Influence of sex on the pharmacokinetic interaction of fleroxacin and ciprofloxacin with caffeine

BACKGROUND

Previous pharmacokinetic studies have shown that a number of the quinolones inhibit the metabolism of caffeine.

OBJECTIVE

To evaluate the effect of sex on the interaction between two quinolones and caffeine.

DESIGN

Multiple-dose, double-blind, randomised, three-period crossover study.

PARTICIPANTS

Twelve male and twelve female healthy volunteers.

METHODS

Subjects received by mouth either fleroxacin 400 mg once daily and caffeine 100 mg three times daily, ciprofloxacin 500 mg twice daily and caffeine 100 mg three times daily, or caffeine alone, for 3 days. Subjects received each of the other regimens after 12-day washout periods. Plasma and urine concentrations were determined by validated high-performance liquid chromatography procedures and the data were analysed by noncompartmental linear pharmacokinetic methods.

RESULTS

Analysis of the interaction by sex revealed that females showed a significant difference in caffeine pharmacokinetics in the presence of ciprofloxacin (area under the concentration-time curve [AUC], peak plasma concentration [C(max)], time to C(max) [t(max)] and apparent total body clearance [CL/F]) and fleroxacin (AUC and CL/F) when compared with males. Significant differences between sexes were also observed in the pharmacokinetics of ciprofloxacin (AUC, elimination rate constant [beta] and CL/F) and fleroxacin (C(max) and beta) in the presence of caffeine. However, these significant differences disappeared when AUC and C(max) were normalised to 70 kg bodyweight and CL/F was expressed as per kg bodyweight.

CONCLUSION

The effect of quinolones on the pharmacokinetics of caffeine, and the reciprocal effect, are different between the sexes, due in part to different bodyweights.

Fleroxacin uptake in ischaemic limb tissue

Antibiotic application to patients with ischaemia of lower limbs may be indicated to avoid or treat infection of soft tissues. Fleroxacin, a fluoroquinolone, active against various Gram-negative and Gram-positive organisms may be used for this purpose. We evaluated the diffusion of fleroxacin into bone, subcutaneous fat, muscle and tendon tissues of lower limb tissue after a 400 mg i.v. dose. Concentrations in ischaemic tissues were similar to those found in non-ischaemic sites. Since the maximum antibiotic levels found were lower than the MICs of various pathogens relevant for infection, we suggest to increase the dose used for this peri-operative prophylaxis to 800 mg.

In vitro and in vivo investigations on fluoroquinolones; effects of the P-glycoprotein efflux transporter on brain distribution of sparfloxacin

The role of mdr1a-encoded P-glycoprotein on transport of several fluoroquinolones across the blood-brain barrier was investigated. In vitro, P-glycoprotein substrates were selected by using a confluent monolayer of MDR1-LLC-PK1 cells. The inhibition of fluoroquinolones (100 microM) on transport of rhodamine-123 (1 microM) was compared with P-glycoprotein inhibitors verapamil (20 microM) and SDZ PSC 833 (2 microM). Subsequently, transport polarity of fluoroquinolones was studied. Sparfloxacin showed the strongest inhibition (26%) and a large polarity in transport, by P-glycoprotein activity. In vivo, using mdr1a (-/-) and wild-type mice, brain distribution of pefloxacin, norfloxacin, ciprofloxacin, fleroxacin and sparfloxacin was determined at 2, 4, and 6 h following intra-arterial infusion (50 nmol/min). Brain distribution of sparfloxacin was clearly higher in mdr1a (-/-) mice compared with wild-type mice. Sparfloxacin was infused (50 nmol/min) for 1, 2, 3 and 4 h in which intracerebral microdialysis was performed. At 4 h, in vivo recovery (dynamic-no-net-flux method) was 6.5+/-2.2 and 1.5+/-0.5%; brain(ECF) concentrations were 5.1+/-0.2 and 26+/-21 microM; and total brain concentrations were 7.2+/-0.3 and 23+/-0.3 microM in wild-type and mdr1a (-/-) mice, respectively. Plasma concentrations were similar (18.4+/-0.7 and 17.9+/-0.5 microM, respectively). In conclusion, sparfloxacin enters the brain poorly mainly because of P-glycoprotein activity at the blood-brain barrier.

Bioavailability of ciprofloxacin and fleroxacin: results of a preliminary investigation in healthy adult Nigerian male volunteers

The absolute bioavailability (BA) of ciprofloxacin and fleroxacin were evaluated in 19 adult Nigerian male volunteers. Subjects meeting the selection criteria were randomized to receive treatment either with fleroxacin (200 mg-i.v. and 200 mg oral dose) or ciprofloxacin (200 mg-i.v. and 250 mg oral dose). The i.v./oral or oral/i.v. switch was made after a one week washout period. Blood and urine samples were collected at pre-determined time intervals over a 72 h period for analysis of drug levels. Following intravenous administration the maximum serum concentration (Cmax) was 2.7+/-1.06mg/l for ciprofioxacin and 0.99+/-0.41 mg/l for fleroxacin; the area under the blood level curve (AUC) was 8.82+/-3.19 mg x h/l with ciprofloxacin and 8.52+/-3.83 mg x h/l with fleroxacin. Following oral administration the Cmax was 1.52+/-0.94 mg/l with ciprofloxacin and 0.57+/-0.08 mg/l with fleroxacin; the AUC was 9.87+/-4.10 and 7.55+/-1.42 mg x h/l, respectively. The absolute BA following oral administration was found to be 0.79+/-0.47 for ciprofloxacin and 1.01+/-0.78 for fleroxacin. When these BA results were corrected for renal clearance [Cl(r)] and elimination half-life (t1/2) the values were reduced to 0.37+/-0.17 and 0.31+/-0.18, respectively, for ciprofloxacin and 0.53+/-0.23 and 0.99+/-0.38, respectively, for fleroxacin. Only 38% with ciprofloxacin and 59% with fieroxacin, of the administered dose, was excreted unchanged following oral administration. More work, however, needs to be done on ciprofloxacin to support and/or confirm the above findings. Fleroxacin, on the one hand, exhibited a different trend from that observed in the literature with respect to Cmax and AUC where the values observed in this study were 3--4 fold lower than expected following identical doses, whilst on the other hand the observed BA profile in this study was consistent with literature trends.

The pharmacokinetics of oral fleroxacin and ciprofloxacin in plasma and sputum during acute and chronic dosing

AIMS

To examine the pharmacokinetics of ciprofloxacin and fleroxacin in plasma and sputum of patients with an acute exacerbation of chronic bronchitis or bronchiectasis following the first dose and again during the third day of treatment.

METHODS

Twelve patients, aged >35 years, with acute infective exacerbation of bronchitis or bronchiectasis were allocated randomly to treatment with either fleroxacin 400 mg daily or ciprofloxacin 500 mg twice daily in an open, parallel group design. Plasma and sputum were collected during the first and third days of treatment. The time course of concentrations in sputum was modelled assuming that it acted as a negligibly small compartment of distribution.

RESULTS

The mean sputum to plasma ratios of both ciprofloxacin and fleroxacin were approximately 1 on both days 1 and 3. Peak concentrations of ciprofloxacin in sputum were achieved 1.6 (95% CI on mean difference 0.8-2.3) and 1.2 (0.4-1.9) h later than in plasma on day 1 and day 3, respectively (mean difference +/- 95% confidence interval). For fleroxacin, the corresponding delay in time to peak concentrations was less marked and not significant. Fleroxacin accumulated in plasma (accumulation index 1.52+/-0.07) and sputum (accumulation index 1.79+/-0.39) from day 1 to day 3. Accumulation did not occur for ciprofloxacin because the dose interval (12 h) was considerable longer than its half life (3-4 h).

CONCLUSIONS

The sputum to plasma ratio of ciprofloxacin and fleroxacin is approximately 1. The time to peak concentrations of ciprofloxacin in sputum is slightly delayed compared with plasma. Fleroxacin accumulates over time in both plasma and sputum consistent with its longer half-life.

Single-dose pharmacokinetic study of ciprofloxacin and fleroxacin in healthy adult Nigerian volunteers

The kinetics of absorption, distribution and elimination of ciprofloxacin and fleroxacin (following an intravenous dose of 200 mg), were evaluated in 24 adult healthy male Nigerian volunteers. Appropriate mathematical models were applied with the aid of a microcomputer software program for the estimation of the basic pharmacokinetic parameters. Appropriate statistical tests and profiles formed the basis for accepting or rejecting a proposed model. For parametric comparisons between the profile of the two drugs, the null hypothesis of no difference in their pharmacokinetic profile was proposed. All statistical tests were performed at a significance level of 95% (alpha = 0.05) and the 95% confidence level was determined where appropriate. Additionally, the model-independent or stochastic method of analysis was also employed in the pharmacokinetic evaluation of the blood level data. The parametric estimates obtained from both methods were compared. The plasma elimination half-life (t1/2) was estimated as 13.8 +/- 5.5 h for fleroxacin and 7.5 +/- 4.0 h for ciprofloxacin; the maximal plasma concentration (Cmax) was 0.8 +/- 0.3 and 2.3 +/- 1.0 mg/l for fleroxacin and ciprofloxacin, respectively, whilst the volume of distribution (Vd) was 2.5 +/- 1.6 and 0.4 +/- 0.3 liters/kg for fleroxacin and ciprofloxacin, respectively. 71 and 70% of unchanged drug were excreted in urine for fleroxacin and ciprofloxacin, respectively. With respect to comparative values, the results confirmed trends already observed in the literature, particularly as regards the t1/2. However, for fleroxacin there was a significant deviation from the literature trends with respect to Vd, Cmax and AUC. The results also confirmed earlier findings, advocating a once-daily dosage schedule for fleroxacin also in the Negroid population.

Drug disposition in cystic fibrosis

There are many pathological changes in patients with cystic fibrosis (CF) which can lead to alterations in drug disposition. Although, in patients with CF, the extent of drug absorption varies widely and the rate of absorption is slower, bioavailability is not altered. Plasma protein binding for the majority of drugs studied did not differ in patients with CF compared with control groups. The difference in volume of distribution of most drugs between patients with CF and healthy individuals vanished when corrected for lean body mass. Despite hepatic dysfunction, patients with CF have enhanced clearance of many, but not all, drugs. Phase I mixed-function oxidases are selectively affected: cytochrome P450 (CYP) 1A2 and CYP2C8 have enhanced activity, while other CYP isoforms such as CYP2C9 and CYP3A4 are unaffected. Increased phase II activities are also demonstrated: glucuronyl transferase, acetyl transferase (NAT1) and sulfotransferase. The increased hepatic clearance of drugs in the presence of CF may be the consequence of disease-specific changes in both enzyme activity and/or drug transport within the liver. The renal clearance (CLR) of many drugs in patients with CF is enhanced although there has been no pathological abnormality identified which could explain this finding: glomerular filtration rate and tubular secretion appear normal in patients with CF. The precise mechanisms for enhanced drug clearance in patients with CF remain to be elucidated. The optimisation of antibiotic therapy in patients with CF includes increasing the dose of beta-lactams by 20 to 30% and monitoring plasma concentrations of aminoglycosides. The appropriate dosage of quinolones has not been definitively established.

Urinary excretion and bactericidal activities of a single oral dose of 400 milligrams of fleroxacin versus a single oral dose of 800 milligrams of pefloxacin in healthy volunteers

Twelve healthy volunteers participated in this randomized crossover study to compare the concentrations and recovery levels of fleroxacin and pefloxacin in urine and to assess their bactericidal activities against 12 strains of urinary pathogens with different susceptibilities over a wide range of MICs. The volunteers received a single oral dose of 400 mg of fleroxacin or 800 mg of pefloxacin. The mean cumulative renal excretion of unchanged fleroxacin, N-demethyl-fleroxacin, and N-oxide-fleroxacin accounted for 67, 7, and 6% of the total dose, respectively. The total urinary recovery of pefloxacin and the active metabolite norfloxacin was 34%. In the time-kill and the urinary bactericidal titer (UBT) studies, only the subjects' urine not supplemented with broth was used. With most tested organisms and both quinolones it took more than 8 h to achieve a reduction in CFU of 99.9% (3 log units). Overall, there was a good correlation between UBTs and MICs for the strains. Against Escherichia coli ATCC 25922 the median UBTs were similar for both antibiotics and at least 1:8 for 96 h; against the E. coli strain for which the MIC was 0.5 microgram/ml the UBT was at least 1:4 for 48 h. The UBTs of both drugs against Klebsiella pneumoniae were at least 1:16 for 72 h. The UBTs for Staphylococcus aureus (the MIC for which was 16 micrograms/ml) of both antibiotics were low, and in some of the samples, no bactericidal titers were observed. UBTs for Proteus mirabilis of pefloxacin are significantly higher than those of fleroxacin. For Pseudomonas aeruginosa the median UBTs were present for the 24-to-48-h interval. The same is true for Enterococcus faecalis. Against Staphylococcus saprophyticus, UBTs were present for at least 48 h with both quinolones. Overall, a single oral dose of 400 mg of fleroxacin exhibits UBTs comparable to those of 800 mg of pefloxacin. Therefore, it may be expected that half of the dose of fleroxacin gives comparable results in the treatment of urinary tract infections; this should be substantiated in comparative clinical trials.

Rapid and simple determination of fleroxacin in rat plasma using a solid-phase extraction column

We studied the use of high-performance liquid chromatography (HPLC) with a spectroflurometric detector, using a solid-phase extraction column (Bond Elut cartridge column), for the simple, rapid and sensitive determination of plasma fleroxacin (FLRX) levels in rats. Extracted aliquots were analyzed by HPLC, using a reverse phase octadecyl silica column. The analytical mean recovery of FLRX added to the blank plasma averaged 101.4%. The detection limit was 58 ng/ml in the plasma. The reproducibilities (C.V.) were 0.50-3.22% in the within-day assay and 2.87 C.V.% in the between-day assay, indicating that the analysis method was effective in the determination of FLRX plasma levels.

Characterization of peripheral-compartment kinetics of antibiotics by in vivo microdialysis in humans

The calculation of pharmacokinetic/pharmacodynamic surrogates from concentrations in serum has been shown to yield important information for the evaluation of antibiotic regimens. Calculations based on concentrations in serum, however, may not necessarily be appropriate for peripheral-compartment infections. The aim of the present study was to apply the microdialysis technique for the study of the peripheral-compartment pharmacokinetics of select antibiotics in humans. Microdialysis probes were inserted into the skeletal muscle and adipose tissue of healthy volunteers and into inflamed and noninflamed dermis of patients with cellulitis. Thereafter, volunteers received either cefodizime (2,000 mg as an intravenous bolus; n = 6), cefpirome (2,000 mg as an intravenous bolus; n = 6), fleroxacin (400 mg orally n = 6), or dirithromycin (250 mg orally; n = 4); the patients received phenoxymethylpenicillin (4.5 x 10(6) U orally; n = 3). Complete concentration-versus-time profiles for serum and tissues could be obtained for all compounds. Major pharmacokinetic parameters (elimination half-life, peak concentration in serum, time to peak concentration, area under the concentration-time curve [AUC], and AUC/MIC ratio) were calculated for tissues. For cefodizime and cefpirome, the AUCtissue/AUCserum ratios were 0.12 to 0.35 and 1.20 to 1.79, respectively. The AUCtissue/AUCserum ratios were 0.34 to 0.38 for fleroxacin and 0.42 to 0.49 for dirithromycin. There was no visible difference in the time course of phenoxymethylpenicillin in inflamed and noninflamed dermis. We demonstrated, by means of microdialysis, that the concept of pharmacokinetic/pharmacodynamic surrogate markers for evaluation of antibiotic regimens originally developed for serum pharmacokinetics can be extended to peripheral-tissue pharmacokinetics. This novel information may be useful for the rational development of dosage schedules and may improve predictions regarding therapeutic outcome.

Pharmacokinetics of fleroxacin after multiple oral dosing in patients receiving regular hemodialysis

The pharmacokinetic profile of fleroxacin was studied in eight noninfected patients receiving regular hemodialysis (four women and four men; mean age, 63 years; age range, 48 to 73 years). Dialysis clearances (mean +/- standard deviation) calculated from the amount of drug recovered in the dialysate exceeded those calculated from rates of extraction from plasma for fleroxacin (126 +/- 29 versus 73 +/- 11 ml/min) and its metabolite N-demethylfleroxacin (103 +/- 31 versus 72 +/- 15 ml/min) but not that for the metabolite fleroxacin N-oxide (100 +/- 25 versus 100 +/- 12 ml/min). Data were fitted to a two-compartment model over the total observation period of 8 days (six oral daily doses of 200 mg of fleroxacin on days 1 to 6 and hemodialysis treatments on day 1,3, and 6) by nonlinear mixed-effects modeling. The random variability of plasma fleroxacin concentrations was 13% about its prediction. The estimated metabolic clearance was 25 ml/min (coefficient of variation, 43%), and the calculated steady-state volume of distribution was 84 liters (coefficient of variation, 16%). The model was expanded for the two major metabolites by the addition of a two-compartment metabolite distribution. Formation clearances of N-demethylfleroxacin and fleroxacin N-oxide were estimated to be 54 and 33% of fleroxacin's metabolic clearance, respectively. The conclusions were as follows. Because of the slow metabolic clearance and intermittent dialysis treatment, steady-state conditions were not reached after 1 week of oral fleroxacin therapy, and there was relevant accumulation of fleroxacin as well as that of fleroxacin N-oxide in our patients with end-stage renal disease. We recommend that infected hemodialysis patients be treated with an initial oral dose of 400 mg of fleroxacin and then daily oral doses of 200 mg. One cannot recommend the treatment of this patient population with fleroxacin over prolonged time periods until more date about the levels of accumulation of fleroxacin and its metabolites in infected patients with renal disease are available.

Kinetics of quinolone antibiotics in rats: efflux from cerebrospinal fluid to the circulation

PURPOSE

An active transport system, which pumps quinolone antimicrobial agents (quinolones) from cerebrospinal fluid (CSF) to systemic blood, exists at the choroid plexus, an epithelial tissue that forms the blood-CSF barrier (BCSFB). The present study was carried out to clarify the contribution of this transport system to the disposition of quinolones in the central nervous system.

METHOD

Six quinolones were administered intracerebroventricularly to rats and their elimination from the CSF was examined. The inhibitory effect of probenecid and quinolones on the efflux of fleroxacin from the CSF was also examined. Probenecid or two types of quinolone (AM-1155, pefloxacin) were co-administered intracerebroventricularly with fleroxacin.

RESULTS

The elimination clearance from the CSF for norfloxacin, AM-1155, fleroxacin, ofloxacin, sparfloxacin and pefloxacin was 14, 22, 21, 20, 47 and 35 microliters/min/rat, respectively. An approximately 3.5-fold difference was thus observed between norfloxacin and sparfloxacin. These values were 4- to 14-fold larger than the [14C]mannitol clearance. Furthermore, the elimination clearance of quinolones from the CSF was 7- to 60-fold larger than the active efflux clearance at the BCSFB estimated from our previous in vitro data. Co-administration of AM-1155, pefloxacin and probenecid did not inhibit the elimination of fleroxacin from the CSF.

CONCLUSIONS

The active transport system at the BCSFB plays only a small part in the elimination of quinolones from the CSF. Passive diffusion via the BCSFB and diffusion across the ependymal surface into brain extracellular fluid, followed by efflux across the blood-brain barrier, may be the predominant pathway for quinolone elimination from the CSF.

Oral fleroxacin prophylaxis in transurethral surgery

PURPOSE

A prospective trial was done to test the efficacy of antimicrobial prophylaxis in patients undergoing transurethral surgery.

MATERIALS AND METHODS

A total of 75 adults with preoperatively sterile urine was randomized to receive either 400 mg. oral fleroxacin once daily or placebo as long as the catheter was in place. Urine cultures were obtained preoperatively and after removal of the catheter just before hospital discharge. Growth of 10(4)/ml. or more bacteria was considered a positive urine culture.

RESULTS

Postoperative urinary tract infection rates were significantly lower in the fleroxacin group (3%) than in the placebo group (23%). Our study demonstrated the benefit of antimicrobial prophylaxis in preventing urinary tract infection after transurethral surgery, including resection of the prostate, in patients with sterile urine.

CONCLUSIONS

The oral administration of 1 daily tablet of fleroxacin for the duration of catheterization is a safe, efficacious and clinically feasible regimen.

Characterization of the transport properties of a quinolone antibiotic, fleroxacin, in rat choroid plexus

PURPOSE

It is reported that the cerebrospinal fluid (CSF) to plasma unbound concentration ratio of fleroxacin at steady-state is approximately 0.5 in experimental animals. These results can be accounted for by assuming the presence of an active transport system for the efflux of this compound across the choroid plexus. In the present study, the transport system for fleroxacin was characterized in isolated rat choroid plexus.

METHODS

Choroid plexus was isolated from the lateral ventricles of rats. The accumulation of [14C] fleroxacin or [3H] benzylpenicillin by the choroid plexus was examined by the centrifugal filtration method.

RESULTS

The accumulation of [14C] fleroxacin by the rat isolated choroid plexus was significantly inhibited by metabolic inhibitors (rotenone, 30 microM and carbonyl cyanide rho-trifluorometh oxyphenylhydrazone (FCCP), 100 microM) and sulfhydryl reagent (p-chloromercuribenzenesulfonic acid (PCMBS), 100 microM). This accumulation was composed of a saturable component (Vmax = 240 pmol.min-1.microliter tissue-1, Km = 664 microM) and non-saturable one (P = 0.424 min-1.microliter tissue-1). Accumulation of fleroxacin was competitively inhibited by benzylpenicillin and probenecid with Ki values of 29 microM and 51 microM, respectively. These values are comparable with the Km of benzylpenicillin transport and the Ki of probenecid for the benzylpenicillin transport at the choroid plexus, respectively. Furthermore, fleroxacin inhibited competitively the accumulation of [3H] benzylpenicillin with a Ki of 384 microM, a value comparable with the Km of [14C] fleroxacin transport.

CONCLUSIONS

Fleroxacin and benzylpenicillin showed mutual competitive inhibition, suggesting that both are transported via a common transport system in the choroid plexus and are pumped out from CSF into the circulation.

Pharmacokinetics of oral fleroxacin in male and premenopausal female volunteers

The pharmacokinetics of oral fleroxacin were compared in men and premenopausal women. The total volume of distribution of the drug was significantly smaller in women in the single-dose trial. No difference in other pharmacokinetic parameters was noted. Since adverse events appear to occur in women more commonly than in men, dose-response studies of fleroxacin in women may be appropriate.

Pharmacokinetics of [18F]fleroxacin in patients with acute exacerbations of chronic bronchitis and complicated urinary tract infection studied by positron emission tomography

The pharmacokinetics of fleroxacin, a new broad-spectrum fluoroquinolone, were measured by positron emission tomography (PET) with [18F]fleroxacin in five patients with acute bacterial exacerbations of chronic bronchitis and in five patients with symptomatic, complicated urinary tract infection. Two studies were performed with each patient, one within 24 h of the initiation and one within 24 h of the completion of a 7-day course of fleroxacin, 400 mg/day. For each study, the patient received an infusion of that day's therapeutic dose of fleroxacin (400 mg) supplemented with approximately 740 MBq of [18F]fleroxacin, and serial PET images and blood samples were collected for 6 to 8 h starting at the initiation of the infusion. Between studies, the drug was administered orally. In all infected tissues, there was rapid accumulation of radiolabeled drug, with stable levels achieved within 1 h after completion of the infusion. In kidneys, accumulation was greater in the presence of active infection (P < 0.01), while in lungs, accumulation was lower (P < 0.02). Infection of the lung or urinary tract had no effect on drug delivery to uninvolved tissues. Also, there was no difference between the results obtained at the beginning and the end of therapy. Overall, peak concentrations of drug many times the MIC at which 90% of the infecting organisms are inhibited (MIC90) were achieved in the kidneys (> 30 micrograms/g), prostate glands (> 11 micrograms/g), and lungs (> 14 micrograms/g). Plateau concentrations (2 to 8 h; given as mean micrograms per gram +/- standard error of the mean) of drug in kidneys (15.11 +/- 0.55), prostate glands (5.08 +/- 0.19), and lungs (5.75 +/- 0.22) were also well above the MIC90 for most relevant pathogens. All patients had a good therapeutic response to fleroxacin.

Penetration of ciprofloxacin and fleroxacin into biliary tract

Forty patients with chronic cholecystitis or cholelithiasis were prospectively randomized for therapy with either ciprofloxacin or fleroxacin to study the penetration of these two agents into gallbladder tissue, plasma, and bile. Patients received a 3-day course of ciprofloxacin (500 mg twice a day) or fleroxacin (400 mg once daily) and were subdivided into four groups reflecting intraoperative sample collection at 4, 7, 14, and 25 to 26 h following the last quinolone dose. Mean concentrations in plasma for ciprofloxacin and fleroxacin at 4 and 25 to 26 h postdose were 2.5 and 10 micrograms/ml and 0.3 and 1.8 micrograms/ml, respectively. The concentrations of ciprofloxacin and fleroxacin in bile and gallbladder wall tissue at 25 to 26 h postdose were 4.5 and 8.6 micrograms/ml and 1.2 and 4.4 micrograms/ml, respectively. Both agents demonstrate rapid tissue penetration with persistence at levels appropriate for treatment of biliary pathogens.

Fleroxacin overview

Fleroxacin is a new oral and intravenous trifluorinated 4-quinolone, which acts by inhibiting the essential bacterial enzyme DNA gyrase. Fleroxacin exhibits a broad spectrum of action, characterized by pronounced activity against aerobic gram-negative bacteria, but also against gram-positive pathogens such as staphylococci. Fleroxacin is distinguished by its excellent bioavailability, high concentrations in the plasma and other body fluids, good tissue penetration, and a long half-life of 10-12 h, thus allowing once-a-day administration. A single oral dose of 400 mg fleroxacin is effective in uncomplicated cystitis in women, uncomplicated gonococcal infections, bacterial enteritis, and traveler's diarrhea. A single daily dose of 200 mg administered for 3 days is effective in uncomplicated urinary tract infection (UTI), while longer treatment and higher doses may be required in acute uncomplicated pyelonephritis and complicated UTI. Skin, soft tissue, bone and joint infections, and lower respiratory tract infections including exacerbation of chronic bronchitis and non-pneumococcal pneumonia are further indications for fleroxacin.

Factors influencing elimination and distribution of fleroxacin: metaanalysis of individual data from 10 pharmacokinetic studies

A metaanalysis was conducted on data from 172 subjects (healthy volunteers and uninfected patients) included in 10 pharmacokinetic studies of fleroxacin after oral administration. The objectives of this analysis were (i) to estimate the typical values of two key pharmacokinetic parameters, clearance over systemic availability (CL/F) and volume of distribution over systemic availability (V/F), after the administration of therapeutic doses and (ii) to study qualitatively and quantitatively the factors which influence the elimination and distribution of fleroxacin. The main pharmacokinetic parameters, CL/F and V/F, were analyzed separately by a standard two-stage approach. The covariates investigated were predicted creatinine clearance (CLCR), age, gender, body surface area, body weight, and lean body weight (LBW). The predicted CL/F and V/F were 83.5 ml/min and 101 liters, respectively, for a typical male subject (CLCR, 70 ml/min; LBW, 54 kg; age, 54 years). Modeling of CL/F indicated that this parameter increases linearly with CLCR, decreases linearly with age, and is 10.8 ml/min lower in females than in males. The best model for V/F showed a linear increase with LBW and a linear decrease with age. V/F was found to be 20.4 liters greater in males than in females. In conclusion, this metaanalysis has shown that CLCR, age, and gender influence the elimination of fleroxacin from the body, whereas V/F is influenced by LBW, age, and gender.

Sustained release of fleroxacin in vitro from lactic acid polymer

The time-delayed release of fleroxacin, a newer fluoroquinolone, from a mixture of racemic D-L-Lactic acid is reviewed. Ten in vitro experiments for each fleroxacin concentration of 1% and 10%, were performed. Pre-formed D-L-Lactic acid, plus fleroxacin clots were preserved in sterile 1 cm diameter tubes with one ml of nutrient broth at 37 degrees C until they were fully disintegrated. Every 24 hours the tubes were sampled and replaced by standard broth volumes. Fleroxacin levels were measured by a microbiological method. The release of fleroxacin impregnated in D-L-Lactic acid clots in these two concentrations (1% and 10%) is very promising; the levels obtained over a two month period were much higher than the minimum bacterial concentration of the expected pathogens implicated in bone infections.

Uptake and intracellular activity of fleroxacin in phagocytic cells

The uptake and intracellular activity of fleroxacin in murine J774.1 macrophages and human polymorphonuclear leukocytes were studied. The uptake of fleroxacin by J774.1 macrophages was rapid and reversible. The cellular to extracellular concentration ratios of fleroxacin in both types of phagocytes ranged from 5 to 6. These ratios were almost equal to those of ofloxacin and ciprofloxacin, and higher than those of the beta-lactam antibiotics, flomoxef and piperacillin. The intracellular activity of fleroxacin in J774.1 macrophages, examined with Staphylococcus aurenus as a test bacterium, showed that its bactericidal action was dependent on both the extracellular concentration and the exposure time. Fleroxacin reduced the number of viable cells of ingested S. aureus at an extracellular concentration that simulated the clinical serum levels, that is, killing more than 70% of the bacteria at 4 micrograms/ml. The bactericidal activity of fleroxacin in phagocytes was superior to that of erythromycin, flomoxef and piperacillin. These results indicate that fleroxacin is taken up well by phagocytes, reaching a concentration several fold higher than the extracellular concentration, and that it has potent activity against intracellular pathogens.

Fleroxacin. A review of its pharmacology and therapeutic efficacy in various infections

The fluoroquinolone antibacterial agent fleroxacin has a broad spectrum of in vitro activity which encompasses most Gram-negative species (particularly Enterobacteriaceae) and a number of Gram-positive organisms, including methicillin-sensitive staphylococci. It is available as oral and intravenous formulations. In clinical trials, fleroxacin has been evaluated in the treatment of uncomplicated urinary tract infections (single or multiple once-daily oral doses of 200 or 400mg), gonorrhoea and chancroid (single oral doses of 200 or 400mg), complicated urinary tract, nonpneumococcal lower respiratory tract and skin and soft tissue infections and typhoid fever (multiple once-daily oral or intravenous regimens, usually 400 mg/day), bacterial enteritis, and traveller's diarrhoea (single or multiple once-daily oral doses of 400mg). Bacteriological cure rates were generally around 90% or higher in complicated and uncomplicated urinary tract infections, uncomplicated gonorrhoea (approximately 100%), pyelonephritis, bacterial enteritis and typhoid fever, and exceeded 80% in lower respiratory tract, and skin and soft tissue infections and chancroid. These cure rates were similar to, or better than, those achieved with standard comparator antibacterial agents such as penicillins, cephalosporins, cotrimoxazole, or other quinolones. Fleroxacin 400mg once daily also achieved bacteriological cure in approximately 80% of patients with bone and joint infections in preliminary studies. In Japanese studies using a lower dosage of 200 or 300 mg/day, fleroxacin was reported to be bacteriologically effective in a range of infections, including urinary tract and upper and lower respiratory tract infections. Fleroxacin has a relatively long elimination half-life, which allows once-daily administration, and it appears to have less propensity for interactions with other medications in comparison to many other fluoroquinolones. Its tolerability profile is typical of this class of compound, with adverse events mostly relating to the gastrointestinal tract, CNS, and skin and appendages (including phototoxicity). Recent pooled tolerability data from worldwide clinical trials indicate that adverse events are reported by approximately 27% of patients receiving 200 mg/day orally or 400 mg/day orally or intravenously, and 17% of those receiving a single oral dose of 400mg. These exceed incidences reported for established fluoroquinolones, possibly indicating recent trends towards increased rates of reported adverse effects with these agents. However, in direct comparative studies with twice-daily fluoroquinolones, fleroxacin 400mg once daily produced a similar incidence of adverse effects to ofloxacin 800 mg/day and a slightly higher incidence than ciprofloxacin 1000 mg/day, while fleroxacin 200mg once daily produced a similar incidence to norfloxacin 800 mg/day.(ABSTRACT TRUNCATED AT 400 WORDS)

Intestinal elimination of sparfloxacin, fleroxacin, and ciprofloxacin in rats

The intestinal transepithelial elimination of sparfloxacin and fleroxacin was compared with that of ciprofloxacin in a rat model following a single parenteral administration of 25 mg of each of the antibiotics per kg of body weight. All three fluoroquinolones were eliminated through the small intestine. Ciprofloxacin was eliminated in the proximal jejunum at a rate of 1.97 +/- 0.70 micrograms/cm2, while the elimination rates of fleroxacin and sparfloxacin were 0.64 +/- 026 and 0.21 +/- 0.10 micrograms/cm2, respectively, over a 90-min collection period. In the ileum, the elimination rates of ciprofloxacin, fleroxacin, and sparfloxacin over the same period were 1.44 +/- 0.77, 1.00 +/- 0.33, and 0.41 +/- 0.26 micrograms/mc2, respectively. These data suggest that these fluoroquinolones undergo a transepithelial elimination process in the small intestine. This route of elimination may be important in the therapy of bacterial diarrhea.

Single-dose pharmacokinetics of oral fleroxacin in bacteremic patients

Fleroxacin is a new broad-spectrum quinolone which can be given by the oral route. The present study was designed to assess the influence of bacteremia on the pharmacokinetics of a single oral dose of fleroxacin. Thirteen patients with proven bacteremia (one or more pairs of positive blood cultures, no hypotension) were given a single 400-mg fleroxacin dose orally on two occasions while also receiving standard antibiotic therapy. The first dose was administered 12 to 36 h after the last positive blood culture was drawn (day 1), and a second dose was administered 7 days later (day 7 +/- 2) to compare the pharmacokinetics between the acute and the convalescent phases of the disease. Following each administration of fleroxacin, serial plasma samples were collected for up to 72 h and were analyzed for unchanged drug by a reversed phase high-pressure liquid chromatography technique. There were no significant changes in the following pharmacokinetic parameters (mean standard deviation) the maximum concentration of drug in serum (6.4 +/- 1.5 versus 6.7 +/- 1.9 mg/liter), the minimum concentration of drug in serum, defined as the concentration of drug in serum at 24 h postdose (3.0 +/- 1.7 versus 2.5 +/- 1.2 mg/liter), the time to the maximum concentration of drug in serum (2.3 +/- 1.4 versus 2.0 +/- 1.2 h), and the elimination half-life (19.7 +/- 8.0 versus 17.9 +/- 6.9 h). Fleroxacin clearances were compared for each individual patient. A positive correlation (R2 = 0.787) was found between the values measured on day 1 and day 7. Oral clearance of fleroxacin (CL = CL/F, where F is bioavailability was slightly, but not significantly, reduced during the bacteremic phase (oral clearance, 43.8+/- 23.5 versus 48.5 +/- 17.5 ml/min.). When compared with previous results obtained in healthy young subjects, longer times to the maximum concentration of drug in serum and elimination half-lives and higher areas under the curve were observed. This could be due to the bacteremic state, the old age of the patients (mean, 66 years), and the low renal clearance (mean calculated creatinine clearance, 71.1 ml/min). A single oral dose of 400 mg of fleroxacin provides sufficient levels in serum to cover susceptible microorganisms for at least 24 h in bacteremic patients. Renal function appeared to be the key element that had to be taken into consideration to adapt fleroxacin dosage profiles in our patient population. Bacteremia itself appeared to amplify that phenomenon, but to a much lesser extent than renal function did.

Effect of a fat- and calcium-rich breakfast on pharmacokinetics of fleroxacin administered in single and multiple doses

The effect of a fat- and liquid-calcium-rich meal on the pharmacokinetics of single and multiple doses of fleroxacin in 20 healthy men and women was investigated in a randomized crossover fashion. Fleroxacin was administered as 400 mg daily for 3 days and as a single 400 mg dose. Concurrent administration of fleroxacin with food resulted in a statistically significant (P < or = 0.05) decrease in the area under the curve (13.9% for multiple-dose administration, 10% for single-dose administration) and in the peak concentration (25.9% for multiple-dose administration, 27% for single-dose administration) and a lengthening of the time to peak (more than doubled for single- and multiple-dose phases). In addition, by using an equivalence criteria of 80 to 125%, the two one-sided tests procedure indicated that the mean areas under the curves for fleroxacin administered in a fed and a fasted state were statistically bioequivalent (P < or = 0.05) for both the single- and multiple-dose regimens. Although a meal high in fat and containing liquid calcium reduces the peak concentration by approximately 25%, a minimal effect on bioavailability is seen with concomitant food administration. In addition, multiple-dose bioavailability studies appear to give similar information to single-dose studies while representing the clinical setting more closely.

Pharmacokinetics of [18F]fleroxacin in healthy human subjects studied by using positron emission tomography

Positron emission tomography (PET) with [18F]fleroxacin was used to study the pharmacokinetics of fleroxacin, a new broad-spectrum fluoroquinolone, in 12 healthy volunteers (9 men and 3 women). The subjects were infused with a standard therapeutic dose of fleroxacin (400 mg) supplemented with approximately 20 mCi of [18F]fleroxacin. Serial PET images were made and blood samples were collected for 8 h, starting at the initiation of the infusion. The subjects were then treated with unlabeled drug for 3 days (400 mg/day). On the fifth day, infusion of radiolabeled drug, PET imaging, and blood collection were repeated. In most organs, there was rapid accumulation of radiolabeled drug, with stable levels achieved within 1 h after completion of the infusion. Especially high peak concentrations (in micrograms per gram) were achieved in the kidney (> 34), liver (> 25), lung (> 20), myocardium (> 19), and spleen (> 18). Peak concentrations of drug more than two times the MIC for 90% of Enterobacteriaceae strains tested (> 10-fold for most organisms) were achieved in all tissues except the brain and remained above this level for more than 6 to 8 h. The plateau concentrations in tissues (2 to 8 h, in micrograms per gram +/- standard error of the mean) of drug were as follows: brain, 0.83 +/- 0.032; myocardium, 4.53 +/- 0.24; lung, 5.80 +/- 0.48; liver, 7.31 +/- 0.33; spleen, 6.00 +/- 0.47; bowel, 3.53 +/- 0.74; kidney, 8.85 +/- 0.64; bone, 2.87 +/- 0.29; muscle, 4.60 +/- 0.33; prostate, 4.65 +/- 0.48; uterus, 3.87 +/- 0.39; breast, 2.68 +/- 0.11; and blood, 2.35 +/- 0.09. Concentrations of fleroxacin in tissue were similar in males and females, before and after pretreatment with unlabeled drug.

Influence of rifampin on fleroxacin pharmacokinetics

Staphylococcus aureus infections have been successfully treated in animal models with the combination of fleroxacin and rifampin. We studied the influence of rifampin, a potent cytochrome P-450 inducer, on the pharmacokinetics and biotransformation of fleroxacin in 14 healthy young male volunteers. Subjects were given 400 mg of fleroxacin orally once a day for 3 days to reach steady state. After a wash-out period of 2 days, the same subjects received 600 mg of rifampin orally once daily for 7 days. On days 5 to 7 of rifampin treatment, 400 mg of fleroxacin was again administered once daily. Concentrations of fleroxacin as well as its two major urinary metabolites, N-demethyl- and N-oxide-fleroxacin, in plasma and urine were determined by reverse-phase high-performance liquid chromatography. The extent of hepatic enzyme induction by rifampin was confirmed by a significant increase of 6-beta-hydroxycortisol urinary output from 160.8 +/- 41.4 to 544.8 +/- 120.7 micrograms/4 h. There were no significant changes in the peak fleroxacin concentration in plasma (6.3 +/- 1.2 versus 6.2 +/- 1.9 mg/liter), time to maximum concentration of fleroxacin in plasma (1.1 +/- 0.9 versus 1.3 +/- 1.1 h), or renal clearance (58.3 +/- 16.4 versus 61.9 +/- 19.2 ml/min). The area under the curve AUC (71.4 +/- 15.8 versus 62.2 +/- 13.7 mg.h/liter) and the terminal half-life of fleroxacin (11.4 +/- 2.2 versus 9.2 +/- 1.1 h) decreased (P < 0.05), while the total plasma clearance increased from 97.7 +/- 21.6 to 112.3 +/- 25.8 ml/min (P < 0.01). Despite being statistically significant, this 15% increase in total plasma clearance does not appear to be clinically relevant. Metabolic clearance by N demethylation was increased ( 6.9 +/- 2.4 versus 12.5 +/- 3.2 ml/min; P < 0.01), whereas clearance by N oxidation did not change (5.8 +/- 1.1 versus 5.8 +/- 1.5 ml/min). Fleroxacin elimination was slightly increased (about 15%) through induction of metabolic clearance to N-demethyl-fleroxacin. Since fleroxacin levels remained above the MIC for 90% of the tested isolates of methicillin-susceptible S. aureus for at least 24 h, dose adjustment does not appear necessary, at least for short-term treatments.

Developmental toxicity of fleroxacin and comparative pharmacokinetics of four fluoroquinolones in the cynomolgus macaque (Macaca fascicularis)

The potential developmental toxicity of fleroxacin was studied (Phase I) and its pharmacokinetics was compared to ciprofloxacin, temafloxacin, and norfloxacin (Phase II) in the cynomolgus macaque (Macaca fascicularis). Phase I studies involved oral administration of fleroxacin (35 and 70 mg/kg-day) during Gestational Days (GD) 20-34 or 35-49 (N = 10/group); controls received vehicle only. Increased maternal toxicity (weight loss, anorexia, emesis) and embryolethality (4/10, 40%; GD 20-34) were observed at 70 mg/kg-day. Urinary excretion of estrogen conjugates was reduced for females with nonviable pregnancies during both treatment periods (GD 20-34 and 35-49), although steroid hormone levels in serum remained unchanged during treatment; no malformations or growth retardation were observed at gross examination. For Phase II studies, the pharmacokinetics of fleroxacin (70 mg/kg), ciprofloxacin (100 mg/kg), temafloxacin (100 mg/kg), and norfloxacin (150 mg/kg) were studied during a 3-day oral treatment regimen in the nonpregnant (N = 12; 3/quinolone) and pregnant (N = 3; fleroxacin only) macaque. Serial blood samples were collected on the first and third days of treatment in all animals; for pregnant females, the conceptus was removed on GD 31 for analysis of fleroxacin levels. Marked differences between the quinolones were noted in the AUC0-24 hr for nonpregnant females. Based on AUC0-24 hr on the first day of treatment, the rank order was fleroxacin > temafloxacin > ciprofloxacin > norfloxacin. On the third of treatment, the rank order for exposure was temafloxacin > fleroxacin > ciprofloxacin > norfloxacin. Overall, results indicated (1) no marked differences in pharmacokinetic parameters in pregnant versus nonpregnant females, (2) fleroxacin levels in embryonic tissues were similar to maternal plasma levels, and (3) there was a correlation between exposure and embryolethal doses for all fluoroquinolones which resulted in embryolethality except norfloxacin.

Penetration of fleroxacin into body tissues and fluids

Concentrations of fleroxacin in human body fluids and tissues were studied to obtain information about the efficacy of the drug at the site of infection and the ratio of fleroxacin concentrations in tissue or fluid versus those in plasma as a measure of the extent of penetration. Samples of body fluids and tissues were obtained at various intervals after oral administration, and fleroxacin concentrations were determined by high-performance liquid chromatography. After administration of the standard dose of 400 mg once daily, the maximal plasma concentrations were 5-7 mg/L at steady-state and the minimal concentrations were approximately 1 mg/L at the end of the dosing interval. In most biologic specimens, such as myometrium, fallopian tube, bile bladder wall, bone, tonsils, maxillary sinus mucosa, prostatic adenoma, sputum, inflammatory fluid, synovia, lymph, saliva, and tears, the levels of fleroxacin were similar to those in plasma. In bile, nasal secretions, seminal fluid, lung, bronchial mucosa, and ovaries, the drug concentrations were 2-3 times higher than those in plasma. Penetration of fleroxacin into fat, lens, bronchial secretions, sweat, and aqueous humor was limited, with drug levels reaching only 10-40% of the concomitant levels in plasma. The measured concentration ratios did not vary markedly with time, and the decline in drug concentrations in tissues and fluids was generally parallel to that in plasma. The breakpoint for susceptibility is 1 micrograms/mL. The susceptibility breakpoint was exceeded by the drug concentration in plasma for the entire dosing interval and was also reached or exceeded in most body tissues and fluids.

Overview of the pharmacokinetics of fleroxacin

The pharmacokinetic properties of fleroxacin in relation to other quinolones are presented. Fleroxacin, like all quinolones, is well absorbed, reaching peak concentrations within 2 hours. Interactions with Ca2+ and Al3+ are minimal and possibly of little clinical importance. The drug is eliminated via filtration in the kidney. It is therefore sensitive to changes in renal function. Accumulation of drug in the body is minimal, and change from intravenous to oral dosing results in nearly identical serum concentrations. Aside from the modest effect of metals on its absorption, fleroxacin does not interact/compete with substances oxidized in the liver, such as theophylline, and drug interactions are minimal. Its long serum half-life (8-12 hours) allows once-a-day dosing. This feature, along with its modest drug interactions, makes fleroxacin an attractive quinolone, at least with respect to its pharmacokinetics.

Pharmacokinetics of fleroxacin as studied by positron emission tomography and [18F]fleroxacin

A new method of tracing the disposition of fleroxacin was tested in infected and noninfected animals in an effort to develop a technique that might be applicable in humans. [18F]fleroxacin was synthesized and shown to be identical physically, chemically, and in its antimicrobial activity to the commercially produced product. Tracer amounts of [18F]fleroxacin were coinjected with a pharmacologic dose of unlabeled drug (10 mg/kg) into normal mice, rats with focal thigh infection due to Escherichia coli, and normal and infected rabbits. The rats and mice were killed at fixed time intervals after injection, and the concentration of drug was determined by radioactive counting in a well-type counter; the rabbits were studied both by this method and by positron emission tomographic (PET) imaging. These studies validated the reliability of the new approach and suggested that it could be applied safely to humans. In all three animal species studied, delivery of [18F]fleroxacin to most tissues was rapid, with the notable exception of the brain. Accumulation of drug in infected thigh muscle was similar to that in normal muscle. The concentrations of drug reached in various tissues suggest that fleroxacin will be particularly useful in the treatment of gastrointestinal, urinary tract, hepatobiliary, and skeletal infections and that it shows promise for the treatment of lung and soft tissue infection. The minimal concentrations of drug delivered to the brain should decrease the occurrence of central nervous system toxicity with this particular fluoroquinolone.

Pharmacokinetics of fleroxacin in renal impairment

Fleroxacin is excreted primarily via the kidneys in its unchanged form, and therefore renal impairment has a major influence on the pharmacokinetics of this drug. This study examined the pharmacokinetics of oral and intravenous fleroxacin in patients with renal impairment. Patients with renal disease (mean glomerular filtration rate [GFR], 22 mL/min) and healthy subjects (mean GFR, 100 mL/min) received 400 mg of fleroxacin orally and 100 mg of fleroxacin intravenously in a crossover design. Serial blood samples and a complete urine collection were obtained for > or = 72 hours after dosing. Unchanged drug in plasma and urine was determined by reverse-phase high-performance liquid chromatography. Fleroxacin was well tolerated by all study participants. Renal impairment had no influence on the complete absorption of fleroxacin from the gastrointestinal tract, the maximal plasma concentration, and the steady-state volume of distribution (Vd-ss > 1 L/kg). However, systemic clearance in patients was significantly decreased (p < 0.05) to 44.4 mL/min compared with 87.1 mL/min in healthy subjects. This decrease could be ascribed to a reduction in renal clearance from 59.1 mL/min in healthy subjects to 8.8 mL/min in patients. Metabolic clearance was not reduced significantly. As a consequence of reduced clearance, the mean elimination half-life in patients increased from 13.6 hours to 21.4 hours and the area under the concentration-time curve from 87.0 mg.h/L to 170.5 mg.h/L. To avoid an unacceptable accumulation of fleroxacin in the body during multiple dosing, the following dose adjustment was recommended: patients with renal disease whose GFR is < 40 mL/min should receive the normal loading dose, i.e., 400 mg, but should receive maintenance doses that are reduced by 50%, i.e., to 200 mg.

Penetration of fleroxacin into breast milk and pharmacokinetics in lactating women

Fleroxacin was administered to seven lactating women as a single oral dose of 400 mg. Plasma, urine, and milk samples were collected for up to 48 h after administration. Drug concentrations were determined by a reversed-phase high-pressure liquid chromatography method and were used for the pharmacokinetic evaluation. At approximately 2 h after oral administration, a maximum concentration of 5.6 mg/liter was determined in plasma; the area under the plasma concentration-time curve (AUC) amounted to 70.3 mg.h/liter, and the elimination half-life in the postdistributive phase was 8 h. Total systemic clearance was 97.3 ml/min, and urinary excretion was 38% of the dose within 48 h. In addition, 8.6% of the N-demethyl metabolite and 4.4% of the N-oxide metabolite were recovered from urine. In comparison with previous results obtained with healthy male volunteers, the time to reach maximum concentrations in plasma was twice as long in the nursing women, and total clearance as well as urinary elimination were reduced by 25%. In breast milk, the mean maximum concentration was 3.5 mg/liter, which was reached 2.6 h after drug administration. The elimination half-life of fleroxacin in milk was identical to that in plasma, and the AUC reached 43.3 mg.h/liter. On the basis of the comparison of the AUC in milk versus the AUC in plasma, the proportion of fleroxacin penetration into milk was 62%. The cumulative excretion in milk amounted to only 0.219 mg within 48 h. On the basis of an average daily intake of milk of a breast-fed child of 150 ml/kg of body weight, the maximum daily ingested fleroxacin dose would not exceed 10 mg. However, quinolones are known to induce arthropathy in juvenile animals, and therefore, administration of fleroxacin to breast-feeding women cannot be allowed.

Synthesis and biodistribution of 18F-labeled fleroxacin

[18F]Fleroxacin (6,8-difluoro-1,4-dihydro-1-(2-[18F]fluoroethyl)-4- oxo-7-(4-methyl-1-piperazinyl)-3-quinolinecarboxylic acid) was synthesized from its methylsulfonyl ester precursor. 6,7,8-Trifluoro-4-hydroxyquinoline-3-carboxylic acid ethyl ester (Ro 19-7423) was alkylated with 2-bromoethanol to produce 6,7,8-trifluoro-1,4-dihydro-1-(2-hydroxyethyl)-4-oxo-3-quinolinecarboxyl ic acid ethyl ester in 76% yield which was then condensed with 1-methyl-piperazine to produce 6,8-difluoro-1,4-dihydro-1-(2-hydroxyethyl)-7-(4-methyl-1-piperazinyl)4- oxo-3- quinolinecarboxylic acid ethyl ester in 67% yield. This product was reacted with methanesulfonyl chloride to produce the mesylate precursor of fleroxacin in 66% yield. Nucleophilic substitution of the mesylate with 18F- in the presence of Kryptofix 2.2.2 followed by basic hydrolysis produced [18F]fleroxacin with a radiochemical yield of 5-8% [EOS] within 90 min. The pattern of biodistribution of [18F]fleroxacin was similar to the 14C-labeled drug.

Hepatic drug metabolism in cystic fibrosis: recent developments and future directions

OBJECTIVE

To review the most current information pertaining to hepatic drug metabolism in patients with cystic fibrosis (CF) and to explore the possible association between CF and specific pathways for the hepatic biotransformation of xenobiotics.

DATA SOURCES

A MEDLINE search (key terms: cystic fibrosis, pharmacokinetics, metabolism, pharmacogenetics) was used to identify pertinent literature, including reviews. Research findings from the author's laboratory are also presented.

STUDY SELECTION

Only recently reported (from 1988 to present), controlled, clinical investigations of hepatic drug metabolism in patients with CF are included. These investigations examined a mechanistic basis for altered drug biotransformation. Although uncontrolled clinical trials, case reports, and review articles are not included in the discussion, appropriate reference citations are made to these works.

DATA EXTRACTION

Data from well-designed, controlled, clinical and basic investigations of altered hepatic drug biotransformation in patients with CF are summarized and discussed. New data from an ongoing study concerning the renal excretion of antipyrine metabolites in these patients are presented.

DATA SYNTHESIS

In vivo studies of the formation clearance for metabolites of fleroxacin, sulfamethoxazole, and theophylline clearly demonstrate increased activity for important P-450 isoenzymes. These data are supported by an in vitro study that confirmed increased microsomal metabolism of theophylline to 1-methylxanthine, 3-methylxanthine, and 1,3-dimethyluric acid in a liver specimen from a patient with CF. These findings not only substantiate disease-specific increases in hepatic phase I biotransformation in patients with CF, but also verify the premise of substrate specificity for this pharmacogenetic phenomenon. Likewise, pharmacokinetic studies of drugs that undergo significant hepatic phase II biotransformation (e.g., furosemide, lorazepam, ibuprofen) appear to support increased hepatic drug clearance in patients with CF. This assertion has also been confirmed by a study of acetaminophen disposition, which demonstrated significantly increased formation clearance of the sulfate and glucuronide conjugates of the drug. Finally, the marked increase in the plasma clearance of indocyanine green, a pharmacologic probe for the biliary uptake and excretion of drugs, lends credence to the assertion that increased hepatic clearance of drugs in the presence of CF may be the consequence of disease-specific changes in both enzyme activity and/or drug transport within the liver.

CONCLUSIONS

Investigations of drug biotransformation in CF have revealed disease-specific increases in the formation of drug metabolites. Future application of techniques in molecular biology and biochemical pharmacology will need to characterize the mechanistic basis for altered drug metabolism in CF and expand our knowledge of the relationship between drug metabolism phenotype and genotype; the impact of growth, development, and disease severity on drug metabolism; the potential role of CF gene products (i.e., CFTR) on intrahepatic drug transport and biotransformation; and the pharmacogenetic determinants of substrate specificity for hepatic drug metabolism in CF.

Effect of sucralfate on pharmacokinetics of fleroxacin in healthy volunteers

The effect of sucralfate on the pharmacokinetics of fleroxacin was assessed in 20 healthy male volunteers. The study was of a two-way crossover design in which subjects were randomized to one of the following two regimens at the time of entry: (i) a single 400-mg dose of fleroxacin alone or (ii) a 400-mg dose of fleroxacin given once and 1 g of sucralfate given every 6 h starting 24 h before fleroxacin treatment and continuing for 48 h after fleroxacin treatment. Blood samples were collected immediately before fleroxacin administration and at 0.5, 1, 1.5, 2, 2.5, 3, 4, 6, 8, 10, 12, 16, 24, 36, and 48 h postdosing. Fleroxacin concentrations in plasma and urine were determined by high-performance liquid chromatography. While concurrent of fleroxacin and sucralfate resulted in a decrease in the area under the plasma concentration-time curve, a decrease in the maximum concentration, and an increase in the time to the maximum concentration (P < 0.05), these changes were modest compared with the interaction of other quinolones with sucralfate. The relative bioavailability of fleroxacin given with sucralfate, calculated from the area under the concentration-time curve, was 76% compared with that of fleroxacin alone. This is significantly better than the bioavailabilities of other quinolones (1.8 to 12.3%) when they are administered with sucralfate.

Fluoroquinolone supersusceptibility mediated by outer membrane protein OprH overexpression in Pseudomonas aeruginosa: evidence for involvement of a nonporin pathway

Overexpression of Pseudomonas aeruginosa outer membrane protein OprH led to an 8- to 32-fold increase in susceptibility to chloramphenicol and the quinolones nalidixic acid, norfloxacin, ciprofloxacin, and fleroxacin in comparison with the susceptibility of the wild-type strain H103 grown on Mg(2+)-sufficient medium. This was true regardless of whether OprH overexpression was induced by growth of strain H103 on Mg(2+)-deficient medium, the addition of 5 mM m-toluate to cells containing the cloned oprH gene behind the inducible tol promoter in plasmid pGB25, or mutation in the polymyxin-resistant derivative strain H181. In contrast, OprH overexpression failed to reverse the quinolone resistance phenotype of a nalB mutant. OprH was purified to homogeneity by selective detergent solubilization and fast protein liquid chromatography. The addition of OprH to the solution bathing a black lipid bilayer membrane failed to give rise to an increase in membrane conductance. This suggests that OprH is not a porin but, instead, may cause increased uptake of quinolones and chloramphenicol via a non-porin pathway.

In vitro activities of fleroxacin against clinical isolates of Legionella spp., its pharmacokinetics in guinea pigs, and use to treat guinea pigs with L. pneumophila pneumonia

The activities of fleroxacin against 22 clinical Legionella isolates were determined by agar and broth microdilution susceptibility testing. The fleroxacin MIC required to inhibit 90% of strains tested on buffered charcoal yeast extract agar medium supplemented with 0.1% alpha-ketoglutarate was 0.64 micrograms/ml and was 0.04 microgram/ml when testing was done with buffered yeast extract broth supplemented with 0.1% alpha-ketoglutarate. Fleroxacin (0.25 microgram/ml) reduced the bacterial counts of two L. pneumophila strains grown in guinea pig alveolar macrophages by 1 log10 CFU/ml, but regrowth occurred over a 3-day period; fleroxacin was significantly more active than erythromycin in this assay. Single-dose (10 mg/kg of body weight given intraperitoneally) pharmacokinetic studies performed in guinea pigs with L. pneumophila pneumonia revealed peak levels in plasma and lungs to be 3.3 micrograms/ml and 3.5 micrograms/g, respectively, at 0.5 h and 0.8 microgram/ml and 0.8 microgram/g, respectively, at 1 h. The half-life of the terminal phase of elimination from plasma and lung was approximately 2 h. All 17 infected guinea pigs treated with fleroxacin (10 mg/kg/day) for 2 days survived for 14 days post-antimicrobial therapy, as did all 16 guinea pigs treated with the same dose of fleroxacin for 5 days. Only 1 of 16 animals treated with saline survived. The animals treated with fleroxacin for 2 days lost more weight and had higher temperatures than those treated with the antibiotic for 5 days. Fleroxacin is effective against L. pneumophila in vitro and in a guinea pig model of Legionnaires' disease. Fleroxacin should be evaluated as a treatment for human Legionnaires' disease.

Pharmacokinetics of 18F-labeled fleroxacin in rabbits with Escherichia coli infections, studied with positron emission tomography

18F-labeled fleroxacin was used to measure the pharmacokinetics of fleroxacin in healthy and infected animals by positron emission tomography (PET) and tissue radioactivity measurements. In all experiments, a pharmacological dose of unlabeled drug (10 mg/kg) was coinjected with the tracer. The pharmacokinetics of [18F]fleroxacin was measured in groups of healthy mice (n = six per group) at 10, 30, 60, and 120 min after injection and in groups of rats with Escherichia coli thigh infections (n = six per group) at 60 and 120 min after injection by radioactivity measurements in excised tissues. In healthy rabbits (n = 4) and in rabbits with E. coli thigh infections (n = 4), tissue concentrations of drug were determined by serial PET imaging over 2 h; after the final image was acquired, animals were sacrificed and concentrations measured by PET were compared with the results of tissue radioactivity measurements. In all three species, there was rapid equilibration of [18F]fleroxacin to significant concentrations in most peripheral organs; low concentrations of drug were detected in the brain. Accumulations of radiolabeled drug in infected and healthy thigh muscles were similar. Peak concentrations of drug of more than three times the MIC for 90% of members of the family Enterobacteriaceae (greater than 100-fold for most organisms) were achieved in all tissues except brain and remained above this level for more than 2 h. Especially high peak concentrations were achieved in the kidney (greater than 75 micrograms/g), liver (greater than 50 micrograms/g), blood (greater than 25 micrograms/g), and bone and lung (greater than 10 micrograms/g). Since the MICs for 90% of all Enterobacteriaceae are <2 micrograms/ml, fleroxacin should be particularly useful in treating gram-negative infections affecting these tissues. In contrast, the low concentration of drug delivered to the brain should limit the toxicity of the drug for the central nervous system.

Penetration of fleroxacin and ciprofloxacin into skin blister fluid: a comparative study

The penetration of multiple-dose concentrations of oral fleroxacin (400 mg every 24 h) and ciprofloxacin (500 mg every 12 h) into skin blister fluid in 12 healthy volunteers was determined in a randomized crossover study. Serum, blister fluid, and paper disk samples were analyzed by large-plate microbiologic assay. The mean areas under the concentration-time curve (AUC) for serum were 88.6 and 18.2 micrograms.h/ml/70 kg for fleroxacin and ciprofloxacin, respectively. The mean AUC for blister fluid and paper disks were 71.2 and 15.0 micrograms.h/ml/70 kg and 77.8 and 15.4 micrograms.h/ml/70 kg for fleroxacin and ciprofloxacin, respectively. Calculated penetration into interstitial fluid ranged from 74 to 92% for fleroxacin and 56 to 96% for ciprofloxacin; penetration was calculated by using the ratio of maximum drug concentration or AUC in blister fluid and paper disks to maximum drug concentration or AUC in serum. There was no significant difference between fleroxacin and ciprofloxacin in the percent penetration into skin blister fluid.

Fleroxacin pharmacokinetics in patients with liver cirrhosis

In this open-label study, the disposition of fleroxacin in liver disease in 12 healthy male volunteers, 6 male cirrhotics without ascites (group A), and 6 male cirrhotics with ascites (group B) was evaluated. Fleroxacin (400 mg) was administered orally and intravenously to each subject in a random crossover fashion. Fleroxacin was completely absorbed and achieved similar peak concentrations in plasma in all three study groups (P greater than 0.05). The volume of distribution exceeded 1 liter/kg in healthy controls and was not affected by liver impairment (P greater than 0.05). Only group B demonstrated differences in the pharmacokinetic parameters evaluated: the systemic and renal clearances of fleroxacin and the renal clearances and clearances of the two major metabolites of fleroxacin formed, N-demethyl fleroxacin and fleroxacin N-oxide, were significantly lower and the half-lives of the parent drug and its metabolites were significantly longer in group B than in healthy controls and group A (P less than 0.05). The elimination of the two metabolites appeared to be formation rate limited in all three study groups. It was concluded from this study that a 50% reduction in the fleroxacin maintenance dose in patients with liver disease appears justified only in patients with ascites. However, no change in the fleroxacin loading dose is needed in patients with compromised liver function.

Fleroxacin clinical pharmacokinetics

Fleroxacin is a new member of the class of fluoroquinolones. The drug has good activity (i.e. minimum inhibitory concentrations at less than 2 mg/L against 90% of strains) against a wide range of Gram-positive and Gram-negative bacteria. High performance liquid chromatography is used to determine concentrations of fleroxacin and its metabolites in biological fluids. Absorption of orally ingested drug is rapid as the peak plasma concentration of approximately 5 mg/L is reached in 1 to 2h after a single dose of 400mg. The systemic availability is close to 100%. Fleroxacin is poorly bound to plasma proteins (23%) and exhibits excellent tissue distribution. Renal clearance accounts for 60 to 70% of elimination. The drug is metabolised to form antimicrobially active N-demethyl-fleroxacin and inactive N-oxide-fleroxacin. In multiple dose studies the accumulation ratio of a once-daily dosage regimen is about 1.3, as predicted from the elimination half-life of 10 to 12h. Compared with ciprofloxacin, fleroxacin has a greater systemic availability and a longer half-life. Fleroxacin concentrations are higher in elderly patients, but further studies are needed to establish whether a dosage reduction should be recommended for this age group. In patients with renal disease dosage adjustment is recommended since a decreased renal clearance of fleroxacin leads to a significant prolongation of the elimination half-life. Fleroxacin is only poorly eliminated by peritoneal dialysis or haemodialysis. The most important drug-drug interaction is a decrease in systemic availability of fleroxacin after ingestion of aluminium- or magnesium-containing antacids. There is no evidence of a significant interaction between fleroxacin and theophylline. Only limited data are available on adverse reactions of fleroxacin. The most important adverse effects appear to be photosensitivity and a dose-dependent incidence of central nervous system reactions including sleep disorders.

Penetration of fleroxacin into human and animal tissues

Fleroxacin concentrations in human and rat tissues were determined by HPLC following extraction with dichloromethane:isopropanol. This method yielded a high recovery of more than 85%. In the investigated tissues the fleroxacin levels were equal to or higher than those concomitantly measured in plasma. The concentration ratios 'tissue/plasma' were 1.6-2.7 for lung, 1.9-2.1 for muscle, 1.1-1.9 for gynaecological tissues and 1.2 for bone. Only in the case of fat and lens/eye lower ratios of 0.05-0.5 were found. The actual measured fleroxacin concentrations in most tissues and in plasma were high. Following oral administration of the recommended therapeutic dose of 400 mg, once daily, peak concentrations of 5-6 mg/l were reached in human plasma at steady state. Even 24 h after drug intake the fleroxacin level was still approximately 1 mg/l and thus in the range of the MIC90 values of susceptible bacteria causative for many types of tissue infections.

Fleroxacin pharmacokinetics in aqueous and vitreous humors determined by using complete concentration-time data from individual rabbits

Although composite data from separate subjects can be used to generate single-subject estimates, intersubject variation precludes rigorous ocular pharmacokinetic analysis. Therefore, a rabbit model in which sequential aqueous and vitreous humor samples were obtained following the administration of the quinolone fleroxacin was developed. Mean data from individual animals were used for pharmacokinetic analysis. Following direct intravitreal or systemic drug administration, sequential paracenteses did not alter pharmacokinetic constants or ocular penetration and were not associated with an increase in ocular protein; contamination of vitreous humor with blood was minimal (less than 0.1%). Following direct injection or intravenous administration, vitreous humor concentration-time data were best described by one- and two-compartment models, respectively. The maximum concentration and the penetration into the aqueous and vitreous humors were 1.54 and 0.5 micrograms/ml and 27 and 10%, respectively. Elimination rates from aqueous and vitreous humors and serum were similar following parenteral drug administration. Drug elimination following direct injection was rapid, and the elimination rate from the vitreous humor was not prolonged by the coadministration of probenecid. Our animal model provides a new approach to the rigorous examination of the ocular pharmacokinetics of quinolone antimicrobial agents in the eye.