Effects of drug vehicles on ocular contact time

Optimizing instilled drug delivery: a scoping review of microdrops in ophthalmology

Eyedrop instillation constitutes the most commonly used ocular drug delivery method that serves for both diagnostic and therapeutic purposes. Ocular disposition and bioavailability of instilled drugs depend on the anatomy and physiology of the ocular surface as well as the physicochemical properties of the active agent. Intraocular bioavailability is positively associated with the amount of drug available onto the ocular surface and the precorneal residence time. Concerns are raised regarding systemic absorption of the instilled drugs intraocularly, percutaneously, via the conjunctiva, through the nasolacrimal system, or through the nasal, oral, and gastrointestinal mucosa. Special considerations exist regarding the anatomical features and the limited pharmacokinetic data on the pediatric population that complicate further the efficacy and systemic toxicity of the instilled medications. Both preclinical and clinical studies propose the reduction of the instilled drop volume, in the form of microdrops, as a means to enhance intraocular bioavailability of topically applied drugs, while minimizing patient discomfort and systemic adverse events. We summarize existing data on the clinical application of microdrops in a wide age range, from preterm infants to elderly adults. Studies regarding microdrops of mydriatics and ocular hypotensives show promising results in optimizing the provided everyday care.

Closing eyes with artificial tears: A simple and effective strategy to combat screen-related asthenopia and dry eye symptoms

Background

The widespread use of various video display terminals (VDTs) always had a detrimental impact on ocular health. Prolonged use of smartphones has been one of the leading causes of dry eye (DE) and asthenopia. Therefore, the purpose of this study is to find a simple and effective strategy to combat screen-related DE and asthenopia.

Methods

A group of healthy participants aged 18 and above were randomly assigned to three groups and tasked with a 2 h smartphone reading task. After 1 ​h of usage, each group adopted different methods of rest: no rest (Group A), a 10 min eye-closed rest (Group B), or a 10 min eye-closed joint artificial tears rest (Group C). Ophthalmological examinations and questionnaires were administered to all participants before and after the 2 h reading task.

Results

90 qualified volunteers, including 29 males and 61 females, were randomly assigned to three groups. Group A demonstrated a significant increase in the severity of DE and asthenopia as evidenced by all the evaluated indices. On the other hand, Group C did not exhibit any notable change in DE and asthenopia symptoms, with an improvement in corneal fluorescein staining (CFS) results (P ​> ​0.05) when compared to the pre-reading values. Group B showed a significant increase in ocular surface disease index (OSDI) (P ​≤ ​0.05) and a decrease in critical flicker frequency (CFF) (P ​≤ ​0.05).

Conclusions

Close-eye rest with artificial tears may be a convenient and effective prevention strategy for screen-related DE and asthenopia.

Impact of Apparatus and Adapter on In vitro Drug Release of Ophthalmic Semisolid Drug Products

PURPOSE

In vitro release testing (IVRT) is a widely used tool for evaluating the quality and performance of drug products. However, standardized sample adaptors or drug release apparatus setups for IVRT studies are still lacking for ophthalmic ointments. The aim of this study was to provide a better understanding of the impact of apparatus and sample adaptor setups on IVRT of ophthalmic ointments.

METHODS

Dexamethasone (DEX), a steroidal ingredient commonly used in ophthalmic drug products, was selected as a model drug. Ointments were prepared by mixing DEX in white petrolatum using a high shear mixer. A novel two-sided adapter was developed to increase the drug release surface area. DEX ointment was placed in one-sided or two-sided release adaptors coupled with 1.2 μm polyethersulfone membrane, and the drug release was studied in different USP apparatuses (I, II, and IV).

RESULTS

The sample adaptor setups had a minimal impact on cumulative drug release amount per area or release rate while USP IV apparatus with agitated flow enhanced drug release rates. The USP apparatus I with a two-sided semisolid adapter, which uses membranes on both sides, showed dramatically higher cumulative drug release and discriminative release profiles when evaluating ophthalmic formulations.

CONCLUSIONS

USP apparatuses and sample adaptors are critical considerations for IVRT. Two-sided semisolid adapter provides higher cumulative release, facilitating the discrimination between low drug content ophthalmic ointment formulations with good sensitivity and repeatability without affecting the drug release rate.

Extending the use of biologics to mucous membranes by attachment of a binding domain

Biologics are almost exclusively administered systemically, but localized delivery is preferable as it minimizes off-target exposure and allows more aggressive treatments. Topical application of biologics to epithelia is generally ineffective because most are covered with fluids and biologics are washed out too quickly to have significant therapeutic effects. Here we explore the idea that attaching a binding domain can serve as an "anchor" to extend the residency time of biologics on wet epithelia, allowing their effective use even with infrequent applications. We use topical application to the ocular surface as a challenging test since foreign substances are washed out especially efficiently by tear flow and blinking. Our results demonstrate that conjugation of antibodies to wheat germ agglutinin, which binds GlcNAc and sialic acid that are ubiquitously present in tissues, increases their half-life 350-fold upon application to the ocular surface in a mouse model of dry eye, a common and onerous disease in humans. Importantly, antibodies to IL-17A, IL-23, and IL-1β conjugated to the agglutinin reduces manifestations of dry eye, even when applied just once daily. In contrast, unconjugated antibodies are ineffective. Attaching an anchor to biologics is a simple means to overcome washout and to extend their therapeutic use.

Topical Ocular Therapeutics in Small Animals

This article reviews the administration of common topical ophthalmic medications, in relation to factors influencing absorption including composition of topical ophthalmic preparations, and potential systemic effects. Commonly prescribed, commercially available topical ophthalmic medications are discussed with respect to pharmacology, their indications for use, and adverse effects. Knowledge of topical ocular pharmacokinetics is essential for the management of veterinary ophthalmic disease.

Precorneal retention time of ocular lubricants measured with fluorophotometry in healthy dogs

OBJECTIVE

Determine the precorneal retention time of five different ocular lubricants commonly used in dogs.

ANIMALS STUDIED

Six healthy Beagle dogs (n = 12 eyes).

PROCEDURES

Five ocular lubricants were studied: Artificial Tears Solution® (1.4% polyvinyl alcohol), I-Drop® Vet Plus (0.25% hyaluronate), Optixcare® Eye Lube Plus (0.25% hyaluronate), Systane® Ultra (0.4% polyethylene glycol 400 and 0.3% propylene glycol), and Artificial Tears Ointment® (mineral oil/white petrolatum). Each lubricant was mixed with 10% sodium fluorescein to achieve 1% fluorescein formulations. Following topical administration of 35 mg in each eye, tear fluid was collected with capillary tubes at selected times (0, 1, 5, 10, 20, 30, 40, 50, 60, 90, 120, 180 min) and fluorescein concentrations were measured with a computerized scanning ocular fluorophotometer.

RESULTS

Tear fluorescence was significantly greater with Artificial Tears Ointment® compared with other lubricant formulations from 1 to 20 min post-administration. Median (range) precorneal retention times were significantly different among the 5 lubricants, ranging from 40 minutes (20-90 min) for Artificial Tears Ointment®, 35 min (20-90 min) for Systane® Ultra, 30 min (10-60 min) for I-Drop® Vet Plus, 25 min (10-60 min) for Optixcare® Eye Lube Plus, and 10 min (10-20 min) for Artificial Tears Solution®. Precorneal retention time was significantly lower for Artificial Tears Solution® compared with the other 4 formulations.

CONCLUSIONS

This study established normative data for the retention time of common lubricants on the ocular surface of dogs, which may be used to guide clinicians with their choice of lubricant and frequency of administration.

Ocular chemical burn associated with gel type alcohol-based hand sanitizer: A case report

INTRODUCTION

Alcohol-based hand sanitizers (ABHS) are widely used for hand hygiene due to the coronavirus disease pandemic. However, risk awareness regarding its adverse effects is lacking. We aim to report a case of ocular chemical burn that showed severe clinical presentation associated with ABHS.

PATIENT CONCERNS

A 5-year-old girl presented with severe left eye pain after 62% gel-type ABHS splashed into her eye.

DIAGNOSIS

On slit lamp examination, a near total corneal and conjunctival epithelial defect with limbal pale on the lower half of the cornea was noted. Severe ocular burn by ABHS was prominent with suspected limbal stem cell damage.

INTERVENTIONS

She was hospitalized and was prescribed topical medications including antibiotics, steroid eye drops with preservative-free artificial tears, and oral nonsteroidal anti-inflammatory drugs.

OUTCOMES

Despite intensive medical treatments, the corneal and conjunctival epithelial defects showed no improvement up to the 4th hospital day. After additional instillation of autoserum eye drops to promote epithelial healing, the corneal epithelium barely recovered from the temporal limbus. On the third week of admission, the epithelial defect was completely resolved without corneal opacity, although with minimal symblepharon in the lower fornix.

CONCLUSIONS

Gel-type ABHS can cause severe form of ocular chemical burn such as delayed ocular surface healing. In clinical setting, immediate and thorough rinsing of alcohol-based gel and early intensive treatment are crucial.

Ocular Physiologically Based Pharmacokinetic Modeling for Ointment Formulations

Purpose

The purpose of this study is to show how the Ocular Compartmental Absorption & Transit (OCAT™) model in GastroPlus^® can be used to characterize ocular drug pharmacokinetic performance in rabbits for ointment formulations.

Methods

A newly OCAT™ model developed for fluorometholone, as well as a previously verified model for dexamethasone, were used to characterize the aqueous humor (AH) concentration following the administration of multiple ointment formulations to rabbit. The model uses the following parameters: application surface area (SA), a fitted application time, and the fitted Higuchi release constant to characterize the rate of passage of the active pharmaceutical ingredient from the ointment formulations into the tears in vivo.

Results

Parameter sensitivity analysis was performed to understand the impact of ointment formulation changes on ocular exposure. While application time was found to have a significant impact on the time of maximal concentration in AH, both the application SA and the Higuchi release constant significantly influenced both the maximum concentration and the ocular exposure.

Conclusions

This initial model for ointment ophthalmic formulations is a first step to better understand the interplay between physiological factors and ophthalmic formulation physicochemical properties and their impact on in vivo ocular drug pharmacokinetic performance in rabbits.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11095-020-02965-y.

Multiple drug delivery from the drug-implants-laden silicone contact lens: Addressing the issue of burst drug release

A fixed combination of bimatoprost/timolol eye drop solution is used to manage the elevated intra-ocular pressure in glaucoma patients, including individuals whose condition is poorly controlled by monotherapy. Eye drop solutions are generally given in high dose, due to poor ocular bioavailability. The high ocular dose of bimatoprost and timolol lead to hyperaemia and systemic cardiac side effects respectively. Here, we introduce multiple implant-laden contact lenses (IM) to passively deliver timolol, bimatoprost and hyaluronic acid at therapeutically relevant doses without high burst release. The drug-loaded implants were individually implanted in the outer periphery of the silicone contact lenses. Atomic force microscopy showed the smooth surface of the implant contact lens, as the implants were inside the contact lens matrix. The implant lens (IM) showed major loss of drugs [timolol = 60.60%, bimatoprost = 61.75% and HA = 46.03%] during the monomer extraction and wet sterilization, while the option of dry radiation sterilization (IM-R lens) and hydration for 24 h prior to use showed relatively lower loss of drugs [timolol = 16.87%, bimatoprost = 47.95% and HA = 24.41%]. The in-vitro drugs release data of IM-R lens, showed sustained release for 72 h, with low burst release in comparison to the soaked (SM) and direct drug-laden contact lenses (DL). The in vivo drug release data in the rabbit tear fluid showed sustained release using IM-R lens in comparison to the SM lens and eye drop therapy. The burst release with the IM-R lens was many folds reduced, which could bypass the side effects associated with multiple eye drop therapy. The in vivo pharmacodynamic study in the rabbit model showed peak and valley profile with multiple eye drop therapy, while IM-R lens showed prolong reduction in intra ocular pressure (IOP) for 120 h. The study demonstrates the application of implantation technology to deliver multiple drug through contact lenses to treat glaucoma.

Novel Polyvinyl Pyrrolidone-Loaded Olopatadine HCl-Laden Doughnut Contact Lens to Treat Allergic Conjunctivitis

Olopatadine HCl is an antiallergic drug used for the management of allergic conjunctivitis. Currently, it is delivered via eye drop solution, which is highly inefficient due to low bioavailability. Silicone contact lenses can be used to sustain the release of ophthalmic drugs. However, the presence of drug alters the optical transmittance and physical properties of the contact lens. The objective was to design a novel polyvinyl pyrrolidone (PVP)-coated olopatadine-ethyl cellulose microparticles-laden doughnut contact lens to sustained ocular delivery with limited alteration to the optical and swelling properties of the contact lens. The doughnut was implanted within the periphery of the lens using modified casting technique. Olopatadine HCl was loaded by soaking (SM-OL), direct loading (DL-OL), and doughnut casting method (DNT-OL). PVP (comfort agent) was loaded on the surface of contact lens for all the batches via novel curing technique. The in vitro olopatadine HCl release data of SM-OL (up to 48-72 h) and DL-OL batches (up to 72 h) showed high burst release, whereas DNT-OL batch showed sustained release up to 120 h without significant (p > 0.05) alteration in the optical and swelling properties of contact lens. All the batches showed sustained release of PVP up to 120 h. The in vivo studies in the rabbit tear fluid showed improvement in the olopatadine HCl and PVP retention time in comparison to eye drop solution. The PVP-loaded DNT-OL-500 lens showed tear stabilization (comfort wear) in Schirmer strip test (rabbits) with no protein adherence in comparison to DNT-OL-500 lens without PVP. The study demonstrated the successful delivery of olopatadine HCl and PVP-K30 from the doughnut contact lens for the extended period with limited alteration to the optical and swelling properties of contact lens.

The use of preservatives in dry eye drops

Topical ocular preparations are widely recommended by health care professionals, or chosen by patients, to help manage dry eye disease (DED). The chronic and progressive nature of DED may result in the administration of topical products several times a day, over a period of many years. Given DED is a condition that by definition affects the ocular surface, it is important to understand how the repeated use of eye drops may impact the ocular surface, influence clinical signs, affect symptoms, and impact the overall disease process of dry eye. The component in topical preparations with the greatest potential to adversely affect the ocular surface is the preservative. This paper reviews the literature in relation to the use of preservatives in formulations for dry eye. The ocular effects of benzalkonium chloride (BAK) are summarised and compared to the performance of alternative preservatives and preservative-free formulations. Use of preserved and preservative-free drops in relation to the management of varying stages of DED is discussed.

Ocular Biodistribution Studies using Molecular Imaging

Classical methodologies used in ocular pharmacokinetics studies have difficulties to obtain information about topical and intraocular distribution and clearance of drugs and formulations. This is associated with multiple factors related to ophthalmic physiology, as well as the complexity and invasiveness intrinsic to the sampling. Molecular imaging is a new diagnostic discipline for in vivo imaging, which is emerging and spreading rapidly. Recent developments in molecular imaging techniques, such as positron emission tomography (PET), single-photon emission computed tomography (SPECT) and magnetic resonance imaging (MRI), allow obtaining reliable pharmacokinetic data, which can be translated into improving the permanence of the ophthalmic drugs in its action site, leading to dosage optimisation. They can be used to study either topical or intraocular administration. With these techniques it is possible to obtain real-time visualisation, localisation, characterisation and quantification of the compounds after their administration, all in a reliable, safe and non-invasive way. None of these novel techniques presents simultaneously high sensitivity and specificity, but it is possible to study biological procedures with the information provided when the techniques are combined. With the results obtained, it is possible to assume that molecular imaging techniques are postulated as a resource with great potential for the research and development of new drugs and ophthalmic delivery systems.

A self-healing hydrogel eye drop for the sustained delivery of decorin to prevent corneal scarring

Scarring/Opacity on the surface of the eye and vascularisation following infectious diseases, inflammation and corneal trauma are often a leading cause of blindness. The 'gold standard' treatment to prevent corneal scarring is the application of amniotic membrane (AM) to the ocular surface in the acute stage of injury. Although clinically effective, the use of the AM is associated with biological variability and unpredictable responses. Potential health risks including disease transmission, significant ethical issues surrounding the tissue donation process and stringent regulations/storage conditions, preclude widespread use. Consequently, there is a demand for the development of a new, synthetic alternative, that is stable at room temperature, capable of protecting the wound and has the capacity to deliver anti-scarring and anti-inflammatory mediators. Here we have developed a micro-structured fluid gel eye drop, to deliver a potent anti-scarring molecule, decorin. We have compared the release of decorin from the formulated dressing to a typical gel film, demonstrating enhanced release for the fluid gel eye-drops. Therefore, we have investigated the effect of the fluid gel system in 2D human corneal fibroblast culture models, as well as shown the retention of the gellan fluid gel in an in vivo rat model. At the same time the efficacy of the fluid gel eye drop was studied in an organ culture model, whereby the fluid gel containing decorin, significantly (P < 0.05) increased re-epithelialisation within 4 days of treatment.

Effect of gold nanoparticles on timolol uptake and its release kinetics from contact lenses: In vitro and in vivo evaluation

Contact lenses are ideally suited for extended drug delivery to the ocular tissues, but incorporation of any particulate system affects the critical properties of the contact lens. Timolol loading by the conventional soaking method does not significantly alter the critical properties of the contact lens. However, there are challenges of low drug loading and high burst release. This research work aimed to investigate the effect of gold nanoparticles (GNPs) on loading and its release kinetics from the contact lens using the soaking method. In one approach, GNPs were loaded into the timolol soaking solution (GNPs-SS), and in another approach, GNPs were incorporated into the contact lenses (GNPs-CL) during fabrication. The contact lenses were soaked at two different concentrations of timolol (i.e., 2 mg/ml and 4 mg/ml). Swelling and optical transmittance were not significantly affected by the presence of GNPs in the contact lenses. A significant uptake/loading of timolol using the GNPs in both the approaches was observed. The in vitro flux data showed no significant improvement in the release rate profiles of timolol when using both approaches. However, the in vivo study in the rabbit tear fluid showed high timolol concentration with the GNPs-laden contact lens at all timepoints in comparison to the soaked contact lenses without GNPs. The in vivo pharmacodynamic study in rabbits showed a 2 mmHg average fall in intraocular pressure (72 h) using the GNPs-laden contact lenses, while the soaked contact lenses without GNPs and eye drops solution (0.5 %w/v) showed 2 mmHg. The drug distribution study in the ocular tissue showed a significant improvement in the drug deposition with the GNPs-laden contact lenses in the ciliary muscle and conjunctiva. This study successfully demonstrated the potential of GNPs to enhance the uptake of drug from the drug soaking solution to treat glaucoma without compromising the critical properties of contact lens. STATEMENT OF SIGNIFICANCE: In this study, we have overcome the limitation of the conventional soaking method of low drug loading and high burst release from the contact lenses. We have investigated the effect of gold nanoparticles (GNPs) on the timolol loading and its release kinetics from the contact lenses. The study revealed the potential of GNPs to enhance the uptake of timolol from the timolol soaking solution to treat glaucoma without compromising the critical lens properties.

Perioperative Corneal Abrasion: Updated Guidelines for Prevention and Management

Corneal abrasion is the most common ocular complication in surgery. Treatment requires pain control, antimicrobial prophylaxis, and close monitoring. Pain improves significantly after 24 hours and should be resolved by 48 hours. Persistent, worsening, or new symptoms warrant immediate specialist consultation. The authors review the pathophysiology of perioperative corneal abrasion, and propose updated evidence-based guidelines for improved patient care.

The design of contact lens based ocular drug delivery systems for single-day use: Part (I) Structural factors, surrogate ophthalmic dyes and passive diffusion studies

The poor retention and efficacy of instilled drops as a means of delivering drugs to the ophthalmic environment is well-recognised. The potential value of contact lenses as a means of ophthalmic drug delivery, and consequent improvement of pre-corneal retention is one obvious route to the development of a more effective ocular delivery system. Furthermore, the increasing availability and clinical use of daily disposable contact lenses provides the platform for the development of viable single-day use drug delivery devices based on existing materials and lenses. In order to provide a basis for the effective design of such devices, a systematic understanding of the factors affecting the interaction of individual drugs with the lens matrix is required. Because a large number of potential structural variables are involved, it is necessary to achieve some rationalisation of the parameters and physicochemical properties (such as molecular weight, charge, partition coefficients) that influence drug interactions. Ophthalmic dyes and structurally related compounds based on the same core structure were used to investigate these various factors and the way in which they can be used in concert to design effective release systems for structurally different drugs. Initial studies of passive diffusional release form a necessary precursor to the investigation of the features of the ocular environment that over-ride this simple behaviour. Commercially available contact lenses of differing structural classifications were used to study factors affecting the uptake of the surrogate actives and their release under ‘passive’ conditions. The interaction between active and lens material shows considerable and complex structure dependence, which is not simply related to equilibrium water content. The structure of the polymer matrix itself was found to have the dominant controlling influence on active uptake; hydrophobic interaction with the ophthalmic dye playing a major role.

Corneal protection during general anesthesia for nonocular surgery

Corneal abrasion is the most common ophthalmologic complication that occurs during general anesthesia for nonocular surgery. Such abrasions can be caused by a variety of mechanisms and can lead to sight-threatening microbial keratitis and permanent scarring. There is no standard mode of protecting the cornea during general anesthesia for nonocular surgery. Methods described in the literature are not entirely effective and may be associated with unwanted side effects. Taping alone provides protection that is equivalent or superior to other interventions and has fewer side effects. Petroleum gel is flammable and is best avoided when electrocautery and open oxygen are to be used around the face. Preservative-free eye ointment is preferred, as preservative can cause corneal epithelial sloughing and conjunctival hyperemia. Recently, the application of Geliperm and bio-occlusive dressings has been advocated. Geliperm may be particularly useful during endonasal surgery when continuous perioperative observation of the eye is required. In this article, the literature on the etiology of perioperative corneal abrasions is reviewed and various protection strategies are compared in order to identify the best methods to prevent corneal abrasions during general anesthesia.

Time course of changes in ocular wavefront aberration after administration of eye ointment

PURPOSE

To investigate the influence of an eye ointment on ocular aberration.

DESIGN

Prospective, comparative study.

METHODS

In 10 normal volunteers, ocular aberration was assessed before and 5, 30 min, 1, 2, 3, 6, and 12 h after administration of ofloxacin eye ointment. Ocular aberration was sequentially measured over a period of 10 s, and the root mean square (RMS) of the second-, third-, fourth-, and total higher-order aberrations (HOAs) were determined. From the sequential changes in total HOAs during 10 s, the fluctuation index (FI) and stability index (SI) were calculated. The obtained data were compared with those of another 17 normal volunteers who received timolol maleate gel-forming ophthalmic solution.

RESULTS

No significant changes in second-order RMS were observed after administration of the ointment. HOAs such as third-, fourth-, and total higher-order RMS significantly changed during the study period (P<0.05, repeated-measures analysis of variance). The RMS of each HOA component significantly increased 5 min after administration compared with the baseline values (P<0.05, Dunnett test). FI also increased significantly 5 min after administration (P<0.05), but SI did not change significantly. When compared with the results of the gel-forming solution group, HOAs and FI showed significantly higher values at several time points during 6 h after application (P<0.05, Mann-Whitney U-test).

CONCLUSIONS

Administration of eye ointment significantly degrades optical quality of the eye by increasing and oscillating HOAs. These changes were more pronounced than those after instillation of gel-forming ophthalmic solution for at least several hours.

Shelf life of cefuroxime eye-drops when dispensed in artificial tear preparations

There has recently been a clinical demand for cefuroxime formulated as an eyedrop. Cefuroxime exhibits a broad spectrum of activity against most common ocular infections and is considered to be less toxic to the compromised epithelium than some other topical antibiotics. A formulation in an artificial tear solution would be expected to enhance drug penetration by prolonging pre-corneal drug retention, and the presence of a preservative might enable a suitable formulation to be given a shelf life of more than 24 hours.

This paper reports studies on the stability of cefuroxime 50mg/ml (5 per cent) in artificial tear solutions, sodium chloride eye-drops and in solutions of benzalkonium chloride, hypromellose or water for injections. Cefuroxime was assayed by high performance liquid chromatography. The method had a coefficient of variation of 0.23 per cent at the concentration investigated and recovery of added cefuroxime was 100 per cent. The preparation of cefuroxime in artificial tear solutions which were preservative free or contained benzalkonium chloride less than 0.002 per cent appeared to be physically stable. Preparation of cefuroxime in Sno Tears also produced a stable solution. This preparation can be given a shelf life of 28 days at 4C, 24 hours at 25C and 14 days if stored in a domestic refrigerator, enabling a full course of treatment to be given on a single visit to the pharmacy.

Prophylactic efficacy of ophthalmic quinolones in experimental endophthalmitis in rabbits

PURPOSE

The aim of this study was to determine the efficacy of 0.3% gatifloxacin ophthalmic solution in preventing bacterial endophthalmitis in rabbits.

METHODS

Eighty-four (84) albino phakic rabbits were injected unilaterally with 2 x 10(4) colony forming units of Enterococcus faecalis into the anterior chamber. The eyes received 0.3% ofloxacin ophthalmic ointment or 0.3% gatifloxacin ophthalmic solution with different regimens in three separate experiments: (1) 1 or 3 drops of gatifloxacin every 2 h or a single application of ofloxacin for 1 day; (2) 3 drops/day of gatifloxacin application started at 0, 6, and 24 h postinoculation, or 1 drop at 0 h, and 3 times daily gatifloxacin for the following 3 days; and (3) 1 or 3 drops of gatifloxacin application started at 0 h and no further application for the following 3 days. The control eyes received no treatment in the three experiments. The effectiveness of these different regimens was assessed by slit-lamp biomicroscopy and bacterial colony counts. The ocular penetration of the drugs was determined in a separate experiment, using 36 normal albino rabbits.

RESULTS

The concentration-time curves for gatifloxacin and ofloxacin appeared parallel, with mean peak concentrations of 1161 and 219 ng/mL, respectively, at 1 h postinstillation. In Experiment 1, gatifloxacin significantly reduced the inflammation and the number of living bacteria in the aqueous humor, compared with controls, whereas ofloxacin ointment did not. A single application of ofloxacin ointment was not better than 1 drop of gatifloxacin. The results of Experiment 2 showed that the effectiveness of gatifloxacin decreased as the interval between the inoculation and the onset of treatment increased. In Experiment 3, only 3 drops of gatifloxacin on day 1 kept the inflammation significantly lower than that in the control for 4 days.

CONCLUSIONS

Immediate postoperative prophylaxis would likely be effective in reducing the risk of enterococcal endophthalmitis by topical gatifloxacin.

Controlled-release of epidermal growth factor from cationized gelatin hydrogel enhances corneal epithelial wound healing

We designed a new ophthalmic drug-delivery system for epidermal growth factor (EGF) from the biodegradable hydrogel of cationized gelatin. We placed a cationized gelatin hydrogel (CGH) with incorporated (125)I-labelled EGF in the conjunctival sac of mice and measured the residual radioactivity at different times to evaluate the in vivo profile of EGF release. Approximately 60-67% and 10-12% of EGF applied initially remained 1 and 7 days after application, respectively; whereas EGF delivered in topically applied solution or via EGF impregnation of soft contact lenses disappeared within the first day. We also placed CGH films with 5.0 mug of incorporated EGF on round corneal defects in rabbits to evaluate the healing process using image analysis software and to assess epithelial proliferation immunohistochemically by counting the number of Ki67-positive cells. The application of a CGH film with incorporated EGF resulted in a reduction in the epithelial defect in rabbit corneas accompanied by significantly enhanced epithelial proliferation compared with the reduction seen after the topical application of EGF solution or the placement of an EGF-free CGH film. The controlled release of EGF from a CGH placed over a corneal epithelial defect accelerated ocular surface wound healing.

Rheological evaluation of poloxamer as an in situ gel for ophthalmic use

The contact time of a vehicle on the cornea is of utmost importance for ocular drug delivery. In the present study rheological measurements were performed to study the gel and the sol-gel transition of an in situ gel, Poloxamer 407. The rheological measurements and a small in vivo study of ocular residence times in humans were used to evaluate poloxamer as an ocular vehicle. An increasing concentration of poloxamer resulted in a slightly increasing elasticity of the gels and a decreasing sol-gel transition temperature. The contact time increased with increasing concentration of poloxamer which could be explained and correlated with the rheology of poloxamer solutions/gels mixed with simulated tear fluid. The maximum contact time for the preparations studied was about 1 h. The poloxamer system did not seem to be promising as an ophthalmic in situ gel due to the strong concentration dependence of the sol-gel transition temperature combined with the dilution that occurs in the eye.

The aetiology and prevention of peri-operative corneal abrasions

Corneal abrasion is the most frequent ocular complication to occur during the peri-operative period. This review describes the aetiology of corneal abrasions and evaluates the current methods of prevention. Most abrasions are caused by lagophthalmos (failure of the eyelids to close fully) during general anaesthesia, resulting in corneal drying. General anaesthesia reduces both the production and the stability of tears and therefore increases the incidence of this painful condition. Taping the eyelids closed, soft contact lenses, the instillation of aqueous gels or paraffin-based ointments are all effective in preventing corneal abrasions, but ointments are associated with significant morbidity.

Effects of pilocarpine and other antiglaucoma drugs on cultured human Tenon's fibroblast cells

It has been found that long-term therapy with topical antiglaucoma drugs may decrease the success of glaucoma filtering surgery. In this study, various antiglaucoma drugs, including carteolol, betaxolol, levobunolol, pilocarpine, and timolol, were investigated for their proliferative effect on cultured human Tenon's fibroblast cells. It was found that the 3H-thymidine uptake of cultured fibroblast cells was inhibited by commercial antiglaucoma drugs, including carteolol of 0.1% concentration (13%), 0.01% (50%) and 0.001% (53%), betaxolol of 0.05% concentration (14%), 0.005% (42%) and 0.0005% (62%), levobunolol of 0.05% concentration (2%), 0.005% (32%) and 0.0005% (55%), and timolol of 0.025% concentration (4%), 0.0025% (47%) and 0.00025% (55%), whereas the 3H-thymidine uptake was increased by commercial pilocarpine eyedrop from 103% (0.2% of concentration), 170% (0.02% of concentration) to 171% (0.002% of concentration), when cells were treated with commercial drugs for 100 min. Meanwhile, the proliferations of cultured fibroblast cells were stimulated by simultaneously combining 0.2%, 0.02% and 0.002% concentrations of pilocarpine eyedrops with other antiglaucoma drugs, such as carteolol of 0.1% concentration (50%), 0.01% (113%) and 0.001% (138%), betaxolol of 0.05% concentration (24%), 0.005% (128%) and 0.0005% (142%), levobunolol of 0.05% concentration (32%), 0.005% (87%) and 0.0005% (119%), and timolol of 0.025% concentration (15%), 0.0025% (94%) and 0.00025% (118%). Following incubation with pure pilocarpine, the proliferation of Tenon's fibroblast cells was inhibited for 84% (0.2% concentration), 84% (0.02% concentration) and 90% (0.002% concentration). When fibroblast cells were treated with commercial pilocarpine eyedrops for 24 hours, the 3H-thymidine uptake was increased to 160% (0.02% concentration) and 172% (0.002% concentration). This result shows that the commercial pilocarpine may play a crucial role for the proliferation of cultured human Tenon's fibroblast cells.

Gamma scintigraphic comparison of eyedrops containing pilocarpine in healthy volunteers

The aim of the present study was to compare, in healthy human volunteers (male and female), the corneal contact time of various formulations, each containing one viscosity enhancer from the following list: a phase-transition system (gellan gum, Gelrite), a heteropolysaccharide (xanthan gum) and currently used polymers hydroxyethylcellulose, hydroxypropylmethylcellulose, or poly(vinyl alcohol). These different solutions were compared to a reference solution containing no viscosity enhancers. The corneal contact time of the formulations was evaluated over more than 20 minutes by gamma scintigraphy using Technetium-99m (Tc-99m DTPA) as a radioactive label. An eyedrop containing pilocarpine salts (25 microliters) was instilled in one eye only. Each volunteer received 4 formulations, the interval between the instillations being one week. The protocol has been approved by the relevant institutional human experimentation committee. One minute after instillation, only 23% of the reference solution remained on the ocular surface, whereas the novel formulations maintained, respectively, 77% (xanthan gum) or 82% (Gelrite) of the tracer on the ocular surface. Twenty-one min after instillation, 12% (reference solution), 25% (xanthan gum solution), and 39% (gelrite solution) of the tracer remained on the ocular surface. The results confirm that an increase in viscosity of the formulation (xanthan) delays the clearance of the instilled solution by the tear flow. The effect of the gelation mechanism is superior, especially at the later time points. In this respect, xanthan gum and, particularly, Gelrite are suitable vehicles for ophthalmic drugs.

Clinical pharmacokinetics of various topical ophthalmic delivery systems

The eye provides an interesting study in contrasts: it is a delicate structure with a transparent anterior wall as thin as 0.5mm; yet this structure in combination with the ocular adnexa provides a resilient physicochemical barrier. The lids, tears and lacrimal apparatus work in concert to continuously protect the cornea and conjunctiva with a stable tear film, which also serves as the primary refracting surface. This elaborate defence system simultaneously prevents ready intraocular access of pharmaceutical agents. Additionally, the trilaminate structure of the cornea has variable permeability to chemical agents, thereby further limiting the passage of highly hydrophobic and hydrophilic moieties. Presenting topical pharmaceutical agents to the eye via different delivery systems allows clinicians to directly affect the profile of drug bioavailability and, ultimately, bioactivity. While achieving optimum bioavailability is therapeutically important, one must simultaneously limit the occurrence of drug-induced adverse effects, both systemic and local. Utilising the different pharmacokinetic properties of drug delivery systems permits clinicians to maximise their therapeutic plans for addressing specific clinical situations while minimising the potential for adverse drug effects.

Povidone-iodine for ophthalmia neonatorum prophylaxis

PURPOSE

The agents currently used to prevent ophthalmia neonatorum are less than optimal, with reports indicating evidence of bacterial resistance, ineffectiveness, and toxicity. Povidone-iodine ophthalmic solution, which has been shown to be effective in the preoperative preparation of the eye, generates no resistance, is an effective antimicrobial agent, and has low toxicity. We evaluated the effectiveness and safety of povidone-iodine for ophthalmia neonatorum prophylaxis.

METHODS

A bacterial culture was taken from the conjunctiva of each eye of 100 infants within 30 minutes of birth. A drop of 2.5% povidone-iodine solution was then placed on one eye, while the other eye received either one drop of silver nitrate 1% ophthalmic solution or 0.5% erythromycin ointment. Conjunctival bacterial cultures were again taken two to four hours after birth. At each culture and at 24 hours after birth, the eyes were examined for toxic changes. To measure the effectiveness of the medications, the number of bacterial colony-forming units and species from each culture was compared.

RESULTS

All three agents significantly reduced the number of colony-forming units, but povidone-iodine caused the most significant decrease. The number of species was reduced significantly by povidone-iodine (P = .00051) and silver nitrate (P = .007), with povidone-iodine yielding the most significant decrease. Erythromycin did not significantly reduce the number of species. Silver nitrate demonstrated more ocular toxicity at the 24-hour determination point than did either of the other two medications (P < .001).

CONCLUSIONS

Povidone-iodine 2.5% ophthalmic solution is an effective antibacterial agent on the conjunctiva of newborns and causes less toxicity than silver nitrate.

In situ measurement of fluorescein release by collagen shields in human eyes

Fluorescein (F) and FITC Dextran (FD; MW 4400) have been used as inert analogs of active drugs to examine the factors controlling the rate of loss of drugs from collagen shields in vivo. The diffusion constants in the shield (120 microns thick) determined from in vitro release experiments were found to be 0.42 x 10(-6) for F and 0.16 x 10(-6) cm2/sec for FD at 34 degrees C and these values correspond to 0.7 and 0.27 min-1 rates of loss for the exponential parts of their release. In the eyes of 6 subjects, the F loaded shields lost the dye at an average rate of 0.016 min-1 initially, increasing to 0.026 min-1 at the end of an hour. Somewhat higher values were noted with FD and were attributed to variations of manufacturing of the shields. Comparing the rates of loss in in vitro and in vivo, it is clear that the latter is not controlled by the rate of diffusion in the shield, but is limited by the rates of tear secretion and flow over the surfaces of the shield. The penetration of F into the anterior chamber from a series of four drops applied 12 min apart was compared with that from a shield soaked in the drop solution to determine the enhancement in the bioavailability. This showed that the shield increased the penetration into the eye by about 16 times over that from a single drop. However, the rate of loss of F from the shield in vivo is only about 8 times slower than that from a drop instilled in the eye.(ABSTRACT TRUNCATED AT 250 WORDS)

Collagen-based drug delivery and artificial tears

For patients with conditions requiring chronic rather than acute therapy, the advantages of collagen shields in providing high and sustained levels of drugs and/or lubricants to the cornea are outweighed by the difficulty of insertion of the shield and the problem of blurred vision. We have developed a delivery system in which collagen pieces suspended in a viscous vehicle can be instilled into the lower forniceal space, thereby simplifying application and reducing blurring of vision. The collagen pieces (Collasomes) can be formulated with various constituents such as antibiotics or cyclosporine, or with chemical alterations such as the inclusion of a lipid (Lacrisomes) for the treatment of dry eyes. In the normal eyes of volunteers, Collasomes hydrated in a solution of sodium fluorescein and suspended in a methylcellulose vehicle as a model for delivery of water-soluble drugs produced fluorescein concentrations 17 to 42 times higher in the cornea and 6 to 8 times higher in the aqueous humor, compared with fluorescein-containing vehicle alone. In a preliminary controlled study, 76% of patients with moderately severe keratoconjunctivitis sicca (KCS) preferred Lacrisomes to the vehicle control because of a more soothing effect and longer duration of comfort. All preparations were well tolerated by all study subjects. Current studies involve improving drug delivery by chemically modifying the collagen molecule to slow diffusion of the drug from the Collasome matrix, as well as varying the amount of cetyl alcohol and combining it with modified collagen in Lacrisomes to maximize comfort in patients with dry eyes.

In vivo evaluation of dosage forms: application of gamma scintigraphy to non-enteral routes of administration

The trend to deliver drugs to defined areas of the body involves sophisticated carriers systems. In addition to the in vitro drug release profile one must be aware of the in vivo behaviour of the dosage form and the drug. Gamma scintigraphy is an elegant way to gain insights of the actual in vivo distribution pattern of dosage forms. This technique relies on the use of radioactive tracers included into the medicament and selected so as to enable an optimum detection by a gamma ray camera. The choice of a convenient label enables the in vivo determination of the targeting of the formulation administered through a large number of routes. The present paper reviews applications of gamma scintigraphy for the evaluation of dosage forms administered by the parenteral, rectal, buccal, nasal, pulmonary, and ophthalmic routes.

Relationship between precorneal retention of viscous eye drops and tear fluid composition

The influence of viscolysers on the precorneal residence of a fluorescent tracer was determined, using slit lamp fluorophotometry. The solution acceptability was evaluated by the volunteers by answering a standard questionnaire. The relationship between precorneal retention of viscous eye drops, discomfort and tear fluid composition after instillation of various cellulosic solutions was examined. Irritating hydroxypropylcellulose solution increases the total protein concentration of tears, without change in the ratio of lysozyme to total protein.

Influence of ophthalmic ointments on the penetration of pilocarpine drops

To evaluate the influence of prior administered ointments upon the intraocular penetration of drops, we applied either a combination antibiotic ointment, a combination antibiotic-steroid ointment, or a lubricant ointment at different time periods before instillation of 2% pilocarpine drops into rabbit eyes. The level of pilocarpine measured in aqueous humor at one hour was compared to the level achieved in eyes without ointment application. No change was found in pilocarpine levels following application of the lubricant ointment. Pilocarpine concentrations were significantly lower (38%-48%) in animals receiving the antibiotic ointment at 5 or 15 minutes before pilocarpine drops. Pilocarpine levels also were decreased significantly when the steroid-antibiotic ointment was applied 15, 30 or 60 minutes before the drops. To verify these effects at other time periods, ointments were applied 15 minutes before pilocarpine drops and aqueous humor samples aspirated at 30 minutes or two hours. A 22% decrease in aqueous humor pilocarpine was found at 30 minutes with both the antibiotic and steroid-antibiotic combination; no effect was observed at two hours. To determine the influence of each drug component within the ointment on the penetration of pilocarpine, solutions of dexamethasone, neomycin, bacitracin and polymyxin B were mixed individually with pilocarpine drops and applied into the animal eyes. Bacitracin and polymyxin B significantly reduced one-hour pilocarpine levels in aqueous humor; however, no significant effect was observed with either neomycin or dexamethasone.