Fluoroquinolones: mechanism of action, classification, and development of resistance

[In vitro antibiotic susceptibility to fluoroquinolones]

OBJECTIVE

To determine the antibiotic susceptibility of bacteria recovered from cultures of ocular infections in the Fundación Oftalmológica de Santander - Clínica Carlos Ardila Lulle (FOSCAL).

MATERIALS AND METHODS

Retrospective descriptive study of a series of registries of cultures of samples from ocular surfaces and intraocular fluids from the OCULAB-FOSCAL laboratory in Floridablanca (Colombia) made between January and December of 2007. Antibiotic sensitivity screening by the method of Kirby-Bauer with impregnated Sensi-Discs™ of determined antibiotic concentrations was performed.

RESULTS

A total of 352 samples were studied: 160 from conjunctiva, 150 from cornea and 42 from intraocular fluids. Of the total of the samples more than one microorganism was recovered 45.65% of the samples. Gram positive and Gram negative bacteria were identified in 78.7 and 18.4%, respectively. Resistance to gatifloxacin, moxifloxacin, ciprofloxacin and levofloxacin was observed in 6.3, 8.9, 33.2 and 35.6%, respectively, of Gram positive bacteria. Resistance to gatifloxacin, moxifloxacin, ciprofloxacin and levofloxacin was also observed in 7.4, 16.7, 16.7%and 25.9%, respectively, of Gram negative bacteria. The overall bacterial resistance (Gram positive and Gram negative) to moxifloxacin was 10.15%, and to gatifloxacin it was 6.46%, being which showed a statistically significant difference (P<.05).

CONCLUSIONS

In our study the development of bacterial resistance to fourth generation fluoroquinolones was demonstrated in ocular samples. However, lower levels of resistance to fourth generation fluoroquinolones compared with that of third and second generation were found, particularly to Gram positive. Gatifloxacin showed lower resistance levels than moxifloxacin. Nevertheless, interpretation of this superiority must be made with caution in the clinical field, since other factors, like tissue penetration and in vivo activity, must be taken into account.

Formulation and evaluation of micro hydrogel of Moxifloxacin hydrochloride

The field of ocular drug delivery is one of the interesting and challenging endeavors facing the pharmaceutical scientist. Novel approaches for ophthalmic drug delivery need to be established to increase the ocular bioavailability by overcoming the inherent drawbacks of conventional dosage forms. In situ hydrogels are instilled as drops into the eye and undergoes a sol-to-gel transition in the cul-de-sac, improved ocular bioavailability by increasing the duration of contact with corneal tissue, thereby reducing the frequency of administration. The purpose of the present work was to develop an ophthalmic drug delivery system using three different gelling agents with different mechanisms for in situ gelation of Moxifloxacin hydrochloride, a fluoroquinolone antibiotic. polyox (a pH-sensitive gelling agent), sodium alginate (an ion-sensitive gelling agent), and poloxamer (a temperature-sensitive gelling agent) were employed for the formation of in situ hydrogel along with HPMC K4M as viscofying agent, which increases the residence time of the drug in the ocular cavity. The promising formulations MF(4), MF(5), and MF(9) were evaluated for pH, drug content, in vitro gelation, in vitro drug release, in vivo drug release, ocular irritation, and stability. Percent drug content of 98.2, 98.76, and 99.43%; viscosity of 15.724 × 100, 16.108 × 100, and 15.213 × 100 cP at 20 rpm, cumulative percent release of 75.364, 74.081, and 71.752%, and C (max) of 1,164.16, 1,187.09, and 1,220.58 ng/ml was observed for formulation MF(4), MF(5), and MF(9), respectively. The developed formulations were therapeutically efficacious, stable, and non-irritant and provided sustained release of the drug over 8 h.

Quinolones: review of psychiatric and neurological adverse reactions

Quinolones are a class of antibacterial agents for the treatment of several infectious diseases (e.g. urinary and respiratory tract infections). They are used worldwide due to their broad spectrum of activity, high bioavailability and good safety profile. The safety profile varies from quinolone to quinolone. The aim of this article was to review the neurological and psychiatric adverse drug reaction (ADR) profile of quinolones, using a literature search strategy designed to identify case reports and case series. A literature search using PubMed/MEDLINE (from inception to 31 October 2010) was performed to identify case reports and case series related to quinolone-associated neurological and psychiatric ADRs. The search was conducted in two phases: the first phase was the literature search and in the second phase relevant articles were identified through review of the references of the selected articles. Relevant articles were defined as articles referring to adverse events/reactions associated with the use of any quinolone. Abstracts referring to animal studies, clinical trials and observational studies were excluded. Identified case reports were analysed by age group, sex, active substances, dosage, concomitant medication, ambulatory or hospital-based event and seriousness, after Medical Dictionary for Regulatory Activities (MedDRA®) coding. From a total of 828 articles, 83 were identified as referring to nervous system and/or psychiatric disorders induced by quinolones. 145 individual case reports were extracted from the 83 articles. 40.7% of the individual case reports belonged to psychiatric disorders only, whereas 46.9% related to neurological disorders only. Eight (5.5%) individual case reports presented both neurological and psychiatric ADRs. Ciprofloxacin, ofloxacin and pefloxacin were the quinolones with more neurological and psychiatric ADRs reported in the literature. Ciprofloxacin has been extensively used worldwide, which may explain the higher number of reports, while for ofloxacin and pefloxacin, the number of reports may be over-representative. A total of 232 ADRs were identified from the selected articles, with 206 of these related to psychiatric and/or neurological ADRs. The other 26 were related to other body systems but were reported together with the reactions of interest. Mania, insomnia, acute psychosis and delirium were the most frequently reported psychiatric adverse events; grand mal convulsion, confusional state, convulsions and myoclonus were the most frequently reported neurological adverse events. Several aspects should be taken into account in the development of CNS adverse effects, such as the pharmacokinetics of quinolones, chemical structure and quinolone uptake in the brain. These events may affect not only susceptible patients but also 'healthy' patients.

Design, synthesis and antibacterial activity of fluoroquinolones containing bulky arenesulfonyl fragment: 2D-QSAR and docking study

Here in, we report the design, synthesis, and antibacterial activity of series of bulky arenesulfonamido derivatives using ciprofloxacin and norfloxacin as scaffolds. All the synthesized compounds were investigated in vitro for their antibacterial activities against two Gram-positive and two Gram-negative organisms using dilution broth method. Among the tested compounds examined, compounds 3-7 showed significance difference from the standard drug ciprofloxacin. 2D-QSAR study provides details on the fine relationship linking structure and activity and offers clues for structural modifications that can improve the activity. Docking study of the compound 3b into the active site of the topoisomerase II DNA-gyrase enzymes revealed a similar binding mode to ciprofloxacin with additional classical and nonclassical hydrogen bonds.

Bartonella infection: treatment and drug resistance

Bartonella species, which belong to the α-2 subgroup of Proteobacteria, are fastidious Gram-negative bacteria that are highly adapted to their mammalian host reservoirs. Bartonella species are responsible for different clinical conditions affecting humans, including Carrion's disease, cat scratch disease, trench fever, bacillary angiomatosis, endocarditis and peliosis hepatis. While some of these diseases can resolve spontaneously without treatment, in other cases, the disease is fatal without antibiotic treatment. In this article, we discuss the antibiotic susceptibility patterns of Bartonella species, detected using several methods. We also provide an overview of Bartonella infection in humans and animals and discuss the antibiotic treatment recommendations for the different infections, treatment failure and the molecular mechanism of antibiotic resistance in these bacteria.

Ciprofloxacin surf-plexes in sub-micron emulsions: a novel approach to improve payload efficiency and antimicrobial efficacy

The aim of this study was to investigate antimicrobial efficacy and pharmacokinetic profile of ciprofloxacin (CFn) loaded oil-in-water (o/w) submicron emulsion (SE-CFn). This study emphasized on development of hydrophobic ion-pair complexes of CFn with sodium deoxycholate (SDC) [CFn-SDC], which was incorporated in the core of SE (SE-CFn-SDC). SE-CFn-SDC was characterized for globulet size (278±12 nm), zeta potential (-25.3±1 mV), viscosity (2.6±0.3 cP), transmission electron microscopy (TEM), drug entrapment and for in vitro release profile. The entrapment efficiency (EE) was significantly improved (≥80%; p≤0.05) on ion-pairing while it was merely 27.2±3.1% for free CFn. The cytotoxicity studies of formulations on J774 macrophage cells showed that more than 90±3% of cells were viable, even at high concentration (100 μg/ml). SE-CFn-SDC was further modified with cationic inducer chitosan (SE-CH-CFn-SDC), which showed almost twofold and fourfold enhancement in antimicrobial efficacy as compared to SE-CFn-SDC and SE-CFn, respectively when tested in vitro against E. coli, S. aureus, and P. aeruginosa. When tested in male Balb/c mice, the AUC(0-24h) of SE-CH-CFn-SDC (23.27±2.8 h μg/ml) was found to be 1.7-fold and 5-fold higher as compared to SE-CFn-SDC (13.17±0.88 h μg/ml) and CFn solution (4.70±0.77 h μg/ml), respectively. The study demonstrates that surfactant based ionic complex formation incorporated in surface modified submicron emulsion is a promising approach to improve payload efficiency of poorly water soluble drugs with improved antimicrobial efficacy and pharmacokinetic profile.

[Intracameral moxifloxacin: a safe option for endophthalmitis prophylaxis? In vitro safety profile for intraocular application]

BACKGROUND

Moxifloxacin (Vigamox), a 4th-generation fluoroquinolone, covers most isolates causing endophthalmitis. It is safe and effective for systemic and topical use; however, only very limited data are available on prophylactic intracameral administration to prevent endophthalmitis. This study investigated the safety of Vigamox for intracameral application in a cell-culture model.

METHODS

The endothelial toxicity of moxifloxacin (Vigamox) was evaluated in cultured human corneas. Primary human retinal pigment epithelium cells (RPEs), trabecular meshwork cells (TMCs), lens epithelium cells (LECs), and corneal endothelial cells (CECs) were treated with concentrations of Vigamox. Toxic effects were evaluated after 24 h (MTT assay and live-dead assay). By treating TMC, CEC, and RPE cells either with oxidative stress or tumor necrosis factor-alpha (TNF-a), lipopolysaccharide (LPS), and interleukin-6 (IL-6), the effects of moxifloxacin on cellular viability under conditions of inflammation were investigated.

RESULTS

No corneal endothelial toxicity could be detected after 30 days of treatment with moxifloxacin 500 microg/ml. Primary RPEs, TMCs, LECs, and CECs showed adverse effects on proliferation and viability only at concentrations higher than 150 microg/ml moxifloxacin. After preincubation with TNF-a, LPS, and IL-6 for 24 h and subsequent treatment with moxifloxacin at concentrations of 10-150 microg/ml for 24 h, no significant decrease in proliferation or viability was observed. H2O2 exposure did not increase cellular toxicity

CONCLUSION

Vigamox did not show significant toxicity on primary RPEs, TMCs, LECs, CECs, or human corneal endothelium at concentrations up to 150 microg/ml. The MIC90 of moxifloxacin for pathogens commonly encountered in endophthalmitis is known to be in the range of 0.25-2.5 microg/ml. Therefore, intracameral use of Vigamox at concentrations up to 150 microg/ml may be safe and effective for preventing endophthalmitis after intraocular surgery.

Besifloxacin ophthalmic suspension: emerging evidence of its therapeutic value in bacterial conjunctivitis

Objective

To outline the pharmacodynamics, efficacy and safety of besifloxacin ophthalmic suspension 0.6% in the treatment of bacterial conjunctivitis.

Quality of Evidence

MEDLINE database was searched to review recent pharmacodynamic and clinical studies evaluating besifloxacin and comparing besifloxacin to other topical antibiotics for ophthalmic use. Findings were limited to full-text articles from clinical journals in the English language.

Main Message

Bacterial resistance is a common source for treatment failure in bacterial conjunctivis. Besifloxacin, a novel fourth generation synthetic fluoroquinolone is likely to show lower resistance rates due to its mechanism of action and its short-term use for ocular infections only (decreased systemic exposure). Besifloxacin displays improved pharmacodynamic properties compared to other commonly used fluoroquinolones and has shown to be efficacious and safe in clinical studies.

Conclusion

Besifloxacin ophthalmic suspension 0.6% provides safe and efficacious treatment for bacterial conjunctivitis. The factors leading to bacterial resistance are diminished, which allows besifloxacin to be a favorable treatment option.

Pharmacodynamic modeling of in vitro activity of marbofloxacin against Escherichia coli strains

A mathematical pharmacodynamic model was developed to describe the bactericidal activity of marbofloxacin against Escherichia coli strains with reduced susceptibility levels (determined using MICs) under optimal and intestinal growth conditions. Model parameters were estimated using nonlinear least-square curve-fitting procedures for each E. coli strain. Parameters related to bactericidal activity were subsequently analyzed using a maximum-effect (E(max)) model adapted to account for a direct and a delayed effect. While net growth rates did not vary significantly with strain susceptibility, culture medium had a major effect. The bactericidal activity of marbofloxacin was closely associated with the concentration and the duration of exposure of the bacteria to the antimicrobial agent. The value of the concentration inducing a half-maximum effect (C(50)) was highly correlated with MIC values (R(2) = 0.87 and R(2) = 0.94 under intestinal and optimal conditions, respectively). Our model reproduced the time-kill kinetics with good accuracy (R(2) of >0.90) and helped explain observed regrowth.

Effect of fluoroquinolones on the expression of matrix metalloproteinase in debrided cornea of rats

Matrix metalloproteinases (MMPs) are implicated in regenerative and healing processes in corneal injuries. Based upon reports that topical fluoroquinolones (FQs) may cause perforations during corneal healing by modulating MMPs, this study evaluated the comparative effects of commercially available FQs eye drops on the expression of MMP-2 and MMP-9 in the cornea after ethanol injury. Uniform corneal epithelial defects were created using 70% ethanol in the right eye of the rats (n = 6). The groups studied were (I) sham, (II) normal saline with benzalkonium chloride (NS-BKC), (III) norfloxacin 0.3%, (IV) ciprofloxacin 0.3%, (V) lomefloxacin 0.3%, (VI) sparfloxacin 0.3%, (VII) gatifloxacin 0.3%, and (VIII) moxifloxacin 0.5%. Each treatment was instilled six times/day up to 48 h and rats were sacrificed using excess of anesthesia. The corneas were excised to study the expression of MMP-2 and MMP-9 using gelatin zymography and real-time PCR. All the FQs significantly increased the expression of MMP-2 and MMP-9 as compared to the sham and NS-BKC-treated group. NS-BKC did not show a significant effect on MMPs expression compared to the sham group. Among the studied FQs, ciprofloxacin was observed to exhibit maximal induction of MMP-2 and MMP-9, whereas lomefloxacin exhibited an equivocal effect on both MMP-2 and MMP-9 expression. Findings of the present study demonstrate that topical application of FQs may induce the expression of MMP-2 and MMP-9 in debrided corneal epithelium and, therefore, may delay corneal wound healing. Thus, it can be concluded that selecting a FQ for ophthalmic use having minimal effect on MMPs may impact wound healing in injured or vulnerable cornea.

Emerging antibiotic resistance in ocular infections and the role of fluoroquinolones

Resistance to antibiotic agents is becoming increasingly prevalent among ocular infections. Between 19% and 60% of Streptococcus pneumoniae and Staphylococcus aureus isolates have been shown to be resistant to macrolide antibiotic agents, penicillin, and older fluoroquinolones. Although topical fluoroquinolones are considered first-line treatment of ocular infections, as much as 85% of methicillin-resistant S aureus isolates are resistant to ophthalmic fluoroquinolones, including the newer 8-methoxy fluoroquinolones, gatifloxacin and moxifloxacin. Besifloxacin, an 8-chlorofluoroquinolone, has a lower minimum inhibitory concentration against multidrug-resistant staphylococcal strains than other fluoroquinolones and less selective pressure for resistance development because of the lack of a systemic counterpart. In addition to the development of new antibacterial agents, antibiotic resistance in ocular infections may be reduced by following the same strategies used to minimize antimicrobial resistance in systemic infections.

Randomized clinical study for comparative evaluation of fourth-generation fluoroquinolones with the combination of fortified antibiotics in the treatment of bacterial corneal ulcers

PURPOSE

Comparative evaluation of efficacy of monotherapy with moxifloxacin (0.5%) or gatifloxacin (0.3%) with combination therapy of cefazolin (5%) and tobramycin (1.3%) in treatment of bacterial corneal ulcers.

METHODS

Patients diagnosed with bacterial keratitis (ulcer diameter 2-8 mm) were randomized to 1 of the 3 treatment groups (tobramycin 1.3% and cefazolin 5%, gatifloxacin 0.3%, or moxifloxacin 0.5%). After obtaining corneal scrapings, assigned study medication was instilled hourly for 48 hours and tapered as per clinical response. Healing of ulcer, duration to cure, adverse reactions, antibiogram profile, treatment failures, final visual acuity, and corneal opacity size were evaluated.

RESULTS

A total of 61 patients were enrolled [cefazolin and tobramycin (n = 20), gatifloxacin (n = 21), and moxifloxacin (n = 20)]. Overall, 57 patients (93%) healed on treatment. On comparison of the mean time taken to heal, no statistically significant difference was found among all the 3 treatment groups (P = 0.98). Positive bacterial culture was obtained in only 38 patients (62%). There was no significant difference in the bacterial isolates in each treatment group. There were 4 (7%) treatment failures (perforation or nonhealing ulcer): 1 (5%) each in moxifloxacin and gatifloxacin group and 2 (10%) in fortified antibiotics group. All regimens were well tolerated.

CONCLUSION

The study failed to find a difference in the efficacy of monotherapy with fourth-generation fluoroquinolones in the treatment of bacterial corneal ulcers of 2-8 mm size when compared with combination therapy of fortified antibiotics.

Mutant prevention concentration (MPC) of ciprofloxacin against Salmonella enterica of epidemic and poultry origin

Salmonella isolates resistant or with reduced susceptibility to quinolones increased in recent years. The mutant prevention concentration (MPC) is a new alternative that can prevent the selection and multiplication of resistant Salmonella spp. strains. The MPC of ciprofloxacin (CipMPC) was evaluated for 312 Salmonella enterica strains of epidemic and poultry origin susceptible and resistant to nalidixic acid (NAL). The CipMPC for NAL-susceptible strains were in the range from 0.002 to 4 μg/ml and for NAL-resistant strains, it ranged from 0.004 to 16 μg/ml. The average MPC/MIC ratio for NAL-resistant strains was higher than NAL susceptible. S. Enteritidis showed the highest CipMPC and the highest MPC/MIC ratio also for NAL-resistant strains and with mutations in gyrA. Serovar Corvallis, a NAL-resistant strain without mutations, and of poultry origin showed the highest CipMPC value. The lowest value was observed for epidemic NAL-susceptible strains serovars Typhimurium and London. The average MPC/MIC ratio for strains with mutations in Aspartate 87 was higher than that mutated in Serine 83. The results show the importance of MPC in determining the correct dosage of Cip for treatment of Salmonella spp.

Efficacy and safety of besifloxacin ophthalmic suspension 0.6% in children and adolescents with bacterial conjunctivitis: a post hoc, subgroup analysis of three randomized, double-masked, parallel-group, multicenter clinical trials

BACKGROUND

Acute conjunctivitis is the most frequent eye disorder seen by primary care physicians and one that often affects children. Besifloxacin is a new topical fluoroquinolone, the first chlorofluoroquinolone, for the treatment of bacterial conjunctivitis.

OBJECTIVE

To examine the efficacy and safety of besifloxacin ophthalmic suspension 0.6% in patients aged 1-17 years with bacterial conjunctivitis.

METHODS

This was a post hoc analysis of a subgroup of pediatric patients aged 1-17 years who had participated in three previously reported, randomized, double-masked, parallel-group, multicenter, clinical trials evaluating the safety and efficacy of besifloxacin in the treatment of bacterial conjunctivitis. The studies were conducted in a community setting (clinical centers). All three clinical trials included children (aged > or = 1 year) with a clinical diagnosis of bacterial conjunctivitis in at least one eye, based on the presence at baseline of grade 1 or greater purulent conjunctival discharge and conjunctival injection, and pin-hole visual acuity of at least 20/200 in both eyes for verbal patients. Two trials were vehicle controlled; the third trial was comparator controlled (moxifloxacin hydrochloride ophthalmic solution 0.5% as base). In all studies, besifloxacin ophthalmic suspension 0.6% was administered as one drop in the affected eye(s) three times daily, at approximately 6-hourly intervals, for 5 days. The main outcome measures were clinical resolution and microbial eradication at visit 2 (day 4 +/- 1 in one study; day 5 +/- 1 in the other two studies) and visit 3 (day 8 or 9). Data from the two vehicle-controlled studies were combined for the assessments to provide greater statistical power.

RESULTS

This analysis included 815 pediatric patients aged 1-17 years (447 with culture-confirmed bacterial conjunctivitis). Clinical resolution was significantly greater (p < 0.05) in the besifloxacin group than in the vehicle group at both visit 2 (53.7% vs 41.3%) and visit 3 (88.1% vs 73.0%). Similarly, microbial eradication was significantly higher with besifloxacin than with vehicle at visit 2 (85.8% vs 56.3%) and visit 3 (82.8% vs 68.3%). No significant differences in clinical resolution and microbial eradication were noted between besifloxacin and moxifloxacin. Besifloxacin was well tolerated, with similar incidences of adverse events in the besifloxacin, vehicle, and moxifloxacin groups.

CONCLUSION

Besifloxacin ophthalmic suspension 0.6% was shown to be safe and effective for the treatment of bacterial conjunctivitis in children and adolescents aged 1-17 years.

Phenothiazinium-fluoroquinolone drug conjugates

Synthesis and antibacterial screening of a homologous series of 3-dialkylaminophenothiazinium-7-norfloxacin conjugates was carried out alongside a corresponding series of symmetrical methylene blue derivatives. The norfloxacin conjugates maintained typical methylene blue derivative photoproperties, such as long wavelength absorption, but produced no measurable singlet oxygen in the standard assay and provided no significant increase in the magnitude of photoantibacterial action, this being similar to the methylene blue homologues, although both the conjugates and homologues were considerably more active than methylene blue itself both against Staphylococcus aureus and Escherichia coli. DNA binding via intercalation was considerably greater for the series of norfloxacin conjugates than for the methylene blue homologues.

Impact of antibiotic resistance in the management of ocular infections: the role of current and future antibiotics

Purpose:

This article reviews the effects of the increase in bacterial resistance on the treatment of ocular infections.

Design:

Interpretive assessment.

Methods:

Literature review and interpretation.

Results:

Ocular bacterial infections include conjunctivitis, keratitis, endophthalmitis, blepharitis, orbital cellulitis, and dacryocystitis. Treatment for most ocular bacterial infections is primarily empiric with broad-spectrum antibiotics, which are effective against the most common bacteria associated with these ocular infections. However, the widespread use of broad-spectrum systemic antibiotics has resulted in a global increase in resistance among both Gram-positive and Gram-negative bacteria to a number of the older antibiotics as well as some of the newer fluoroquinolones used to treat ophthalmic infections. Strategies for the prevention of the increase in ocular pathogen resistance should be developed and implemented. In addition, new antimicrobial agents with optimized pharmacokinetic and pharmacodynamic properties that have low toxicity, high efficacy, and reduced potential for the development of resistance are needed.

Conclusions:

New antimicrobial agents that treat ocular infections effectively and have a low potential for the development of resistance could be a part of strategies to prevent the global increase in ocular pathogen resistance.

The natural history of Anaplasma marginale

The intracellular pathogen Anaplasma marginale (Rickettsiales: Anaplasmataceae), described by Sir Arnold Theiler in 1910, is endemic worldwide in tropical and subtropical areas. Infection of cattle with A. marginale causes bovine anaplasmosis, a mild to severe hemolytic disease that results in considerable economic loss to both dairy and beef industries. Transmission of A. marginale to cattle occurs biologically by ticks and mechanically by biting flies and by blood-contaminated fomites. Both male ticks and cattle hosts become persistently infected with A. marginale and serve as reservoirs of infection. While erythrocytes are the major site of infection in cattle, A. marginale undergoes a complex developmental cycle in ticks that begins by infection of gut cells, and transmission to susceptible hosts occurs from salivary glands during feeding. Major surface proteins (MSPs) play a crucial role in the interaction of A. marginale with host cells, and include adhesion proteins and MSPs from multigene families that undergo antigenic change and selection in cattle, thus contributing to maintenance of persistent infections. Many geographic strains of A. marginale have been identified worldwide, which vary in genotype, antigenic composition, morphology and infectivity for ticks. Isolates of A. marginale may be maintained by independent transmission events and a mechanism of infection/exclusion in cattle and ticks. The increasing numbers of A. marginale genotypes identified in some geographic regions most likely resulted from intensive cattle movement. However, concurrent A. marginale strain infections in cattle was reported, but these strains were more distantly related. Phylogenetic studies of selected geographic isolates of A. marginale, using msp4 and msp1alpha, provided information about the biogeography and evolution of A. marginale, and msp1alpha genotypes appear to have evolved under positive selection pressure. Live and killed vaccines have been used for control of anaplasmosis and both types of vaccines have advantages and disadvantages. Vaccines have effectively prevented clinical anaplasmosis in cattle but have failed to block A. marginale infection. Vaccines are needed that can prevent clinical disease and, simultaneously, prevent infection in cattle and ticks, thus eliminating these hosts as reservoirs of infection. Advances in genomics, proteomics, immunology and biochemical and molecular technologies during the last decade have been applied to research on A. marginale and related organisms, and the recent development of a cell culture system for A. marginale has provided a format for studying the pathogen/tick interface. Recent advancements and new research methodologies should provide additional opportunities for development of new strategies for control and prevention of bovine anaplasmosis.

Intracameral moxifloxacin: in vitro safety on human ocular cells

PURPOSE

The fourth-generation fluoroquinolone, moxifloxacin, covers most gram-positive and gram-negative isolates causing endophthalmitis. It is safe and effective for systemic and topical use, but only limited data are available on prophylactic intracameral administration to prevent endophthalmitis. This study uses a cell culture model to investigate the safety of moxifloxacin for intracameral application.

METHODS

Endothelial toxicity of moxifloxacin was evaluated in cultured human corneas. Possible toxic effects of moxifloxacin (10-750 microg/mL) in corneal endothelial cells (CEC), primary human trabecular meshwork cells (TMC), and primary human retinal pigment epithelial (RPE) cells were evaluated after 24 hours and under conditions of oxidative and inflammatory stress by treatment with tumor necrosis factor alpha, lipopolysaccharides, or interleukin-6. Toxicity was evaluated by tetrazolium dye reduction assay, and cell viability was quantified by a microscopic live-dead assay.

RESULTS

No corneal endothelial toxicity could be detected after 30 days of treatment with 500 microg/mL moxifloxacin. Concentrations up to 150 microg/mL had no influence on CEC, TMC, or RPE cell proliferation or on cell viability when administered for 24 hours. After preincubation with tumor necrosis factor alpha, lipopolysaccharides, or interleukin-6 for 24 hours and subsequent treatment with moxifloxacin at concentrations from 10 to 150 microg/mL for 24 hours, no significant decrease in proliferation or viability was observed. Hydrogen peroxide exposure did not increase cellular toxicity.

CONCLUSIONS

This study showed no significant toxicity for moxifloxacin on CEC, TMC, RPE cells, or human corneal endothelium for concentrations up to 150 microg/mL. The minimum inhibitory concentration of moxifloxacin to inhibit 90% of pathogens commonly encountered in endophthalmitis is known to be in the range of 0.25-2.5 microg/mL. Therefore, prophylactic intracameral use of moxifloxacin at concentrations up to 150 microg/mL may be safely used to prevent endophthalmitis after intraocular surgery.

Comparison of fluoroquinolones: cytotoxicity on human corneal epithelial cells

PURPOSE

To compare the cytotoxicity of different fluoroquinolones (FQs) towards human corneal epithelial cells (HCECs).

METHODS

HCECs were incubated with FQs (norfloxacin, ciprofloxacin, ofloxacin, levofloxacin, moxifloxacin, and gatifloxacin), both as commercial ophthalmic formulations and as unpreserved solutions. Cells incubated in different formulations of gentamicin, cefazolin, and benzalkonium chloride (BAC) were also compared. A cell viability assay, using 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS) assay, was used to evaluate the drug effects on cell viability after five incubation times (30 min, 1 h, 4 h, 8 h, and 24 h). Transepithelial electrical resistance (TEER) was measured with a voltohmmeter to help understand changes in paracellular permeability at five time points (4 h, 8 h, 12 h, 24 h, and 48 h). Cell morphology was observed with an inverted fluorescence microscope, with multiple stage position and in time-lapse mode.

RESULTS

The preserving solutions and BAC at concentrations above 0.005% significantly decreased cell viability, when assayed by MTS. Increased paracellular permeability and decreased membrane integrity were also observed by TEER measurements and inverted fluorescence microscopy. Ofloxacin and levofloxacin were both free of preservatives and showed the least cytotoxicity towards HCECs in commercial FQ eye drops.

CONCLUSIONS

The cytotoxicity observed with FQ eye drops seems to be caused mainly by the preservative, which induced a significant decrease in membrane integrity and increased paracellular permeability. We found the new generation of FQs (moxifloxacin and gatifloxacin) no less cytotoxic towards HCECs than the old generation ones.

Sequential determination of norfloxaxin and levofloxacin in the presence of other fluorquinolones using synchronous scanning room-temperature phosphorimetry and Th (IV) as the selective signal inducer

The selective determination of norfloxacin in mixtures with other fluorquinolones was achieved by synchronous scanning solid surface room-temperature phosphorimetry (SSRTP) and Th(NO(3))(4) as selective phosphorescence inducer. The method also allowed the determination of levofloxacin in a sequential way. The optimization of experimental conditions was made through an univariate approach, in order to find the best conditions for norfloxacin phosphorescence, followed by a 2(3) factorial design in order to verify interaction among relevant variables, to check robustness for each variable and to perform final adjustment of parameters. Absolute limit of detection (ALOD) for norfloxacin was 12ng with a linear signal response extending up to 400ng. Under the same experimental conditions set for norfloxacin, the ALOD for levofloxacin was 13ng with linear signal response up to 450ng. Accuracy of the method, using Th (IV) as selective phosphorescence inducer, was evaluated through the analysis of commercial and simulated pharmaceutical formulations with recoveries between 94.4 and 101% for norfloxacin and 95.9 and 103.8% for levofloxacin. The use of Cd (II), a traditional phosphorescence inducer for fluorquinolones, did not allow selective determination of norfloxacin. Further studies indicated the potential application of the method in urine samples.

Conjunctival tissue pharmacokinetic properties of topical azithromycin 1% and moxifloxacin 0.5% ophthalmic solutions: a single-dose, randomized, open-label, active-controlled trial in healthy adult volunteers

BACKGROUND

Effective ocular tissue concentrations and prolonged residence times of antibacterial agents are important in treating both acute and chronic diseases. Conjunctival biopsy allows the determination of specific tissue concentration data for topical ophthalmic agents. Drug concentration analysis at various time points following instillation allows interpretation of the residence time and a rationale for dosing frequency.

OBJECTIVE

This study compared the pharmacokinetic parameters of 2 currently available topical ocular antibiotics-azithromycin ophthalmic solution 1% and moxifloxacin ophthalmic solution 0.5%-in the conjunctiva of healthy volunteers after a single topical administration.

METHODS

This single-dose, randomized, open-label, active-controlled clinical trial was conducted at ORA Clinical Research and Development, North Andover, Massachusetts. Subjects were randomly assigned to receive a single dose of azithromycin or moxifloxacin and to undergo biopsy sampling at 30 minutes or 2, 12, or 24 hours after administration. Concentrations of azithromycin and moxifloxacin were determined using liquid chromatography tandem mass spectrometry. Adverse events (AEs) were assessed at all visits using visual acuity measurements, slit-lamp biomicroscopy, and direct questioning.

RESULTS

Forty-eight subjects (mean age, 40.0 years; 48% female; 96% white, 2% black, and 2% Asian) underwent conjunctival biopsy. Mean (SD) concentrations of azithromycin in conjunctival tissue (lower limit of quantitation [LLOQ], 1 microg/g for 1-mg biopsy specimen) were 131 (89), 59 (19), 48 (24), and 32 (20) microg/g at 30 minutes and 2, 12, and 24 hours, respectively (median values, 117, 69, 46, and 30 microg/g). Mean concentrations concentrations of moxifloxacin in conjunctival tissue (LLOQ, 0.05 microg/g for 1-mg biopsy sample) were 1.92 (2.03), 3.77 (8.98), 0.02 (0.04), and 0.01 (0.02) microg/g at 30 minutes and 2, 12, and 24 hours, respectively (median values, 1.12, 0.12, <0.05, and <0.05 microg/g). Thirteen subjects (6 in the azithromycin group and 7 in the moxifloxacin group) experienced 20 AEs, 11 of which were considered possibly related to study treatment, and 15 of which were ocular (most commonly conjunctival hemorrhage).

CONCLUSIONS

In this single-dose study of 2 currently available topical ocular antibiotics in healthy volunteers, therapeutic concentrations were achieved with both agents. Both treatments were well tolerated in the population studied. Clinical Trials Identification Number: NCT00564447.

Fluoroquinolone efflux mediated by ABC transporters

Quinolones and fluoroquinolones are broad spectrum bactericidal drugs, which are widely used in both human and veterinary medicine. These drugs can quite easily enter cells and are often used to treat intracellular pathogens. Some fluoroquinolones have been reported to undergo efflux, which could explain their low bioavailability. There is a growing need to understand resistance mechanisms to quinolones, involving for instance mutations or the action of efflux pumps. Several members of the ATP-binding cassette (ABC) drug efflux transporter family (MDR, MRP, ABCG2) significantly affect the pharmacokinetic disposition of quinolones. Active secretory mechanisms common to all fluoroquinolones have been suggested, as well as competition between fluoroquinolones at transporter sites. For grepafloxacin and its metabolites, MRP2 has been demonstrated to mediate biliary excretion. However, MDR1 is responsible for grepafloxacin intestinal secretion. Recently it has been shown that ciprofloxacin and enrofloxacin are efficiently transported ABCG2 substrates which are actively secreted into milk. It appears that multiple ABC transporters contribute to the overall secretion of fluoroquinolones. The objective of this work is to review the recent advances in insights into ABC transporters and their effects on fluoroquinolone disposition and resistance including data on drug secretion into milk.

Review of third-and fourth-generation fluoroquinolones in ophthalmology: in-vitro and in-vivo efficacy

INTRODUCTION

Beginning with second-generation ciprofloxacin 0.3% and ofloxacin 0.3%, fluoroquinolones have been widely used in the treatment and prophylaxis of ocular infections. However, their in-vitro potencies have been decreasing steadily since their introduction. Third-generation levofloxacin 0.5% produces higher ocular tissue penetration, thereby reducing the risk of selecting for decreased fluoroquinolone potency. Fourth-generation gatifloxacin 0.3% and moxifloxacin 0.5% have structural modifications that both reduce risk of resistance and improve potency against Gram-positive bacteria. A new third-generation formulation, levofloxacin 1.5%, was recently introduced, demonstrating increased ocular penetration compared with gatifloxacin 0.3% but clinical equivalence to its second-generation parent, ofloxacin 0.3%, in two randomized trials.

METHODS

We investigated the therapeutic potential of levofloxacin 1.5% and compared it to that of existing fourth-generation fluoroquinolones. A MEDLINE search was conducted using the following search terms: moxifloxacin or gatifloxacin; levofloxacin; minimum inhibitory concentration or prevention or prophylaxis; keratitis or endophthalmitis.

RESULTS

Nine eligible studies published between 2002 and 2008 were identified, eight of which are presented. The five in-vitro studies demonstrated that moxifloxacin and gatifloxacin are statistically more potent than levofloxacin against Gram-positive organisms and similar in potency in most cases of Gram-negative bacteria. In-vivo animal models testing moxifloxacin or gatifloxacin against levofloxacin 0.5% (no clinical trials testing the efficacy of levofloxacin 1.5% have yet been published) demonstrated that fourth-generation agents were superior to third-generation levofloxacin 0.5% for prophylaxis of Gram-positive bacteria-induced infections and were equal to, or better than, levofloxacin 0.5% for the treatment of Gram-negative infections.

CONCLUSION

Fourth-generation agents have increased potency against Gram-positive bacteria compared with levofloxacin, while maintaining similar potency against Gram-negative bacteria. Although levofloxacin 1.5% has demonstrated superior ocular penetration relative to gatifloxacin, the limited available data do not suggest this translates into superior clinical activity compared with moxifloxacin, which has significantly greater ocular penetration and better Gram-positive potency than gatifloxacin.

Evaluation of toxicity of commercial ophthalmic fluoroquinolone antibiotics as assessed on immortalized corneal and conjunctival epithelial cells

PURPOSE

To evaluate the toxicity of a variety of the fluoroquinolone antibiotics on the ocular surface by using tissue culture models of corneal epithelial cells and conjunctival epithelial cells.

METHODS

Immortalized conjunctival (CCC) and human corneal (HCE) epithelial cells were grown and when confluent the cells allowed to air dry for 1 hour. Medium was then replaced with 100 microL of one of the following: 1) Vigamox [moxifloxacin (0.5%: MX)]; (2) Zymar [gatifloxacin (0.3%: GA)]; 3) Quixin [levofloxacin (0.5%: LE)]; 4) Ocuflox [ofloxacin (0.3%: OF)]; 5) Ciloxan [ciprofloxacin (0.3%: CP)]; 6) medium (viable control); 7) "normal"/physiologic saline; 8) formalin (dead control). After one hour, 150 microL of MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazonium bromide was added and incubated for 4 hours. After decanting, precipitate was dissolved in 150 microL of isopropanol. Absorbance was determined at 572 nm.

RESULTS

The lowest amount of cell death was associated with the viable control. All ophthalmic preparations showed both corneal and conjunctival cell toxicity. Aside from the viable control, normal saline showed the next lowest amount of toxicity. Of the topical ocular antibiotics tested, MX showed the least amount of toxicity. All of the other antibiotics tested were statistically indistinguishable from each other.

CONCLUSIONS

All of the topical ocular antibiotics tested showed evidence of both corneal and conjunctival toxicity (MX < OF < or = LE < or = CP < or = GA), although only MX was statistically significant. Whether this finding reflects on in vivo wound healing remains to be determined. This model provides a rapid and cost-effective method to screen for surface toxicity of topical agents.

A bioinformatic approach to understanding antibiotic resistance in intracellular bacteria through whole genome analysis

Intracellular bacteria survive within eukaryotic host cells and are difficult to kill with certain antibiotics. As a result, antibiotic resistance in intracellular bacteria is becoming commonplace in healthcare institutions. Owing to the lack of methods available for transforming these bacteria, we evaluated the mechanisms of resistance using molecular methods and in silico genome analysis. The objective of this review was to understand the molecular mechanisms of antibiotic resistance through in silico comparisons of the genomes of obligate and facultative intracellular bacteria. The available data on in vitro mutants reported for intracellular bacteria were also reviewed. These genomic data were analysed to find natural mutations in known target genes involved in antibiotic resistance and to look for the presence or absence of different resistance determinants. Our analysis revealed the presence of tetracycline resistance protein (Tet) in Bartonella quintana, Francisella tularensis and Brucella ovis; moreover, most of the Francisella strains possessed the blaA gene, AmpG protein and metallo-beta-lactamase family protein. The presence or absence of folP (dihydropteroate synthase) and folA (dihydrofolate reductase) genes in the genome could explain natural resistance to co-trimoxazole. Finally, multiple genes encoding different efflux pumps were studied. This in silico approach was an effective method for understanding the mechanisms of antibiotic resistance in intracellular bacteria. The whole genome sequence analysis will help to predict several important phenotypic characteristics, in particular resistance to different antibiotics. In the future, stable mutants should be obtained through transformation methods in order to demonstrate experimentally the determinants of resistance in intracellular bacteria.

Antimicrobial susceptibility and mechanism of resistance to fluoroquinolones in Staphylococcus intermedius and Staphylococcus schleiferi

The objective of the present study was to determine the antimicrobial susceptibility of 136 canine isolates of Staphylococcus intermedius and 10 canine isolates of S. schleiferi subspecies coagulans to 16 fluoroquinolones (FQs), and to investigate the mechanisms of resistance in the nonsusceptible isolates. Of the 136 of S. intermedius tested 98.5% were susceptible to all 16 FQs whereas only 40% of the 10 isolates of S. schleiferi subspecies coagulans were susceptible. Two isolates of S. intermedius and six isolates of S. schleiferi, were found to be resistant to 13 out of 16 FQs, while they retained their susceptibility to fourth generation FQs such as gatifloxacin, moxifloxacin and trovafloxacin. Sequencing of the quinolone-resistance determining regions of gyrA and grlA genes showed that in S. intermedius, dichotomous resistance to FQs was associated with the occurrence of one alteration in GyrA-84 and one in GrlA-80, while in S. schleiferi the same pattern of resistance was observed in isolates showing these changes only in gyrA. This study is the first to screen FQs of the second, third and fourth generation for antimicrobial resistance in clinical isolates of S. intermedius and S. schleiferi of canine origin, and to describe mutations in gyrA and grlA associated with FQ resistance in these bacterial species.

Comparison of azithromycin and moxifloxacin against bacterial isolates causing conjunctivitis

OBJECTIVE

To examine in vitro resistance to azithromycin and moxifloxacin in bacterial conjunctivitis isolates.

METHODS

MIC90s (Minimum Inhibitory Concentration) and resistance rates to azithromycin and moxifloxacin were determined based upon microtiter broth dilution and/or antimicrobial gradient test strips in a multicenter phase III study and confirmed externally.

RESULTS

The most common isolates collected from bacterial conjunctivitis patients in the phase III study were Haemophilus influenzae (40.6%), followed by Staphylococcus epidermidis (19.3%), Propionibacterium acnes (17.3%), Streptococcus pneumoniae (16.8%), and Staphylococcus aureus (0.06%). MIC90s for all of these organisms were well below established resistance breakpoints for moxifloxacin, indicating no bacterial resistance. On the other hand, the MIC90 for H. influenzae was 3-fold higher than the resistance breakpoint for azithromycin, > or = 128-fold higher for S. epidermidis, 16-fold higher for S. pneumoniae and > or = 128-fold higher for S. aureus, indicating moderate to very high bacterial resistance to azithromycin.

CONCLUSIONS

Resistance to azithromycin is more common than resistance to moxifloxacin in clinical isolates causing bacterial conjunctivitis.

Epidemiology and evolution of genotype and antimicrobial resistance of an imported Shigella sonnei clone circulating in central Taiwan

Shigella sonnei replaced Shigella flexneri to become the predominant species for shigellosis in 2001 to 2003 in central Taiwan. A total of 425 S. sonnei isolates collected from 1996 to 2004 were available for characterization by pulsed-field gel electrophoresis (PFGE), inter-IS1 spacer typing (IST), and antimicrobial susceptibility testing. The results showed that at least 21 IST clones had emerged for the S. sonnei infections in 1996 to 2004. Most IST clones lasted for a short time; some circulated for 2 to 3 years. An IST1 clone, detected for the first time in 2000, was the most prevalent and responsible for the shigellosis epidemic in 2001 to 2003. Over 3 years of sustained transmission, the IST1 clone evolved into many strains with different PFGE genotypes and antibiograms. The ancestor, with a J16N09.0019 PFGE genotype, remained to be the predominant circulating strain in the period studied; however, new strains with certain PFGE genotypes and antibiograms could become major circulating strains for subsequent infections.

Lens concentration of ofloxacin and lomefloxacin in an experimental endophthalmitis model

Abstract.

BACKGROUND

Bacterial endophthalmitis is a serious complication of ocular surgery and penetrating trauma. The primary causative organisms are strains of Staphylococcus aureus and Staphylococcus epidermidis. Fluoroquinolones are widely used to treat endophthalmitis. There are a few studies on the penetration of fluoroquinolones into the lens in inflamed eyes. A literature search did not identify any data regarding penetration of topical ofloxacin into the lens in normal and inflamed eyes.

OBJECTIVE

The aim of this study was to determine the penetration of topical ofloxacin and lomefloxacin into the lens in a rabbit endophthalmitis model.

METHODS

New Zealand white rabbits were randomly divided into 2 groups. The left eyes were infected with an intravitreal inoculation of S aureus. The right eyes were used as a noninoculated control. Groups 1 and 2 received topical ofloxacin and lomefloxacin treatment, respectively, 24 hours after the inoculation. Two drops of the study drugs were instilled in the eyes every 30 minutes for 3 hours and then every 60 minutes for 3 hours. Lens samples were obtained 30 minutes after the last ofloxacin or lomefloxacin drops were administered. High-performance liquid chromatography was used to determine the fluoroquinolone concentration.

RESULTS

Ten rabbits were equally divided into the 2 treatment groups. There was no significant difference in mean (SD) lens concentrations between the control and inoculated eyes in either treatment group-ofloxacin (0.26 [0.32] μg/mL vs 0.11 [0.05] μg/mL, respectively) and lomefloxacin (0.50 [0.87] μg/mL vs 0.12 [0.08] μg/mL, respectively).

CONCLUSION

The results of this small experimental study found that topical ofloxacin and lomefloxacin can accumulate in the crystalline lens after installation. Inflammation did not affect the penetration of ofloxacin or lomefloxacin into the lens.

Prophylactic gatifloxacin therapy in prevention of bacterial keratitis in a rabbit laser in situ keratomileusis model

PURPOSE

Use the ID(50) (infectious dose to 50% of experimental animals) to quantify the most effective prophylactic dosing regimen to use with gatifloxacin 0.3% (Zymar) for the prevention of keratitis in a rabbit laser in situ keratomileusis model of Staphylococcus epidermidis infection.

SETTING

University Laboratory, University of Arizona, Tucson, Arizona, USA.

METHODS

Two groups of rabbits were compared in each of 2 experiments that were separated by 12 months. In the first experiment, rabbits receiving no postoperative antibiotic therapy (Group 1) were compared with rabbits receiving postoperative antibiotic therapy (Group 2). In the second experiment, postoperative antibiotic therapy (Group 3) was compared with preoperative and postoperative antibiotic therapy (Group 4). All antibiotic regimens used gatifloxacin 0.3%. Before antibiotic therapy began, corneal pockets were created in the right eye of each rabbit and all rabbits received balanced salt solution (BSS) only or BSS and S epidermidis inoculations in the corneal pocket. Rabbits were monitored for corneal infiltrates after surgery.

RESULTS

The ID(50) of the first, second, third, and fourth groups of rabbits was 10(2), 10(4), 10(5), and 10(7) organisms, respectively. The data showed a statistically significant difference between rabbits receiving BSS only and most rabbits receiving BSS plus inoculate at each postoperative measurement (P<.05).

CONCLUSIONS

The findings suggest that the use of both preoperative and postoperative antibiotic therapy may be most effective in preventing infection. Postoperative antibiotic therapy increased the number of S epidermidis necessary to cause infection by at least 100-fold over no antibiotic intervention. Preoperative plus postoperative antibiotic therapy increased the number of bacteria necessary to cause infection by at least 100-fold over postoperative therapy alone and by more than 10000-fold over no antibiotic intervention.

In vitro activity of fluoroquinolones against ocular bacterial isolates in São Paulo, Brazil

PURPOSE

To compare the in vitro susceptibility profiles of bacterial ocular isolates and to determine minimum inhibitory concentrations (MICs) of gatifloxacin and moxifloxacin (fourth-generation fluoroquinolones) versus ciprofloxacin and ofloxacin (second-generation fluoroquinolones).

METHODS

Gram-positive and gram-negative isolates were recovered from cases of keratitis, conjunctivitis, and endophthalmitis between 2002 and 2004 and were identified and extracted from the Microbiology Data Bank of the Federal University of São Paulo, São Paulo, Brazil. The comparison of in vitro MIC and susceptibility profiles for ofloxacin, ciprofloxacin, gatifloxacin, and moxifloxacin in gram-positive and gram-negative (n = 219) isolates was performed using the E test method.

RESULTS

The fourth-generation fluoroquinolones were statistically more potent than the second generations for gram-positive bacteria. The MIC90 level was lower for moxifloxacin than that for gatifloxacin against Staphylococcus aureus, methicillin-susceptible coagulase-negative Staphylococcus (CoNS), and S. pneumoniae, whereas the levels were equal against S. viridans and the gatifloxacin MIC90 was lower in methicillin-resistant CoNS. There was no statistically significant difference between moxifloxacin and gatifloxacin when the permutation method from the MULTTEST procedure (SAS proc multtest) was used to obtain the adjusted P value. MIC90 for ciprofloxacin was lower in gram-negative bacteria. MIC90 for ofloxacin was higher against Haemophilus spp. and Moraxella spp. Ciprofloxacin was the most statistically potent fluoroquinolone for Pseudomonas spp. Ciprofloxacin was statistically just as potent as gatifloxacin for the other gram-negative isolates.

CONCLUSION

From susceptibility profiles achieved with in vitro testing, the fourth-generation fluoroquinolones may offer some advantages over the currently available fluoroquinolones; however, a combination of the pharmacodynamics and pharmacokinetics of the drug, infection site, and the MIC is needed to predict the in vivo efficacy and best clinical applicability.

Acute endophthalmitis in eyes treated prophylactically with gatifloxacin and moxifloxacin

PURPOSE

To study the use of prophylactic fourth-generation fluoroquinolone antibiotics, gatifloxacin and moxifloxacin, and bacterial sensitivity in cases of acute postoperative endophthalmitis following cataract surgery.

DESIGN

Retrospective, consecutive, observational case series.

METHODS

Forty-two eyes of 42 patients with acute endophthalmitis occurring within six weeks after cataract surgery were identified. All patients were seen in a referral vitreoretinal practice over a two-year time interval. The number of patients using prophylactic gatifloxacin or moxifloxacin and results of bacterial culture and sensitivity to all fluoroquinolone antibiotics were recorded.

RESULTS

Thirty-one of 42 eyes (74%) were treated with perioperative gatifloxacin or moxifloxacin and 24 eyes (57%) were continuously taking one of these antibiotics at the time of diagnosis. Nineteen eyes (45%) had a positive bacterial culture. The most frequent organism isolated was coagulase-negative Staphylococcus. Sensitivities were performed for 14 gram-positive organisms, and sensitivities to ciprofloxacin (50%), ofloxacin (44%), levofloxacin (46%), gatifloxacin (38%), and moxifloxacin (38%) were noted. Five organisms were resistant to gatifloxacin and moxifloxacin with a minimum inhibitory concentration of 8 microg/ml. All gram-positive organisms were sensitive to vancomycin. Median visual acuity improved from hand motions to 20/40 at last follow-up.

CONCLUSION

Acute endophthalmitis can develop after cataract surgery despite the prophylactic use of fourth-generation fluoroquinolone antibiotics. Gram-positive organisms causing acute endophthalmitis are frequently resistant to all fluoroquinolones, including a significant number of cases resistant to gatifloxacin and moxifloxacin.