Clinical pharmacokinetics and tolerance of fleroxacin in healthy male volunteers

Together or Apart? Revealing the Impact of Dietary Interventions on Bioavailability of Quinolones: A Systematic Review with Meta-analyses

BACKGROUND AND OBJECTIVE

Managing drug-food interactions is essential for optimizing the effectiveness and safety profile of quinolones. Following PRISMA guidelines, we systematically reviewed the influence of dietary interventions on the bioavailability of 22 quinolones.

METHODS

All studies describing or investigating the impact of food, beverages, antacids, and mineral supplements on pharmacokinetic parameters or pharmacokinetic/pharmacodynamic indices of orally taken quinolones were considered for inclusion. We excluded reviews, in vitro and in silico studies, studies performed on animals, and those involving alcohol. We performed the search in Medline (via PubMed), Embase, and Cochrane Library, covering reports from database inception to December 2022. We used the following tools to assess the risk of bias: version 2 of the Cochrane risk-of-bias tool for parallel trials, the Cochrane risk-of-bias tool for cross-over studies, and the NIH quality assessment tool for before-after studies. We performed quantitative analyses for each quinolone if two or more food-effect studies with specified and comparable study designs were available. If meta-analyses were not applicable, we qualitatively summarized the results.

RESULTS

We included 109 studies from 101 reports. Meta-analyses were conducted for 12 antibiotics and qualitative synthesis was employed for the remaining drugs. Of the studies, 60.5% were open-label, cross-over, as recommended by FDA. We judged 46% of studies as having a high risk of bias and only 4% of having a low risk of bias. Among 19 quinolones with available food impact data, 14 (74%) had potentially clinically important interactions. For nalidixic acid, oxolinic acid, and tosufloxacin, food exerted a high positive impact on bioavailability (AUC or Cmax increased by > 45%), whereas, for all the remaining drugs, postprandial absorption was lower. The most significant negative influence of food (AUC or Cmax decreased by > 40%) occurred for delafloxacin capsules and norfloxacin, whereas the moderate influence (AUC or Cmax decreased by 30-40%) occurred for nemonoxacin and rufloxacin. All 14 analysed quinolones showed a substantial reduction in bioavailability when co-administered with antacids and mineral supplements, except for calcium preparations. The impact of beverages was evaluated for 10 quinolones, with 50% experiencing significantly reduced absorption in the presence of milk (the highest negative impact for ciprofloxacin). Moreover, both ciprofloxacin and levofloxacin demonstrated compromised bioavailability when consumed with orange juice, particularly calcium-fortified.

DISCUSSION

Several factors may influence interactions, including the physicochemical characteristics of quinolones, the type of intervention, drug formulation, and the patient's health status. We assessed the quality of evidence as low due to the poor actuality of included studies, their methodological diversity, and uneven data availability for individual drugs.

Fluoroquinolone antibiotics in the environment

Fluoroquinolones (FQs) are used in large amounts for human and animal medical care. They are excreted as parent compound, as conjugates, or as oxidation, hydroxylation, dealkylation, or decarboxylation products of the parent compound. A considerable amount of FQs and their metabolites may reach the soil as constituents of urine, feces, or manure. The residues of FQs in foods of animal origin may pose hazards to consumers through emergence of drug-resistant bacteria. FQs bind strongly to topsoil, reducing the threat of surface water and groundwater contamination. The strong binding of FQs to soil and sediments delays their biodegradation and explains the recalcitrance of FQs. Wastewater treatment is an efficient elimination step (79%-87% removal) for FQs before they enter rivers. FQs are susceptible to photodegradation in aqueous medium, involving oxidation, dealkylation, and cleavage of the piperazine ring.

Microbiological transformation of enrofloxacin by the fungus Mucor ramannianus

Enrofloxacin metabolism by Mucor ramannianus was investigated as a model for the biotransformation of veterinary fluoroquinolones. Cultures grown in sucrose-peptone broth were dosed with enrofloxacin. After 21 days, 22% of the enrofloxacin remained. Three metabolites were identified: enrofloxacin N-oxide (62% of the total absorbance), N-acetylciprofloxacin (8.0%), and desethylene-enrofloxacin (3.5%).

Analysis of fluoroquinolones in biological fluids by high-performance liquid chromatography

High-performance liquid chromatographic methods for the analysis of fluoroquinolones in biological fluids are reviewed. In particular, sample preparation and handling procedures, chromatographic conditions, and detection methods are discussed. A summary of published high-performance liquid chromatographic assays for individual fluoroquinolones is included.

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.

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.

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.

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.

Single- and multiple-dose pharmacokinetics of AM-1155, a new 6-fluoro-8-methoxy quinolone, in humans

The pharmacokinetics of AM-1155, a new 6-fluoro-8-methoxy quinolone, was examined in healthy male volunteers after the oral administration of a single dose of 100, 200, 400, or 600 mg and multiple doses of 300 mg twice daily for 6.5 days (13 total doses). Throughout the whole study period, AM-1155 was well tolerated in every subject. In the single-dose study, the concentrations in serum reached a peak between 1 and 2 h, and the peak concentrations were 0.873, 1.71, 3.35, and 5.41 micrograms/ml at the doses of 100, 200, 400, and 600 mg, respectively. The elimination half-life was 7 to 8 h, independently of the doses. The unchanged drug was excreted mainly in the urine, with 82 to 88% of the doses appearing for 72 h. The fecal recovery of the unchanged drug amounted to 5.7% for 72 h after a single oral administration of a 400-mg dose. Urinary excretion of metabolites was minimal. The serum protein binding was 20%, independently of the concentrations in serum. The concentrations in saliva were approximately 80% of those in serum. The intake of food had no effect on the pharmacokinetic parameters and urinary excretion of AM-1155 except the slight decrease in area under the concentration-time curve. The concurrent administration of probenecid prolonged the elimination half-life, increased the area under the concentration-time curve, and decreased the apparent total body clearance, renal clearance, urinary recovery of unchanged drug, and the excretion ratio (intrinsic renal clearance of AM-1155/creatinine clearance). This indicated that the tubular secretion contributed to the renal excretion of AM-1155. In the multiple-dose study, the concentrations of AM-1155 in serum and urine reached a steady state within 2 to 3 days. The measured concentrations in serum fitted well the simulation curve, which reflected the persistence of linear pharmacokinetics of AM-1155. In conclusion, AM-1155 is expected to be clinically useful because of its potent antibacterial activity and favorable pharmacokinetics.

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.

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.

Impact of the fluoroquinolones on gastrointestinal flora

A number of studies have been performed to evaluate the effect of the fluoroquinolones on gastrointestinal flora. The fluoroquinolones have only slight or no effect on the oropharyngeal flora, except when Neisseria, Haemophilus or Branhamella spp. are present. Studies have consistently shown that Gram-negative facultative bacteria of the lower intestinal flora are strongly suppressed during administration of these agents. Total faecal anaerobes are generally unchanged. The effect of the fluoroquinolones on Gram-positive bacteria is more variable with mild to moderate suppression reported with some agents. In view of the high faecal concentrations of the fluoroquinolones, the general lack of effect on anaerobes is surprising; it may be attributable to the large number of microorganisms found in faeces and faecal binding of the fluoroquinolones. Several recent studies suggest that the effects of some fluoroquinolones on faecal anaerobes and Gram-positive cocci may be more profound in certain patient populations such as bone marrow transplant recipients and patients undergoing gastrointestinal surgery. Colonisation with yeasts and the emergence of resistant bacterial strains have been reported during or after fluoroquinolone administration in some studies. Future studies will need to investigate the effect of the newer agents with greater activity against anaerobes and Gram-positive cocci on the gastrointestinal flora and to continue surveillance for resistant organisms.

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.

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.

The effect of food or milk on the absorption kinetics of ofloxacin

We have studied the effects of food or milk on the absorption of ofloxacin in 21 healthy male volunteers in a three-way crossover design. Milk did not alter the rate or extent of absorption of ofloxacin or its elimination. Food altered the onset and/or rate of absorption, but not the extent of absorption or the elimination rate. Thus, food reduced peak ofloxacin concentrations (Cmax) by 20% compared with fasting conditions and the time to reach maximum concentration (tmax) was prolonged on average by 1 h. However, the extent of absorption and the half-life (t 1/2) of ofloxacin were the same after each treatment. These data indicate that food and milk have a clinically insignificant effect on ofloxacin absorption.

Pharmacokinetics of quinolones: newer aspects

Differences in pharmacokinetic properties are emerging as important determinants in distinguishing among clinical uses of individual new quinolone antimicrobial agents. Selected data on pharmacokinetics, new pharmacokinetic studies, and pharmacodynamics are reviewed, with reference to norfloxacin, ciprofloxacin, ofloxacin, pefloxacin, enoxacin, fleroxacin, lomefloxacin, and other new quinolones. Considering pharmacokinetics, oral bioavailability is excellent (greater than 95%) for most quinolones. Differences in peak serum concentrations and beta-half-lives of elimination exist, however, and are reflected in up to ten-fold differences in values of the area under the curve of serum concentration versus time for administration of similar drug doses. As suggested by high apparent volumes of distribution and low binding to serum proteins, penetration into many body tissues and fluids is favorable. Considering new findings, orally administered ciprofloxacin has been found to be absorbed primarily in the duodenum and jejunum. Studies also suggest this drug to be cleared by transepithelial elimination into the bowel lumen as well as by the renal route. Oral bioavailability of quinolones has been demonstrated to be in general good in ill as well as healthy subjects but is reduced on co-administration with magnesium- and aluminum-containing acids, sucralfate (which contains aluminum), or ferrous sulfate. Pharmacodynamic parameters, such as the relationship of serum concentrations and drug potency in vitro to clinical response and suppression of bacterial resistance, have been little studied and merit further investigation.

Pharmacokinetics and biliary concentrations of fleroxacin in cholecystectomized patients

Patients with biliary tract infections received 800 mg of fleroxacin orally once daily on five consecutive days; cholecystectomy was on day 3. Starting on the day when dose 5 was administered, serial blood and T-drain bile samples were taken for 72 h and urine was collected for 96 h. The mean (+/- the standard deviation) peak concentration in plasma was 8.2 +/- 4.0 mg/liter at 8.3 h. The harmonic mean elimination half-life was 10.5 h, which is comparable to that reported for healthy volunteers. This increase resulted from reduced renal clearance (mean [+/- standard deviation], 38 +/- 22 ml/min), as the volume of distribution in the patients (1.4 +/- 0.7 liter/kg) did not differ from that reported for healthy subjects. Maximum concentrations in T-drain bile were high (median, 22.1 mg/liter) and exceeded those measured in plasma by a factor of 2 to 3; the individual ratios of the area under the curve for bile divided by that for plasma ranged from 1.3 to 9.9. As observed in healthy volunteers, the major pathway for elimination of fleroxacin was via the kidneys. The fraction of dose 5 eliminated in the 0- to 24-h urine was reduced, however, and the fraction of the dose in the urine as the N-demethyl and N-oxide metabolites was elevated. At the dose regimen used in this study, the MICs for most pathogens that cause biliary tract infections were surpassed in plasma and bile for more than 24 h.

Determination of the new fluoroquinolone fleroxacin and its N-demethyl and N-oxide metabolites in plasma and urine by high-performance liquid chromatography with fluorescence detection

A high-performance liquid chromatographic method is described for the determination of the new fluoroquinolone fleroxacin and its metabolites in plasma and urine. Plasma samples are deproteinized with acetonitrile, and, after evaporation and reconstitution of the supernatant, samples are analysed on a reversed-phase column. The limit of quantification is 10-20 ng/ml for the parent drug and 10 ng/ml for the metabolites, using a 0.2-ml sample. Urine samples are diluted with the mobile phase. An aliquot is then injected directly onto the column. The limits of quantification are 1 micrograms/ml for the parent drug and 0.5 micrograms/ml for the metabolites, using a 0.1-ml sample. The method has been successfully applied to pharmacokinetic studies of human volunteers and patients.

Renal handling of fleroxacin in rabbits, dogs, and humans

The renal handling of fleroxacin was studied by renal clearance and stop-flow techniques in rabbits and dogs and by analyzing the pharmacokinetics with and without probenecid in humans. In rabbits the excretion ratios (fleroxacin intrinsic renal clearance/glomerular filtration rate) were greater than unity (2.01) without probenecid and were decreased to a value below unity (0.680) with probenecid. In dogs, on the other hand, the excretion ratios were less than unity (0.608 and 0.456) both without and with probenecid, and so were not affected by probenecid. This fact suggested that fleroxacin was excreted into urine by both glomerular filtration and renal tubular secretion in rabbits, but only by glomerular filtration in dogs, accompanied by partial renal tubular reabsorption in both species; these mechanisms were also supported by stop-flow experiments. In humans probenecid treatment induced increases in the elimination half-life and area under the serum concentration-time curve and decreases in apparent serum clearance, renal clearance, and urinary recovery of fleroxacin. The excretion ratio without probenecid was 1.13, which was significantly decreased to 0.750 with probenecid. These results indicated that both renal tubular secretion and reabsorption contributed to renal excretion of fleroxacin in humans. The contribution of tubular secretion was species dependent and was extensive in rabbits, minimal in dogs, and moderate in humans. Renal tubular reabsorption was commonly found in every species. The long elimination half-life of fleroxacin in humans might be explained by its small total serum clearance and small renal clearance, which are attributed to less tubular secretion and more tubular reabsorption.

Successful single-dose prophylaxis of Staphylococcus aureus foreign body infections in guinea pigs by fleroxacin

Single-dose administration of fleroxacin was evaluated as a means of preventing foreign body infection due to staphylococci. Tissue cages were implanted into guinea pigs and subsequently infected (100% rate) with 10(2) or more CFU of Staphylococcus aureus Wood 46. When a single dose of 30 mg of fleroxacin or vancomycin per kg of body weight was administered intraperitoneally, bactericidal levels of the antimicrobial agent were found in the tissue cage fluid after 3 h (when guinea pigs were inoculated with S. aureus) and during the next 24 h. Either fleroxacin or vancomycin successfully prevented experimental infection in all tissue cages challenged by 10(2) CFU of S. aureus Wood 46. When tissue cages were challenged with 10(4) CFU of S. aureus Wood 46, however, fleroxacin was more effective than vancomycin (P less than 0.05) in reducing colony counts below the detection limit of 10 CFU/ml in the inflammatory fluid of all tissue cages during the initial 48 h. In contrast to their initially different actions, the effects of the antibiotics were similar after 7 days, mostly because bacterial regrowth occurred more frequently in the fleroxacin-treated than in the vancomycin-treated tissue cages. These data show that experimental infections of subcutaneous tissue cages are a useful model for studying the prophylaxis of foreign body infections with antimicrobial agents.

Fluoroquinolone antimicrobial agents

The fluoroquinolones, a new class of potent orally absorbed antimicrobial agents, are reviewed, considering structure, mechanisms of action and resistance, spectrum, variables affecting activity in vitro, pharmacokinetic properties, clinical efficacy, emergence of resistance, and tolerability. The primary bacterial target is the enzyme deoxyribonucleic acid gyrase. Bacterial resistance occurs by chromosomal mutations altering deoxyribonucleic acid gyrase and decreasing drug permeation. The drugs are bactericidal and potent in vitro against members of the family Enterobacteriaceae, Haemophilus spp., and Neisseria spp., have good activity against Pseudomonas aeruginosa and staphylococci, and (with several exceptions) are less potent against streptococci and have fair to poor activity against anaerobic species. Potency in vitro decreases in the presence of low pH, magnesium ions, or urine but is little affected by different media, increased inoculum, or serum. The effects of the drugs in combination with a beta-lactam or aminoglycoside are often additive, occasionally synergistic, and rarely antagonistic. The agents are orally absorbed, require at most twice-daily dosing, and achieve high concentrations in urine, feces, and kidney and good concentrations in lung, bone, prostate, and other tissues. The drugs are efficacious in treatment of a variety of bacterial infections, including uncomplicated and complicated urinary tract infections, bacterial gastroenteritis, and gonorrhea, and show promise for therapy of prostatitis, respiratory tract infections, osteomyelitis, and cutaneous infections, particularly when caused by aerobic gram-negative bacilli. Fluoroquinolones have also proved to be efficacious for prophylaxis against travelers' diarrhea and infection with gram-negative bacilli in neutropenic patients. The drugs are effective in eliminating carriage of Neisseria meningitidis. Patient tolerability appears acceptable, with gastrointestinal or central nervous system toxicities occurring most commonly, but only rarely necessitating discontinuance of therapy. In 17 of 18 prospective, randomized, double-blind comparisons with another agent or placebo, fluoroquinolones were tolerated as well as or better than the comparison regimen. Bacterial resistance has been uncommonly documented but occurs, most notably with P. aeruginosa and Staphylococcus aureus and occasionally other species for which the therapeutic ratio is less favorable. Fluoroquinolones offer an efficacious, well-tolerated, and cost-effective alternative to parenteral therapies of selected infections.

Developments in quinolones. Bacteriology, pharmacokinetics and initial clinical experience of several investigational quinolone derivatives

The properties of several new, investigational quinolones are reviewed. Desirable characteristics of new quinolones are improved activity against especially Gram-positive bacteria, longer elimination half-life, slower development of resistance, fewer side effects etc. Fleroxacin and lomefloxacin have entered phase III trials: their main advantage lies in improved pharmacokinetics. AM-1091, AT-4140 and T-3262 are still in early phases of development and show improved activity against Gram-positive bacteria. They also show a reduced penetration of the blood-brain barrier, probably resulting in fewer side effects in the central nervous system. AM-1091 shows incomplete cross-resistance with ciprofloxacin.