Optimization and evaluation of thermoresponsive diclofenac sodium ophthalmic in situ gels

Design and in vitro evaluation of tenofovir-loaded vaginal gels for the prevention of HIV infections

Infection with the human immunodeficiency virus (HIV) is affecting women disproportionally with increasing incidence rates over the last decades. Tenofovir is one of the most commonly used antiretroviral agents, which belongs to the nucleoside/nucleotide reverse transcriptase inhibitor family, for the prevention of HIV acquisition. In scope of this study, a thermogelling system containing tenofovir-loaded chitosan nanoparticles for the controlled release of tenofovir was developed and characterized. The in vitro release studies have shown that the burst release effect was decreased to 27% with f-TFV CS NPs-Gel. Gelation temperature of developed formulation was found as 26.6 ± 0.2 °C, which provides ease of administration while gelation occurs after the administration to the vagina. The work of adhesion values was used as parameters for comparison of mucoadhesive performance and the mucoadhesion of f-TFV CS NPs-Gel was found as 0.516 ± 0.136 N.s at 37 °C. The biocompatibility of blank formulations was evaluated by cell viability studies using L929 cells, in which Gel + CS NPs formulation was found to be safe with 82.4% and 90.2% cell viability for 1:16 and 1:32 dilutions, respectively. In conclusion, an improved tenofovir containing vaginal gel formulation was successfully developed and evaluated for preventing HIV transmission.

Synthesis, characterisation and phase transition behaviour of temperature-responsive physically crosslinked poly (N-vinylcaprolactam) based polymers for biomedical applications

Poly (N-vinylcaprolactam) (PNVCL) is a polymer which offers superior characteristics for various potential medical device applications. In particular it offers unique thermoresponsive capabilities, which fulfils the material technology constraints required in targeted drug delivery applications. PNVCL phase transitions can be tailored in order to suit the requirements of current and next generation devices, by modifying the contents with regard to the material composition and aqueous polymer concentration. In this study, physically crosslinked Poly (N-vinylcaprolactam)-Vinyl acetate (PNVCL-VAc) copolymers were prepared by photopolymerisation. The structure of the polymers was established by Fourier transform infrared spectroscopy, nuclear magnetic resonance and gel permeation chromatography. The polymers were further characterised using differential scanning calorimetry and swelling studies. Determination of the LCST of the polymers in aqueous solution was achieved by employing four techniques; cloud point, UV-spectrometry, differential scanning calorimetry and rheometry. Sol-gel transition was established using tube inversion method and rheological analysis. This study was conducted to determine the characteristics of PNVCL with the addition of VAc, and to establish the effects on the phase transition. The PNVCL based polymers exhibited a decrease in the LCST as the composition of VAc increased. Sol-gel transition could be controlled by altering the monomeric feed ratio and polymer concentration in aqueous milieu. Importantly all copolymers (10wt% in solution) underwent gelation between 33.6 and 35.9°C, and based on this and the other materials properties recorded in this study, these novel copolymers have potential for use as injectable in situ forming drug delivery systems for targeted drug delivery.

Optimization and evaluation of astragalus polysaccharide injectable thermoresponsive in-situ gels

The objective of this study was to develop an injectable in situ forming gel system based on Poloxamer for sustained release of Astragalus polysaccharide (APS), thus achieved once or twice administration instead of frequent dosing during long-term treatment. The optimal formulation is 10 g APS, 18 g poloxamer 407, 2 g poloxamer 188, 0.15 g CMC-Na, 0.85 g sodium chloride in 100 ml gel in situ which had a preferable sol-gel transition temperature(T sol-gel) (34.1 ± 0.4°C), and good stability. In vitro release studies, all formulations containing polymer additives had prolonged release time and decreased initial burst to some extent. The optimal formulation containing 0.15% CMC-Na showed a best sustained release profile for about 132 h with the lowest initial burst in vitro about 16.30% in 12 h). In vivo, Male BALB/c mice (18–20 g) were administrated with APS in-situ gel just once, the values of immune organ indices, spleen lymphocyte proliferation, and serum IgM, IgG, IL-2 and IL-6 had significant increase, which was consistent with the mice given daily APS injections (7 times), while the above indices were increased more significantly in which administrated with APS in-situ gel twice. Based on these results, it can be concluded that the Poloxamer depot is a promising carrier for the sustained release of APS with an ideal release behavior.

Poloxamer-based thermoresponsive ketorolac tromethamine in situ gel preparations: Design, characterisation, toxicity and transcorneal permeation studies

This study was aimed at preparing, characterising and evaluating in situ gel formulations based on a blend of two hydrophilic polymers i.e. poloxamer 407 (P407) and poloxamer 188 (P188) for a sustained ocular delivery of ketorolac tromethamine (KT). Drug-polymer interaction studies were performed using DSC and FT-IR. The gelation temperature (T_sol-gel), gelation time, rheological behaviour, mucoadhesive characteristics of these gels, transcorneal permeation and ocular irritation as well as toxicity was investigated. DSC and FT-IR studies revealed that there may be electrostatic interactions between the drug and the polymers used. P188 modified the T_sol/gel of P407 bringing it close to eye temperature (35°C) compared with the formulation containing P407 alone. Moreover, gels that comprised P407 and P188 exhibited a pseudoplastic behaviour at different concentrations. Furthermore, mucoadhesion study using mucin discs showed that in situ gel formulations have good mucoadhesive characteristics upon increasing the concentration of P407. When comparing formulations PP11 and PP12, the work of adhesion decreased significantly (P<0.001) from 377.9±7.79mNmm to 272.3±6.11mNmm. In vitro release and ex vivo permeation experiments indicated that the in situ gels were able to prolong and control KT release as only 48% of the KT released within 12h. In addition, the HET-CAM and BCOP tests confirmed the non-irritancy of KT loaded in situ gels, and HET-CAM test demonstrated the ability of ocular protection against strongly irritant substances. MTT assay on primary corneal epithelial cells revealed that in situ gel formulations loaded with KT showed reasonable and acceptable percent cell viability compared with control samples.

An Ophthalmic Formulation of Disulfiram Nanoparticles Prolongs Drug Residence Time in Lens

Disulfiram (DSF) is a dimer of diethyldithiocarbamate (DDC) that we previously added to a solution of 2-hydroxypropyl-β-cyclodextrin (DSF solution). We found that the instillation of this DSF solution delayed lens opacification in a hereditary cataractous ICR/f rat. In this study, we attempted to design an ophthalmic formulation containing DSF nanoparticles for use as a lens targeted drug delivery system (nano-DSF suspension), and investigated the changes in drug content in the lens after the instillation of DSF solution or nano-DSF suspension. The nano-DSF suspension was prepared by a bead mill method to yield a mean particle size of nano-DSF of 181 nm. Following the instillation of 1.4% DSF solution or the nano-DSF suspension, DDC was detected only in the aqueous humor and lens; in both, the area under the curve (AUC) and mean residence time (MRT) for the nano-DSF suspension were higher than for the DSF solution. In addition, we found that the DDC residence time in the cortex and nucleus of the lens was higher than in the capsule-epithelium. Although DDC was not detected in the cortex and nucleus of lenses following the instillation of the 1.4% DSF solution, the instillation of a 1.4% nano-DSF suspension led to the accumulation of DDC in both areas. In conclusion, it is possible that the instillation of a nano-DSF suspension can supply more DDC into the aqueous humor and lens than a conventional formulation, and these findings provide information significant for the prevention of cataracts and the design of a lens targeted drug delivery system.

Self-Assembled Thermoresponsive Nanogels Prepared by Reverse Micelle → Positive Micelle Method for Ophthalmic Delivery of Muscone, a Poorly Water-Soluble Drug

This study aimed to design a nanocarrier ophthalmic delivery system of muscone, a poorly water-soluble drug. The muscone thermoresponsive nanogels were self-assembled by reverse micelle → positive micelle method. Muscone was demonstrated to have uniform narrow particle size distribution in nanogel by the dynamic light scattering test. The developed nanocomposite hydrogel had a high muscone loading, and the rheology results showed that the phase transition temperature was 34.05°C. Thixotropy test indicated that the nanogel was able to resist the blinking of eyes because of the thixotropy recovery time, which is <5 s. Compared with muscone eye drops, muscone nanogels showed longer retention time on the corneal surface using fluorescent labeling technology and produced a 3.4-fold increase in apparent permeability coefficients (Papp). Draize testing showed that the developed nanogel caused no eye irritation. In vivo pharmacokinetic study indicated that the nanogel could significantly increase the bioavailability of muscone after administration compared with eye drops. These results indicate that self-assembled thermoresponsive nanogel prepared by reverse micelle → positive micelle method has potential for the ophthalmic delivery of poorly water-soluble drugs.

Dendrimer-coupled sonophoresis-mediated transdermal drug-delivery system for diclofenac

The purpose of the present study was to develop a novel transdermal drug-delivery system comprising a polyamidoamine dendrimer coupled with sonophoresis to enhance the permeation of diclofenac (DF) through the skin. The novel transdermal drug-delivery system was developed by using a statistical Plackett–Burman design. Hairless male Wistar rat skin was used for the DF-permeation study. Coupling media concentration, ultrasound-application time, duty cycle, distance from probe to skin, and a third-generation polyamidoamine-dendrimer concentration were selected as independent variables, while in vitro drug release was selected as a dependent variable. Independent variables were found to be statistically significant (P<0.05). DF gel without dendrimer and ultrasound treatment to skin (passive delivery, run 13) showed 56.69 µg/cm² cumulative drug permeated through the skin, while the DF-dendrimer gel without sonophoresis treatment (run 14) showed 257.3 µg/cm² cumulative drug permeated through the skin after 24 hours. However, when the same gel was applied to sonophoresis-treated skin, drastic permeation enhancement was observed. In the case of run 3, the cumulative drug that permeated through the skin was 935.21 µg/cm². It was concluded that dendrimer-coupled sonophoresis-mediated transdermal drug delivery system has the potential to enhance the permeation of DF through the skin.

Liposome incorporated ion sensitive in situ gels for opthalmic delivery of timolol maleate

This study was aimed to design a liposomal based ion-sensitive in situ ophthalmic delivery system of timolol maleate (TM). The TM liposome was produced by the reverse evaporation technique coupled with pH-gradients method (REVPR), and then was incorporated into deacetylated gellan gum gels. The TM liposome was demonstrated to be a round and uniform shape in TEM pictures. Compared with the TM eye drops, the TM liposome produced a 1.93 folds increase in apparent permeability coefficients (Papp), resulting in a significant increase of the corneal penetration. The TM-loaded liposome incorporated ion sensitive in situ gels (TM L-ISG) showed longer retention time on corneal surface compared with the eye drops using gamma scintigraphy technology. Draize testing showed that TM L-ISG was non-irritant for ocular tissues. The biggest efficacy of TM L-ISG occurred 30 min after eye drops administration, and efficacy disappeared after 240min. Then, compared with the eye drops, the optimal TM L-ISG could quickly reduce the intraocular pressure and the effective time was significantly longer (P≤0.05). These results indicate that liposome incorporated ion sensitive in situ gels have a potential ability for the opthalmic delivery.

Optimization and evaluation of a thermoresponsive ophthalmic in situ gel containing curcumin-loaded albumin nanoparticles

This study aimed to optimize and evaluate a thermoresponsive ophthalmic in situ gel containing curcumin-loaded albumin nanoparticles (Cur-BSA-NPs-Gel). Albumin nanoparticles were prepared via a desolvation method, and the gels were prepared via a cold method. The central composite design and response surface method was used to evaluate the effects of varying Pluronic^® F127 and Pluronic^® F68 concentrations on the sol–gel transition temperature, which is an indicator of optimum formulations. The optimized formulation was a free-flowing liquid below 30.9°C that transformed into a semi-solid gel above 34.2°C after dilution with simulated tear fluid. Results of the in vitro release and erosion behavior study indicated that Cur-BSA-NPs-Gel achieved superior sustained-release effects and that incorporation of albumin nanoparticles exerted minimal effects on the gel structure. In addition, in vivo ophthalmic experiments employing Cur-BSA-NPs-Gel were subsequently performed in rabbits. In vivo eye irritation results showed that Cur-BSA-NPs-Gel might be considered safe for ophthalmic drug delivery. The in vivo study also revealed that the formulation could significantly increase curcumin bioavailability in the aqueous humor. In conclusion, the optimized in situ gel formulation developed in this work has significant potential for ocular application.

A nanoparticle formulation reduces the corneal toxicity of indomethacin eye drops and enhances its corneal permeability

Indomethacin (IMC) has been shown to reduce post-operative inflammation and to decrease intraocular irritation after cataract extraction and in cystoid macular edema; however, the clinical use of its most commonly used eye drops is limited due to topical side-effects that include burning sensation, irritation and epithelial keratitis. It is known that decreasing direct cell stimulation and reducing the amount applied via increasing bioavailability are useful for improving these issues. In this study, we designed ophthalmic formulations containing 0.5% IMC nanoparticles using zirconia beads and Bead Smash 12 (IMCnano eye drops; particle size 76 ± 59 nm, mean ± S.D.), and investigated the corneal toxicity of these IMCnano eye drops. IMCnano eye drops are tolerated better by a human cornea epithelial cell line (HCE-T) than commercially available NDSAIDs preparations (IMC, pranoprofen, diclofenac, bromfenac and nepafenac eye drops), and corneal wound healing in rat eyes with debrided corneal epithelium instilled with IMCnano eye drops is significantly better than that of eyes instilled with commercially available IMC eye drops. In addition, the accumulation of IMC in HCE-T cells treated with the IMCnano eye drops for 30 min was 19.9% that of the accumulation from commercially available IMC eye drops. On the other hand, the corneal penetration of IMC from IMCnano eye drops was significantly greater than in the case of the commercially available IMC eye drops in both in vivo and in vitro studies using rabbit corneas. Taken together, we hypothesize that a nanoparticle formulation reduces the corneal toxicity of IMC eye drops, probably because the accumulation of IMC from IMCnano eye drops in the eye is lower than that from commercially available IMC eye drops. In addition, the nanoparticle formulation may allow a decrease in the amount of IMC used due to the increase in bioavailability, resulting in reduced drug toxicity. These findings provide significant information that can be used to design further studies aimed at developing less toxic eye drops.

Improved corneal toxicity and permeability of tranilast by the preparation of ophthalmic formulations containing its nanoparticles

We prepared ophthalmic formulations containing 0.5% tranilast (TL) nanoparticles using 0.005% benzalkonium chloride (BAC), 0.5% D-mannitol, and 2-hydroxypropyl-β-cyclodextrin (HPβCD), and investigated their usefulness in the ophthalmologic field by evaluating corneal toxicity and permeability. TL nanoparticles were prepared using zirconia beads and Bead Smash 12, which allowed the preparation of high quality dispersions containing 0.5% TL nanoparticles (particle size, 34 ± 20 nm, means ± S.D.). Dispersions containing TL nanoparticles are tolerated better by human corneal epithelium cells than a commercially available 0.5% TL preparation (RIZABEN(®) eye drops). In addition, the addition of TL nanoparticles to the dispersions does not affect the antimicrobial activity of BAC against Escherichia coli (ATCC 8739), and the corneal penetration of TL from dispersions containing TL nanoparticles was significantly higher than in the case of the commercially available 0.5% TL eye drops. It is possible that dispersions containing TL nanoparticles will show increased effectiveness against ocular inflammation, and that ocular drug delivery systems using drug nanoparticles may lead to an expansion of their usefulness for therapy in the ophthalmologic field.

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.

Positively charged polymeric nanoparticle reservoirs of terbinafine hydrochloride: preclinical implications for controlled drug delivery in the aqueous humor of rabbits

Frequent instillation of terbinafine hydrochloride (T HCl) eye drops (0.25%, w/v) is necessary to maintain effective aqueous humor concentrations for treatment of fungal keratitis. The current approach aimed at developing potential positively charged controlled-release polymeric nanoparticles (NPs) of T HCl. The estimation of the drug pharmacokinetics in the aqueous humor following ocular instillation of the best-achieved NPs in rabbits was another goal. Eighteen drug-loaded (0.50%, w/v) formulae were fabricated by the nanopreciptation method using Eudragit® RS100 and chitosan (0.25%, 0.5%, and 1%, w/v). Soybean lecithin (1%, w/v) and Pluronic® F68 (0.5%, 1%, and 1.5%, w/v) were incorporated in the alcoholic and aqueous phases, respectively. The NPs were evaluated for particle size, zeta potential, entrapment efficiency percentage (EE%), morphological examination, drug release in simulated tear fluid (pH 7.4), Fourier-transform IR (FT-IR), X-ray diffraction (XRD), physical stability (2 months, 4°C and 25°C), and drug pharmacokinetics in the rabbit aqueous humor relative to an oily drug solution. Spherical, discrete NPs were successfully developed with mean particle size and zeta potential ranging from 73.29 to 320.15 nm and +20.51 to +40.32 mV, respectively. Higher EE% were achieved with Eudragit® RS100-based NPs. The duration of drug release was extended to more than 8 h. FT-IR and XRD revealed compatibility between inactive formulation ingredients and T HCl and permanence of the latter's crystallinity, respectively. The NPs were physically stable, for at least 2 months, when refrigerated. F5-NP suspension significantly (P<0.05) increased drug mean residence time and improved its ocular bioavailability; 1.657-fold.

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.

Advancement in stimuli triggered in situ gelling delivery for local and systemic route

INTRODUCTION

Current research efforts focused on the design and evaluation of drug delivery systems that are easy to administer require decreased administration frequency, and provide sustained drug release in order to increase clinical efficacy and compliance of the patients. The gel forming smart polymeric formulations offer numerous applications resemble sustained and prolonged action in contrast to conventional drug delivery systems.

AREAS COVERED

Article summarizes type of bioactive, sol-gel triggering factors, dose, rationales, and polymers involved in gelation with respect to their route of administration. A lot of work has been done with smart polymeric gelling system taking the advantage of stimuli (temperature and pH) triggered sol-gel phase-transition in the administered area that have great prospective in biomedical and pharmaceutical applications, particularly in target-specific controlled drug delivery systems.

EXPERT OPINION

Although the principle of gelation is so attractive, key issues remain to be solved which include (i) variability of the drug release, (ii) avoidance of burst release in case of depot formulation, and (iii) issues related to toxicity. Unfortunately, till now area concerning the detailed processes of the gelling formation is still not much explored. Despite this proclamation, many efforts are made in industry and institutions to improve concerned approaches. New materials and approaches enter the preclinical and clinical phases and one can be sure that this strategy will gain further clinical importance within the next years. Thus, this review article will assuredly serve as an informative tool for the innovators working in the concern area.

Diclofenac/biodegradable polymer micelles for ocular applications

In this paper, methoxypoly(ethylene glycol)-poly(ε-caprolactone) (MPEG-PCL) micelle formulations as promising nano-carriers for poorly water soluble drugs were investigated for the delivery of diclofenac to the eye. Diclofenac loaded MPEG-PCL micelles were prepared by a simple solvent-diffusion method and characterized by dynamic light scattering (DLS), atomic force microscopy (AFM), Fourier transform infra-red (FTIR), X-ray diffraction (XRD), differential scanning calorimetery (DSC), etc. With the analysis of XRD and DSC, the diclofenac was present as an amorphous state in the formulation. The in vitro release profile indicated a sustained release manner of diclofenac from the micelles. Meanwhile, in vivo studies on eye irritation were performed with blank MPEG-PCL micelles (200 mg ml(-1)). The results showed that the developed MPEG-PCL micelles were non-irritants to the eyes of rabbits. In vitro penetration studies across the rabbit cornea demonstrated that the micelle formulations exhibited a 17-fold increase in penetration compared with that of diclofenac phosphate buffered saline (PBS) solution. The in vivo pharmacokinetics profile of the micelle parent drug in the aqueous humor of the rabbit was evaluated and the data showed that the diclofenac loaded MPEG-PCL micelles exhibited a 2-fold increase in AUC(0-24 h) than that of the diclofenac PBS solution eye drops. These results suggest a great potential of our micelle formulations as a novel ocular drug delivery system to improve the bioavailability of the drugs.