

The present review summarizes the latest developments in in situ gel technology, with regard to ophthalmic drug delivery. Starting with the mechanism of ocular absorption, the review expands on the fabrication of various polymeric in situ gel systems, made up of two or more polymers presenting multi-stimuli sensitivity, coupled with other interesting features, such as bio-adhesion, enhanced penetration or sustained release. Various key issues and challenges in this area have been addressed and critically analyzed.

EXPERT OPINION

The advent of in situ gel systems has inaugurated a new transom for 'smart' ocular delivery. By virtue of possessing stimuli-responsive phase transition properties, these systems can easily be administered into the eye, similar to normal eye drops. Their unique gelling properties endow them with special features, such as prolonged retention at the site of administration, followed by sustained drug release. Despite the superiority of these systems as compared with conventional ophthalmic formulations, further investigations are necessary to address the toxicity issues, so as to minimize regulatory hurdles during commercialization.

Dendrimer nanoparticles for ocular drug delivery

Eye is a unique organ of perfection and complexity, and is a microcosm of the body in many ways. It represents a great opportunity for nanomedicine, since it is readily accessible-allowing for direct drug/gene delivery to maximize the therapeutic effect and minimize side effects. The development of appropriate delivery systems that can sustain and deliver therapeutics to the target tissues is a key challenge that can be addressed by nanotechnology. Dendrimers are tree-like, nanostructured polymers that have received significant attention as ocular drug delivery systems, due to their well-defined size, tailorable structure, and potentially favorable ocular biodistribution. In this review, we highlight recent developments in dendrimer-based ocular therapies for both anterior and posterior segment diseases.

Simultaneous determination of gastrodin and puerarin in rat plasma by HPLC and the application to their interaction on pharmacokinetics

Gastrodin (Gas) and puerarin (Pur) are bioactive substances derived from traditional Chinese medicine Gastrodia elata and Radix Puerariae, respectively, which were often used together in Chinese clinical prescriptions. Their injections were used in combined way for treatment of some cardiocerebrovascular diseases in clinic, especially for vertigo due to vertebrobasilar ischemia. In this paper, interaction of gastrodin and puerarin in rat plasma pharmacokinetics via intragastic (i.g.)/intravenous (i.v.) administration was investigated. A reliable HPLC method was developed for simultaneous determination of Gas and Pur in rat plasma with a linear range of 0.101-101 μg/mL for Gas and 0.0500-5.98 μg/mL for Pur (r(2)>0.993). The LLOQ, LOD of Gas and Pur were determined to be 0.101, 0.0486 μg/mL, and 0.05, 0.0245 μg/mL, respectively. The intra-day and inter-day precision were all less than 12.0%, whilst the accuracy were all within 96.4±6.00%. The proposed method has been successfully applied to the pharmacokinetic study of the analytes in rats after i.g./i.v. administration of Gas and Pur alone or combined with each other (i.g.: 40 mg/kg Gas, 400 mg/kg Pur; i.v.: 20 mg/kg Gas, 20 mg/kg Pur). Blood samples were collected from retinal vein plexus of rats at predetermined time points and plasma containing the internal standard tyrosol (IS) were precipitated by methanol and chromatography was carried out on a C(18) column with a gradient mobile phase of ACN-H(2)O with 0.05% phosphoric acid as a modifier. The pharmacokinetic profiles of combined administration were found to be distinct from those of given alone. The C(max), T(max), T(1/2), MRT of Gas administrated alone or combined with Pur via i.g. were 21.7 μg/mL, 0.250 h, 2.81 h, 0.830 h and 18.4 μg/mL, 0.550 h, 0.970 h, 1.37 h, respectively, of Pur administrated alone or combined with Gas via i.g. were 0.490 μg/mL, 1.95 h, 1.33 h, 2.10 h and 2.01 μg/mL, 0.570 h, 4.00 h, 5.10 h, respectively. The relative oral bioavailability of Pur in combined administration was 10.7 times as much as that of single administration, whilst 1.52 folds in Gas. These results indicate that co-administration of Gas and Pur is a promising combination to gain higher bioavailability and it is suggested that doctors pay more attention to the dosages of the two when simultaneously using both of them.