New directions in the optimization of ocular drug delivery

Topical ocular delivery of vancomycin loaded cationic lipid nanocarriers as a promising and non-invasive alternative approach to intravitreal injection for enhanced bacterial endophthalmitis management

Vancomycin (VCM) is a drug of choice for treating infections caused by Staphylococcus species, reported being the most causative agent of bacterial endophthalmitis. However, the ocular bioavailability of topically applied VCM is low due to its high molecular weight and hydrophilicity. The current study sought to explore whether the nanostructured lipid carriers (NLCs) fabricated via cold homogenization technique could improve ocular penetration and prolong the ophthalmic residence of VCM. A 2³ full factorial design was adopted to evaluate the influence of different process and formulation variables on VCM-loaded NLC formulae. The optimized formula with the particle size of 96.4 ± 0.71 nm and narrow size distribution showed spherical morphology obtained by AFM and represented sustained drug release up to 67% in 48 h fitted to the Korsmeyer-Peppas model with probably non-Fickian diffusion kinetic. FTIR studies visualized the drug-carrier interactions in great detail. High encapsulation of VCM (74.8 ± 4.3% w/w) in NLC has been established in DSC and PXRD analysis. The optimal positively charged (+ 29.7 ± 0.47 mV) colloidal dispersion was also stable for 12 weeks at both 4 °C and 25 °C. According to in vivo studies, incorporation of VCM in NLC resulted in a nearly 3-fold increase in the intravitreal concentration of VCM after eye-drop instillation over control groups. Besides, microbiological evaluation admitted its therapeutic effect within five days is comparable to intravitreal injection of VCM. Further, the optimized formula was found to be nonirritant and safe for ophthalmic administration in RBC hemolytic assay. Also, fluorescent tracking of NLCs on rabbit's cornea showed an increase in corneal penetration of nanoparticles. Thus, it is possible to infer that the evolved NLCs are promising drug delivery systems with superior attainments for enhanced Vancomycin ophthalmic delivery to the eye's posterior segment and improved bacterial endophthalmitis management.

Formulation and evaluation of thermosensitive flurbiprofen in situ nano gel for the ocular delivery

The contemporary research implicates the formulation and evaluation of a thermosensitive in situ nano gelling method to improve solubility and ocular residence time of flurbiprofen. This study was carried out in two phases. In the first phase, an insolubility drug has been formulated in the form of a nanoparticulate system and evaluated for its characteristics. The nanoparticles obtained demonstrated an average size array of 150 to 250 nm in diameter, up to 79.35% encapsulation efficiency, and up to 93.42% drug release throughout 2 h. In the second phase, nanoparticulate systems were dispersed in aqueous solutions of Pluronic F 127 (14%) and various concentrations of Carbopol 934 in combination to form an in situ nano gel. The prepared in situ gel was investigated for its physicochemical properties like pH, flowability, sol-gel transition temperature, gelling capacity, and rheological properties. Carbopol 934 did not significantly affect sol-gel transition temperature in optimized concentration (<0.3%) but altered gelling capacity, pH, and transparency of the formulations. In vivo resident time and eye irritation test was evaluated in the rabbit eye. In optimized in situ gelling formulation (NIGF3), approximately 95% of in vitro drug release was observed after 6 h. NIGF3 increased precorneal residence time and high concentration in aqueous humor when paralleled to flurbiprofen eye drops. Greater concentration of drug in aqueous humor was due to its improved saturation solubility of the drug, and amplified residence time was attributed to the formation of gel matrix-embedded nanoparticles. This demonstrated that in situ nano gels (NIGF3) comprehending aqueous solutions of 0.3% w/v concentrations of Carbopol 934 with Pluronic F 127 may ominously persist the residence time and mend bioavailability of a water-insoluble drug.

Potential of Natural Biomaterials in Nano-scale Drug Delivery

BACKGROUND

The usage of natural biomaterials or naturally derived materials intended for interface with biological systems has steadily increased in response to the high demand of amenable materials, which are suitable for purpose, biocompatible and biodegradable. There are many naturally derived polymers which overlap in terms of purpose as biomaterials but are equally diverse in their applications.

METHODS

This review examines the applications of the following naturally derived polymers; hyaluronic acid, silk fibroin, chitosan, collagen and tamarind polysaccharide (TSP); further focusing on the biomedical applications of each as well as emphasising on individual novel applications.

RESULTS

Each of the polymers was found to demonstrate a wide variety of successful biomedical applications fabricated as wound dressings, scaffolds, matrices, films, sponges, implants or hydrogels to suit the therapeutic need. Interestingly, blending and amelioration of polymer structures were the two selection strategies to modify the functionality of the polymers to suit the purpose. Further, these polymers have shown promise to deliver small molecule drugs, proteins and genes as nano-scale delivery systems.

CONCLUSION

The review highlights the range of applications of the aforementioned polymers as biomaterials. Hyaluronic acid, silk fibroin, chitosan, collagen and TSP have been successfully utilised as biomaterials in the subfields of implant enhancement, wound management, drug delivery, tissue engineering and nanotechnology. Whilst there are a number of associated advantages (i.e. biodegradability, biocompatibility, non-toxic, nonantigenic as well as amenability) the selected disadvantages of each individual polymer provide significant scope for their further exploration and overcoming challenges like feasibility of mass production at a relatively low cost.

Routes for the delivery of insulin to the central nervous system: A comparative review

Central nervous system (CNS) insulin resistance is a condition in which the cells within the CNS do not respond to insulin appropriately and is often linked to aberrant CNS insulin levels. CNS insulin is primarily derived from the periphery. Aberrant CNS insulin levels can arise due to various factors including i) decreased endogenous insulin transport into the brain, across the blood-brain barrier (BBB), ii) reduced CNS sequestration of insulin, and iii) increased CNS degradation. While the sole route of endogenous insulin transport into the brain is via the BBB, there are multiple therapeutic routes of administration that have been investigated to deliver exogenous insulin to the CNS. These alternative administrative routes can be utilized to increase the amount of CNS insulin and aid in overcoming CNS insulin resistance. This review focuses on the intravenous, intracerebroventricular, intranasal, ocular, and intrathecal routes of administration and compares the impact of insulin delivery.

A Nanoparticle-Based Ophthalmic Formulation of Dexamethasone Enhances Corneal Permeability of the Drug and Prolongs Its Corneal Residence Time

We designed ophthalmic formulations containing dexamethasone-loaded solid nanoparticles (DEX_nano dispersion), and investigated corneal permeability and toxicity. 0.1% dexamethasone (DEX) powder (DEX microparticles), 0.026% methyl p-hydroxybenzoate (MP), 0.014% propyl p-hydroxybenzoate (PP), and 0.5% methylcellulose were used, and the DEX_nano dispersion was prepared by the bead mill method. The mean particle size of DEX_nano dispersion was 78 nm. Antimicrobial activity of the DEX_nano dispersion were measured by using Escherichia coli, and the corneal epithelium-debrided rat model and HCE-T cells (immortalized human corneal epithelial cell line) were used to estimate the corneal toxicity. The transcorneal penetration of the DEX_nano dispersion were evaluated in the corneas of rabbit. The DEX_nano dispersion was found to be highly stable until 14 d after its preparation. Although DEX itself did not exhibit antimicrobial activity, the DEX_nano dispersion containing parabens (MP and PP) showed high antimicrobial activity, approximately equal to that of the solution containing parabens without DEX. The corneal penetration rate (J_c) and mean residence time (MRT) of DEX from the DEX_nano dispersion were approximately 5.1- and 1.3-fold higher, respectively, than those of a dispersion containing DEX microparticles (mean particle size, 11.3 µm). In addition, no significant difference was found in corneal stimulation between the vehicle and DEX_nano dispersion. In conclusion, we successfully prepared high quality dispersion containing DEX solid nanoparticles, and the nanoparticle-based ophthalmic formulation of DEX enhanced the corneal permeability and residence time of the drug. It is possible that DEX_nano dispersion will show increased effectiveness in treating ocular inflammation.

Effect of methyl cellulose on gelation behavior and drug release from poloxamer based ophthalmic formulations

The effect of weight average molecular weight (Mw) of methyl cellulose (MC) on the gelation behavior of Poloxamer 407 (PM) and in vitro release of Ketorolac Tromethamine (KT) from different ophthalmic formulations based on PM is examined. A drop of gelation temperature of PM is observed using MC of various M(w) by test tube tilting method, UV-vis spectroscopy, viscometry and rheometry. It is also observed that the viscosity and gel strength of all the formulations are increased with the increase in Mw of MC. PM with highest Mw of MC provides best drug release property among all the formulations. It is evident from this investigation that there is a distinct effect of M(w) of MC on the gelation behavior of PM as well as on the drug release profile of KT from PM-MC based ophthalmic formulations.

Use of collagen as a biomaterial: An update

Biomaterial science is an expanding area, which encompasses a wide range of medical knowledge involving arthroplasty, cochlear implants, heart valves designing, lenses, dental fixation and tissue engineering. Within this context, in vitro cell culture on polymer scaffolds is one of the adopted strategies for tissue creation. It consists of a specific cell line that is seeded onto a particular substrate. This scaffold should provide excellent biocompatibility, controllable biodegradability, appropriate mechanical strength, flexibility as well as the ability to absorb body fluids for delivery of nutrients. Collagen certainly fulfils these demands; therefore, it is often chosen as a biomaterial. Moreover, this protein is abundant in the animal kingdom and plays a vital role in biological functions, such as tissue formation, cell attachment and proliferation.

Carbopol/chitosan based pH triggered in situ gelling system for ocular delivery of timolol maleate

The poor bioavailability and therapeutic response exhibited by conventional ophthalmic preparations due to rapid precorneal elimination, dilution and nasolacrimal drainage of the drug may be vanquished by the use of in situ gelling systems that are instilled as drops in to the eye and undergo a sol-gel transition in the cul-de-sac. Timolol eye drops may cause systemic side effects in glaucoma patients due to absorption of the drug into systemic circulation. In situ gelling system of this drug can provide localized effect with reduced contraindications, improved patient compliance and better therapeutic index. The present work describes the formulation and evaluation of an ophthalmic delivery system of an antiglaucoma drug, timolol maleate (TM) based on the concept of pH-triggered in situ gelation. Polyacrylic acid (carbopol) was used as the gelling agent in combination with chitosan (amine polysaccharide), which was acted as a viscosity-enhancing agent. Formulations were evaluated for pH, viscosity, gelling capacity and drug content. The 0.4% w/v carbopol/0.5% w/v chitosan based in situ gelling system was in liquid state at room temperature and at the pH formulated (pH 6.0) and underwent rapid transition into the viscous gel phase at the pH of the tear fluid (lacrimal fluid) (pH 7.4). The in vitro drug release and in vivo effects of the developed in situ gelling system were compared with that of Glucomol® (a 0.25% TM ophthalmic solution), 0.4% w/v carbopol solution as well as liposomal formulation. The results clearly demonstrated that developed carbopol-chitosan based formulation was therapeutically efficacious and showed a fickian (diffusion controlled) type of release behaviour over 24 h periods. The developed system is thus a viable alternative to conventional eye drops and can also prevent the rapid drainage as in case of liposomes.

Piroxicam bioadhesive ocular inserts: physicochemical characterization and evaluation in prostaglandin-induced inflammation

PURPOSE

An attempt has been made in the present research to formulate piroxicam into bioadhesive ocular inserts with an objective to sustain drug release, reduce frequency of dosing, and enhance ocular bioavailability of piroxicam.

MATERIAL AND METHODS

Drug matrices were prepared using film forming polymer, PVP and bioadhesive polymers, HPMC, CMC, and carbopol. Ocular inserts were prepared by film casting method and prepared films were subjected to investigations for their physical and mechanical properties, swelling behaviors, ex vivo bioadhesion, and in vitro drug release. The optimized formulation was tested and compared with eye drops of piroxicam for ocular anti-inflammatory activity in rabbits against PGE(2)-induced inflammation.

RESULTS

The physicochemical, bioadhesive, and swelling properties of films were found to vary significantly depending on the type of the polymers and their combination. The above properties were found to be optimum for all films; however, formulation containing carbopol 0.5% and HPMC 1% was found to be the best film as it shows good adhesion, acceptable pH, and gives a reasonable drug release (99% at 12 hr). Kinetic studies indicated both diffusion and swelling as mechanism of drug release from this matrix. Further in vivo studies with this formulation indicated a significant inhibition of PGE(2)-induced lid closure and PMN migration as compared to eye drops formulation.

CONCLUSION

Formulation was found promising, as it sustained the drug release and enhanced the ocular bioavailability of piroxicam as compared to piroxicam eye drops.

Dual-drug delivery system based on in situ gel-forming nanosuspension of forskolin to enhance antiglaucoma efficacy

The present study was designed to improve the bioavailability of forskolin by the influence of precorneal residence time and dissolution characteristics. Nanosizing is an advanced approach to overcome the issue of poor aqueous solubility of active pharmaceutical ingredients. Forskolin nanocrystals have been successfully manufactured and stabilized by poloxamer 407. These nanocrystals have been characterized in terms of particle size by scanning electron microscopy and dynamic light scattering. By formulating Noveon AA-1 polycarbophil/poloxamer 407 platforms, at specific concentrations, it was possible to obtain a pH and thermoreversible gel with a pH(gel)/T (gel) close to eye pH/temperature. The addition of forskolin nanocrystals did not alter the gelation properties of Noveon AA-1 polycarbophil/poloxamer 407 and nanocrystal properties of forskolin. The formulation was stable over a period of 6 months at room temperature. In vitro release experiments indicated that the optimized platform was able to prolong and control forskolin release for more than 5 h. The in vivo studies on dexamethasone-induced glaucomatous rabbits indicated that the intraocular pressure lowering efficacy for nanosuspension/hydrogel systems was 31% and lasted for 12 h, which is significantly better than the effect of traditional eye suspension (18%, 4-6 h). Hence, our investigations successfully prove that the pH and thermoreversible polymeric in situ gel-forming nanosuspension with ability of controlled drug release exhibits a greater potential for glaucoma therapy.

Characterization of pilocarpine-loaded chitosan/Carbopol nanoparticles

Patients using ophthalmic drops are faced with frequent dosing schedules and difficult drop instillation. Therefore, a long-lasting pilocarpine-loaded chitosan (CS)/Carbopol nanoparticle ophthalmic formulation was developed. The physicochemical properties of the prepared nanoparticles were investigated using dynamic light scattering, zeta-potential, transmission electron microscopy, Fourier transform infrared ray spectroscopy (FT-IR) and differential scanning calorimetry (DSC). The sustained-release effects of pilocarpine-loaded nanoparticles were evaluated using in-vitro release and in-vivo miotic tests, and compared with pilocarpine in solution, gel and liposomes. We found that the prepared nanoparticles were about 294 nm in size. DSC and FT-IR studies suggested that an electrostatic interaction between CS and Carbopol contributes at least in part to the stabilization of pilocarpine/CS/Carbopol nanoparticles. When compared with pilocarpine in solution, gel or liposomes, the best slow-release profile of pilocarpine from the prepared nanoparticles occurred in a dissolution test. In the in-vivo miotic study, pilocarpine-loaded CS/Carbopol nanoparticles showed the most significant long-lasting decrease in the pupil diameter of rabbits. The advantages of CS and Carbopol are good biocompatibility, biodegradability and low toxicity. CS is also a mucoadhesive polymer. Thus, pilocarpine/CS/Carbopol nanoparticles may provide an excellent potential alternative ophthalmic sustained-release formulation of pilocarpine for clinical use. CS/Carbopol nanoparticles may also be useful for a variety of other therapeutic delivery systems.

Release of Ciprofloxacin from Chondroitin 6-Sulfate-Graft-Poloxamer Hydrogel In Vitro for Ophthalmic Drug Delivery

The system was designed to use Poloxamer as a vehicle for ophthalmic drug delivery using in situ gel formation property. To enhance the wound healing and cell adhesion as well as transparency of Poloxamer hydrogel, chondroitin 6-sulfate (C6S) was introduced into Poloxamer. For this purpose, mono amine-terminated Poloxamer (MATP), which was end-capped with ethylene amine group only in one side of terminal hydroxyl groups of Poloxamer, was synthesized. Subsequently, C6S-graft-Poloxamer copolymer (C6S-g-Poloxamer) was prepared by reaction between the amine groups of MATP and carboxyl groups of C6S in the presence of 1-ethyl-3-(3-dimethylaminopropyl)-carboimide (EDC). The coupling of MATP with C6S was clarified by 1H-NMR and FT-IR spectroscopy. The gelation temperature of graft copolymers was determined by measuring the temperature at which immobility of the meniscus in each solution was first noted. Release behavior of ciprofloxacin from C6S-g-Poloxamer hydrogel in vitro was investigated as a function of C6S content in the graft copolymer by a spectrophotometric assay at 287 nm using an UV spectrophotometer. Differences in the adhesion and morphology of human lens cell between Poloxamer- and C6S-g-Poloxamer-coated surfaces were also investigated. The gelation temperatures of C6S-g-Poloxamer copolymers were lowered with increasing of the concentration of the copolymer and decreasing of C6S content. The release of ciprofloxacin from the graft copolymer was sustained compared with Poloxamer itself and decreased with increasing the content of C6S in the copolymer due to the in situ gel formation of the copolymer and viscous properties of C6S. Human lens cells (B3) adhered to C6S-g-Poloxamer-coated surface were observed as transformed shapes after 2 days. The bioadhesive and thermally gelling of these graft copolymers will be expected to be an excellent drug carrier for the prolonged delivery to surface of the eye.

Ocular novel drug delivery: impacts of membranes and barriers

BACKGROUND

Ocular drug delivery is an extremely challenging area due to its restrictive barrier functionalities.

OBJECTIVE

Drug transport via corneal/non-corneal routes involves several intricate biological processes such as drug penetration across the ocular barriers and transfer to the anterior or posterior chambers, thus the influence of these processes on the pharmacotherapy of the eye should be fully addressed.

METHODS

To pursue the impacts of such impediments in novel drug therapy, recent publications were reviewed regarding advanced strategies such as nanomedicines.

CONCLUSION

The ocular barriers are highly specialized and selectively control the inward/outward traverse of compounds, hence a better understanding of these biological obstacles would provide a platform to advance ophthalmic drug therapy towards specified delivery/targeting with minimal adverse consequences.

Formulation and evaluation of ciprofloxacin hydrochloride soluble ocular drug insert

PURPOSE

An attempt has been made in the present research to formulate soluble ocular inserts of ciprofloxacin hydrochloride to increase residence time and prolong drug release.

MATERIAL AND METHODS

Drug matrices were prepared using natural polymer. Gelatin, a biodegradable polymer, was tried for the first time in the preparation of soluble ocular drug insert matrices. The inserts were then evaluated for their physicochemical parameters. The in vitro drug release studies were carried out using a bi-chambered donor receiver compartment model. In vivo drug release was carried out using rabbits as animal models.

RESULTS

Formulations CF4 and CF8, which showed controlled and prolonged in vitro drug release, were subjected to in vivo study. In vitro and in vivo correlation was found to be strong, revealing the efficacy of the formulation.

CONCLUSION

Formulation CF8 was found promising, as it achieved the target of the present study.

Eye drop NGF administration promotes the recovery of chemically injured cholinergic neurons of adult mouse forebrain

We have recently shown that conjunctivally applied nerve growth factor (NGF) in rats can reach the retina, the optic nerve and the CNS. In the present study, we investigated whether NGF application as collyrium can promote the recovery of chemically injured basal forebrain cholinergic neurons. NGF was administered on the eye of adult male mice previously treated i.c.v. with ibotenic acid to impair cholinergic pathways. Mice were tested in the passive avoidance test, and after 2 weeks of NGF administration were killed and the brains used for structural, biochemical and molecular analyses. The results showed that application of NGF on the eye surface protected choline acetyl transferase levels. These findings strengthen the hypothesis that application of NGF on the eye can represent an alternative delivery route to promote the recovery of brain cells during degeneration, including neurons involved in learning and memory activities.

Evaluation of the in vivo behaviour of gentamicin sulphate ocular mini-tablets in ponies

The in vivo behaviour of 5% gentamicin sulphate ocular mini-tablets (2-mm diameter, 6.525 mg weight) was compared with gentamicin eye drops in six ponies. Two mini-tablets were inserted on the bulbar conjunctiva of the right eye while a similar dose of gentamicin was administered via eye drops in the left eye. Irritation induced by the mini-tablets and the eye drops was evaluated using a visual analogue scale (0-10). Tears were sampled with ophthalmologic absorption triangles for 1 min for the determination of the concentration of gentamicin sulphate using a microbiological plate diffusion method. Irritation induced by the tablets was minor and clinically acceptable (overall median score of 1.7 +/- 1.4). Eye drops induced a sharp increase in gentamicin sulphate concentration (364.4 microg/mL after 5 min) followed by a fast decline (10.8 microg/mL after 60 min). The increase in concentration induced by the ocular mini-tablets was less pronounced (up to 56.2 microg/mL after 30 min) and followed by a gradual decrease; the concentration remained above 15 microg/mL for 8 h. Ocular 5% gentamicin sulphate mini-tablets are clinically well-tolerated in ponies, assuring a constant concentration in the tears for at least 8 h.

Pluronic F127-g-poly(acrylic acid) copolymers as in situ gelling vehicle for ophthalmic drug delivery system

To prolong the precorneal resident time and improve ocular bioavailability of the drug, Pluronic F127-g-poly(acrylic acid) copolymers were studied as in situ gelling vehicle for ophthalmic drug delivery system. The rheological properties and in vitro drug release of Pluronic-g-PAA copolymer gels were investigated. The rheogram and in vitro drug release studies indicated that the drug release rates decreased as acrylic acid/Pluronic molar ratio and copolymer solution concentration increased. But the drug concentration had no obvious effect on drug release. The release rates of the drug from such copolymer gels were mainly dependent on the gel dissolution. In vivo resident experiments showed the drug resident time and the total resident amount in rabbit's conjunctiveal sac increased by 5.0 and 2.6 folds for in situ gel, compared with eye drops. The decreased loss angle at body temperature and prolonged precorneal resident time also indicated that the copolymer gels had bioadhesive properties. These in vivo experimental results, along with the rheological properties and in vitro drug release studies, demonstrated that in situ gels containing Pluronic-g-PAA copolymer may significantly prolong the drug resident time and thus improve bioavailability. Pluronic-g-PAA copolymer can be a promising in situ gelling vehicle for ophthalmic drug delivery system.

Preparation and characterization of demeclocycline liposomal formulations and assessment of their intraocular pressure-lowering effects

The objective of the present study is to enhance the ocular permeability and to study the ocular disposition of demeclocycline (DEM), liposomal topical formulation for treatment of elevated intraocular pressure using Male New Zealand albino rabbits as an animal model.

METHODS

Different liposomal formulations of the DEM were prepared and characterized for their drug entrapment, drug-liposome affinity and the in vivo distribution of DEM in various ocular tissues. Liposomal formulations of promising drug distribution within the various ocular tissues have been scaled up for the in vivo intraocular pressure (IOP) measurements by Pneuma-tonometer using different dosing regimens.

RESULTS

The amounts of drug entrapped in the charged liposomal formulations were comparable and lower than that entrapped with neutral ones. DEM was found to be more concentrated (69-95%) in the lipid phase of the liposome. The concentrations of DEM in the cornea, aqueous humor, and conjunctiva were 4.76, 2.18, and 23.32 microg/g of tissue, respectively. Test formulations have shown significant reductions in the IOP on using different treatment protocols.

CONCLUSION

Preparation of liposomal formulations of DEM has substantially enhanced its transcorneal transport. Furthermore, the test formulations have shown promising and long-lasting intraocular pressure-lowering effect comparable with that of pilocarpine formulation as a control.

Nerve growth factor eye drop administrated on the ocular surface of rodents affects the nucleus basalis and septum: biochemical and structural evidence

It has been shown that conjunctivally applied NGF in rats can reach the retina and optic nerve. Whether topical eye NGF application reaches the central nervous system is not known. In the present study, we have addressed this question. It was found that topical eye NGF application affects brain cells. Time-course studies revealed that repeated NGF application leads to high concentration of this neurotrophins after 6 h and normal levels after 24 h. Our results also showed that topical eye application of NGF causes an enhanced expression of NGF receptors and ChAT immunoreactivity in forebrain cholinergic neurons, suggesting that ocular NGF application could have a functional role on damaged brain cells. The present findings suggest that eye NGF application can represent an alternative route to prevent degeneration of NGF-receptive neurons involved in disorders such as Alzheimer and Parkinson.

Design and evaluation of soluble ocular drug insert for controlled release of ciprofloxacin hydrochloride

PURPOSE

Soluble ocular inserts of ciprofloxacin hydrochloride were prepared with the aim of achieving once a day administration.

DESIGN

Drug reservoir was prepared using natural hydrophilic polymer viz. gelatin while rate-controlling membrane was prepared using hydrophobic ethyl cellulose. Ocular inserts were evaluated for their physicochemical parameters like thickness, weight uniformity, drug content, percent moisture loss, and percent moisture absorption. The in vitro drug release studies were carried out using Bi-chambered donor receiver compartment model. Since targeted prolong release was observed in formulation CF2 and CF5, these formulations were further subjected to in vivo drug release study using rabbits as an animal model. In vitro drug release kinetic data was treated according to Zero, First, and Higuchi kinetics to access the mechanism of drug release.

RESULTS

Correlation between in vitro and in vivo drug release was found to be strong revealing the efficacy of the formulation.

CONCLUSION

Formulation CF5 has achieved target of present study such as increase residence time, prolong drug release, reduction in frequency of administration, and, thus may improve the patient compliance.

Ultrasound-Enhanced Transcorneal Drug Delivery

PURPOSE

Ultrasound has been shown to enhance, by up to 10 times, the corneal permeability to different compounds such as beta-blockers and fluorescein. Here, we report on our investigation of the mechanisms of ultrasound-enhanced drug delivery through the cornea using light and electron microscopy.

METHODS

Enhancement of permeability for a hydrophilic compound, sodium fluorescein, in rabbit cornea in vitro was achieved using ultrasound at a frequency of 880 kHz and intensities of 0.19-0.56 W/cm2 with an exposure duration of 5 minutes. Light and electron microscopy (transmission and scanning) were used to observe ultrasound-induced structural changes in the cornea.

RESULTS

The permeability increased by 2.1, 2.5, and 4.2 times when ultrasound was applied at 0.19, 0.34, and 0.56 W/cm2, respectively (P<0.05). The surface cells of corneal epithelium exposed to ultrasound appeared swollen and lighter in color (indications of membrane rupture) as compared with the control cells. Some of the surface epithelial cells were absent. The cells in the inner layers of the epithelium were occasionally lighter in color. Also, holes 3-10 microm in diameter were observed on the epithelial surface. No structural changes were observed in the stroma.

CONCLUSION

Ultrasound enhancement of drug delivery through the cornea appears to result from minor structural alterations in the epithelium. Careful investigation of the recovery of cornea structure and barrier function after the ultrasound application, in vivo, is needed.

Drug delivery into the eye with the use of ultrasound

OBJECTIVE

To evaluate ultrasound enhancement of drug delivery through the cornea and the histologic appearance of the cornea up to 24 hours after treatment.

METHODS

Corneas were exposed to ultrasound at a frequency of 880 kHz and intensities of 0.19 to 0.56 W/cm2 (continuous mode) with an exposure duration of 5 minutes. The aqueous humor concentration of a topically applied hydrophilic dye, sodium fluorescein, was determined quantitatively in ultrasound- and sham-treated rabbit eyes in vivo. Gross and light microscopic examinations were used to observe structural changes in the cornea 0 to 24 hours after ultrasound exposure. Cavitation activity was measured with a passive cavitation detector.

RESULTS

Most cells with an appearance different from that of the normal cells were present in the surface layer of the corneal epithelium. No structural changes were observed in the stroma. The increase in dye concentration in the aqueous humor (relative to sham treatment), after the simultaneous application of ultrasound and the dye solution, was 2.4 times at 0.19 W/cm2, 3.8 times at 0.34 W/cm2, and 10.6 times at 0.56 W/cm2 (P <.05). Dye delivery was found to increase with increasing ultrasound intensity, which corresponded to an increase in cavitation activity. Corneal pits, observed in the ultrasound-treated epithelium, completely disappeared within 90 minutes.

CONCLUSIONS

Application of 880-kHz ultrasound provided up to 10-fold enhancement in the delivery of a hydrophilic compound through the cornea while producing minor changes in the corneal epithelium.

Accumulation of porcine insulin in the rat brain and cerebrospinal fluid following ocular application

We previously reported that insulin accumulated in the retina and optic nerve following ocular application. Since the optic nerve is surrounded by meninges and cerebrospinal fluid (CSF) and since it extends back to the thalamus, we examined whether the topical application of insulin eye drops also resulted in the accumulation of insulin in the CSF and brain. The data presented in this paper show that this is in fact the case. Following the ocular application of a 0.75% solution of porcine insulin, significant concentrations of insulin were demonstrable in the CSF extracted from the cisterna magnum, as well as in three brain regions. While it is not yet clear how insulin got into these target tissues, our data argue against a mechanism involving uptake from the blood (a fraction of topically applied compounds normally enters the vasculature through the conjunctiva and nasal mucosa). It is theorized that insulin may enter the CSF surrounding the optic nerve and by so doing, not only disseminate throughout the CSF space but also throughout the brain. The implications of these findings for central nervous system drug delivery are discussed.

Pilocarpine permeability across ocular tissues and cell cultures: influence of formulation parameters

In vitro permeation studies of drugs across biological barriers are promising tools for estimating the quality and quantity of drug transport in vivo. The objective of this work was to compare the permeability of the hydrophilic model drug pilocarpine-HCl (P-HCl) through different ocular tissues and cell cultures: isolated pig cornea (PCr) and sclera (PSc), rabbit conjunctiva (RCo), and rabbit conjunctival (RCoEC) or corneal epithelial cell culture (RCrEC). Furthermore, the study included investigations about the influence of the excipients benzalkonium chloride (BAC) and ethylene diamine tetra acetic acid disodium salt (EDTA) on the permeability of the small drug. In general, BAC caused a facilitated drug transport, while EDTA hardly influenced the P-HCl concentration on the acceptor side, except for RCoEC. Additionally, the impact of variation in buffer solution pH and tonicity on drug transport in both cell cultures was tested. The higher the tonicity of the buffer solution (80, 300, and 600 mOsm/kg) the lower the permeability coefficient (P(eff)). At different pH values (6.4, 7.4, and 8.4) the P(eff) showed a directly proportional demeanor. In summary, a good correlation between the isolated tissues and cell cultures with regard to P-HCl transport could be observed.

Biomedical applications of collagen

Collagen is regarded as one of the most useful biomaterials. The excellent biocompatibility and safety due to its biological characteristics, such as biodegradability and weak antigenecity, made collagen the primary resource in medical applications. The main applications of collagen as drug delivery systems are collagen shields in ophthalmology, sponges for burns/wounds, mini-pellets and tablets for protein delivery, gel formulation in combination with liposomes for sustained drug delivery, as controlling material for transdermal delivery, and nanoparticles for gene delivery and basic matrices for cell culture systems. It was also used for tissue engineering including skin replacement, bone substitutes, and artificial blood vessels and valves. This article reviews biomedical applications of collagen including the collagen film, which we have developed as a matrix system for evaluation of tissue calcification and for the embedding of a single cell suspension for tumorigenic study. The advantages and disadvantages of each system are also discussed.

Carbopol/pluronic phase change solutions for ophthalmic drug delivery

The major purpose of this study is to develop and characterize a series of carbopol- and pluronic-based solutions as the in situ gelling vehicles for ophthalmic drug delivery. The rheological properties, in vitro release as well as in vivo pharmacological response of various polymer solutions, including carbopol, pluronic and carbopol/pluronic solution, were evaluated. It was found that the optimum concentration of carbopol solution for the in situ gel forming delivery systems was 0.3% (w/w), and that for pluronic solution was 14% (w/w). The mixture of 0.3% carbopol and 14% pluronic solutions showed a significant enhancement in gel strength in the physiological condition; this gel mixture was also found to be free flowing at pH 4.0 and 25 degrees C. The rheological behaviors of carbopol/pluronic solution were not affected by the incorporation of pilocarpine hydrochloride. Both the in vitro release and in vivo pharmacological studies indicated that the carbopol/pluronic solution had the better ability to retain drug than the carbopol or pluronic solutions alone. The results demonstrated that the carbopol/pluronic mixture can be used as an in situ gelling vehicle to enhance the ocular bioavailability.

Roles of acid/base nature and molecular weight in drug release from matrices of gelfoam and monoisopropyl ester of poly(vinyl methyl ether-maleic anhydride)

Ophthalmic drug inserts are usually placed in the conjunctival sac. Being in contact with the conjunctiva, they may provide means to deliver large and hydrophilic molecules, such as peptides and oligonucleotides into the eye. We evaluated Gelfoam and monoisopropyl ester of poly(vinyl methyl ether/maleic anhydride) (PVM/MA) as potential polymers for ocular inserts. Matrices were solvent cast with model drugs that had different pKa, molecular weight and hydrophilicity. Drug release from the matrices as well as charge and swelling of Gelfoam(R)-matrix were studied. The release of drugs from PVM/MA-matrices was by erosion of the polymer matrix. The molecular weight and other variants of the releasing compound did not affect their release. In Gelfoam(R)-matrices the release was diffusion controlled and it was affected by the pH of the external solution as well as the charge and molecular weight of the studied compound.

Ophthalmic drug delivery systems--recent advances

Eye-drops are the conventional dosage forms that account for 90% of currently accessible ophthalmic formulations. Despite the excellent acceptance by patients, one of the major problems encountered is rapid precorneal drug loss. To improve ocular drug bioavailability, there is a significant effort directed towards new drug delivery systems for ophthalmic administration. This chapter will focus on three representative areas of ophthalmic drug delivery systems: polymeric gels, colloidal systems, cyclodextrins and collagen shields. Hydrogels generally offer a moderate improvement of ocular drug bioavailability with the disadvantage of blurring of vision. In situ activated gel-forming systems are preferred as they can be delivered in drop form with sustained release properties. Colloidal systems including liposomes and nanoparticles have the convenience of a drop, which is able to maintain drug activity at its site of action and is suitable for poorly water-soluble drugs. Among the new therapeutic approaches in ophthalmology, cyclodextrins represent an alternative approach to increase the solubility of the drug in solution and to increase corneal permeability. Finally, collagen shields have been developed as a new continuous-delivery system for drugs that provide high and sustained levels of drugs to the cornea, despite a problem of tolerance. It seems that new tendency of research in ophthalmic drug delivery systems is directed towards a combination of several drug delivery technologies. There is a tendency to develop systems which not only prolong the contact time of the vehicle at the ocular surface, but which at the same time slow down the elimination of the drug. Combination of drug delivery systems could open a new directive for improving results and the therapeutic response of non-efficacious systems.

How can the bioavailability of timolol be enhanced? A pharmacokinetic pilot study of novel hydrogels

BACKGROUND

Carbomerbased hydrogels with timolol maleate (T-Gel) were chosen to study the vehicle effect on ocular bioavailability. Pharmacokinetic profiles of T-Gel 0.05% (0.05% timolol), T-Gel 0.025% (0.025% timolol) and commercial timolol ophthalmic solution (TOS 0.1%; 0.1% timolol) were determined and compared.

METHODS

A single dose was administered to rabbits' eyes. Timolol was determined by HPLC in aqueous humour, blood samples and washings of the ocular surface (as a measure of residence time). Sampling times were 0.5 h, 1 h and 4 h after instillation.

RESULTS

Concentration versus time curves (AUC) of timolol in aqueous humour demonstrate no significant differences between TOS 0.1% and T-Gel 0.025% (P = 0.19), whereas the difference between T-Gel 0.05% and TOS 0.1% is significant (P = 0.006); the AUC ratio of T-Gel 0.05%:TOS 0.1%:T-Gel 0.025% was 2.14:1:0.87. Timolol blood levels were highest with TOS 0.1% at every time point. Peak levels occurred after 0.5 h with all test products; the ratio of peak levels (Cmax) for T-Gel 0.05%:TOS 0.1%:T-Gel 0.025% was 0.55:1:0.17. Timolol was detected in the washings up to 1 h after instillation of test products; the highest levels were observed after T-Gel 0.05%.

CONCLUSION

The new vehicle obviously improves the bioavailability of topically applied timolol.

In situ-forming gels for ophthalmic drug delivery

Poor bioavailability of ophthalmic solutions caused by dilution and drainage from the eye can be overcome by using in situ-forming ophthalmic drug delivery systems prepared from polymers that exhibit reversible phase transitions. Joshi et al. (1), have demonstrated that aqueous compositions that reversibly gel in response to simultaneous variations in at least two physical parameters, such as temperature, pH, and ionic strength, can be formed by appropriate combinations of macromolecular polymers which exhibit reversible gelation properties. In the present study, the rheological characterization of such a system, prepared by a combination of Carbopol (C) and methyl cellulose (MC), was carried out at two different pH (4.0 and 7.4) and temperatures (25 and 37 degrees C) by rotational cone and plate viscometry. The shear stress (tau) vs. shear rate (D) flow curves of the aqueous polymer solutions indicated a pseudoplastic behavior, with a yield point. An increase in pH from 4.0 to 7.4, or temperature from 25 to 37 degrees C, resulted in an increase in viscosity (eta), tau, and yield point, the magnitude of changes being highest when both the parameters were altered simultaneously. An increase in concentration of either C or MC, or an increase in MC molecular weight results in an increase in eta, tau, and yield point. Among the compositions studied, a solution containing 1.5% MC 0.3% C was found to have low eta, and formed a strong gel under simulated physiological conditions. Such a system can be formulated as drug containing liquid suitable for administration by instillation into the eye, which upon exposure to physiological conditions will shift to the gel (semi-solid) phase, thus increasing the precorneal residence time of the delivery system and enhancing ocular bioavailability.

Absorption of fluorescein given under the upper lid

BACKGROUND

The need for a more efficacious approach to administer topical ocular medications prompted the authors to consider applying conventional eye drops under the upper lid rather than beneath the lower lid. Preliminary observations on patients with glaucoma using a beta-blocker beneath the upper lid suggested a drop in intraocular pressure into the normal range in some previously refractory patients being treated with the same medications. To test this clinical observation, the authors observed if there were any physiologic differences in topical fluorescein absorption into the anterior chamber when given beneath the upper lid versus the lower lid.

METHODS

A 5-microliters drop of fluorescein solution was placed under the upper-lid fornix of one eye and under the lower-lid fornix of the other eye in human volunteers, and absorption into the anterior chamber was measured at hourly intervals, for a total of 3 hours.

RESULTS

Hotelling T2 multivariate analysis for all 3 hours demonstrates that upper-lid administration of fluorescein results in significantly higher absorption of fluorescein into the anterior chamber than does lower-lid administration (P = 0.0088; for hours 2 and 3, the statistical differences is even more dramatic: P < 0.0044).

CONCLUSION

Using conventional eye drops beneath the upper lid, the authors observed increased absorption of fluorescein into the anterior chamber when compared with lower-lid administration. Profuse tearing, especially by younger subjects, significantly and rapidly diminished anterior chamber absorption of fluorescein. It is reasonable to consider further clinical studies to test this new approach to drug delivery.

Ocular absorption and distribution of bendazac after topical administration to rabbits with different vehicles

Ocular and systemic absorption of bendazac was investigated after topical administration to rabbits of 0.5% solutions of bendazac lysine in different polysaccharide vehicles. The results show that the drug is absorbed into the retina-choroid via an extracorneal, or sclero-conjunctival route; the iris and the ciliary body are presumably supplied via both the transcorneal and the extracorneal pathways. The extent of absorption via the extracorneal route is not related to vehicle viscosity but rather to the chemical features of vehicle. The transcorneal penetration appears to be hindered by the binding of the drug to corneal tissues.

Microparticulates for ophthalmic drug delivery

Microparticulates are drug-containing small polymeric particles (erodible, non-erodible or ion-exchange resins) that are suspended in a liquid carrier medium. Upon administration of particle suspension in the eye, the particles reside at the delivery site (cul-de-sac, sub conjunctiva or vitreous cavity) and the drug is released from the particles through diffusion, chemical reaction, polymer degradation, or ion-exchange mechanism. Several distinct approaches have been used to formulate drugs in microparticulate dosage form for intraocular and topical application. These include erodible microparticulates, swelling mucoadhesive particulates, pH responsive microparticulates, nanoparticles/latex systems, ion-exchange resins, etc. Injection of bioerodible microparticulates in the vitreous for treating infections of posterior segment and the release of acceptable levels of drug up to two weeks has been demonstrated. Both corneal and non-corneal routes of drug entry in the eye from topical instillations are postulated. The in vitro and in vivo studies have shown that this dosage form holds great promise for sustained drug release in the eye. However, several formulation challenges, including production of stable suspensions, uniform dose per unit volume, efficient drug entrapment, reproducible and large scale manufacturing, uniform particle size, etc., have to be addressed. Fruitful resolution of technological challenges will result in a superior dosage form for both topical and intraocular ophthalmic application. Recent developments and future challenges of microparticulate ophthalmic drug delivery system are discussed in this review.

Beta-cyclodextrins enhance bioavailability of pilocarpine

Cyclodextrins have been used to improve drug solubility, stability and absorption for oral and parenteral administration. However, their potential for improving ocular drug delivery has received little attention. To evaluate the ability of hydroxypropyl-beta-cyclodextrins to improve ophthalmic drug bioavailability following topical administration, the miotic effect of topical solutions of pilocarpine was studied in New Zealand White rabbits. Pilocarpine varying in dose from 5 to 500 micrograms in the presence or absence of 5% cyclodextrin was administered (50 microliters) topically and the change in pupil diameter determined. These results demonstrated that pilocarpine alone or in the presence of cyclodextrin produces a dose-related reduction in pupil diameter. The addition of cyclodextrins produced a significant left-shift in the dose response curve, with an ED50 of 64 micrograms and 19 micrograms for pilocarpine and pilocarpine/5% cyclodextrin solutions, respectively. Studies in which the concentration of cyclodextrin was varied revealed that a one-to-one molar ratio of pilocarpine to cyclodextrin was sufficient to provide maximum increase in pilocarpine bioavailability. Electrophysiology and scanning electron microscopic studies demonstrated that cyclodextrin does not disrupt the normal ion transport currents, barrier properties or surface features of the corneal epithelium. Viscosity measurements indicated that difference in the viscosity of pilocarpine and pilocarpine/cyclodextrin solutions cannot account for increased bioavailability of pilocarpine. These data support the idea that the addition of cyclodextrin significantly improves the ocular bioavailability of pilocarpine. This enhanced bioavailability of pilocarpine does not appear to be due to a mechanism destructive to the epithelium or to an increase in vehicle viscosity.

Intraocular pressure reduction and systemic absorption of timolol after administration of one side-coated inserts in rabbits

The object of this study was to test whether flat, circular ophthalmic inserts releasing drug only from one side, would show improved activity parameters and reduced systemic absorption. To this purpose, uncoated and one-side coated hydroxypropylcellulose inserts containing timolol were prepared and evaluated. An acrylic copolymer (Eudragit RS) was used as coating material. Timolol release from inserts was studied both in vitro and in vivo. Timolol release in vitro from the coated inserts was much slower than from the uncoated ones, due to the smaller releasing surface area. Compared with timolol eyedrops (0.5%, 50 microliters), administration of 250 micrograms of timolol in uncoated or coated inserts produced a significantly greater hypotensive effect at 6 and 8 hr post instillation in rabbits with artificially increased intraocular pressure. The coated inserts containing 62.5 micrograms of timolol antagonised isoproterenol-induced ocular hypotension significantly more than timolol eyedrops (0.5%, 12.5 microliters) and uncoated inserts containing 62.5 micrograms of timolol. Both uncoated and coated inserts provided a significant sustaining of timolol release in tear fluid and decreased systemic peak concentrations of timolol with respect to the eyedrop control. However, one-side coated inserts failed to show significant improvements with respect to the uncoated samples.