Comparative toxicity of intravitreal aminoglycoside antibiotics

Recent Advances of Ocular Drug Delivery Systems: Prominence of Ocular Implants for Chronic Eye Diseases

Chronic ocular diseases can seriously impact the eyes and could potentially result in blindness or serious vision loss. According to the most recent data from the WHO, there are more than 2 billion visually impaired people in the world. Therefore, it is pivotal to develop more sophisticated, long-acting drug delivery systems/devices to treat chronic eye conditions. This review covers several drug delivery nanocarriers that can control chronic eye disorders non-invasively. However, most of the developed nanocarriers are still in preclinical or clinical stages. Long-acting drug delivery systems, such as inserts and implants, constitute the majority of the clinically used methods for the treatment of chronic eye diseases due to their steady state release, persistent therapeutic activity, and ability to bypass most ocular barriers. However, implants are considered invasive drug delivery technologies, especially those that are nonbiodegradable. Furthermore, in vitro characterization approaches, although useful, are limited in mimicking or truly representing the in vivo environment. This review focuses on long-acting drug delivery systems (LADDS), particularly implantable drug delivery systems (IDDS), their formulation, methods of characterization, and clinical application for the treatment of eye diseases.

Effect of gentamicin on CD3+ T-lymphocyte proliferation for treatment of equine recurrent uveitis: An in vitro study

OBJECTIVE

The objective of the study was to determine the effect of gentamicin on CD3+ T-lymphocyte proliferation and cell viability using an in vitro cell culture model as a means of investigating the mechanism of action of low-dose intravitreal gentamicin injection.

ANIMALS STUDIED

Three adult horses with no evidence of ophthalmic or systemic disease.

PROCEDURE

Peripheral blood lymphocytes were treated with gentamicin at concentrations 37.5 μg/mL, 112.5 μg/mL, 187 μg/mL, 375 μg/mL, or 750 μg/mL then stimulated to proliferate with concanavalin A (ConA). 4',6-diamidino-2-phenylindole (DAPI) and carboxyfluoroscein succinimidyl ester (CSFE) were used as markers of cell viability and cell proliferation, respectively. Following 5-day culture, live cell counts and CSFE fluorescent intensity data were collected via automated cell count and flow cytometry. The experimental design was duplicated using preservative-free gentamicin and a proprietary brand formulation. Statistical analysis was performed using two-way ANOVA with Tukey's multiple comparison test.

RESULTS

No statistically significant comparisons in CD3+ T-lymphocyte live cell counts and geometric mean fluorescent intensity of CSFE were identified between gentamicin concentrations or formulations.

CONCLUSIONS

Gentamicin had no effect on equine peripheral blood CD3+ T-lymphocyte cell viability and proliferation in concentrations ranging from "safe" to "retinotoxic" in relation to intravitreal injection volumes. Low-dose intravitreal gentamicin may not suppress the Th1- and Th17-mediated immune response.

The Impact of Systemic Medications on Retinal Function

This study will provide a thorough review of systemic (and select intravitreal) medications, along with illicit drugs that are capable of causing various patterns of retinal toxicity. The diagnosis is established by taking a thorough medication and drug history, and then by pattern recognition of the clinical retinal changes and multimodal imaging features. Examples of all of these types of toxicity will be thoroughly reviewed, including agents that cause retinal pigment epithelial disruption (hydroxychloroquine, thioridazine, pentosan polysulfate sodium, dideoxyinosine), retinal vascular occlusion (quinine, oral contraceptives), cystoid macular edema/retinal edema (nicotinic acid, sulfa-containing medications, taxels, glitazones), crystalline deposition (tamoxifen, canthaxanthin, methoxyflurane), uveitis, miscellaneous, and subjective visual symptoms (digoxin, sildenafil). The impact of newer chemotherapeutics and immunotherapeutics (tyrosine kinase inhibitor, mitogen-activated protein kinase kinase, checkpoint, anaplastic lymphoma kinase, extracellular signal-regulated kinase inhibitors, and others), will also be thoroughly reviewed. The mechanism of action will be explored in detail when known. When applicable, preventive measures will be discussed, and treatment will be reviewed. Illicit drugs (cannabinoids, cocaine, heroin, methamphetamine, alkyl nitrite), will also be reviewed in terms of the potential impact on retinal function.

Infectious Uveitis in Horses and New Insights in Its Leptospiral Biofilm-Related Pathogenesis

Uveitis is a sight-threatening eye disease in equids known worldwide that leads to considerable pain and suffering. By far the most common type of uveitis in Germany and neighboring countries is classical equine recurrent uveitis (ERU), which is caused by chronic intraocular leptospiral infection and is the main cause of infectious uveitis in horses. Other infectious causes are extremely rare and are usually clinically distinguishable from ERU. ERU can be treated very effectively by vitreous cavity lavage (vitrectomy). For proper indications of this demanding surgery, it is necessary to differentiate ERU from other types of uveitis in which vitrectomy is not helpful. This can be conducted on the basis of anamnesis in combination with ophthalmologic findings and by aqueous humor examination. During vitrectomy, vitreous material is obtained. These vitreous samples have historically been used for numerous etiologic studies. In this way, a chronic intraocular leptospiral infection has been shown to be the cause of typical ERU and, among other findings, ERU has also been recognized as a biofilm infection, providing new insights into the pathogenesis of ERU and explaining some thus far unexplainable phenomena of ERU. ERU may not only have transmissible aspects to some types of uveitis in humans but may also serve as a model for a spontaneously occurring biofilm infection. Vitreous material obtained during therapeutically indicated vitrectomy can be used for further studies on in vivo biofilm formation, biofilm composition and possible therapeutic approaches.

Fungi of the human eye: Culture to mycobiome

The focus of the current review is multi-fold and compares the diversity and abundance of fungi on the ocular surface by the conventional culture-based method with the more sensitive, high throughput, culture-independent NGS method. The aim is to highlight the existence of a core ocular mycobiome and explore the transition of the ocular fungal microbiota from the normal eye to the diseased eye. PubMed, Google Scholar and Medline were used to search for publications and reviews related to cultivable fungi and the mycobiome of the normal and diseased eye. The conventional cultivable approach and the NGS approach confirm that the eye has its own mycobiome and several confounding factors (age, gender, ethnicity etc.) influence the mycobiome. Further, dysbiosis in the mycobiome appears to be associated with ocular diseases and thus impacts the health of the human eye. Considering that the mycobiome of the eye is influenced by several confounding factors and also varies with respect to the disease status of the eye there is a need to extensively explore the mycobiome under different physiological conditions, different ethnicities, geographical regions etc. Such studies would unravel the diversity and abundance of the mycobiomes and contribute to our understanding of ocular health. Research focused on ocular mycobiomes may eventually help to build a targeted and individualized treatment.

A non-invasive nanoparticle-based sustained dual-drug delivery system as an eyedrop for endophthalmitis

Endophthalmitis is an infectious disease that affects the entire eye spreading to the internal retinal layers and the vitreous and causes severe sight-threatening conditions. Current treatment strategies rely on intraocular injections of antibiotics that are invasive, may lead to procedural complications and, ultimately, blindness. In this study, we developed a non-invasive strategy as an eyedrop containing nanoparticle-based dual-drug delivery system in which the hydrophobic poly-L-lactide core was loaded with azithromycin or triamcinolone acetonide, and the hydrophilic shell was made of chitosan. The developed nanoparticles were ~200-250 nm in size, spherical in shape, moderately hydrophilic, lysozyme tolerant, cytocompatible, and hemocompatible. Application of these chitosan-coated nanoparticles as eye drops to C57BL/6 mice showed higher bioavailability in choroid and retina when compared to the uncoated nanoparticles. The delivery system showed sustained release of drug for 300 h and exhibited antimicrobial effects against Gram-positive and Gram-negative bacteria and anti-inflammatory effects on activated microglial cells. Interestingly, the combination of the nanoparticles loaded with azithromycin and the nanoparticles loaded with triamcinolone acetonide acted synergistically as compared to either of the nanoparticles/drugs alone. Overall, the developed dual-drug delivery system is non-invasive, has antimicrobial and anti-inflammatory effects, and shows potential as an eye drop formulation against endophthalmitis.

Development of an experimental model for ocular toxicity screening in Zebrafish

BACKGROUND

To investigate the efficacy of a novel experimental model for exploring visual function using a contrast-optomotor response (C-OMR) assay made by applying the contrast sensitivity test to the OMR assay in zebrafish.

METHODS

Zebrafish larvae were treated with 0 (control), 5, 10, or 15 μM gentamicin and digoxin for 24 h at four days post-fertilization (dpf). Zebrafish larvae were assessed using the C-OMR assay with graded contrast gray-white stripes at 5 dpf, and the results were expressed as the percentage of larvae that finished swimming for 30 s (n = 20 per each group). The same C-OMR assay was repeated four times using different larvae.

RESULTS

The percentage of larvae that finished swimming within 30 s was significantly reduced in larvae treated with 5, 10, and 15 μM gentamicin and 10 and 15 μM digoxin as compared to the Control groups. The C-OMR assay could distinguish that the decrease in visual function was different depending on the concentration of gentamicin and digoxin (5, 10, and 15 μM), whereas the OMR test with one contrast gray-white stripe could not.

CONCLUSIONS

The method of analyzing zebrafish OMR using graded contrast gray-white stripes is more sensitive than the OMR assay alone and may be more useful for assessing the drug toxicity and eye-related diseases to improve the understanding of drug-induced ocular side effects in the clinic.

Microbes of the human eye: Microbiome, antimicrobial resistance and biofilm formation

BACKGROUND

The review focuses on the bacteria associated with the human eye using the dual approach of detecting cultivable bacteria and the total microbiome using next generation sequencing. The purpose of this review was to highlight the connection between antimicrobial resistance and biofilm formation in ocular bacteria.

METHODS

Pubmed was used as the source to catalogue culturable bacteria and ocular microbiomes associated with the normal eyes and those with ocular diseases, to ascertain the emergence of anti-microbial resistance with special reference to biofilm formation.

RESULTS

This review highlights the genetic strategies used by microorganisms to evade the lethal effects of anti-microbial agents by tracing the connections between candidate genes and biofilm formation.

CONCLUSION

The eye has its own microbiome which needs to be extensively studied under different physiological conditions; data on eye microbiomes of people from different ethnicities, geographical regions etc. are also needed to understand how these microbiomes affect ocular health.

Tolerability Assessment of Formulation pH in New Zealand White Rabbits Following Intravitreal Administration

Development of intravitreal drugs presents several challenges due to the delicate ocular environment and volume constraints of what can be safely administered in the eye. Formulation development of intravitreally administered drugs may necessitate the use of nonphysiological pH in order to accommodate manufacturing processes or achieve favorable drug properties. Clinical and nonclinical data show that intravitreal drugs formulated in the pH 5.5 to 7.4 range are well tolerated. The aim of this study was to provide ocular toxicity data for formulations in the pH 4.0 to 5.5 range following intravitreal administration in New Zealand White rabbits. This range was evaluated as part of formulation development for an intravitreal drug that necessitated the use of pH outside the available tolerability data for formulations. Toxicity was assessed by ophthalmic examinations, intraocular pressure (IOP) measurement, clinical observations, body weights, and microscopic analysis of ocular tissue. Histidine chloride pH 5.0 to 5.5 and acetate chloride pH 4.0 to 5.0 solutions were well tolerated, and no test article-related ocular inflammation, IOP changes, or gross or microscopic findings were observed in any eye. The data presented here add to the knowledge of pH ranges that can be explored for intravitreal drug formulation development.

Exogenous endophthalmitis caused by Enterococcus casseliflavus: A case report

BACKGROUND

Endophthalmitis caused by Enterococci is rare, and cases involving vancomycin-resistant enterococci are even rarer. We report the first case of Enterococcus casseliflavus endophthalmitis associated with injury caused by a pig. We also review reported cases of exogenous endophthalmitis caused by Enterococcus casseliflavus and discuss the clinical management and prognosis of this disease.

CASE SUMMARY

A 43-year-old man with no previous visual problems complained of endophthalmitis in his left eye following injury caused by a pig. Visual acuity was light perception and B-ultrasonography revealed vitreous opacities with retinal detachment. He was treated with intravitreal vancomycin and ceftazidime after refusing vitrectomy. However, the vitreous opacities and retinal detachment deteriorated and he underwent vitrectomy 5 d post-injury. Intraoperatively, advanced rhegmatogenous and tractional retinal detachment with proliferative vitreoretinopathy were observed. On postoperative day 5, vitreous cultures grew Gram-positive cocci identified as Enterococcus casseliflavus. A 2-wk course of intravenous ampicillin and dexamethasone was commenced. On postoperative day 14, visual acuity improved to hand movement. At 6 mo post-injury, visual acuity improved to 20/667, but optic atrophy was present.

CONCLUSION

Systemic administration of linezolid in the treatment of Enterococcus casseliflavus endophthalmitis can improve visual acuity. However, intravitreal amikacin should be considered despite concerns of toxicity when oral linezolid fails to prompt improvement.

Recent Updates on Treatment of Ocular Microbial Infections by Stem Cell Therapy: A Review

Ocular microbial infection has emerged as a major public health crisis during the past two decades. A variety of causative agents can cause ocular microbial infections; which are characterized by persistent and destructive inflammation of the ocular tissue; progressive visual disturbance; and may result in loss of visual function in patients if early and effective treatments are not received. The conventional therapeutic approaches to treat vision impairment and blindness resulting from microbial infections involve antimicrobial therapy to eliminate the offending pathogens or in severe cases; by surgical methods and retinal prosthesis replacing of the infected area. In cases where there is concurrent inflammation, once infection is controlled, anti-inflammatory agents are indicated to reduce ocular damage from inflammation which ensues. Despite advances in medical research; progress in the control of ocular microbial infections remains slow. The varying level of ocular tissue recovery in individuals and the incomplete visual functional restoration indicate the chief limitations of current strategies. The development of a more extensive therapy is needed to help in healing to regain vision in patients. Stem cells are multipotent stromal cells that can give rise to a vast variety of cell types following proper differentiation protocol. Stem cell therapy shows promise in reducing inflammation and repairing tissue damage on the eye caused by microbial infections by its ability to modulate immune response and promote tissue regeneration. This article reviews a selected list of common infectious agents affecting the eye; which include fungi; viruses; parasites and bacteria with the aim of discussing the current antimicrobial treatments and the associated therapeutic challenges. We also provide recent updates of the advances in stem cells studies on sepsis therapy as a suggestion of optimum treatment regime for ocular microbial infections.

Successful management of post-traumatic vancomycin-resistant enterococcus endophthalmitis

PURPOSE

To highlight good visual outcome with intravitreal amikacin administered 18 days following trauma-inducing vancomycin resistant enterococcal endophthalmitis treated initially with vitrectomy and oral linezolid.

OBSERVATIONS

Despite initial vitrectomy, intravitreal vancomycin, ceftazidime and oral linezolid, smoldering vitreous infiltrates prompted treatment with intravitreal amikacin 18 days later and restored vision to 20/40 in a vancomycin-resistant traumatic endophthalmitis.

CONCLUSIONS AND IMPORTANCE

Good visual outcome was attained with intravitreal injection of amikacin 18 days following penetrating trauma and vancomycin resistant enterococcal endophthalmitis that smoldered following initial treatment of vitrectomy, intravitreal antibiotics and oral linezolid.

NOCARDIA CHOROIDAL ABSCESS: Risk Factors, Treatment Strategies, and Visual Outcomes

PURPOSE

To describe the risk factors, clinical course, ancillary test findings, treatment strategies, and visual outcomes of a series of patients with choroidal abscesses caused by endogenous Nocardia.

METHODS

This retrospective, consecutive noncomparative case series included all patients with Nocardia ocular infections at 3 tertiary medical centers over the past 20 years.

RESULTS

Five eyes in 5 patients were identified with choroidal abscesses because of Nocardia. All patients were immunocompromised: one suffered from AIDS and four had autoimmune disorders. Three of the 5 patients (60%) underwent systemic evaluation, and in all 3, nonocular nocardiosis was identified. Four patients (80%) underwent diagnostic ophthalmic surgery and received systemic and intravitreal antibiotics. The final patient deferred these interventions. Outcomes at the last follow-up examination were 20/25, 1/200, hand motion at 1 foot, and 2 patients underwent enucleation. Mean follow-up (± standard deviation) was 159 (± 103) days.

CONCLUSION

Immunosuppression is the most significant risk factor for developing Nocardia choroidal abscesses. Definitive diagnosis generally requires subretinal biopsy, which is also critical to implementing appropriate antibiotic therapy.

A case of aminoglycosides induced retinal toxicity treated with megadoses of steroids and an intravitreal dexamethasone implant (Ozurdex(®))

CASE REPORT

The case is described of a patient who had a sudden loss of vision in her right eye after glaucoma surgery. A diagnosis of retinal toxicity due to tobramycin (an aminoglycoside) was reached, which was characterised by retinal whitening with a red cherry stain, macular oedema, and vasculitis that progressed to papillary and macular atrophy with arteriolar sclerosis. Given the severity of symptoms an early attempt was made with megadoses of steroids and an intravitreal dexamethasone implant (Ozurdex®, Allergan S.A.), without response.

DISCUSSION

Aminoglycoside toxicity is a rare, idiosyncratic, very serious complication for which there is no effective treatment.

Exogenous endophthalmitis caused by Enterococcus casseliflavus: A case report and discussion regarding treatment of intraocular infection with vancomycin-resistant enterococci

Due to poor penetration of systemic or topical antibiotics into the vitreous chamber, treating endophthalmitis is challenging, especially in rare cases in which vancomycin-resistant enterococci are present. Caused by the unique mechanism of high-velocity water stream trauma, a case of exogenous endophthalmitis in a four-year-old-boy is discussed.

Endophthalmitis caused by enterococci is rare, and cases involving vancomycin-resistant enterococci are even more so. Due to the poor bioavailability of many antibiotics in the vitreous chamber, special considerations are required when choosing antibiotics to treat these infections. The authors report the first case of exogenous endophthalmitis caused by Enterococcus casseliflavus via the unique mechanism of high-velocity water stream trauma from a toy water gun.

A previously healthy four-year old boy presented with endophthalmitis of the left eye after injury from a water gun. Empirical treatment for endophthalmitis was started on presentation to the ophthalmologist. After the identification of the pathogen and a review of the literature, the antibiotic regimen was changed to include intravitreal ampicillin and amikacin with systemic linezolid.

Endophthalmitis caused by E casseliflavus and other vancomycin-resistant enterococci are challenging to treat. Rapid identification of vancomycin-resistant enterococcal endophthalmitis is important to guide appropriate antibiotic therapy. Systemic linezolid achieves excellent intravitreal concentrations, and should be used in combination with intravitreal and topical antibiotics.

Impact of changes in antibiotic prophylaxis on postoperative endophthalmitis in a Spanish hospital

OBJECTIVE

This study aims to assess whether changes in antibiotic prophylaxis used in cataract surgery in the La Mancha Centro General Hospital, Spain, were associated with a reduced incidence of postoperative endophthalmitis (POE).

METHODS

The hospital employed two different antibiotic prophylaxis regimens during two clearly differentiated periods. In the first period (January 2000 to April 2003), subconjunctival injections of gentamicin were used while in the second (May 2003 to December 2008), vancomycin and gentamicin were added to the irrigating solution. During both periods, povidone iodine was used at the site of surgery and aminoglycoside eye drops were administered postoperatively. A Poisson regression model was used to evaluate the relationship between the incidence rate of endophthalmitis and variables such as time trends, seasonality, and change in antibiotic prophylaxis regimen.

RESULTS

During the period between 2000 and 2008, 26 cases of POE were detected after 14,285 operations for an incidence rate (IR) of 1.8 cases per 1000 procedures (95% confidence interval 1.2-2.7 cases out of 1000 procedures). In the period prior to the change in prophylaxis, 23 cases were detected (IR 4.5 cases/1000 procedures) while only three cases were observed in the period after the change (IR 0.3 cases/1000 procedures). A total of 84% of the microorganisms isolated were gram-positive, and all were sensitive to vancomycin.

CONCLUSIONS

The change in antibiotic prophylaxis regimen for cataract surgery was associated with a relevant and significant decrease in the incidence of POE.

Early safety assessment of human oculotoxic drugs using the zebrafish visualmotor response

INTRODUCTION

Many prescribed drugs can adversely affect the eye by causing damage to the function of visual pathways or toxicity to the retina. Zebrafish have the potential to efficiently predict drugs with adverse ocular effects at pre-clinical stages of development. In this study, we explore the potential of using a semi-automated visual behaviour assay to predict drug-induced ocular toxicity in wild-type zebrafish larvae.

METHODS

3 dpf larvae were treated with six known oculotoxic drugs and five control drugs in embryo medium containing 0.1% DMSO. After 48 h, larvae were assessed using the visualmotor response (VMR), an assay which quantifies locomotor responses to light changes; the optokinetic response (OKR), a behavioural assay that quantifies saccadic eye responses to rotating stimuli; and the touch response, a locomotor response to tactile stimuli.

RESULTS

9 of 10 negative control drugs had no effect on zebrafish visual behaviour. 5 of the 6 known oculotoxic drugs (digoxin, gentamicin, ibuprofen, minoxidil and quinine) showed adverse effects on zebrafish visual behaviour assessed by OKR or the more automated VMR. No gross morphological changes were observed in treated larvae. The general locomotor activity of treated larvae, tested using the touch response assay, showed no differences with respect to controls. Overall the VMR assay had a sensitivity of 83%, a specificity of 100% and a positive predictive value of 100%.

DISCUSSION

This study confirms the suitability of the VMR assay as an efficient and predictive pre-clinical approach to evaluate adverse ocular effects of drugs on visual function in vivo.

Post-traumatic vancomycin-resistant enterococcal endophthalmitis

The emergence of antibiotic-resistant organisms among severe ocular infections is of grave concern. We describe the first reported case of vancomycin-resistant enterococcal endophthalmitis following ocular trauma, uniquely caused by Enterococcus gallinarum. The organism demonstrated intrinsic resistance to ceftazidime and vancomycin but responded favorably to a combination of intravitreal and intravenous ampicillin, plus intravitreal amikacin. When faced with a multidrug-resistant organism, the ophthalmologist must consider alternative antibiotic strategies.

Unanticipated vision loss after pars plana vitrectomy

Although advances in vitreoretinal surgical techniques and technology have helped to minimize the risks associated with surgical manipulation of the retina, retinal pigment epithelium, and optic nerve, unanticipated or unexplained visual loss still occurs. We review causes of vision loss encountered after pars plana vitrectomy, including retinal toxicities, vascular events, and optic neuropathies, and we suggest strategies to limit or prevent them.

Intravitreal gentamicin-induced macular infarction: SD-OCT features

A 75-year-old woman developed acute-onset endophthalmitis following phacoemulsification in the left eye. She was treated with intravitreal injections of vancomycin, ceftazidime, and gentamicin. The patient had persistent visual loss in the left eye after treatment. Her best-corrected visual acuity was 2/200 in the left eye and examination revealed a pale disc, retinal hemorrhages, and multiple nerve fiber layer infarcts. Fluorescein angiography showed retinal vascular non-perfusion in the macula. On spectral-domain optical coherence tomography (SD-OCT), there was diffuse retinal thinning, absence of the foveal depression, and increased reflectivity of the nerve fiber and ganglion cell layers, but with an intact inner segment/outer segment junction. This case demonstrates SD-OCT features in macular infarction following intravitreal gentamicin, specifically changes involving the inner retina with a relatively intact outer retina.

Solvent-free biodegradable scleral plugs providing sustained release of vancomycin, amikacin, and dexamethasone--an in vivo study

Delivering effective drugs at sufficiently high concentrations to the area of infection is a standard treatment for infectious disease, such as endophthalmitis. This is currently done by empirical trans pars plana intravitreal injection of both antibiotics directed against gram-positive and gram-negative microorganisms and steroids. However, injections by needles repeatedly may increase the risks of intraocular infection and hemorrhage, as well as retinal detachment. This article explores the alternative of using biodegradable polymers as scleral plugs for a long-term drug release in vivo. To manufacture plugs, poly(lactide-glycolide) copolymers were first mixed with vancomycin, amikacin, and dexamethasone. The mixture was compressed and sintered at 55 degrees C to form scleral plugs 1.4 mm in diameter. Biodegradable scleral plugs released high concentrations of antibiotics (well above the minimum inhibitory concentrations, MIC) and steroids in vivo for the period of time needed to treat intraocular infection. In addition, no major complications such as infectious or sterile endophthalmitis, retinal detachment, ocular phthisis, or uvea protrusion at sclerotomy site were observed throughout the experiment. The sclerotomy wound healed after total degradation of the scleral implants without leakage or local necrosis. Antibiotic/steroid-impregnated biodegradable scleral plugs may have a potential role in the treatment of various intraocular infections.

An overview on the toxic morphological changes in the retinal pigment epithelium after systemic compound administration

Many medications that are administered systemically for nonocular conditions may evoke ocular toxicological complications. Therefore, the eye is routinely investigated histopathologically in preclinical in vivo toxicity studies. The retinal pigment epithelium is a likely target for systemically administered compounds, since the underlying choroid is highly vascularized. The specialized pigment epithelium has numerous functions that all maintain the integrity and function of photoreceptors. Consequently, toxic effects on the pigment epithelium will eventually affect the neural retina. The potential of pigment epithelial cells to respond to toxic injury is limited, but a standardized terminology to describe its morphological changes does not exist in the scientific literature. Detailed morphologic analysis, however, might allow early detection of retinotoxicity and may provide evidence on the underlying pathomechanism. We here review toxic effects on the pigment epithelium focusing in particular on the morphology of toxic cell injury. Morphological changes comprise hypertrophy, intracytoplasmic accumulation of cellular components, loss of cell polarity, degeneration, metaplasia, and formation of subretinal membranes. Some of these changes are reversible whereas others are permanent, leading to impaired function of the pigment epithelium and eventually to photoreceptor loss and retinal atrophy.

Ocular drug delivery

Drug delivery to the eye is hampered by anatomical factors, including the corneal epithelium, the blood-aqueous barrier and the blood-retinal barrier. This review aims to outline the major routes of ocular drug delivery, including systemic, topical, periocular and intravitreal. The pharmacokinetics, the disadvantages and the clinical relevance of these drug delivery routes have been emphasised. Recent advances in surgical techniques, therapeutic approaches and material sciences have produced exciting new therapies for ocular diseases. The role of ophthalmic drug formulation in targeting the desired ocular tissue and enhancing drug delivery by the chosen route whilst minimising side effects is also discussed.

SUBCONJUNCTIVAL ANTIBIOTICS IN THE TREATMENT OF ENDOPHTHALMITIS MANAGED WITHOUT VITRECTOMY

PURPOSE

To determine if the treatment outcomes for endophthalmitis are influenced by subconjunctival antibiotics.

METHODS

A retrospective, nonrandomized consecutive series of patients with clinically diagnosed bacterial endophthalmitis confirmed with positive cultures who presented between December 1, 1995, and February 28, 2002, was studied. Patients with cataract surgery, glaucoma filtering blebs, or trauma who presented with visual acuity of hand motions or better were included. All patients received intravitreal and topical antibiotics. Management by pars plana vitrectomy or vitreous tap and use or nonuse of subconjunctival antibiotics were at the discretion of the treating physician.

RESULTS

There were 59 patients identified; 54 met the follow-up criteria. These patients were divided into two groups based on whether subconjunctival antibiotics were used (group ABX; n = 21) or not used (group noABX; n = 33). The median pretreatment visual acuity was hand motions in both groups. The median age in both groups was 74 years. Etiology, duration of symptoms, vitreous culture organisms, percentage of cases with wound complications such as leaks or vitreous incarceration, and intraocular lens type were similar in the two study groups. Intravitreal and topical antibiotics and corticosteroids used were not significantly different in the two groups, except that topical ceftazidime was used less frequently in group ABX than in group noABX (43% vs. 82%, respectively; P = 0.007). The median follow-up was 13 months in both groups (range: 3-87 months for group ABX and 3-63 months for group noABX). Final visual acuity in groups ABX and noABX was at least 20/50 (33% vs. 39%, respectively), 20/60 to 5/200 (29% vs. 39%, respectively), 4/200 to better than hand motions (0 vs. 3%, respectively), or hand motions or worse (38% vs. 18%, respectively). These differences were not significant (P = 0.37). Reinjection rates (14% vs. 15%, respectively) were also similar in groups ABX and noABX. The additional procedures rate was significantly higher in group ABX than in group noABX (P = 0.024), with cumulative rates of 33% and 3%, respectively, at the 12-month follow-up.

CONCLUSIONS

These data suggest that subconjunctival antibiotics may not be necessary to treat infectious endophthalmitis managed with otherwise standard tap and injection techniques and topical antibiotics.

Endogenous oxidoreductase expression is induced by aminoglycosides

Oxidoreductases such as glutaredoxin are a major class of enzymes that reversibly catalyze thiol-disulfide exchange reactions. Transfection experiments using geneticin (G418) selection to identify the specific protein S-thiolated substrates of glutaredoxin-1 (Grx-1) noted the curious phenomenon that nontransfected control cells treated with G418 had increased levels of Grx-1 expression. Varied concentrations of gentamicin, kanamycin, and hygromycin increased Grx-1 expression in a time- and dose-dependent fashion in human cultured retinal pigment epithelial cells. Reactive oxygen species formation after aminoglycoside exposure correlated directly to aminoglycoside treatment. Further indication that oxidation regulates Grx-1 expression was noted by the positive effect of phorbol 12-myristate 13-acetate, a known inducer of redox-sensitive AP-1 transcription factor. In agreement with this hypothesis was the finding that the physiologic reductant N-acetylcysteine decreased Grx-1 expression whereas tert-butyl hydroperoxide increased Grx-1 expression. Our data suggest that aminoglycosides increased Grx-1 expression in response to oxidative stress.

Evaluation of the cytotoxicity of selected systemic and intravitreally dosed drugs in the cultures of human retinal pigment epithelial cell line and of pig primary retinal pigment epithelial cells

The cytotoxicity of the selected systemic and intravitreally dosed drugs tamoxifen, toremifene, chloroquine, 5-fluorouracil, gentamicin and ganciclovir was studied in retinal pigment epithelium (RPE) in vitro. The cytotoxicity was assayed in the human RPE cell line D407 and the pig RPE cell culture using the WST-1 test, which is an assay of cell proliferation and viability. The effects of experimental conditions on the WST-1 test (cell density, serum content in the culture medium, the exposure time) were evaluated. The EC50 values in tamoxifen-treated D407 cells ranged between 6.7 and 8.9 micromol/l, and in pig RPE cells between 10.1 and 12.2 micromol/l, depending on the cell density used. The corresponding values for toremifene were 7.4 to 11.1 micromol/l in D407 cells and 10.0 to 11.6 micromol/l in pig RPE cells. In chloroquine-treated cells, the EC50 values were 110.0 micromol/l for D407 cells and 58.4 micromol/l for pig RPE cells. Gentamicin and ganciclovir did not show any toxicity in micromolar concentrations. The exposure time was a significant factor, especially when the drug did not induce cell death, but was antiproliferative (5-fluorouracil). Serum protected the cells from the toxic effects of the drugs. Both cell cultures were most sensitive to tamoxifen and toremifene, and next to chloroquine. The drug toxicities obtained in the present study were quite similar in both cell types; that is, the pig RPE cells and the human D 407 cell line, despite the differences in, for example, the growth rate and melanin contents of the cell types. Owing to the homeostatic functions important for the whole neuroretina, RPE is an interesting in vitro model for the evaluation of retinal toxicity, but, in addition to the WST-1 test, more specific tests and markers based on the homeostatic functions of the RPE are needed.

Bacterial endophthalmitis prophylaxis for cataract surgery: an evidence-based update

PURPOSE

To assess commonly used cataract surgery bacterial endophthalmitis prophylaxis techniques based on a systematic literature review and evidence rating.

CLINICAL RELEVANCE

Prophylactic techniques to decrease the risk of bacterial endophthalmitis related to cataract surgery are commonly used, but the evidence justifying their use is unclear.

LITERATURE REVIEWED

A MEDLINE search of the literature published in English or with English abstracts from 1966 to 2000 was performed using various combinations of relevant key words. Eighty-eight peer-reviewed papers were identified and judged worthy of review on the basis of predefined criteria.

RESULTS

No prophylactic technique received the highest of three possible clinical recommendations (A, crucial to clinical outcome). Preoperative povidone-iodine preparation received the intermediate clinical recommendation (B, moderately important to clinical outcome). All other reported prophylactic interventions, including postoperative subconjunctival antibiotic injection, preoperative lash trimming, preoperative saline irrigation, preoperative topical antibiotics, antibiotic-containing irrigating solutions, and the use of intraoperative heparin, received the lowest clinical recommendation (C, possibly relevant but not definitely related to clinical outcome) based on weak and often conflicting evidence justifying their use.

CONCLUSIONS

With regard to bacterial endophthalmitis prophylaxis in cataract surgery, current literature most strongly supports the use of preoperative povidone-iodine antisepsis.

Bacterial endophthalmitis: epidemiology, therapeutics, and bacterium-host interactions

Endophthalmitis is a severe inflammation of the interior of the eye caused by the introduction of contaminating microorganisms following trauma, surgery, or hematogenous spread from a distant infection site. Despite appropriate therapeutic intervention, bacterial endophthalmitis frequently results in visual loss, if not loss of the eye itself. Although the pathogenicity of bacterial endophthalmitis has historically been linked with toxin production during infection, a paucity of information exists as to the exact mechanisms of retinal toxicity and the triggers for induction of the intraocular immune response. Recently, research has begun to examine the bacterial and host molecular and cellular events that contribute to ocular damage during endophthalmitis. This review focuses on the causative agents and therapeutic challenges of bacterial endophthalmitis and provides current data from the analysis of the role of bacterial virulence factors and host inflammatory interactions in the pathogenesis of eye infections. Based on these and related studies, a hypothetical model for the molecular pathogenesis of bacterial endophthalmitis is proposed. Identifying and understanding the basic mechanisms of these bacterium-host interactions will provide the foundation for which novel, information-based therapeutic agents are developed in order to prevent vision loss during endophthalmitis.

Effects of intraocular cefotaxime on the human corneal endothelium

PURPOSE

To ascertain whether 0.4 mL of cefotaxime 0.25% applied intracamerally causes toxic alteration of the human corneal endothelium.

METHODS

In this prospective randomized masked study, 66 patients had cataract extraction using phacoemulsification, a frown incision, and implantation of a poly(methyl methacrylate) intraocular lens. This was followed by intraocular injection of 0.4 mL of cefotaxime 0.25% or balanced salt solution (BSS(R)). Contact specular microscopy and photography were performed preoperatively and 1 to 4 days and 3 months postoperatively.

RESULTS

In the cefotaxime group, the mean endothelial cell count was 2729 cells/mm(2) +/- 474 (SD) preoperatively, 2520 +/- 462 cells/mm(2) 1 to 4 days postoperatively, and 2560 +/- 495 cells/mm(2) 3 months postoperatively. The mean endothelial cell count in the BSS (control) group was 2657 +/- 413 cells/mm(2), 2475 +/- 384 cells/mm(2), and 2486 +/- 427 cells/mm(2), respectively. There was no significant difference in cell count or morphology between groups (P <.05).

CONCLUSIONS

Intraocular application of cefotaxime produced no significant changes in endothelial cell count or morphology when compared with application of a control substance. With its broad spectrum of antibiotic activity, cefotaxime might be an appropriate alternative to other intraocularly administered antibiotics in anterior segment surgery for prophylaxis and management of infection.

Retinal toxicity of liposome-incorporated and free ofloxacin after intravitreal injection in rabbit eyes

BACKGROUND

Ofloxacin (OFLX) is a fluoroquinolone-antibiotic with a broad antimicrobial spectrum that may have a potential role in the treatment of bacterial endophthalmitis. However, its elimination half life after intravitreal injection is short. To prolong the intravitreal antibacterial level OFLX was incorporated into liposomes. This study was performed to investigate the retinal toxicity of liposome-incorporated and free OFLX.

MATERIALS AND METHODS

OFLX was incorporated into multilamellar large vesicles. 0.1 ml of this suspension (= 180.2 microg OFLX) was injected into the midvitreous of rabbit eyes (n = 6). Free OFLX in doses of 100 microg, 500 microg and 1,000 microg was injected into the midvitreous of a second group of rabbit eyes (n = 18). The other eye served as a control and received empty liposomes or normal saline solution, respectively. Before injection and at the end of follow-up an ERG was obtained. After a follow-up of 1 day, 14 and 28 days the animals were perfused with glutaraldehyde and the eyes were examined by light- and transmission electron microscopy.

RESULTS

The ERG as well as the histologic studies did not reveal any pathological changes after injection of liposome-incorporated OFLX compared to the control eyes. Significant reduction of the ERG was observed after 500 microg free OFLX in 2 out of 6 eyes after 1 and 14 days, respectively, and in 2 eyes 1 day after 1,000 microg free OFLX. Three days after injection of 1,000 microg OFLX the retina showed focal destruction in 1 out of 6 eyes. In another eye with the same dose 14 days after injection the photoreceptor outer segments showed disorganisation.

CONCLUSION

This study shows that liposome-incorporated OFLX did not have any retinal toxicity in this animal model. Free OFLX appears to have no retinal toxicity in rabbit eyes at a dose of 100 microg after intravitreal injection. Injection of higher doses resulted in ERG changes and marked retinal damage.

Controversies in the management of open-globe injuries involving the posterior segment

There are numerous unresolved issues and controversies regarding the management of open-globe injuries involving the posterior segment. These areas include, but are not limited to, the following issues. Although vitrectomy has been shown to improve visual outcomes and allow retention of the eye in many cases, the extent of visual improvement is often limited because of the nature of the injury. Timing of vitrectomy surgery has been and will continue to be debated by proponents of early versus delayed intervention. The multiple features of acute ocular injury make it very difficult to interpret retrospective data regarding the most appropriate timing for surgical intervention. The use of prophylactic cryotherapy, in the setting of a scleral laceration with possible retinal damage, is not as controversial at present, as there is now sufficient data indicating that cryotherapy may actually exacerbate intraocular proliferation and worsen the situation. The role and benefit of a prophylactic scleral buckle is very widely contested, and it is not known if it truly decreases the risk of subsequent retinal detachment. Another area of debate centers on the use of antibiotics. When there is a known clinical infection, intravitreal antibiotics are the mainstays of therapy. However, in the absence of clinical infection, the use of prophylactic antibiotics and their routes of administration are quite controversial. Although there are significant data regarding the use of antibiotics in the postoperative setting, this information cannot be extrapolated into the setting of open-globe injuries, as organisms and virulence factors differ. Similarly, the use of vitrectomy versus vitreous tap in the setting of traumatic endophthalmitis is not fully resolved, although vitrectomy is used in most cases to repair concurrent damage from the injury itself. Finally, the placement of intraocular lenses in the acute trauma setting is controversial, as the risk of complications is quite high. Prospective, controlled clinical studies have not been done. This article reviews pertinent data regarding these management issues and controversies, and provides recommendations for treatment based on the available published data and the authors' personal experience.

Endophthalmitis

Endophthalmitis is an inflammatory reaction of intraocular fluids or tissues. Infectious endophthalmitis is one of the most serious complications of ophthalmic surgery. Occasionally, infectious endophthalmitis is the presenting feature of an underlying systemic infection. Successful management of infectious endophthalmitis depends on timely diagnosis and institution of appropriate therapy. Recognition of the different clinical settings in which endophthalmitis occurs and awareness of the highly variable presentation it may have facilitate timely diagnosis. Biopsy of intraocular fluid/tissue is the only method that permits reliable diagnosis and treatment. The different presenting clinical settings, a rational approach to diagnosis (i.e., when, what, and how to biopsy), and the treatment of infectious endophthalmitis are reviewed.

Acanthamoeba keratitis in New Zealand, including two cases with in vivo resistance to polyhexamethylene biguanide

BACKGROUND

Acanthamoeba keratitis is an uncommon corneal infection that can run a protracted course with, at times, serious visual results. Eighty-five per cent of cases occur in soft contact lens wearers. The first New Zealand case occurred in 1990 and only seven cases have been identified in New Zealand to the end of 1996.

METHODS

We surveyed the ophthalmologists looking after these seven cases of acanthamoeba keratitis as to time to diagnosis, treatment and outcome.

RESULTS

New Zealand has a low incidence of this disease. All cases were soft contact lens wearers with defective care in every instance. After an initial two late-diagnosed cases, the time to diagnosis for four of the five other cases has been within 2 weeks. Medical treatment has varied over this series, but since the introduction of the cationic antiseptics polyhexamethylene biguanide (PHMB) and chlorhexidine in 1992, the last five cases were all treated with PHMB. One case diagnosed within 2 weeks ran a devastating course, despite intensive PHMB, and a second case remained culture positive after 1 year of PHMB and the late addition of chlorhexidine. Debridement, 0.1% PHMB and hexamidine eventually settled this eye.

CONCLUSIONS

For treatment PHMB, hexamidine rather than propamidine and surgical debridement are favoured. While all Acanthamoeba isolates show good in vitro sensitivity to PHMB, the in vivo response is not always proportionate. A bacterial endosymbiont may have been a factor in the favourable outcome of one protracted case.

Antibiotic selection in the treatment of endophthalmitis: the significance of drug combinations and synergy

Emerging resistance of organisms to standard antibiotic therapy has forced clinicians to continually evaluate the best intraocular antibiotics for the treatment of endophthalmitis. Early diagnosis and appropriate treatment with intraocular antibiotics are important factors in the successful management of endophthalmitis. Although drug combinations are necessary to cover the full range of bacteria causing endophthalmitis, antimicrobial synergy is probably less important in endophthalmitis treatment because of the high intravitreal concentration of individual antibiotics achieved by intravitreal injection. In the treatment of bacterial endophthalmitis, the combination of intravitreal vancomycin (1 mg/0.1 cc) and ceftazidime (2.25 mg/ 0.1 cc) is a reasonable alternative to the combination vancomycin and amikacin (0.4 mg/ 0.1 cc).

Experimental Bacillus cereus post-traumatic endophthalmitis and treatment with ciprofloxacin

BACKGROUND

Bacillus species remain an important cause of post-traumatic endophthalmitis, often causing permanent visual loss.

METHODS

Twenty two rabbits were used to evaluate the clinical and histological findings of Bacillus cereus experimental post-traumatic endophthalmitis. Eyes that had received a scleral laceration and surgical repair were inoculated with Bacillus cereus. Thirty four other rabbits were used to evaluate the efficacy of intravitreal ciprofloxacin in treating experimental disease.

RESULTS

Animals developed a post-traumatic endophthalmitis that closely mimicked human disease, characterised by a rapidly progressive and destructive endophthalmitis. Histological evaluation revealed retinal detachment, retinal necrosis, and the infiltration of inflammatory cells into the subretinal space. Intravitreal ciprofloxacin (100 micrograms) prevented the development of disease when given 1 hour and 6 hours after trauma and inoculation.

CONCLUSIONS

Clinical and histological examination of experimental Bacillus cereus post-traumatic endophthalmitis suggests that retinal detachment and retinal necrosis play important roles in visual loss. Ciprofloxacin may be of benefit in the management of certain intraocular infections following penetrating injury.

Macula toxicity after intravitreal amikacin

BACKGROUND

Although intravitreal aminoglycosides have substantially improved visual prognosis in endophthalmitis, macular infarction may impair full visual recovery.

METHODS

We present a case of presumed amikacin retinal toxicity following treatment with amikacin and vancomycin for alpha-haemolytic streptococcal endophthalmitis.

RESULTS

Endophthalmitis resolved with improvement in visual acuity to 6/24 at three months. Fundus fluorescein angiography confirmed macular capillary closure and telangiectasis.

CONCLUSIONS

Currently accepted intravitreal antibiotic regimens may cause retinal toxicity and macular ischaemia. Treatment strategies aimed at avoiding retinal toxicity are discussed.

Vitreous disposition of two acycloguanosine antivirals in the albino and pigmented rabbit models: a novel ocular microdialysis technique

A novel ocular microdialysis-perfusion technique was developed that allowed for the continuous sampling of the vitreous humor for drug. The technique produced accurate and rapid vitreous drug concentration time profiles with a resolution of 20 minutes on the time axis. The vitreous elimination of ganciclovir (GCV) and acyclovir (ACV) was extremely rapid, having vitreous half lives of 2.62 and 2.98 hours, respectively, and a transretinal mechanism of clearance was established for these compounds. Further, it was shown that the compounds do not exhibit saturation kinetics over the dosage ranges used in the clinical setting. Ocular pigmentation had a dramatic effect on the vitreous pharmacokinetics of GCV and ACV. The rate of elimination of GCV and ACV from the vitreous of the pigmented rabbit was much slower than the elimination from the albino rabbit (t 1/2 = 5.59 vs. 2.62 for GCV and 8.63 vs. 2.98 for ACV). The mean residence time of GCV was 2 times greater in the pigmented rabbit than in the albino rabbit and 3 times greater for ACV. Further, the volumes of distribution increased by 3.5 fold for GCV and 6.2 fold for ACV, respectively.