Pharmacokinetics of sparfloxacin in the serum and vitreous humor of rabbits: physicochemical properties that regulate penetration of quinolone antimicrobials

Permeability of the Retina and RPE-Choroid-Sclera to Three Ophthalmic Drugs and the Associated Factors

In this study, Retina-RPE-Choroid-Sclera (RCS) and RPE-Choroid-Sclera (CS) were prepared by scraping them off neural retina, and using the Ussing chamber we measured the average time-concentration values in the acceptor chamber across five isolated rabbit tissues for each drug molecule. We determined the outward direction permeability of the RCS and CS and calculated the neural retina permeability. The permeability coefficients of RCS and CS were as follows: ganciclovir, 13.78 ± 5.82 and 23.22 ± 9.74; brimonidine, 15.34 ± 7.64 and 31.56 ± 12.46; bevacizumab, 0.0136 ± 0.0059 and 0.0612 ± 0.0264 (×10^-6 cm/s). The calculated permeability coefficients of the neural retina were as follows: ganciclovir, 33.89 ± 12.64; brimonidine, 29.83 ± 11.58; bevacizumab, 0.0205 ± 0.0074 (×10^-6 cm/s). Between brimonidine and ganciclovir, lipophilic brimonidine presented better RCS and CS permeability, whereas ganciclovir showed better calculated neural retinal permeability. The large molecular weight drug bevacizumab demonstrated a much lower permeability than brimonidine and ganciclovir. In conclusion, the ophthalmic drug permeability of RCS and CS is affected by the molecular weight and lipophilicity, and influences the intravitreal half-life.

Signal Detection Between Fluoroquinolone Use and the Risk of Rhegmatogenous Retinal Detachment: Sequence Symmetry Analysis Using Nationwide South Korean Healthcare Database Between 2004 and 2015

BACKGROUND AND OBJECTIVES

The association between fluoroquinolone and rhegmatogenous retinal detachment (RRD) has been controversial as a result of inconsistent findings. We set out to detect a possible association of fluoroquinolone use and risk of RRD, using sequence symmetry analysis (SSA).

METHODS

We conducted an SSA, case-only design, using a Korean nationwide healthcare database between 2004 and 2015. Exposure was defined as new fluoroquinolone use and outcome as an incident RRD, defined by a diagnosis of RRD (ICD-10: "H33.0") or surgery for RRD. Pairs of exposure and RRD within a 1-year time-window were included. The sequence ratio (SR) was calculated by the ratio of the number of patients prescribed with exposure first and diagnosed with RRD second divided by the number of patients diagnosed with RRD first and prescribed with exposure second. SR was adjusted (aSR) for underlying trends and 95% confidence intervals (CIs) were calculated. In order to observe whether the estimated ratio stabilized over time, we did repeated time-sequential analyses with the cumulative data starting from the 3-year period 2004-2006 to 2015.

RESULTS

Fluoroquinolone use had a greater association with RRD as compared with other antibiotics [fluoroquinolone: 5234 pairs; aSR = 1.70 (95% CI 1.61-1.80), first-generation cephalosporin: 4139 pairs; aSR = 1.39 (95% CI 1.31-1.80), second-generation cephalosporin: 5914 pairs; aSR = 1.31 (95% CI 1.24-1.38), third-generation cephalosporin: 3650 pairs; aSR = 0.88 (95% CI 0.83-0.95), extended-spectrum penicillin: 4823 pairs; aSR = 1.29 (95% CI 1.31-1.47), macrolides: 4115 pairs; aSR = 1.31 (95% CI 1.24-1.39)]. Time-sequential analyses supported the association between fluoroquinolone and RRD.

CONCLUSIONS

Our detection suggests a possible association between fluoroquinolone use and RRD. However, possible overestimation and reverse causality bias may have influenced our findings due to the limitation of an SSA design.

Least median of squares and iteratively re-weighted least squares as robust linear regression methods for fluorimetric determination of α-lipoic acid in capsules in ideal and non-ideal cases of linearity

This study outlines two robust regression approaches, namely least median of squares (LMS) and iteratively re-weighted least squares (IRLS) to investigate their application in instrument analysis of nutraceuticals (that is, fluorescence quenching of merbromin reagent upon lipoic acid addition). These robust regression methods were used to calculate calibration data from the fluorescence quenching reaction (∆F and F-ratio) under ideal or non-ideal linearity conditions. For each condition, data were treated using three regression fittings: Ordinary Least Squares (OLS), LMS and IRLS. Assessment of linearity, limits of detection (LOD) and quantitation (LOQ), accuracy and precision were carefully studied for each condition. LMS and IRLS regression line fittings showed significant improvement in correlation coefficients and all regression parameters for both methods and both conditions. In the ideal linearity condition, the intercept and slope changed insignificantly, but a dramatic change was observed for the non-ideal condition and linearity intercept. Under both linearity conditions, LOD and LOQ values after the robust regression line fitting of data were lower than those obtained before data treatment. The results obtained after statistical treatment indicated that the linearity ranges for drug determination could be expanded to lower limits of quantitation by enhancing the regression equation parameters after data treatment. Analysis results for lipoic acid in capsules, using both fluorimetric methods, treated by parametric OLS and after treatment by robust LMS and IRLS were compared for both linearity conditions.

Ocular Pharmacokinetics

Although the fundamental concepts of pharmacokinetics remain the same, ocular pharmacokinetics has its own challenges due to the uniqueness of barrier properties posed by various ocular tissues and its growing complexity with different routes of ocular administration. A thorough understanding of the barrier nature will aid in tailoring a drug or its carrier's physicochemical properties to its advantage. In order to deliver the right payload of a drug at the target site, various approaches can be taken to leverage the pharmacokinetics that includes molecular design based on desirable physicochemical properties, formulation approaches, and alternative routes of administration. In this chapter, a brief overview of the barrier properties with respect to various routes of administration is presented along with the physicochemical properties that influence the pharmacokinetics of ocular drugs. Recent advances in ocular pharmacokinetics are discussed in addition to new perspectives in interpreting existing data.

Prediction of Ocular Drug Distribution from Systemic Blood Circulation

Systemically circulating drugs may distribute to ocular tissues across the blood-ocular barriers. Ocular distribution is utilized in the treatment of ocular diseases with systemic medications, but ocular delivery of systemic drugs and xenobiotics may also lead to adverse ocular effects. Ocular distribution after systemic drug administration has not been predicted or modeled. In this study, distribution clearance between vitreous and plasma was obtained from a previous QSPR model for clearance of intravitreal drugs. These values were used in a pharmacokinetic simulation model to describe entry of unbound drug from plasma to vitreous. The simulation models predicted ocular distribution of 10 systemic drugs in rabbit eyes within 1.96 mean fold error and the distribution of cefepime from plasma to vitreous in humans. This is the first attempt to predict ocular distribution of systemic drugs. Reliable predictions were obtained using systemic concentrations of unbound drug, computational value of ocular distribution clearance, and a simple pharmacokinetic model. This approach can be used in drug discovery to estimate ocular drug exposure at an early stage.

Retina-choroid-sclera permeability for ophthalmic drugs in the vitreous to blood direction: quantitative assessment

PURPOSE

To determine the outward permeability of retina-choroid-sclera (RCS) layer for different ophthalmic drugs and to develop correlations between drug physicochemical properties and RCS permeability.

METHODS

A finite volume model was developed to simulate pharmacokinetics in the eye following drug administration by intravitreal injection. The RCS permeability was determined for 32 compounds by best fitting the drug concentration-time profile obtained by simulation with previously reported experimental data. Multiple linear regression was then used to develop correlations between best fit RCS permeability and drugs physicochemical properties.

RESULTS

The RCS drug permeabilities had values that ranged over 3 × 10(-6) m/s. Regression analysis for hydrophilic compounds showed that more than 92% of the variation in permeability values can be explained by correlative models of drug properties that include logarithm of the octanol-water partition coefficient (LogP), protein binding (PB), number of hydrogen bond acceptors (HBA), hydrogen bond donors (HBD), polar surface area (PSA) and dissociation constant (pKa) as independent variables. Regression analysis for lipophilic compounds showed that no significant correlation can be found between just physicochemical properties and RCS permeability.

CONCLUSION

Using the RCS permeability obtained from this study for different drugs, one can predict pharmacokinetics of intravitreal drug delivery systems such as solid implants or colloidal systems. Furthermore, the developed correlations between RCS permeability and physicochemical properties of drugs are useful in early drug development by predicting RCS permeability and drug concentration in the vitreous without experimental data.

A comparison of fluoroquinolone penetration into human conjunctival tissue

INTRODUCTION

Ocular penetration of newer fluoroquinolones (FQs) has not been fully investigated in humans, especially in regard to conjunctival tissue penetration. The aim of our study was to evaluate the conjunctival permeability of 3 FQs, which do not contain benzalkonium chloride, using excised pterygium tissue.

METHODS

Patients undergoing pterygium surgery received a single application of one of the following: 0.5% moxifloxacin (MFLX), 0.3% gatifloxacin (GFLX), or 0.5% levofloxacin (LVFX). Samples of conjunctival tissue were collected 10, 30, or 45 min following administration of the study drug. Each sample was analyzed by high-performance liquid chromatography, and drug concentrations were measured over time.

RESULTS

Conjunctival concentration of all 3 FQs was highest 10 minutes after instillation, then gradually decreased. At all time points, MFLX showed the highest conjunctival concentrations among the 3 drugs. Mean MFLX concentrations were 116.7 +/- 28.9, 19.0 +/- 6.3, and 15.9 +/- 4.7 microg/g at 10, 30, and 45 min, respectively, and were statistically greater than GFLX or LVFX concentrations at 10 and 45 min.

CONCLUSIONS

All tested FQs achieved peak concentrations within 10 min following administration. Initial peak concentrations of MFLX were greater than either GFLX or LVFX, and concentrations of MFLX remained highest among the 3 FQs throughout the 45-min time window.

Intraocular pharmacokinetics of intravenously administered marbofloxacin in rabbits with experimentally induced acute endophthalmitis

OBJECTIVE

To compare penetration of IV administered marbofloxacin in intraocular fluids of healthy and inflamed eyes in rabbits with endotoxin-induced endophthalmitis.

ANIMALS

35 pigmented rabbits.

PROCEDURES

Endophthalmitis was induced in the right eye via intravitreal administration of Escherichia coli endotoxin. The left eye was a control eye. After 24 hours, a single dose of marbofloxacin (4 mg/kg, IV) was administered. Groups of rabbits (n = 5/group) were euthanized 0.5, 1, 2, 4, 6, 10, and 18 hours later, and blood and ocular fluids were collected. Marbofloxacin concentrations were determined via reverse-phase high-performance liquid chromatography, and pharmacokinetic analysis of the data was performed with a mono-compartmental model.

RESULTS

Mean area under the aqueous concentration-time curve was significantly lower in control eyes (1.64 +/- 0.07 microg*h/mL) than in inflamed eyes (3.31 +/- 0.11 microg*h/mL). Similarly, drug penetration into aqueous humor was 33% and 65% for control eyes and inflamed eyes, respectively. Mean area under the vitreous humor concentration-time curve for control eyes(1.75 +/- 0.05 microg*h/mL) was significantly less than for inflamed eyes (2.39 +/- 0.16 microg*h/mL). In the vitreous humor, corresponding penetrations were 34% and 47%, respectively.

CONCLUSIONS AND CLINICAL RELEVANCE

Penetration of marbofloxacin into the aqueous and vitreous humor after IV administration was significantly enhanced by intraocular inflammation, suggesting a role for this antimicrobial in the prophylaxis or treatment of bacterial endophthalmitis caused by susceptible pathogens.

Vitreous and aqueous penetration of orally administered moxifloxacin in humans

OBJECTIVE

To investigate the intraocular penetration of moxifloxacin into the aqueous and vitreous after oral administration in humans.

METHODS

A prospective, nonrandomized study of 27 consecutive patients scheduled for elective parsplana vitrectomy surgery between 1 October and 31 December 2004 was carried out. Aqueous, vitreous, and serum samples were obtained and analysed after oral administration of a single 400 mg tablet of moxifloxacin a few hours before surgery. Assays were performed using high-performance liquid chromatography.

RESULTS

Mean+/-SD moxifloxacin concentrations in the serum (n=27), aqueous (n=25), and vitreous (n=27) were 1.34+/-0.98, 0.21+/-0.21, and 0.09+/-0.09 microg/ml, respectively. The mean+/-SD sampling times after oral administration of the moxifloxacin tablet for serum, aqueous, and vitreous were 2.02+/-0.51, 1.53+/-0.45, and 1.55+/-0.46 h, respectively. The minimum inhibitory concentration for 90% of isolates (MIC90) was far exceeded in the aqueous for a wide spectrum of key pathogens, whereas it was not exceeded in the vitreous for several organisms. Of note, the MIC90 for Staphylococcus epidermidis was not exceeded in any of the samples.

CONCLUSIONS

Orally administered moxifloxacin achieves measurable levels in the noninflammed human eye, with the aqueous levels effective against a variety of pathogens. However, the spectrum of coverage does not appropriately encompass the most common causative organisms in endophthalmitis, especially Staphylococcus epidermidis. Further studies are needed to precisely define the role of oral moxifloxacin in the treatment of or prophylaxis against intraocular infections.

Fourth-Generation Fluoroquinolone Penetration into the Aqueous Humor in Humans

PURPOSE

To compare the penetration and levels of the fourth-generation fluoroquinolones moxifloxacin 0.5% ophthalmic solution and gatifloxacin 0.3% solution in the aqueous humor (AH) in humans after topical application with published levels of other available fluoroquinolones under similar dosing conditions.

DESIGN

Prospective, randomized, double-masked clinical trial.

PARTICIPANTS

Forty-six patients undergoing cataract extraction.

METHODS

Patients scheduled for routine phacoemulsification and intraocular lens implantation were provided either moxifloxacin 0.5% ophthalmic solution (n = 22) or gatifloxacin 0.3% ophthalmic solution (n = 24) to use 4 times daily the day before surgery plus 1 drop 1 hour before the surgical entry into the anterior chamber on the day of surgery. This regimen simulated a realistic postoperative dosing schedule. Aqueous humor samples were obtained and analyzed by high-pressure liquid chromatography. Aqueous humor fluoroquinolone concentrations were calculated by peak comparison with a known concentration peak for ciprofloxacin that was used as an internal standard. These values were compared with published concentrations of other available fluoroquinolones under similar dosing conditions.

RESULTS

The mean age of the moxifloxacin 0.5% group was 67.8+/-9.7 years, whereas that of the gatifloxacin 0.3% group was 69.9+/-8.7 years. The moxifloxacin AH concentration was 1.86+/-1.06 microg/ml, and that of gatifloxacin was 0.94+/-0.72 microg/ml. This 2-fold difference was statistically significant (P = 0.001).

CONCLUSIONS

Aqueous humor antibiotic concentrations achieved at the time of cataract surgery after topical application can serve as an effective surrogate for what can be achieved with typical postoperative topical dosing (e.g., 4 times daily). Both fourth-generation fluoroquinolones achieved a greater AH concentration after 4 times daily dosing relative to prior-generation fluoroquinolones. Moxifloxacin 0.5% ophthalmic solution achieved a 2-fold higher aqueous humor concentration than gatifloxacin 0.3% ophthalmic solution. The superior penetration of moxifloxacin into the AH may be attributed partially to its high degree of lipophilicity, greater solubility at neutral pH, and higher concentration in the commercial formulation. The enhanced penetration of moxifloxacin 0.5% ophthalmic solution may provide better protection against ocular infections.

Moxifloxacin efficacy and vitreous penetration in a rabbit model of Staphylococcus aureus endophthalmitis and effect on gene expression of leucotoxins and virulence regulator factors

Bacterial endophthalmitis is a serious complication of ocular surgery and of eye trauma; the leading causative organisms are Staphylococcus aureus strains. Tissue damage is due both to the host inflammatory response and to toxin synthesis by bacteria. Systemic treatment remains difficult because most antibiotics show poor ocular penetration. Moxifloxacin (MXF), a novel fluoroquinolone, was evaluated for its penetration into the vitreous of normal rabbit eyes and of eyes of rabbits infected for 24 h with methicillin-susceptible and methicillin-resistant S. aureus (MSSA and MRSA) following a single intravenous administration of 5 or 20 mg/kg. MXF penetration was rapid and efficient regardless of the dose, ranging from 28 to 52%. An inflammatory state of the vitreous significantly increased penetration after the 20-mg/kg dose, with penetration reaching 52%. Concentrations determined in the vitreous cavity following a 20-mg/kg administration showed a 3.5-fold decrease of the bacterial density within 5 h for MSSA (MIC, 0.125 micro g/ml) and a 1.6-fold decrease for MRSA (MIC, 4 micro g/ml) strains, respectively. By using a semiquantitative reverse transcription-PCR method, the expression of luk-PV and hlgCB, but not hlgA, encoding staphylococcal leukotoxins, was detected in the vitreous without MXF treatment. A slight decrease in the expression of leucotoxins and sarA, agr, and sigB virulence regulatory factors was observed 1 h following the administration of 5 mg of MXF per kg.

Intraocular concentration and pharmacokinetics of triamcinolone acetonide after a single intravitreal injection

PURPOSE

To describe the pharmacokinetics occurring after the direct injection of triamcinolone acetonide into the vitreous humor of humans.

DESIGN

Interventional case series.

PARTICIPANTS

Five patients who received a single 4-mg intravitreal injection of triamcinolone acetonide.

METHODS

An aqueous humor sample was obtained from 5 eyes via an anterior chamber paracentesis at days 1, 3, 10, 17, and 31 after injection. At each visit, visual acuity and intraocular pressure were measured and indirect ophthalmoscopy was performed. A fluorescein angiogram was carried out at day 10. Concentrations were determined using high performance liquid chromatography; pharmacokinetic analysis was carried out using PK Analyst, an iterative, nonlinear, weighted, least-squares regression program.

MAIN OUTCOME MEASURES

Intraocular concentrations of triamcinolone were measured and population pharmacokinetic parameters were calculated.

RESULTS

Pharmacokinetic data followed a two-compartment model. Peak aqueous humor concentrations ranged from 2151 to 7202 ng/ml, half-lives from 76 to 635 hours, and the integral of the area under the concentration-time curve (AUC(0-t)) from 231 to 1911 ng/h per milliliter. After a single intravitreal injection of triamcinolone, the mean elimination half-life was 18.6 days in nonvitrectomized patients. The half-life in a patient who had undergone a vitrectomy was shorter at 3.2 days.

CONCLUSIONS

There was considerable intrasubject variation among peak concentration, AUC(0-t) values, and elimination half-lives. After intravitreal injection, measurable concentrations of triamcinolone would be expected to last for approximately 3 months (93 +/- 28 days) in the absence of a vitrectomy. Because triamcinolone pharmacokinetics were characterized only in elderly patients with macular edema, the results cannot be extrapolated to other patient populations.

Clinical role of protein binding of quinolones

Protein binding of antibacterials in plasma and tissues has long been considered a component of their pharmacokinetic parameters, playing a potential role in distribution, excretion and therapeutic effectiveness. Since the beginning of the 'antibacterial era', this factor has been extensively analysed for all antibacterial classes, showing that wide variations of the degree of protein binding occur even in the same antibacterial class, as with beta-lactams. As the understanding of protein binding grew, the complexity of the binding system was increasingly perceived and its dynamic character described. Studies of protein binding of the fluoroquinolones have shown that the great majority of these drugs exhibit low protein binding, ranging from approximately 20 to 40% in plasma, and that they are bound predominantly to albumin. The potential role in pharmacokinetics-pharmacodynamics of binding of fluoroquinolones to plasma, tissue and intracellular proteins has been analysed, but it has not been established that protein binding has any significant direct or indirect impact on therapeutic effectiveness. Regarding the factors influencing the tissue distribution of antibacterials, physicochemical characteristics and the small molecular size of fluoroquinolones permit a rapid penetration into extravascular sites and intracellularly, with a rapid equilibrium being established between intravascular and extravascular compartments. The high concentrations of these drugs achieved in tissues, body fluids and intracellularly, in addition to their wide antibacterial spectrum, mean that fluoroquinolones have therapeutic effectiveness in a large variety of infections. The tolerability of quinolones has generally been reported as good, based upon long experience in using pefloxacin, ciprofloxacin and ofloxacin in clinical practice. Among more recently developed molecules, good tolerability has been reported for levofloxacin, moxifloxacin and gatifloxacin, but certain other new compounds have been removed from the market because of renal, hepatic and cardiac toxicity. To what extent the protein binding of fluoroquinolones can play a role in their tolerability is unclear. In terms of drug-drug interactions, the role of protein binding is questionable: several drug combinations can be responsible for toxicity, such as with beta-lactams, metronidazole, theophylline, nonsteroidal anti-inflammatory agents or a series of drugs used for cardiac diseases, but protein binding does not seem to be involved in these interactions. In conclusion, protein binding of fluoroquinolones appears to be a complex phenomenon, but has no clear role in therapeutic effectiveness or toxicity.

Comparative study on salivary distribution of fluoroquinolones in rats

As a basic approach to identifying the distribution mechanism of quinolone antibiotics into saliva, salivary excretion of five fluoroquinolones, ciprofloxacin (CPFX), norfloxacin (NFLX), lomefloxacin (LFLX), ofloxacin (OFLX) and sparfloxacin (SPFX), was compared in rats. Blood, parotid and mandibular saliva were periodically collected from the anesthetized rats after bolus i.v. administration (10 mg/kg) of the quinolones. Quantification of the fluoroquinolones was performed by HPLC methods. The saliva-to-plasma unbound concentration (S/Pu) ratios of the fluoroquinolones in parotid saliva were larger than those of mandibular saliva. These five quinolones had considerably different S/Pu ratios from 0.014 to 1.497, while the S/Pu ratios theoretically calculated by the pH-partition theory were around 1.0 to 1.3, which showed no relationship to the corresponding measured ratios. Satisfactory linear correlations were observed in the plots of measured S/Pu ratios against 1-octanol-water partition coefficients of the fluoroquinolones in both types of saliva. These results indicate that fluoroquinolones possess different diffusibility in salivary distribution among the drugs and between parotid and mandibular glands. It was also clarified that the lipophilicity of the fluoroquinolones primarily determines the extent of salivary excretion.

Human aqueous humor levels of oral ciprofloxacin, levofloxacin, and moxifloxacin

PURPOSE

To evaluate the penetration of ciprofloxacin, levofloxacin, and moxifloxacin into the aqueous humor after oral administration.

SETTING

Alcorcon Hospital, Madrid, Spain.

METHODS

Forty-two patients having cataract surgery were randomly divided into 3 groups the day before surgery. The first group received 2 oral 500 mg doses of ciprofloxacin at 12-hour intervals. The second group received a single oral 500 mg dose of levofloxacin. The third group received a single oral 400 mg dose of moxifloxacin. At the time of surgery, 0.1 mL aqueous fluid was aspirated from the anterior chamber just before the operation and immediately stored at -80 degrees C. Drug concentrations were measured using a biological assay.

RESULTS

The mean aqueous level of ciprofloxacin was 0.50 microg/mL +/- 0.25 (SD); of levofloxacin, 1.50 +/- 0.50 microg/mL; and of moxifloxacin, 2.33 +/- 0.85 microg/mL. The mean aqueous levels of levofloxacin and moxifloxacin were above the 90% minimum inhibitory concentration for most of the common microorganisms that cause endophthalmitis.

CONCLUSIONS

Therapeutic concentrations of fluoroquinolones, mainly levofloxacin and moxifloxacin, were reached with oral administration. These antibiotics may be effective for prophylaxis and adjuvant therapy of bacterial endophthalmitis.