Human aqueous humor concentrations of besifloxacin, moxifloxacin, and gatifloxacin after topical ocular application

Clinical Ocular Exposure Extrapolation for a Complex Ophthalmic Suspension Using Physiologically Based Pharmacokinetic Modeling and Simulation

The development of generic ophthalmic drug products with complex formulations is challenging due to the complexity of the ocular system and a lack of sensitive testing to evaluate the interplay of its physiology with ophthalmic drugs. New methods are needed to facilitate the development of ophthalmic generic drug products. Ocular physiologically based pharmacokinetic (O-PBPK) models can provide insight into drug partitioning in eye tissues that are usually not accessible and/or are challenging to sample in humans. This study aims to demonstrate the utility of an ocular PBPK model to predict human exposure following the administration of ophthalmic suspension. Besifloxacin (Bes) suspension is presented as a case study. The O-PBPK model for Bes ophthalmic suspension (Besivance® 0.6%) accounts for nasolacrimal drainage, suspended particle dissolution in the tears, ocular absorption, and distribution in the rabbit eye. A topical controlled release formulation was used to integrate the effect of Durasite® on Bes ocular retention. The model was subsequently used to predict Bes exposure after its topical administration in humans. Drug-specific parameters were used as validated for rabbits. The physiological parameters were adjusted to match human ocular physiology. Simulated human ocular pharmacokinetic profiles were compared with the observed ocular tissue concentration data to assess the OCAT models' ability to predict human ocular exposure. The O-PBPK model simulations adequately described the observed concentrations in the eye tissues following the topical administration of Bes suspension in rabbits. After adjustment of physiological parameters to represent the human eye, the extrapolation of clinical ocular exposure following a single ocular administration of Bes suspension was successful.

Penetration of Enrofloxacin in Aqueous Humour of Avian Eyes

Enrofloxacin has been shown to be appropriate to treat bacterial eye infections in mammals. However, the anatomy and physiology of the avian eye substantially differ from those in mammals, and pharmacokinetic data substantiating the clinical efficacy of enrofloxacin in birds are still lacking. In total, 40 chickens (Gallus gallus, Lohman Selected Leghorn) received single intramuscular administration of enrofloxacin at a dosage of 25 mg/kg body weight (BW). Serial blood and aqueous humour samples were taken at 12 different time points after administration (0-60 min and 2-32 h) and were analysed for their fluoroquinolone concentrations using a competitive enzyme immunoassay. The metabolization of enrofloxacin to ciprofloxacin was determined using liquid chromatography-mass spectrometry. The maximum serum concentrations of fluoroquinolones were observed at the time point of 2.82 ± 0.1 h and amounted to 10.67 ± 0.5 µg/mL. Fluoroquinolones redistributed to a minor extent into the aqueous humour reaching maximum concentrations of 4.52 ± 1.2 µg/mL after 7.54 ± 1.0 h of drug administration. The mean residence time (MRT), volume of distribution (V_d), and terminal half-life (t_1/2 ß) were 1.68-, 2.84-, and 2.01-fold higher in aqueous humour than in serum, indicating that fluoroquinolones were trapped in aqueous humour. Enrofloxacin was only marginally metabolized into ciprofloxacin. A single intramuscular injection of a therapeutical dose of enrofloxacin (25 mg/kg BW) thus generated sustained and therapeutically active levels of enrofloxacin in the aqueous humour of chicken eyes.

Status of Physicochemical and Microbiological Analytical Methods of Gatifloxacin: A Review

Background

Gatifloxacin (GAT), an antimicrobial of the fourth generation of fluoroquinolones, has a broad spectrum of action with activity against Gram-positive and Gram-negative, aerobic and anaerobic organisms, including mycobacteria.

Objective

The objective of this review is to discuss about (i) characteristics, (ii) properties, and (iii) analytical methods of gatifloxacin.

Results

Among the methods described in the literature for the evaluation of GAT, the most frequent was HPLC (50%) for both the analysis of pharmaceutical and biological matrixes. GAT has no monograph described in official compendia. Methods for evaluating GAT in pharmaceutical matrixes were the most found in the literature, 79%. Acetonitrile (42%), methanol (20%), and buffer solution (16%) were the most used diluents. GAT, being an antimicrobial, must be analyzed by physical-chemical and microbiological methods, since the evaluation of potency is essential. In this context, the literature is scarce (4%).

Conclusions

There is a gap in the literature for environmentally friendly methods for evaluating GAT. Faster, more optimized and dynamic microbiological methods, as well as physicochemical methods, use less aggressive solvents with fewer steps and less waste. Currently, pharmaceutical analyses require reliable analytical methods, but also safe for both the analyst and the environment.

Highlights

This review shows the status of analytical methods, both physicochemical and microbiological, for the analysis of GAT in pharmaceutical and biological matrixes, also addressing its context in green and sustainable analytical chemistry.

A novel, sensitive, and widely accessible besifloxacin quantification method by HPLC-fluorescence: Application to an ocular pharmacokinetic study

Besifloxacin has been embraced for the treatment of ocular bacterial infections. While LC-MS/MS has been used in investigating BSF pharmacokinetics, those costly instruments are not universally available and have complicated requirements for operation and maintenance. Additionally, pharmacokinetics of besifloxacin in dose-intense regimens are still unknown. Herein, a new quantification method was developed employing the widely accessible HPLC with fluorescence detection and applied to an ocular pharmacokinetic study with an intense regimen. Biosamples were pre-treated using protein precipitation. Chromatographic separation was achieved on a C18 column using mobile phase of 0.1% trifluoroacetic acid and acetonitrile. To address the weak fluorescence issue of besifloxacin, effects of detection parameters, elution pattern, pH of mobile phase, and reconstitution solvents were investigated. The method was fully validated per US-FDA guidelines and demonstrated precision (<13%), accuracy (91-112%), lower limit of quantification (5 ng/mL), linearity over clinically relevant concentrations (R² > 0.999), matrix-effects (93-105%), recoveries (95-106%), and excellent selectivity. The method showed agreement with agar disk diffusion assays for in vitro screening and comparable in vivo performance to LC-MS/MS (Deming Regression, y = 1.010x + 0.123, r = 0.997; Bland-Altman analysis, mean difference was -6.3%; n = 21). Pharmacokinetic parameters suggested superior surface-retentive properties of besifloxacin. Maximum concentrations were 1412 ± 1910 and 0.15 ± 0.12 μg/mL; area under the curve was 1,637 and 1.08 µg·h/g; and half-life was 4.9 and 4.1 h; and pharmacokinetic-to-pharmacodynamic ratios were ≥ 409 and ≤ 17.8 against ocular pathogens in tears and aqueous humor, respectively. This readily available method is sensitive for biosamples and practical for routine use, facilitating besifloxacin therapy development.

Analysis of topical dosing and administration effects on ocular drug delivery in a human eyeball model using computational fluid dynamics

Predicting the spatial and temporal drug concentration distributions in the eyes is essential for quantitative analysis of the therapeutic effect and overdose issue via different topical administration strategies. To address such needs, an experimentally validated computational fluid dynamics (CFD) based virtual human eye model with physiologically realistic multiple ophthalmic compartments was developed to study the effect of administration frequency and interval on drug concentration distributions. Timolol was selected as the topical dosing drug for the numerical investigation of how administration strategy can influence drug transport and concentration distribution over time in the human eye. Administration frequencies employed in this study are 1-4 times per day, and the administration time intervals are Δt = 900 s, 1800 s, and 3600 s. Numerical results indicate that the administration frequency can significantly affect the temporal timolol concentration distributions in the ophthalmic compartments. More administrations per day can prolong the mediations at relatively high levels in all compartments. CFD simulation results also show that shorter administration intervals can help the medication maintain a relatively higher concentration during the initial hours. Longer administration intervals can provide a more stable medication concentration during the entire dosing time. Furthermore, numerical parametric analysis in this study indicates that the elimination rate in the aqueous humor plays a dominant role in affecting the drug concentrations in multiple ophthalmic compartments. However, it still needs additional clinical data to identify how much drugs can be transported into the cardiac and/or respiratory systems via blood circulation for side effect assessment.

An ion-paired moxifloxacin nanosuspension eye drop provides improved prevention and treatment of ocular infection

There are numerous barriers to achieving effective intraocular drug administration, including the mucus layer protecting the ocular surface. For this reason, antibiotic eye drops must be used multiple times per day to prevent and treat ocular infections. Frequent eye drop use is inconvenient for patients, and lack of adherence to prescribed dosing regimens limits treatment efficacy and contributes to antibiotic resistance. Here, we describe an ion-pairing approach used to create an insoluble moxifloxacin-pamoate (MOX-PAM) complex for formulation into mucus-penetrating nanosuspension eye drops (MOX-PAM NS). The MOX-PAM NS provided a significant increase in ocular drug absorption, as measured by the area under the curve in cornea tissue and aqueous humor, compared to Vigamox in healthy rats. Prophylactic and treatment efficacy were evaluated in a rat model of ocular Staphylococcus aureus infection. A single drop of MOX-PAM NS was more effective than Vigamox, and completely prevented infection. Once a day dosing with MOX-PAM NS was similar, if not more effective, than three times a day dosing with Vigamox for treating S. aureus infection. The MOX-PAM NS provided increased intraocular antibiotic absorption and improved prevention and treatment of ocular keratitis, and the formulation approach is highly translational and clinically relevant.

Incremental effect of topical and oral moxifloxacin administration with surgical intracameral prophylaxis

OBJECTIVE

To determine how supplemental perioperative topical or oral moxifloxacin administration impacts anterior chamber (AC) antibiotic concentrations beyond those achieved by intracameral (IC) administration alone for postoperative endophthalmitis (POE) prophylaxis.

DESIGN

Mathematical modeling.

METHODS

The mathematical model developed by Arshinoff, Modabber, and Felfeli was adapted to calculate all reported data. A literature review of pharmacokinetic data for topical and oral moxifloxacin was used to inform the expansion of the model.

RESULTS

Our previously constructed IC model yields a dose of moxifloxacin in the AC sufficient to confer bactericidal coverage against the most common POE pathogen, methicillin-sensitive Staphylococcus aureus (MSSA), for ∼40 hours postoperatively. Topical 0.5% moxifloxacin eye drops alone, administered every 4 or 6 hours, achieve an AC concentration just above or at the mutant prevention concentration (MPC) for MSSA, respectively, whereas 8-hour dosing produces levels generally below the MPC. Combining topical moxifloxacin with IC increases the AC concentration above IC alone only after 20 or more hours and maintains the AC concentration at, or just below, the MPC for MSSA for as long as the drops are continued. Combined perioperative oral moxifloxacin with IC increases AC levels over IC alone only after 16 hours and maintains the AC concentration above the MPC for MSSA for an additional 5 hours, owing to the systemic reservoir.

CONCLUSIONS

The addition of topical or oral moxifloxacin supplemental to IC can extend the duration of bactericidal coverage for the most common, but not the most resistant POE-causing pathogens.

Comparing Combination Drop Therapy to a Standard Drop Regimen After Routine Cataract Surgery

PURPOSE

To evaluate the efficacy of a combined steroid/antibiotic/non-steroidal anti-inflammatory drop relative to a regimen of multiple drops after cataract surgery.

SETTING

Single clinical practice in the USA.

DESIGN

Prospective randomized contralateral eye study.

METHODS

Subjects presenting for bilateral cataract surgery were enrolled with contralateral eyes randomly assigned to one of the two groups. Test eyes received a combination therapy (prednisolone acetate 1%, gatifloxacin 0.5%, and bromfenac sodium 0.075%) while control eyes received the same medications in separate drops (bromfenac sodium was 0.07%). Subjects were examined 1, 15 and 30 days after surgery. Visual acuities were measured, along with the refraction, intraocular pressure, patient pain and satisfaction, macular thickness and corneal pachymetry. The primary measure of interest was the change in macular thickness from baseline to the 15- and 30-day visits. The frequency and severity of reported ocular adverse events were tabulated for each group and compared.

RESULTS

Thirty-three subjects completed the study. Changes in central macular thickness were similar between groups, with only one control eye exhibiting significant macular edema. No differences in visual acuity, corneal edema, cells or flare were observed between groups. There were eight mild adverse events reported for all eyes of all subjects; the difference in the number of eyes experiencing adverse events was not statistically significantly different between groups (p ≥ 0.05 for all comparisons). While subjective symptoms were similar, all subjects indicated that they preferred the combination drop.

CONCLUSION

A combination drop showed similar efficacy to multiple drops and was overwhelmingly preferred by subjects.

Comparative Study Between Topical Gatifloxacin 0.5% and Moxifloxacin 0.5% as a Prophylactic Measure Before Intraocular Surgery

Purpose: To compare equal concentrations (0.5%) of moxifloxacin and gatifloxacin ophthalmic solutions with regard to conjunctival bacterial reduction as well as anterior chamber penetration. Methods: One hundred patients were divided into 2 groups. Group A received moxifloxacin 0.5% ophthalmic solution and group B received gatifloxacin 0.5% ophthalmic solution 4 times a day for 3 days before surgery and 5 times with 30 min intervals on the day of surgery. Two conjunctival swabs were obtained: one before instillation of antibiotic and the second 30 min after instillation of the last antibiotic drop. Specimens were sent for culture and susceptibility testing. At the time of surgery, 0.1 mL of aqueous fluid was aspired, and aqueous concentration of fluoroquinolones was identified using reverse-phase high-pressure liquid chromatography assay technique. Results: The most common flora isolated was coagulase-negative Staphylococcus (32.9%), followed by Staphylococcus aureus (24.8%) and Corynebacterium diphtheria (19.1%). Moxifloxacin aqueous concentration was higher compared with gatifloxacin [1.75 ± 0.98 standard deviation (SD) and 0.75 ± 0.22 SD, respectively]. This 2.3-fold difference in aqueous humor antibiotic concentrations was statistically significant (P ≤ 0.001). There was significant difference between the means of conjunctival colony-forming unit after antibiotic administration in both the study groups (2.17 ± 1.54 SD in group A and 1.56 ± 1.09 SD in group B). Conclusions: Moxifloxacin 0.5% was found to penetrate anterior chamber more than gatifloxacin 0.5%, enforcing its use for prophylaxis before intraocular surgeries. However, gatifloxacin 0.5% eye drops were able to reduce conjunctival bacterial load, more supporting its use before extraocular and refractive surgeries.

Analysis of pharmaceuticals and small molecules in aqueous humor

Aqueous humor (AH) is a transparent fluid found in the anterior chamber of the eye. The circulating AH nourishes the cornea and lens and removes the metabolic waste moving through the ocular chambers and drains from the eye to the venous blood. Analysis of drugs in AH is necessary to evaluate their pharmacokinetics parameters, which may be crucial to avoid potential adverse effects. Analysis of endogenous components of AH may help to understand its physiology as well as changes evoked by pathological situation. This review describes analytical methods used for determination of pharmaceuticals and small endogenous molecules in AH, focusing on sample preparation procedures and analytical techniques. Studies on human and animal samples are included. After inspection and filtering of records found in PubMed about 100 research papers were selected to review. In these articles AH samples of human and rabbit origin were studied most often. Sample evaporation and reconstitution in smaller solvent volume was the most popular method for analyte pre-concentration. Acetonitrile, methanol or mixture of both solvents were used most often for protein precipitation.

Diagnosis and Treatment of Listeria monocytogenes Endophthalmitis: A Systematic Review

PURPOSE

Describe patient characteristics, treatment, and vision outcomes of Listeria monocytogenes endophthalmitis, an exceedingly rare form of listeriosis.

METHODS

L. monocytogenes endophthalmitis cases in human adults, located through Medline (32) and from disease surveillance centers (11). L. monocytogenes conjunctivitis and keratitis were excluded.

RESULTS

Most cases occurred in 2000-2015 (22/43), and almost all in Europe or North America (40/43). Patients were a median 61 years, 57% male (24/42) and half were immunosuppressed. Median days from entering care to diagnosis was 8 (IQR = 5-17). Only four were exogenous infections. L. monocytogenes was identified in 31/35 of anterior eye fluid samples (89%). Antibiotic regimens varied markedly (mostly ≥3 drugs). At diagnosis, most were blind in the affected eye (85%, 28/33), only a third regained normal vision (12/36). Older patients had poorer outcomes.

CONCLUSIONS

Cases increased over time. Diagnostic delays were common and visual impairment often refractory to treatment, especially in older adults. The condition's rarity and variation in treatment makes it difficult to identify optimum therapy.

Pathogens and antibiotic sensitivities in endophthalmitis

BACKGROUND

Antibiotic prophylaxis in cataract surgery is intended to minimize endophthalmitis. We describe pathogenic organisms, antibiotic sensitivities and antibiotic prophylaxis in culture-proven endophthalmitis cases.

DESIGN

Retrospective consecutive case series and community-based setting were used.

PARTICIPANTS

Two hundred fifteen cases of endophthalmitis after cataract surgery performed during 2007-2012 in Kaiser Permanente, California.

METHODS AND MAIN OUTCOME MEASURES

Descriptive analysis of isolated organisms and antibiotic sensitivities in relation to antibiotic prophylaxis in culture-proven endophthalmitis cases.

RESULTS

The majority of culture-confirmed organisms (n = 83) were Gram positive (96%), most notably coagulase-negative Staphylococci (n = 34, 52%), of which all that underwent testing were sensitive to vancomycin (n = 32). Among 19 cases that had received only topical antibiotic prophylaxis, seven (37%) were resistant to the antibiotic given: 50% of cases (5 of 10 isolates) that had received ofloxacin were resistant to this antibiotic, 40% (2 of 5 isolates) that had received gatifloxacin were resistant. In contrast, 100% of cases (n = 4) that had received aminoglycosides were susceptible. Few culture-confirmed cases occurred in patients who received intracameral antibiotic (n = 4).

CONCLUSIONS

In cases where fluoroquinolones were administered as antibiotic prophylaxis, isolates demonstrated a degree of bacterial resistance. The majority of endophthalmitis cases isolated occured following topical antibiotic prophylaxis only and were attributed to Gram-positive organisms, while few occurred in association with intracameral antibiotic.

Natural language processing to ascertain two key variables from operative reports in ophthalmology

PURPOSE

Antibiotic prophylaxis is critical to ophthalmology and other surgical specialties. We performed natural language processing (NLP) of 743 838 operative notes recorded for 315 246 surgeries to ascertain two variables needed to study the comparative effectiveness of antibiotic prophylaxis in cataract surgery. The first key variable was an exposure variable, intracameral antibiotic injection. The second was an intraoperative complication, posterior capsular rupture (PCR), which functioned as a potential confounder. To help other researchers use NLP in their settings, we describe our NLP protocol and lessons learned.

METHODS

For each of the two variables, we used SAS Text Miner and other SAS text-processing modules with a training set of 10 000 (1.3%) operative notes to develop a lexicon. The lexica identified misspellings, abbreviations, and negations, and linked words into concepts (e.g. "antibiotic" linked with "injection"). We confirmed the NLP tools by iteratively obtaining random samples of 2000 (0.3%) notes, with replacement.

RESULTS

The NLP tools identified approximately 60 000 intracameral antibiotic injections and 3500 cases of PCR. The positive and negative predictive values for intracameral antibiotic injection exceeded 99%. For the intraoperative complication, they exceeded 94%.

CONCLUSION

NLP was a valid and feasible method for obtaining critical variables needed for a research study of surgical safety. These NLP tools were intended for use in the study sample. Use with external datasets or future datasets in our own setting would require further testing. Copyright © 2017 John Wiley & Sons, Ltd.

Effect of antibiotic prophylaxis on Coagulase-negative Staphylococcus virulence factor profiles in patients undergoing cataract surgery

PURPOSE

In this prospective study, multiplex polymerase chain reaction (PCR) was used to identify genes encoding virulence factors (ica, atlE and mecA) in Coagulase-negative Staphylococcus (CNS) isolates from the ocular microbiota of patients undergoing cataract surgery and to investigate possible changes in the CNS profile due to antibiotic prophylaxis.

METHODS

Between 09/2011 and 08/2013, patients undergoing cataract surgery were recruited at the Department of Ophthalmology, National University of Asuncion, Paraguay. In the eye to be operated on, patients received moxifloxacin 0.5 % eye drops four times at the day before surgery and a last drop 1 hour before surgery (T1). The other eye remained as control (T0). Conjunctival swabs were taken from both eyes 1 hour after the last drop. The presence of genes encoding biofilm formation (ica and atlE) and methicillin resistance (mecA) was detected by a multiplex PCR.

RESULTS

Of the 162 patients (162 study eyes, 162 fellow eye as control group), 87 (53.7 %) eyes were positive for CNS at T0 yielding 96 CNS isolates; 70 eyes (43.2 %) were positive at T1 yielding 77 CNS isolates. For this study, 43 CNS isolates (44.8 %) from T0 and 45 (64.3 %) from T1 were used. Of the total isolates, 81.8 % (72/88) had at least one virulence factor gene (37/43 from T0 and 35/45 from T1) (p = 0.314). Simultaneous detection of ica and atlE genes was higher in T0 (58.0 %) than T1 (46.7 %), but the difference was not significant (p = 0.28).

CONCLUSION

A high frequency of genes encoding virulence factors was observed in the coagulase-negative Staphylococcus isolates. The use of moxifloxacin did not significantly modify the CNS virulence factor profiles.

Transzonular vitreous injection vs a single drop compounded topical pharmaceutical regimen after cataract surgery

Purpose

To compare the relative effectiveness of a Tri-Moxi-Vanc intraocular solution injected transzonularly into the vitreous with the topical formulation of Pred-Moxi-Ketor (given for the first week postoperatively) followed by Pred-Ketor (given for weeks 2–4 after surgery).

Patients and methods

This was a single-site, single-surgeon, prospective, randomized, subject-masked contralateral eye study with an active comparator and was approved by an appropriate ethics committee. Twenty-five subjects with uncomplicated cataract who were scheduled for cataract surgery were enrolled. If surgery was uneventful, subjects received either an injection in that eye or followed a minimum drop postoperative pharmaceutical regimen. The second eye surgery was performed with the opposite treatment. Subjects were followed for 1 month. Measures of interest were the changes in intraocular pressure (IOP) from baseline and the changes in corneal and macular thickness. Subjects were also asked to evaluate pain perception, visual quality, and overall satisfaction with surgery. They were also asked which regimen they preferred.

Results

IOP was not statistically significantly different between the groups (P=0.81); there was also no statistically significant difference in IOP over time (P=0.74). There was no statistically significant difference in central macular thickness at 1 week and 1 month between the groups (P=0.18). The central corneal thickness was significantly greater 1 day postoperatively relative to baseline, but there was no statistically significant difference between the groups at any time point (P=0.92). The difference in reported pain was also not statistically significantly different between the groups (P=0.67). Satisfaction with surgery was similar for both groups, but significantly more subjects preferred the injection for overall experience (P<0.01).

Conclusion

Cataract surgery completed with the two pharmaceutical regimens was similar in outcome. Significantly more subjects preferred the injection, presumably as a function of the greater convenience with no apparent difference in the therapeutic effect.

In vivo 3D measurement of moxifloxacin and gatifloxacin distributions in the mouse cornea using multiphoton microscopy

Moxifloxacin and gatifloxacin are fourth-generation fluoroquinolone antibiotics used in the clinic to prevent or treat ocular infections. Their pharmacokinetics in the cornea is usually measured from extracted ocular fluids or tissues, and in vivo direct measurement is difficult. In this study multiphoton microscopy (MPM), which is a 3D optical microscopic technique based on multiphoton fluorescence, was applied to the measurement of moxifloxacin and gatifloxacin distribution in the cornea. Intrinsic multiphoton fluorescence properties of moxifloxacin and gatifloxacin were characterized, and their distributions in mouse cornea in vivo were measured by 3D MPM imaging. Both moxifloxacin and gatifloxacin had similar multiphoton spectra, while moxifloxacin had stronger fluorescence than gatifloxacin. MPM imaging of mouse cornea in vivo showed (1) moxifloxacin had good penetration through the superficial corneal epithelium, while gatifloxacin had relatively poor penetration, (2) both ophthalmic solutions had high intracellular distribution. In vivo MPM results were consistent with previous studies. This study demonstrates the feasibility of MPM as a method for in vivo direct measurement of moxifloxacin and gatifloxacin in the cornea.

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.

Staphylococcus aureus and its Bearing on Ophthalmic Disease

PURPOSE

To review antibiotic resistance associated with S. aureus endophthalmitis and the virulence of S. aureus.

METHODS

Review of the current and prospective approaches for treating S. aureus endophthalmitis.

RESULTS

Bacterial endophthalmitis remains to be a major threat for vision. S. aureus endophthalmitis specifically, carries a poor visual prognosis making early diagnosis and treatment crucial. Methicillin resistant Staphylococcus aureus (MRSA) endophthalmitis represents a significant number of S. aureus endophthalmitis cases. MRSA with reduced susceptibility to glycopeptide antibiotics such as vancomycin (vancomycin intermediate S. aureus, VISA) have also emerged in the ocular infections, and there has been a rise in S. aureus resistance to new and old generation fluoroquinolones that are commonly used for prophylaxis after intravitreal injections and intraocular surgeries.

CONCLUSIONS

With the rise in the number of penetrating procedures in the ophthalmology practice and the parallel rise in antibiotic resistance, prophylaxis and awareness of the antimicrobial resistance profiles remain crucial and the identification of novel antimicrobials is essential.

Rapid, sensitive and selective HPLC-MS/MS method for the quantification of topically applied besifloxacin in rabbit plasma and ocular tissues: Application to a pharmacokinetic study

Besifloxacin is a fourth-generation broad-spectrum fluoroquinolone registered for the topical treatment of bacterial conjunctivitis. In this study, a rapid, sensitive and selective liquid chromatography tandem mass spectrometry (LC-MS/MS) method was developed for quantification of besifloxacin in rabbit plasma and ocular tissues using nateglinide as the internal standard (IS). The analyte and IS were separated on a Sepax GP-Phenyl column by isocratic elution with methanol-acetonitrile-5 mM ammonium formate-formic acid (29:55:16:0.1, v/v/v/v) as the mobile phase at a flow rate of 1.2 mL/min, and the total run time was 3.0 min. An electrospray ionization (ESI) source was applied and operated in the positive ion mode; multiple reaction monitoring (MRM) mode was used for quantification, and the monitored transitions were 394.2→377.1 for besifloxacin and m/z 318.3→166.1 for the IS. The calibration curve was linear over the range of 0.103-206 ng/mL for plasma and 2.06-2060 ng/mL for tears, aqueous humor, conjunctiva and cornea with correlation coefficient (r) greater than 0.99. The lower limit of quantification (LLOQ) for besifloxacin was 0.103 ng/mL for plasma and 2.06 ng/mL for other ocular tissues with good accuracy and precision. Intra- and inter-batch precision were both lower than 15% and accuracy ranged from 85% to 115% at all QC levels. The method was successfully applied to the pharmacokinetic study of besifloxacin in rabbit plasma and ocular tissues after single and multiple topical administrations.

Antibiotic resistance in acute postoperative endophthalmitis

Acute postoperative endophthalmitis (APE) is a serious, although infrequent, complication of eye surgery that can result in significant morbidity and costs. This review addresses APE risk factors, associated bacterial pathogens, antibiotic resistance, and prevention.

Quantitative evaluation of besifloxacin ophthalmic suspension by HPLC, application to bioassay method and cytotoxicity studies

Besifloxacin (BSF) is a synthetic chiral fluoroquinolone developed for the topical treatment of ophthalmic infections. The present study reports the development and validation of a microbiological assay, applying the cylinder-plate method, for determination of BSF in ophthalmic suspension. To assess this methodology, the development and validation of the method was performed for the quantification of BSF by high performance liquid chromatography (HPLC). The HPLC method showed specificity, linearity in the range of 20-80 µg mL(-1) (r=0.9998), precision, accuracy and robustness. The microbiological method is based on the inhibitory effect of BSF upon the strain of Staphylococcus epidermidis ATCC 12228 used as a test microorganism. The bioassay validation method yielded excellent results and included linearity, precision, accuracy, robustness and selectivity. The assay results were treated statistically by analysis of variance (ANOVA) and were found to be linear (r=0.9974) in the range of 0.5-2.0 µg mL(-1), precise (inter-assay: RSD=0.84), accurate (101.4%), specific and robust. The bioassay and the previously validated high performance liquid chromatographic (HPLC) method were compared using Student's t test, which indicated that there was no statistically significant difference between these two methods. These results confirm that the proposed microbiological method can be used as routine analysis for the quantitative determination of BSF in an ophthalmic suspension. A preliminary stability study during the HPLC validation was performed and demonstrated that BSF is unstable under UV conditions. The photodegradation kinetics of BSF in water showed a first-order reaction for the drug product (ophthalmic suspension) and a second-order reaction for the reference standard (RS) under UVA light. UVA degraded samples of BSF were also studied in order to determine the preliminary in vitro cytotoxicity against mononuclear cells. The results indicated that BSF does not alter the cell membrane and has been considered non-toxic to human mononuclear cells in the experimental conditions tested.

Emerging 8-methoxyfluoroquinolone resistance among methicillin-susceptible Staphylococcus epidermidis isolates recovered from patients with endophthalmitis

Fluoroquinolones remain the most commonly used antimicrobials for the prevention and management of bacterial endophthalmitis. Coagulase-negative staphylococci are the most frequently recovered pathogens. Increasing resistance among this group has paralleled the presence of methicillin resistance. From 2005 to 2010, we recovered 38 methicillin-susceptible Staphylococcus epidermidis (MSSE) isolates from endophthalmitis patients at our institute, including 15 (39.5%) isolates resistant to gatifloxacin and moxifloxacin, members of the C-8-methoxyfluoroquinolones family. Mutations in the quinolone resistance-determining regions (QRDR) of gyrA and parC were determined and correlated with fluoroquinolone MICs based on Etests of these 15 MSSE isolates. High-level resistance (MIC, >32 μg/ml) to gatifloxacin and moxifloxacin was documented for 46.7% of the MSSE isolates, and low-level resistance (MIC, 2 to 4 μg/ml) was determined for 53.3%. The MICs for ciprofloxacin, levofloxacin, and ofloxacin were >32 μg/ml for all isolates. The amino acid substitution Ser84Phe in gyrA was found among all isolates. A second mutation in gyrA (Glu88Lys) resulted in high-level resistance to moxifloxacin and gatifloxacin. Almost all (92.8%) isolates presented double point mutations in the parC gene at codons 80 and 84 with different combinations. Eighty-seven percent of the patients had prior exposure to topical 8-methoxyfluoroquinolones. Prior exposure to the 8-methoxyfluoroquinolones may contribute to the selection of MSSE strains containing multiple mutations in the QRDRs of gyrA and parC that results in low- and high-level resistance to these agents.

Role of topical, subconjunctival, intracameral, and irrigative antibiotics in cataract surgery

PURPOSE OF REVIEW

To summarize current understanding of antibiotic prophylaxis in cataract surgery, with particular emphasis on available evidence and change in practice patterns over the past decade.

RECENT FINDINGS

Povidone-iodine application prior to cataract surgery remains a universal practice, and is backed by good quality evidence. Subsequent to the results of the European multicenter trial documenting decreased risk of endophthalmitis with intracameral cefuroxime injection at the end of surgery, similar benefit with intracameral antibiotic use has been reported in studies with large sample sizes from multiple centers around the world. There has been a distinct change in practice patterns in many countries, with intracameral antibiotic use becoming part of routine protocol. In the USA, topical fluoroquinolone application remains the most popular mode of antibiotic prophylaxis. A promising approach is the development of novel drug delivery methods like polymeric devices designed for sustained antibiotic release.

SUMMARY

Based on current evidence, the recommended measures for endophthalmitis prophylaxis are preoperative topical instillation of povidone-iodine and intracameral antibiotic injection at the end of cataract surgery.

Endophthalmitis following cataract surgery: the role of prophylactic postoperative chloramphenicol eye drops

PURPOSE

The main aim of the study was to assess whether omitting prophylactic postoperative topical antibiotics (chloramphenicol) influenced the risk of developing endophthalmitis after cataract surgery.

METHODS

We conducted a retrospective study including all patients who had cataract surgery at our outpatient cataract unit between 2004 and 2011. Postoperative topical antibiotics (chloramphenicol) were omitted from 2007 onwards, as was the first postoperative day review. Patients with a diagnosis of endophthalmitis after cataract surgery were extracted, and the rate of postoperative endophthalmitis (PE) before and after changing these routines was compared. The diagnosis of PE was defined as severe intraocular inflammation requiring prompt vitreous sampling for culture.

RESULTS

Seven thousand one hundred and twenty-three and 8131 cataract surgeries were performed in the following periods: January 2004 through December 2006 (period 1) and January 2007 through December 2010 (period 2), respectively. Five cases of PE were identified in period 1 (0.070%) and four patients in period 2 (0.049%). The median time between cataract surgery and onset of symptoms was 6 days in period 1 and 4.5 days in period 2. Median time for intervention was 7 and 5 days postsurgery, respectively.

CONCLUSION

We found no difference in the frequency of PE following cataract surgery when changing the postoperative topical medication from a mixture of corticosteroids and antibiotics to only corticosteroids.

Besifloxacin ophthalmic suspension, 0.6%: a novel topical fluoroquinolone for bacterial conjunctivitis

Acute bacterial conjunctivitis, the most common cause of conjunctivitis, is responsible for approximately 1% of all primary-care consultations. Of the topical ophthalmic antibiotics used to treat acute bacterial conjunctivitis, fluoroquinolones are especially useful because they possess a broad antibacterial spectrum, are bactericidal in action, are generally well tolerated, and have been less prone to development of bacterial resistance. Besifloxacin, the latest advanced fluoroquinolone approved for treating bacterial conjunctivitis, is the first fluoroquinolone developed specifically for topical ophthalmic use. It has a C-8 chlorine substituent and is known as a chloro-fluoroquinolone. Besifloxacin possesses relatively balanced dual-targeting activity against bacterial topoisomerase IV and DNA gyrase (topoisomerse II), two essential enzymes involved in bacterial DNA replication, leading to increased potency and decreased likelihood of bacterial resistance developing to besifloxacin. Microbiological data suggest a relatively high potency and rapid bactericidal activity for besifloxacin against common ocular pathogens, including bacteria resistant to other fluoroquinolones, especially resistant staphylococcal species. Randomized, double-masked, controlled clinical studies demonstrated the clinical efficacy of besifloxacin ophthalmic suspension 0.6% administered three-times daily for 5 days to be superior to the vehicle alone and similar to moxifloxacin ophthalmic solution 0.5% for bacterial conjunctivitis. In addition, besifloxacin ophthalmic suspension 0.6% administered two-times daily for 3 days was clinically more effective than the vehicle alone for bacterial conjunctivitis. Besifloxacin has also been shown in preclinical animal studies to be potentially effective for the "off-label" treatment of infections following ocular surgery, prophylaxis of endophthalmitis, and the treatment of bacterial keratitis. Taken together, clinical and preclinical animal studies indicate that besifloxacin is an important new option for the treatment of ocular infections.

Prevention of postcataract endophthalmitis: evidence-based medicine

PURPOSE OF REVIEW

To provide a summary of current peer-reviewed publications on the methods of prophylaxis against postcataract endophthalmitis.

RECENT FINDINGS

Preoperative application of povidone-iodine remains the standard protocol for the prevention of postoperative endophthalmitis. More recent evidence suggests that intracameral cefuroxime administered at the conclusion of surgery significantly reduces the risk of endophthalmitis. However, its clinical use has been limited because of a lack of commercially available antibiotic indicated for intraocular injection. Although topical antibiotic application continues to be a controversial topic with respect to the types of antibiotic prescribed and dosage, most ophthalmologists do prescribe an antibiotic for the perioperative period. Resistance against antibiotics, including the very popular classes of fluoroquinolones, is rising. Most notably, methicillin resistance continues to increase over time.

SUMMARY

Prevention of postcataract endophthalmitis remains a difficult topic to study given the low incidence. In addition to appropriate wound construction, a combination of povidone-iodine and antibiotics provide a reasonable approach in reducing the risk of this rare but serious infection.

The use of the African green monkey as a preclinical model for ocular pharmacokinetic studies

PURPOSE

This investigation evaluated the ocular and systemic pharmacokinetics of besifloxacin in African green monkeys compared with cynomolgus monkeys following topical ocular dosing.

METHODS

A suspension formulation containing 0.6% besifloxacin was administered to African green and cynomolgus monkeys. Animals were euthanized at predetermined time intervals, and ocular tissue and systemic blood samples were collected and analyzed by LC/MS/MS.

RESULTS

In both African green and cynomolgus monkeys, high concentrations of besifloxacin were detected in anterior segment tissues, while levels in posterior segment tissues and plasma were low. Mean concentration versus time profiles of besifloxacin were generally similar between species, with rapid absorption into ocular tissues after a single dose. In anterior segment tissues, concentrations of besifloxacin were measurable throughout the 24-h sampling period in both species. Quantitatively, concentrations were consistently higher in the conjunctiva of African green monkeys compared with cynomolgus monkeys. Besifloxacin levels were also higher during the first 3 h following dosing in the tear fluid of African green monkeys, but lower in the iris/ciliary body during this timeframe. However after the 3-h time point, concentrations in the tear fluid and iris/ciliary body were similar between species. Exposure in cornea tended to be higher in African green monkeys, but the difference was less pronounced than for conjunctiva. Exposure in aqueous humor was comparable between species. In posterior segment tissues, exposure to besifloxacin tended to be higher in cynomolgus monkeys. Systemic exposure also tended to be higher in cynomolgus monkeys, but measurable levels were present in the plasma of both species throughout the 24-h sampling period. With the exception of iris/ciliary body and vitreous humor, mean ocular tissue weights were generally similar between species although a small, but statistically significant, difference was also observed in the choroid.

CONCLUSIONS

African green monkeys may be a suitable model for preclinical ocular pharmacokinetic studies. Additional studies using a variety of compounds would be useful in determining whether the quantitative differences in ocular exposures and ocular tissue weights observed in the present investigation reflect slight variations in the procedures used in these separate experiments, or true physiological and anatomical differences between species.

Challenges in assessing microbial susceptibility and predicting clinical response to newer-generation fluoroquinolones

PURPOSE

To determine the most appropriate methods for assessing the potential effectiveness of the newer topical fluoroquinolones gatifloxacin, moxifloxacin, and besifloxacin.

METHODS

This article is based on a literature search for published articles about the pharmacokinetic (PK) and pharmacodynamic (PD) characteristics of and measure of bacterial susceptibility to topical ophthalmic fluoroquinolones. Search terms included fluoroquinolones, susceptibility, resistance, minimal/minimum inhibitory concentration (MIC), PDs, PKs, and ocular, ophthalmic, or topical antibiotics.

RESULTS

Topical fluoroquinolones, particularly besifloxacin, gatifloxacin, and moxifloxacin, have become important treatment options for common ocular bacterial infections due to their broad-spectrum bactericidal activity and low toxicity. An important challenge in ophthalmology is identifying the most accurate in vivo and in vitro methods for evaluating the efficacy of these topical fluoroquinolones. The MIC is the most commonly used measure of in vitro susceptibility. In systemic therapy, this measure is combined with PK data of antibiotics to generate PD indices PK/PD whose breakpoints differentiate clinically susceptible from nonsusceptible bacterial pathogen populations. PD breakpoints are further tested in prospective studies for their ability to predict clinical efficacy. However, it is not known whether systemically derived breakpoints apply to the assessment of clinical susceptibility to ocular agents. Topical ocular antibiotics likely achieve higher concentrations at the target site than do systemically administered antibiotics, but these higher concentrations can be quickly reduced by reflex tearing and blinking induced by instillation. Hence, studies have been conducted in animals and humans to determine the PK concentrations of topically administered antibiotics in ocular compartments. When combined with MIC values for topical pathogens, the results have the potential to predict clinical efficacy after identification of the appropriate PK/PD target. Ocular studies incorporating PK/PD assessments have recently begun to be reported with newer fluoroquinolones, including besifloxacin, gatifloxacin, and moxifloxacin, whose prolonged contact time and potent bactericidal activity have translated into some of the most favorable PK/PD target values. However, the clinical relevance of these studies has yet to be determined.

CONCLUSION

There is still a clear need for predictive models to extend our understanding of the clinical susceptibility of ocular pathogens.