Masamichi Fukuda

A comparison of moxifloxacin and levofloxacin topical prophylaxis in a fluoroquinolone-resistant Staphylococcus aureus rabbit model

PurposeMoxifloxacin, a fourth-generation fluoroquinolone (FQ), was compared to levofloxacin, a thirdgeneration FQ, for preventing FQ-resistant, methicillin-resistant Staphylococcus aureus (FQrMRSA) endophthalmitis in a rabbit model.MethodsThree regimens of topical treatments (moxifloxacin 0.5%, levofloxacin 0.5%, and saline) were tested to prevent endophthalmitis. For each regimen, drops were instilled every 15 min for 1 h into the left eyes of 15 rabbits. After anesthesia, 2 × 104 cfu of FQrMRSA was injected into the aqueous. One drop of treatment was given immediately, and another four drops were applied over 24 h. At 24 h, the eyes were clinically graded for endophthalmitis. After the rabbits were sacrificed, the aqueous and vitreous were tapped for bacterial colony counts.ResultsTopical moxifloxacin (12/15, 80%) significantly (P = 0.0001) prevented clinical endophthalmitis in more rabbits than levofloxacin (2/15, 13%) or saline (2/15, 13%). The total median clinical score for moxifloxacin treatment (1.0) was significantly (P = 0.0004) lower than that for levofloxacin (20.0) or saline (23.0). Culture-negative eyes were less frequent for levofloxacin (8/15, 53%) and saline (1/15, 7%) treatments than for moxifloxacin treatment (12/15, 80%).ConclusionThis in vivo study indicates that moxifloxacin, a fourth-generation FQ, may be more effective than levofloxacin, a third-generation FQ, in preventing experimental FQrMRSA. endophthalmitis.

Studies on the binding mechanism of fluoroquinolones to melanin

Abstract In order to elucidate the binding mechanism of melanin and fluoroquinolones (ofloxacin, norfloxacin, ciprofloxacin, lomefloxacin, levofloxacin), we investigated the interaction of fluoroquinolones with compounds such as l-β-(3,4-dihydroxyphenyl) alanine (l-DOPA), l-tyrosine, 5-hydroxy-l-tryptophan, l-tryptophan, and l-phenylalanine, which possess the kind of functional groups that melanin does and are closely related to melanin. The recovery of drugs from the melanin-drug complexes by metal ions of Li, Na, Ka, Mg, Ca, Ba, Cu, Ni, and Fe was demonstrated. Smaller and highly charged cations were found to be more effective for this recovery, and magnesium ions were the most effective of all the ions investigated.

Studies on diabetic cataract in rats induced by streptozotocin. II: Biochemical examinations of rat lenses in relation to cataract stages

Biochemical examinations of streptozotocin-induced diabetic cataracts in rats were performed and related to different stages of lens opacifications. Sorbitol levels in lenses showed maximum accumulation at stages I-III and began to decrease from stage IV. Glucose levels indicated a relatively constant accumulation, but became higher between stage V and VI. Fructose levels increased less significantly from stage I-IV, and slightly decreased thereafter. Inositol was not detectable from stage I. The sodium-potassium ratio (Na/K) increased slowly from stage I-IV, and rose remarkably at stage V. Hydration of the lenses showed no change between stage I and IV, and after stage V it rose markedly.

The Effect of the Corneal Epithelium on the Intraocular Penetration of Fluoroquinolone Ophthalmic Solution

PurposePharmacokinetic studies of antibacterial agents for infectious eye diseases have usually been performed on normal rabbit eyes. In this study, the intraocular penetration of fluoroquinolone ophthalmic solutions was determined in normal rabbit eyes and in rabbit eyes that had the corneal epithelium intentionally removed.MethodsWe determined the intraocular penetration of ofloxacin (OFLX), levofloxacin (LVFX), and norfloxacin (NFLX), fluoroquinolone ophthalmic solutions that are already on the market and undergoing clinical studies, by injecting 50 µl of each solution into the cul-de-sacs of rabbit eyes three times at 15-min intervals. The drug concentration at 10, 30, 60, 120, and 240 min after final instillation was determined by high-performance liquid chromatography.ResultsThe maximum concentration in the aqueous humor of normal rabbit eyes was 2.09 ± 1.56 µg/ml (60 min, OFLX), 2.57 ± 1.00 µg/ml (30 min, LVFX), and 0.42 ± 0.12 µg/ml (120 min, NFLX). The drug concentration in the aqueous humor of eyes with intentionally removed corneal epithelium was 12.50 ± 5.62 µg/ml (30 min, OFLX), 9.02 ± 2.45 µg/ml (60 min, LVFX), and 8.54 ± 5.17 µg/ml (30 min, NFLX). The drug penetration of the eye drops into eyes with removed corneal epithelium was around 6 times (OFLX), 3.5 times (LVFX), and 20 times (NFLX) higher than the penetration into the eye with normal cornea.ConclusionAmong the pharmacokinetic parameters of the three ophthalmic solutions according to the one-compartment model, the maximum concentration in the aqueous and the area under the concentration–time curve in the aqueous tended to be higher in the eyes with intentionally removed corneal epithelia than in those with normal corneas. Jpn J Ophthalmol 2004;48:93–96

Quantitative evaluation of corneal epithelial injury caused by n-heptanol using a corneal resistance measuring device in vivo

Purpose We attempted to develop a device for measuring electrical corneal resistance (CR) using corneal contact lens electrodes to quantitatively evaluate corneal injury in vivo. In the present study, full-thickness detachment of the corneal epithelium was induced by n-heptanol, and the feasibility of the quantitative evaluation of this injury by corneal contact lens electrodes was evaluated in vivo. Methods The central area of an albino rabbit’s cornea was exposed to a filter paper pre-immersed in n-heptanol for 1 minute to induce injury of the corneal epithelium. After induction of injury, the electrical CR was measured and the percentage of CR (%CR) was calculated. Fluorescein solution (3 μL) was applied to the wound/affected area of the corneal epithelium for photography with a slit-lamp biomicroscope. The wound/affected area was measured using an image analysis system. The correlation between the %CR and the wound/affected area was analyzed. Results As the size of the wound/affected area of the corneal epithelium increased, the %CR decreased after corneal epithelium detachment. Thus, a close correlation was found between the area of corneal epithelium detachment and the %CR. Conclusion The corneal resistance device that we developed was capable of quantitatively evaluating n-heptanol-induced full-thickness injuries of the corneal epithelium.

Changes in the antibacterial activity of melanin-bound drugs

Affinity to melanin and changes of antibacterial activity of melanin-bound drugs were examined in 11 drugs, all of which showed an affinity for melanin. The highest melanin-binding ratio was seen in aminoglycosides. Among these, sisomicin sulfate (SISO) had the highest binding ratio (95.5%). The melanin-binding ratios seen in sulbenicillin sodium (SBPC), cephalosporins and fluoroquinolones were relatively low during the early phase of the reaction, but increased with time. The highest ratio seen in cefazolin sodium was 60.1%. Melanin-bound aminoglycosides showed a reduction in their antibacterial activity with both Bacillus subtilis and Escherichia coli. The reduction rate in the antibacterial activity of melanin-bound SISO against B. subtilis was 50.0% and that against E. coli was 43.0%. No changes in antibacterial activity were seen in the other 6 drugs bound to melanin.

Calculation of AQCmax: comparison of five ophthalmic fluoroquinolone solutions*.

ABSTRACT Objective: Ocular tissue penetration of five different ophthalmic fluoroquinolone solutions in the rabbit eye was measured and evaluated by an index of the maximum aqueous concentration (AQCmax). Methods: Moxifloxacin 0.5% (MFLX), levofloxacin 0.5% (LVFX), gatifloxacin 0.3% (GFLX), ofloxacin 0.3% (OFLX), or tosufloxacin tosilate 0.3% (TFLX) were instilled into the eyes of white rabbits every 15 min for a total of three doses. Aqueous humor, cornea, iris/ciliary body and vitreous body were collected 10 to 240 min after instillation and drug concentrations were measured by high-performance liquid chromatography. Results: The concentration of MFLX was the highest in each tissue, with maximum concentrations of MFLX in the aqueous humor (10.16 ± 1.59 µg/mL) at 30 min after instillation, cornea (156.07 ± 95.97 µg/g) and iris/ciliary body (11.92 ± 4.00 µg/g) at 10 min after instillation, and vitreous body (0.099 ± 0.033 µg/mL) at 30 min after instillation. The concentration of TFLX was the lowest in each tissue, with LVFX, GFLX, and OFLX sharing the mid-ranks. AQCmax : MIC90 ratio for S. aureus was 150.67 for MFLX, 10.6 for LVFX, 9.69 for GFLX, 3.48 for OFLX, and could not be determined for TFLX. Conclusion: AQCmax is a useful pharmacokinetic parameter for determining the therapeutic efficacy of an ophthalmic antibiotic, especially when combined with MIC90 values for intraocular pathogens. Cmax of MFLX ophthalmic solution was superior in all tissues (cornea, aqueous humor, iris/ciliary body and vitreous body) among the five ophthalmic solutions studied, exceeding the MIC90 of S. aureus in all tissues, and MIC90s of S. epidermidis, B. cereus, and P. acnes in aqueous humor, cornea, and iris/ciliary body. AQCmax was approximately proportional to Cmax in iris/ciliary body and vitreous, and may be used in combination with MIC90s as an index to predict the most appropriate dose and frequency of ophthalmic antibiotics in conjunction with other PK/PD parameters. This study may provide the groundwork for calculation of AQCmax in humans.

General Purpose Antimicrobial Ophthalmic Solutions Evaluated Using New Pharmacokinetic Parameter of Maximum Drug Concentration in Aqueous

PURPOSE In order to determine whether the one-component method for calculating drug concentration in the aqueous (AQC(max)) is useful for selecting an appropriate ophthalmic solution, six general purpose antimicrobial ophthalmic solutions already on the market were investigated. METHODS The drugs examined were levofloxacin (LVFX), chloramphenicol (CP), erythromycin lactobionate (EM), micronomicin sulfate (MCR), cefmenoxime hydrochloride (CMX), and disodium sulfobenzyl penicillin (SBPC). Fifty microliters of each solution was instilled into the cul-de-sac of New Zealand White rabbit eyes three times at 15-minute intervals. The drug concentrations in the aqueous humor 10, 30, 60, 120, and 240 minutes after the final instillation were examined by high performance liquid chromatography (HPLC) and/or bioassay. The AQC(max) was calculated using the one-compartment method. RESULTS The calculated AQC(max) was 2.5 microg/mL (HPLC method) and 2.28 microg/mL (bioassay method) for LVFX, 2.17 microg/mL for CP, and 0.45 microg/mL for EM. The AQC(max) for CMX, MCR, and SBPC could not be calculated by the one-compartment method. CONCLUSIONS The AQC(max) of LVFX was higher than that of the two other general purpose antimicrobial ophthalmic solutions. The AQC(max) of these drugs might be a useful parameter for selecting an appropriate ophthalmic solution for the treatment of infected eyes.

Measurement of AQCmax of five different ophthalmic solutions and discussion of its new application.

PURPOSE After measuring the pharmacokinetic parameters of five fluoroquinolone ophthalmic solutions, we utilized the obtained indices to try to predict the clinical effects of antimicrobial ophthalmic solutions and apply the characteristics to the index for inhibition of resistant bacteria. METHODS Each ophthalmic solution was instilled in white rabbit eyes 3 times every 15 min and the anterior chamber aqueous humor was collected 10, 30, 60, 120, and 240 min after instillation. Drug concentrations were measured by high-performance liquid chromatography (HPLC) to determine the maximum aqueous concentration (AQCmax) of each drug by using a 1-compartment model. RESULTS Moxifloxacin (MFLX) had the highest AQCmax, 9.04 microg/mL, among the five drugs, followed by levofloxacin (LVFX, 2.65 microg/mL), gatifloxacin (GFLX, 1.26 microg/mL), ofloxacin (OFLX, 0.89 microg/mL), and tosufloxacin (TFLX, 0.42 microg/mL) in descending order of AQCmax. Furthermore, the AQCmax/MPC (mutant prevention concentration) against Staphylococcus aureus was 15.07 and 1.06 for MFLX and LVFX, respectively. The AQCmax/MPC against Streptococcus pneumoniae was 18.08 and 1.15 for MFLX and LVFX, respectively. CONCLUSIONS From these results, we can expect that the MFLX ophthalmic solution will be a sufficiently effective therapeutic agent in the treatment of eye infection, prevention of postoperative endophthalmitis, and prevention of drug resistance.

Different Iris Coloration and Uptake of a Fluoroquinolone Agent into the Iris Ciliary Body of Rabbit Eyes

In order to know the correlation of a drug with high affinity to melanin in the iris ciliary body with the amount of melanin contained in the iris ciliary tissues, an in vivo study was performed on pigmented rabbits with brown or blue irises and albino rabbits. The melanin concentrations in the iris ciliary bodies of pigmented rabbits with brown and blue irises and nonpigmented rabbit eyes with whitish irises were determined. The mean concentrations of melanin in the eyes with brown-, blue- and whitish-colored irises were 47.43, 34.73 and below 0.2 microgram/mg tissue, respectively. The amount of sparfloxacin uptake in the iris ciliary bodies of eyes with brown, blue and whitish irises administered as 40 microliters of 0.3% solution 5 times every 5 min was 15.46 +/- 2.07, 8.53 +/- 1.87 and 1.9 micrograms/g, respectively. The results may be useful for intraocular drug dynamics studies.