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

Cannabidiol nanoemulsion for eye treatment - Anti-inflammatory, wound healing activity and its bioavailability using in vitro human corneal substitute

Cannabidiol (CBD) is the non-psychoactive component of the plant Cannabis sativa (L.) that has great anti-inflammatory benefits and wound healing effects. However, its high lipophilicity, chemical instability, and extensive metabolism impair its bioavailability and clinical use. Here, we report on the preparation of a human cornea substitute in vitro and validate this substitute for the evaluation of drug penetration. CBD nanoemulsion was developed and evaluated for stability and biological activity. The physicochemical properties of CBD nanoemulsion were maintained during storage for 90 days under room conditions. In the scratch assay, nanoformulation showed significantly ameliorated wound closure rates compared to the control and pure CBD. Due to the lower cytotoxicity of nanoformulated CBD, a higher anti-inflammatory activity was demonstrated. Neither nanoemulsion nor pure CBD can penetrate the cornea after the four-hour apical treatment. For nanoemulsion, 94 % of the initial amount of CBD remained in the apical compartment while only 54 % of the original amount of pure CBD was detected in the apical medium, and 7 % in the cornea, the rest was most likely metabolized. In summary, the nanoemulsion developed in this study enhanced the stability and biological activity of CBD.

Introducing an Efficient In Vitro Cornea Mimetic Model for Testing Drug Permeability

There is a growing need for novel in vitro corneal models to replace animal-based ex vivo tests in drug permeability studies. In this study, we demonstrated a corneal mimetic that models the stromal and epithelial compartments of the human cornea. Human corneal epithelial cells (HCE-T) were grown on top of a self-supporting porcine collagen-based hydrogel. Cross-sections of the multi-layers were characterized by histological staining and immunocytochemistry of zonula oc-cludens-1 protein (ZO-1) and occludin. Furthermore, water content and bssic elastic properties of the synthetized collagen type I-based hydrogels were measured. The apparent permeability coefficient (Papp) values of a representative set of ophthalmic drugs were measured and correlated to rabbit cornea Papp values found in the literature. A multilayered structure of HCE-T cells and the expression of ZO-1 and occludin in the full thickness of the multilayer were observed. The hydrogel-based corneal model exhibited an excellent correlation to rabbit corneal permeability (r = 0.96), whereas the insert-grown HCE-T multilayer was more permeable and the correlation to the rabbit corneal permeability was lower (r = 0.89). The hydrogel-based human corneal model predicts the rabbit corneal permeability more reliably in comparison to HCE-T cells grown in inserts. This in vitro human corneal model can be successfully employed for drug permeability tests whilst avoiding ethical issues and reducing costs.

Effect of Solution pH on Distribution of Ophthalmically Administered Brimonidine in Posterior Ocular Tissues in Pigmented Rabbits

INTRODUCTION

Brimonidine bioavailability in the aqueous humor depends on the solution pH following topical administration. The purpose of this study was to investigate the effect of solution pH on brimonidine distribution in the posterior ocular tissues in pigmented rabbits.

METHODS

The anterior retina/choroid, posterior retina/choroid, and vitreous body of pigmented rabbits were collected 0.67, 1.5, 3, 6, 12, 24, 168, and 360 h after the administration of a single topical dose of 0.2% brimonidine tartrate ophthalmic solution, pH 6.4 (Alphagan^®; Allergan Inc., Irvine, CA, USA). Brimonidine concentrations in these tissues were quantified using liquid chromatography/tandem mass spectrometry. Pharmacokinetic parameters were determined using noncompartmental analysis, and the results were compared with tissues from eyes administered 0.1% brimonidine tartrate ophthalmic solution, pH 7.3 (Aiphagan^®; Senju Pharmaceutical Co., Ltd., Osaka, Japan) in our previous study conducted using the same procedure.

RESULTS

Topically applied brimonidine was distributed rapidly into the posterior tissues of the eye after a single ophthalmic administration of the 0.2% ophthalmic solution. The areas under the curve from time 0 to 360 h following dosing with the 0.2% ophthalmic solution were 500,000, 14,300, and 28.7 ng h/g in the anterior and posterior retina/choroid, and vitreous body, respectively.

CONCLUSION

The differences in the areas under the curve between two ophthalmic solutions were less than the difference in drug concentrations between these two products in any tissues. This finding indicates that the change in the solution pH from 6.4 to 7.3 increases brimonidine bioavailability into the posterior ocular tissues similarly as into the aqueous humor.

FUNDING

Senju Pharmaceutical Co., Ltd.

In Vitro Cell Models for Ophthalmic Drug Development Applications

Tissue engineering is a rapidly expanding field that aims to establish feasible techniques to fabricate biologically equivalent replacements for diseased and damaged tissues/organs. Emerging from this prospect is the development of in vitro representations of organs for drug toxicity assessment. Due to the ever-increasing interest in ocular drug delivery as a route for administration as well as the rise of new ophthalmic therapeutics, there is a demand for physiologically accurate in vitro models of the eye to assess drug delivery and safety of new ocular medicines. This review summarizes current existing ocular models and highlights the important factors and limitations that need to be considered during their use.

Toward the practical implementation of eye-related bioavailability prediction models

The development and registration of reformulated ophthalmic products (OPs) requires eye-related bioavailability (BA) assessments. Common BA algorithms associated with other routes of application, such as the oral route, cannot be easily applied to eye-related BA testing. Here, we provide an analysis of the current literature and suggestions for further directions in the development of high-capacity, cost-effective, and highly predictive nonclinical models of eye-related drug BA. One, or a combination of these models, has the potential for routine use in research laboratories and/or the pharmaceutical industry to overcome various obstacles in reformulated OP development and registration.

Effect of low concentrations of benzalkonium chloride on acanthamoebal survival and its potential impact on empirical therapy of infectious keratitis

IMPORTANCE

The significant antiacanthamoebal effect of benzalkonium chloride, at or below concentrations used for preservation of common ophthalmic preparations, should be understood both when choosing empiric antibiotic therapy for infectious keratitis and when assessing the persistent rise in Acanthamoeba cases in the United States since 2003.

OBJECTIVE

To characterize the antiacanthamoebal efficacy of low concentrations of benzalkonium chloride (BAK) for drug preservation and therapeutic effect against Acanthamoeba.

DESIGN

Experimental study with a review of the literature.

SETTING

Laboratory.

EXPOSURES

A concentration of 10(4) trophozoites of 3 well-characterized clinical strains of Acanthamoeba were exposed at 0.5, 2.0, 3.5, 5.0, and 6.5 hours to BAK (0.001%, 0.002%, and 0.003%), moxifloxacin hydrochloride (0.5%), and moxifloxacin (0.5%) + BAK (0.001% and 0.003%) with hydrogen peroxide (3%) and amoeba saline controls.

MAIN OUTCOMES AND MEASURES

Amoeba survival was calculated using the most probable number method recorded as log kill values. The relationship of BAK concentration and exposure time as well as the relative effect of BAK and moxifloxacin on acanthamoebal survival were analyzed.

RESULTS

Amoebicidal activity of BAK is both time dependent and concentration dependent in pooled and strain-stratified analyses (P < .001). Moxifloxacin demonstrated no significant independent inhibitory effect or additive effect to BAK efficacy on acanthamoebal survival. The profound antiacanthamoebal effect of BAK, 0.003%, was similar to that of hydrogen peroxide for certain strains.

CONCLUSIONS AND RELEVANCE

Low concentrations of BAK, previously demonstrated to concentrate and persist in ocular surface epithelium, exhibit significant antiacanthamoebal activity in vitro at or below concentrations found in commercially available ophthalmic anti-infectives. The unexplained persistence of the Acanthamoeba keratitis outbreak in the United States, clusters abroad, and clinical studies reporting resolution or modification of Acanthamoeba keratitis without specific antiacanthamoebal therapy suggests that other contributing factors should be considered, including changes in the formulations used for empirical therapy of presumed infectious keratitis occurring in the same period.

Recent advances in ophthalmic drug delivery

Topical ocular drug bioavailability is notoriously poor, in the order of 5% or less. This is a consequence of effective multiple barriers to drug entry, comprising nasolacrimal drainage, epithelial drug transport barriers and clearance from the vasculature in the conjunctiva. While sustained drug delivery to the back of the eye is now feasible with intravitreal implants such as Vitrasert (-6 months), Retisert (-3 years) and Iluvien (-3 years), currently there are no marketed delivery systems for long-term drug delivery to the anterior segment of the eye. The purpose of this article is to summarize the resurgence in interest to prolong and improve drug entry from topical administration. These approaches include mucoadhesives, viscous polymer vehicles, transporter-targeted prodrug design, receptor-targeted functionalized nanoparticles, iontophoresis, punctal plug and contact lens delivery systems. A few of these delivery systems might be useful in treating diseases affecting the back of the eye. Their effectiveness will be compared against intravitreal implants (upper bound of effectiveness) and trans-scleral systems (lower bound of effectiveness). Refining the animal model by incorporating the latest advances in microdialysis and imaging technology is key to expanding the knowledge central to the design, testing and evaluation of the next generation of innovative ocular drug delivery systems.

Prevalidation of a human cornea construct as an alternative to animal corneas for in vitro drug absorption studies

The use of ophthalmic drugs has increased consistently over the past few decades. Currently, most research is conducted using in vivo and ex vivo animal experiments; however, they have many disadvantages, including ethical concerns, high costs, the questionable extension of animal results to humans, and poor standardization. Although several cell culture-based cornea models have been developed, none have been validated and accepted for general use. In this study, a standardized, three-dimensional model of the human cornea (Hemicornea, HC) based on immortalized human corneal cells and cultivated in serum-free conditions was developed for drug absorption studies and prevalidated using compounds with a wide range of molecular characteristics (sodium fluorescein, rhodamine B, fluorescein isothiocyanate-labeled dextran, aciclovir, bimatoprost, dexamethasone, and timolol maleate). The HC model was independently cultured in three different laboratories, and the intralaboratory and interlaboratory reproducibility was analyzed and compared with the rabbit cornea. This analysis showed that the HC has a barrier in the same range as excised animal corneas, although with a higher reproducibility and lower variability. Because of the demonstrated transferability, the HC represents a promising in vitro alternative to the use of ex vivo tissue and offers a well-defined and standardized system for drug absorption studies.

Preservative use in topical glaucoma medications

Benzalkonium chloride (BAK) is the principal preservative employed in topical ocular hypotensive medications, although alternative compounds recently have begun to be employed or examined. Individual clinical trials have shown that exposure to BAK concentrations contained in ophthalmic solutions does not produce adverse sequelae in the majority of glaucoma patients, but concerns continue with regard to its long-term use. These concerns have resulted from an extensive research effort, including preclinical studies with in vitro and in vivo models, as well as recent clinical investigations dedicated specifically to this issue. The aim of this systematic literature review of both preclinical and clinical data was to determine the relevance of these findings to clinical practice. Most preclinical studies reported negative effects of BAK exposure, but with few exceptions, BAK concentrations and exposure times greatly exceeded those likely to be experienced by patients, given the normal physiological dilution by the tear film. In addition, consistent evidence of BAK-related toxicity did not emerge from our review of dedicated clinical investigations. Thus, taken together, current evidence supports the safety of BAK for most glaucoma patients, although subpopulations with abnormal tearing may benefit from alternative preservative compounds or preservative-free formulations. Further studies to identify these populations are needed.

Corneal cell culture models: a tool to study corneal drug absorption

In recent times, there has been an ever increasing demand for ocular drugs to treat sight threatening diseases such as glaucoma, age-related macular degeneration and diabetic retinopathy. As more drugs are developed, there is a great need to test in vitro permeability of these drugs to predict their efficacy and bioavailability in vivo. Corneal cell culture models are the only tool that can predict drug absorption across ocular layers accurately and rapidly. Cell culture studies are also valuable in reducing the number of animals needed for in vivo studies which can increase the cost of the drug developmental process. Currently, rabbit corneal cell culture models are used to predict human corneal absorption due to the difficulty in human corneal studies. More recently, a three dimensional human corneal equivalent has been developed using three different cell types to mimic the human cornea. In the future, human corneal cell culture systems need to be developed to be used as a standardized model for drug permeation.

Development of a serum-free human cornea construct for in vitro drug absorption studies: the influence of varying cultivation parameters on barrier characteristics

The increased use of ophthalmic products in recent years has led to an increased demand for in vitro and in vivo transcorneal drug absorption studies. Cell-culture models of the human cornea can avoid several of the disadvantages of widely used animal experimental models, including ethical concerns and poor standardisation. This study describes the development of a serum-free cultivated, three-dimensional human cornea model (Hemicornea, HC) for drug absorption experiments. The impact of varying cultivation conditions on the corneal barrier function was analysed and compared with excised rabbit and porcine corneas. The HC was cultivated on permeable polycarbonate filters using immortalised human keratocytes and a corneal epithelial cell line. The equivalence to native tissue was investigated through absorption studies using model substances with a wide range of molecular characteristics, including hydrophilic sodium fluorescein, lipophilic rhodamine B and fluorescein isothiocyanate (FITC)-labelled macromolecule dextran. To study the intra-laboratory repeatability and construct cultivation, the permeation studies were performed independently by different researchers. The HC exhibited a permeation barrier in the same range as excised animal corneas, high reproducibility and a lower standard deviation. Therefore, the HC could be a promising in vitro alternative to ex vivo corneal tissues in preclinical permeation studies.

Effects of common topical antiglaucoma medications on the ocular surface, eyelids and periorbital tissue

Glaucoma affects millions of people around the world. With the baby boom generation aging, the number of people affected by primary open-angle glaucoma in the US is expected to reach 3.3 million by 2020, and about half may not know they have the disease. The treatment of most forms of glaucoma includes the use of topical agents that enhance aqueous humour outflow, reduce aqueous production, or both. Topical intraocular pressure-lowering drugs must penetrate across the tissues of the eye to reach their therapeutic targets. Often, these tissues show the first signs and symptoms of drug toxicity and adverse effects. These include eyelid dermatitis, malpositions, lacrimal system scarring, ocular discomfort upon instillation, tear film instability, conjunctival inflammation, subconjunctival fibrosis, conjunctival epithelium changes, and corneal surface and endothelial impairment. For these reasons, ophthalmologists should evaluate the risks and benefits of ophthalmic medications before initiating therapy, identify the minimum dosages necessary to achieve a therapeutic benefit, and monitor patients for local and systemic adverse effects. Adverse events may be reduced by changing to a different class of topical medication, using corticosteroids, lubricating the eyes frequently, and reducing exposure to preservatives. This in turn can lead to higher levels of adherence to antiglaucoma therapy, improved outcomes and a reduction in the costs associated with long-term glaucoma complications. This article reviews the ocular adverse effects associated with the various classes of topical antiglaucoma drugs, with a particular focus on the ocular surface, eyelids and periorbital tissue.

In vitro cell culture models to study the corneal drug absorption

INTRODUCTION

Many diseases of the anterior eye segment are treated using topically applied ophthalmic drugs. For these drugs, the cornea is the main barrier to reaching the interior of the eye. In vitro studies regarding transcorneal drug absorption are commonly performed using excised corneas from experimental animals. Due to several disadvantages and limitations of these animal experiments, establishing corneal cell culture models has been attempted as an alternative.

AREAS COVERED

This review summarizes the development of in vitro models based on corneal cell cultures for permeation studies during the last 20 years, starting with simple epithelial models and moving toward complex organotypical 3D corneal equivalents.

EXPERT OPINION

Current human 3D corneal cell culture models have the potential to replace excised animal corneas in drug absorption studies. However, for widespread use, the contemporary validation of existent systems is required.

Interaction between topically and systemically coadministered P-glycoprotein substrates/inhibitors: effect on vitreal kinetics

The objective of the present study was to investigate the effect of topically coadministered P-glycoprotein (P-gp) substrates/inhibitors on the vitreal kinetics of a systemically administered P-gp substrate. Anesthetized male rabbits were used in these studies. The concentration-time profile of quinidine in the vitreous humor, after intravenous administration, was determined alone and in the presence of topically coadministered verapamil, prednisolone sodium phosphate (PP), and erythromycin. The vitreal pharmacokinetic parameters of quinidine in the presence of verapamil [apparent elimination rate constant (λ(z)), 0.0027 ± 0.0002 min(-1); clearance (CL_F), 131 ± 21 ml/min; area under the curve (AUC(0-∞)), 39 ± 7.0 μg · min/ml; and mean residence time, 435 ± 20 min] were significantly different from those of the control (0.0058 ± 0.0006 min(-1), 296 ± 46 ml/min, 17 ± 3 μg · min/ml, and 232 ± 20 min, respectively). A 1.7-fold decrease in the vitreal λ(z) and a 1.5-fold increase in the vitreal AUC of quinidine were observed in the presence of topical PP. Statistically significant differences between the vitreal profiles of the control and erythromycin-treated group were also observed. Plasma concentration-time profiles of quinidine, alone or in the presence of the topically instilled compounds, remained unchanged, indicating uniform systemic quinidine exposure across groups. This study demonstrates an interaction between topically and systemically coadministered P-gp substrates, probably through the modulation of P-gp on the basolateral membrane of the retinal pigmented epithelium, leading to changes in the vitreal kinetics of the systemically administered agent.

Evaluation of active and passive transport processes in corneas extracted from preserved rabbit eyes

In vitro transcorneal permeability studies are an important screening tool in drug development. The objective of this research is to examine the feasibility of using corneas isolated from preserved rabbit eyes as a model for permeability evaluation. Eyes from male New Zealand White rabbits were used immediately or were stored overnight in phosphate-buffered saline (PBS) or Hanks balanced salt solution (HBSS) over wet ice. Integrity of isolated corneas was evaluated by measuring the TEER and by determining the permeability of paracellular and transcellular markers. Active transport was assessed by measuring transcorneal permeability of selected amino acids. Esterase activity was estimated using p-nitrophenyl assay. In all cases, corneas from freshly enucleated eyes were compared to those isolated from the day-old preserved eyes. Transcellular and paracellular passive diffusion was not affected by the storage medium and observed to be similar in the fresh and preserved eye models. However, amino acid transporters demonstrated lower functional activity in corneas excised from eyes preserved in PBS. Moreover, preserved eyes displayed almost 1.5-fold lower esterase activity in the corneal tissue. Thus, corneas isolated from day-old eyes, preserved in HBSS, closely mimics freshly excised rabbit corneas in terms of both active and passive transport characteristics but possesses slightly reduced enzymatic activity.

The effect of drop vehicle on the efficacy and side effects of topical glaucoma therapy: a review

PURPOSE OF REVIEW

Topically applied medications are frequently used in ophthalmology to treat acute and chronic conditions, and are considered to be safer than their systemically applied counterparts, due to the reduced rate of systemic side effects.

RECENT FINDINGS

Many experimental and clinical studies have reported that the long-term use of topical medications in chronic ophthalmic conditions, such as glaucoma, may adversely affect the ocular surface. Preservatives play a pivotal role in almost all multidose ophthalmic preparations, inhibiting microbial growth and preserving the active drug. Consequently, preservatives are partially responsible for ocular side effects, although the exact mechanism of these side effects is not known.

SUMMARY

The role of preservatives in the efficacy and side effects of antiglaucoma drugs is reviewed. The recent advances in preservative technologies and their role in decreasing the side effects associated with antiglaucoma drugs are also discussed.

Esteraseaktivität eines organotypischen humanen Kornea-Konstrukts (HCC) als In-vitro-Modell für Permeationsuntersuchungen

Organotypic cornea equivalents are used as in vitro models for permeation studies. Many ophthalmic drugs are applied as ester prodrugs to achieve a higher bioavailability. The esterase activity of three corneal human cell lines (epithelial, stromal, endothelial cells) as well as of excised porcine cornea, human donor cornea and human cornea construct (HCC) was investigated and compared. Esterase activity was determined using p-nitrophenyl acetate and hydrocortisone acetate (HCA) as esterase substrates. Hydrocortisone acetate permeation across porcine cornea, human donor cornea and HCC was studied in vitro using Franz-diffusion cells. Corneal epithelial cells showed the highest esterase activity and only small differences to keratocytes and endothelial cells were detectable. The permeation barrier properties of the different corneal tissues were very similar in the case of HCA permeation whereas HCA metabolism rates were in the ranking order of porcine cornea > HCC > human donor cornea. Permeation and metabolism studies indicate that the in vitro permeation model HCC is able to adequately convert hydrocortisone acetate to hydrocortisone.

Cell culture models of the ocular barriers

The presence of tight barriers, which regulate the environment of ocular tissues in the anterior and posterior part of the eye, is essential for normal visual function. The development of strategies to overcome these barriers for the targeted ocular delivery of drugs, e.g. to the retina, remains a major challenge. During the last years numerous cell culture models of the ocular barriers (cornea, conjunctiva, blood-retinal barrier) have been established. They are considered to be promising tools for studying the drug transport into ocular tissues, and for numerous other purposes, such as the investigation of pathological ocular conditions, and the toxicological screening of compounds as alternative to in vivo toxicity tests. The further development of these in vitro models will require more detailed investigations of the barrier properties of both the cell culture models and the in vivo ocular barriers. It is the aim of this review to describe the current status in the development of cell culture models of the ocular barriers, and to discuss the applicability of these models in pharmaceutical research.

Development of Cultured Rabbit Corneal Epithelium for Drug Permeation Studies: A Comparison with Excised Rabbit Cornea

The aim of this study was to prepare and test an artificial corneal epithelium (reconstituted rabbit corneal epithelium, RRCE) exhibiting barrier characteristics and paracellular permeability similar to those of native rabbit cornea. The RRCE was obtained from a rabbit corneal epithelium (RCE) cell line grown for 8 days in submerged culture, then for 7 days in air-interface conditions on Snapwell polyester membranes. Permeation studies on the RRCE were carried out in comparison with rabbit excised corneas in vitro, using timolol maleate (TM) as the test drug, alone and in association with the following ocular permeation enhancers: benzalkonium chloride, ethylene-diaminetetraacetic acid sodium salt, polyethoxylated castor oil, polyoxyethylene stearyl ether, sodium deoxycholate, and escin. The integrity of the RRCE was assessed by measuring the transepithelial electrical resistance (TEER) during culture time and after every permeation experiment. When TM was tested alone, the permeation parameters (apparent permeability coefficient, lag time) obtained with the RRCE were similar to those of excised rabbit corneas. The artificial epithelium, however, was less sensitive than native cornea to the effect of permeation enhancers.

Human corneal equivalent as cell culture model for in vitro drug permeation studies

AIMS

For the study of transcorneal in vitro permeation of ophthalmic drugs, excised animal cornea or corneal epithelial cell culture are frequently used as a replacement for the human cornea. The main purposes of this study were to reconstruct a complete human organotypic cornea equivalent, consisting of all three different cell types (epithelial, stromal, and endothelial); to test the barrier function of this bio-engineered human cornea using three different model drugs (pilocarpine hydrochloride (PHCl), befunolol hydrochloride (BHCl), and hydrocortisone (HC)); and to determine its usefulness as an in vitro model for prediction of ocular drug absorption into the human eye.

METHODS

A multilayer tissue construct was created step by step in Transwell cell culture insert using SV-40 immortalised human endothelial and epithelial cells and native stromal cells (fibroblasts). Morphology was characterised by light microscopy using routine H&E staining. Scanning electron microscopy was used to evaluate ultrastructural features. Ocular permeation of drugs across the human cornea construct was tested using modified Franz cells and compared with data obtained from excised porcine cornea and previously described porcine cornea constructs.

RESULTS

and conclusion: The cornea construct exhibited typical corneal structures such as a monolayer of hexagonally shaped endothelial cells and a multilayered epithelium consisting of seven to nine cell layers with flat superficial cells. The formation of microplicae and microvilli was also confirmed. The human cornea construct showed similar permeation behaviour for all substances compared with excised porcine cornea. However, permeability (permeation coefficients K(p)) of the human cornea equivalent (PHCl 13.4*10(-6) (SD 3.01*10(-6)); BHCl 9.88*10(-6) (SD 1.79*10(-6)); HC 5.41*10(-6) (SD 0.40*10(-6)) cm/s) was about 1.6-1.8 fold higher than excised porcine cornea. Compared with data from the porcine cornea construct the cultivated human equivalent showed a decreased permeability. The reconstructed human cornea could be appropriate to predict drug absorption into the human eye.

Ocular Permeability Screening of Dexamethasone Esters Through Combined Cellular and Tissue Systems

Dexamethasone transport across ocular epithelium was evaluated by means of permeability studies on a series of ester prodrugs with the aim of identifying the most promising candidates for the treatment of the ocular surface. Organotypic conjunctival bovine epithelial cell cultures were assumed representative of an average ocular epithelium and used to describe the mechanism of permeation. Permeability coefficients were also determined in excised rabbit corneas set up and in vivo pharmacokinetic experiments. All dexamethasone esters permeated through the transcellular route and their permeability coefficient rose with the increase of the molecules lipophilicity until a maximum was reached in correspondence of dexamethasone butyrate (Log P = 3.95). It was found that esters hydrolysis occurring in various extent along the transport process, affected the overall permeability rate. There was evidence that the permeation process can be confined at the ocular epithelium layer if the ester is highly hydrophobic and not susceptible of fast hydrolysis.

One-side-coated insert as a unique ophthalmic drug delivery system

We newly prepared a unique one-side-coated insert that releases drug from only uncoated side. The purpose of this study is to determine whether ocular and systemic absorption of ophthalmic drug could be altered by an inserting direction of the insert in rabbit eyes. One-side-coated insert was prepared by attaching a polypropylene tape on the one side of the polymer disc of poly(2-hydroxypropyl methacrylate) (HPM) containing tilisolol as a model ophthalmic drug. The insert was applied in the lower conjunctival cul-de-sac of albino rabbits with the uncoated side facing bulbar conjunctiva/sclera (SC insert) or palpebral conjunctiva (CJ insert). At the adequate intervals, the tear fluid, plasma, aqueous humor, conjunctiva, and sclera were collected and the drug concentrations were determined by an HPLC. A release of tilisolol from the one-side-coated insert was twice slower than from the uncoated insert. Ocular application of the one-side-coated insert produced the constant concentrations of tilisolol in the tear fluid over 180 min. SC insert showed higher drug concentrations in the aqueous humor and sclera, and lower drug concentrations in the plasma and conjunctiva than CJ insert.The one-side-coated insert can alter the ocular and systemic absorption of drug by an inserting direction.