Besifloxacin ophthalmic suspension 0.6% in the treatment of bacterial keratitis: a retrospective safety surveillance study

Corneal gene therapy: Structural and mechanistic understanding

Cornea, a dome-shaped and transparent front part of the eye, affords 2/3rd refraction and barrier functions. Globally, corneal diseases are the leading cause of vision impairment. Loss of corneal function including opacification involve the complex crosstalk and perturbation between a variety of cytokines, chemokines and growth factors generated by corneal keratocytes, epithelial cells, lacrimal tissues, nerves, and immune cells. Conventional small-molecule drugs can treat mild-to-moderate traumatic corneal pathology but requires frequent application and often fails to treat severe pathologies. The corneal transplant surgery is a standard of care to restore vision in patients. However, declining availability and rising demand of donor corneas are major concerns to maintain ophthalmic care. Thus, the development of efficient and safe nonsurgical methods to cure corneal disorders and restore vision in vivo is highly desired. Gene-based therapy has huge potential to cure corneal blindness. To achieve a nonimmunogenic, safe and sustained therapeutic response, the selection of a relevant genes, gene editing methods and suitable delivery vectors are vital. This article describes corneal structural and functional features, mechanistic understanding of gene therapy vectors, gene editing methods, gene delivery tools, and status of gene therapy for treating corneal disorders, diseases, and genetic dystrophies.

Host-microbe interactions in cornea

Corneal infections result through interaction between microbes and host innate immune receptors. Damage to the cornea occurs as a result of microbial virulence factors and is often exacerbated by lack of a controlled host immune response; the latter contributing to bystander damage to corneal structure. Understanding mechanisms involved in host microbial interactions is critical to development of novel therapeutic targets, ultimate control of microbial pathogenesis, and restoration of tissue homeostasis. Studies on these interactions continue to provide exciting findings directly related to this ultimate goal.

Novel Drug Delivery Systems to Improve the Treatment of Keratitis

Keratitis is a disease characterized by inflammation of the cornea caused by different pathogens. It can cause serious visual morbidity if not treated quickly. Depending on the pathogen causing keratitis, eye drops containing antibacterial, antifungal, or antiviral agents such as besiloxacin, moxifloxacin, ofloxacin, voriconazol, econazole, fluconazole, and acyclovir are used, and these drops need to be applied frequently due to their low bioavailability. Studies are carried out on formulations with extended residence time in the cornea and increased permeability. These formulations include various new drug delivery systems such as inserts, nanoparticles, liposomes, niosomes, cubosomes, microemulsions, in situ gels, contact lenses, nanostructured lipid carriers, carbon quantum dots, and microneedles. Ex vivo and in vivo studies with these formulations have shown that the residence time of the active substances in the cornea is prolonged, and their ocular bioavailability is increased. In addition, in vivo studies have shown that these formulations successfully treat keratitis. However, it has been observed that fluoroquinolones are used in most of the studies; similar drug delivery systems are generally preferred for antifungal drugs, and studies for viral and acanthameba keratitis are limited. There is a need for new studies on different types of keratitis and different drug active substances. At the same time, proving the efficacy of drug delivery systems, which give promising results in in vivo animal models, with clinical studies is of great importance for progress in the treatment of keratitis.

In Vitro Antibiotic Resistance among Bacteria from the Cornea in the Antibiotic Resistance Monitoring in Ocular MicRoorganisms Surveillance Study

PURPOSE

This study aimed to report on in vitro susceptibility patterns among corneal isolates collected in the Antibiotic Resistance Monitoring in Ocular micRoorganisms (ARMOR) study.

METHODS

Each year, from 2009 to 2019, Staphylococcus aureus, coagulase-negative staphylococci (CoNS), Streptococcus pneumoniae, Pseudomonas aeruginosa, and Haemophilus influenzae isolates cultured from patients with ocular infections at participating ARMOR sites were submitted to a central laboratory for species confirmation and antibiotic susceptibility testing. In this analysis of corneal isolates, odds ratios for concurrent resistance were based on sample proportions, one-way ANOVA was used to evaluate resistance by patient age, and Cochran-Armitage tests were used to examine changes in antibiotic resistance over time.

RESULTS

A total of 1499 corneal isolates were collected from 61 sites over the 11-year period. Overall, 34.5% (148 of 429) of S. aureus and 41.9% (220 of 525) of CoNS isolates were methicillin resistant and had higher odds ratios for concurrent resistance to azithromycin (17.44 and 5.67), ciprofloxacin (39.63 and 12.81), and tobramycin (19.56 and 19.95), respectively, relative to methicillin-susceptible isolates (P < .001, all); also, a high proportion of methicillin-resistant S. aureus (85.1%) and methicillin-resistant CoNS (81.8%) were multidrug resistant (at least three classes of antibiotics). Resistance among S. pneumoniae isolates was highest for azithromycin (33.1%), whereas P. aeruginosa and H. influenzae isolates demonstrated low resistance overall. Among staphylococci, antibiotic resistance differed by patient age (S. aureus: F = 6.46, P < .001; CoNS: F = 4.82, P < .001), and few small changes in resistance (≤3.60% per year), mostly decreases, were observed over time.

CONCLUSIONS

Although rates of in vitro antibiotic resistance among presumed keratitis isolates obtained in ARMOR seemed stable between 2009 and 2019, resistance among staphylococci and pneumococci remains high (and should be considered when treating keratitis).

Corneal neovascularization

The optical clarity of the cornea is essential for maintaining good visual acuity. Corneal neovascularization, which is a major cause of vision loss worldwide, leads to corneal opacification and often contributes to a cycle of chronic inflammation. While numerous factors prevent angiogenesis within the cornea, infection, inflammation, hypoxia, trauma, corneal degeneration, and corneal transplantation can all disrupt these homeostatic safeguards to promote neovascularization. Here, we summarize its etiopathogenesis and discuss the molecular biology of angiogenesis within the cornea. We then review the clinical assessment and diagnostic evaluation of corneal neovascularization. Finally, we describe current and emerging therapies.

Treatment-Resistant Bacterial Keratitis: Challenges and Solutions

Bacterial keratitis is an important ophthalmic emergency and one of the most common causes of corneal blindness. The main causes of treatment resistance in bacterial keratitis are failure to eliminate predisposing factors, misdiagnosis and mistreatment. At first, exogenous, local and systemic predisposing factors that disturbing ocular surface must be eliminated to improve corneal ulcers and to prevent recurrences. Smears and scrapings for staining and culture are indispensable diagnostic tools for cases of sight-threatening keratitis (centrally located, multifocal, characterized by melting, painful). Main treatment agents in bacterial keratitis treatment are topical antibiotics. Until the results of culture antibiograms reach the ophthalmologist, empirical antibiotic selections based on direct microscopic examination and gram stain findings are the most appropriate initial treatment approach currently. S. aureus and coagulase-negative staphylococci (CoNS), the most common gram-positive agents, have resistance rates of more than 30% for fluoroquinolone and methicillin. Multidrug resistance rates are similarly high in these microorganisms. P. aeruginosa is the most common gram-negative micro-organism, in case of multidrug-resistant isolates, both functional and anatomical prognosis of the eyes are very poor. In cases of sight-threatening and resistant keratitis, antibiotic susceptibility testing containing imipenem, colistin, and linezolid is seeming to be an important requirement. Despite its efficiency limited to superficial cases, a nonpharmaceutical anti-infective treatment option such as corneal crosslinking for bacterial keratitis is an emerging hope, while antibiotic resistance increases.

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Challenges of corneal infections

INTRODUCTION

Ocular infections remain an important cause of blindness worldwide and represent a challenging public health concern. In this regard, microbial keratitis due to fungal, bacterial, or viral infection can result in significant vision loss secondary to corneal scarring or surface irregularity. Left untreated corneal perforation and endophthalmitis can result, leading to loss of the eye. Rigorously studied animal models of disease pathogenesis have provided novel information that suggests new modes of treatment that may be efficacious clinically and emerging clinical data is supportive of some of these discoveries.

AREAS COVERED

This review focuses on advances in our understanding of disease pathogenesis in animal models and clinical studies and how these relate to improved clinical treatment. We also discuss a novel approach to treatment of microbial keratitis due to infection with these bacterial pathogens using PACK-CXL and recommend increased basic and clinical studies to address and refine the efficacy of this procedure.

EXPERT COMMENTARY

Because resistance to antibiotics has developed over time to these bacterial pathogens, caution must be exercised in treatment. Attractive novel modes of treatment that hold new promise for further investigation include lipid based therapy, as well as use of small molecules that bind deleterious specific host responsive molecules and use of microRNA based therapies.

Besifloxacin: Efficacy and Safety in Treatment and Prevention of Ocular Bacterial Infections

This comprehensive review summarizes the mechanism of action, pharmacokinetics, efficacy, and safety of besifloxacin ophthalmic suspension, 0.6% and examines its role in the treatment of ocular surface bacterial infections. Besifloxacin possesses balanced activity against bacterial topoisomerase II (also called DNA gyrase) and topoisomerase IV. It has shown a low potential to select for bacterial resistance in vitro and demonstrated strong in vitro activity against many Gram-positive, Gram-negative, and anaerobic organisms, including methicillin-resistant Staphylococcus aureus and Staphylococcus epidermidis (MRSA and MRSE, respectively). Ocular pharmacokinetic studies have shown that besifloxacin achieves high, sustained concentrations in the tear fluid and conjunctiva following topical administration, with negligible systemic exposure. Large randomized, controlled clinical trials have established the efficacy and safety of besifloxacin administered three times daily for 5 days for treatment of acute bacterial conjunctivitis in both adults and children, with high rates of clinical resolution (up to more than 70% by day 5) and bacterial eradication (more than 90% by day 5), and a low incidence of adverse events. Additionally, besifloxacin applied twice daily for 3 days demonstrated greater efficacy than vehicle in treating bacterial conjunctivitis. Case reports, a large retrospective chart review, and animal studies have provided supporting evidence for the efficacy of besifloxacin in the management of acute bacterial keratitis. There is some evidence to suggest that besifloxacin may provide an advantage over other current-generation fluoroquinolones in antimicrobial prophylaxis for ocular surgery. Besifloxacin is an appropriate option for treatment of bacterial conjunctivitis, and its use in the treatment of bacterial keratitis and lid disorders, as well as for surgical prophylaxis, appears promising and warrants further evaluation.

Besifloxacin in the management of bacterial infections of the ocular surface

Acute bacterial conjunctivitis is a common infection of the ocular surface. Increasing rates of bacterial resistance have prompted the development of new antibiotics with improved activity against the bacterial species most often found in this disease. Besifloxacin is the first topical chlorofluoroquinolone developed solely for ophthalmic use. Studies have attested to its in vitro potency against a broad range of bacteria, as well as its efficacy in clinical studies of bacterial conjunctivitis when dosed 2 or 3 times a day. This review provides an up-to-date summary of studies on causative pathogens in acute bacterial conjunctivitis; recent geographic trends in bacterial resistance among ocular pathogens, including that of methicillin-resistant Staphylococcus aureus; the efficacy of besifloxacin in preclinical and clinical studies; its safety; and the role of besifloxacin in combating resistant strains. Further, this review provides a brief update on bacterial keratitis, causative pathogens, the development of resistance among those pathogens, and the potential role of besifloxacin in the treatment of bacterial keratitis.