Comparative pharmacokinetics of new quinolones

Single and Multiple-Dose Kinetics of Ofloxacin in Patients on Continuous Ambulatory Peritoneal Dialysis (CAPD)

To evaluate the pharmacokinetics of ofloxacin, a novel quinolon antibiotic, in patients with end-stage renal disease (ESRO) on continuous ambulatory peritoneal dialysis (CAPO), we investigated 6 patients in a single-dose study and 9 patients in a multiple-dose study, all without peritonitis. In the single-dose study, patients received 200 mg ofloxacin orally. Serum concentrations (Cmax) peaked at 3.1 ± 0.3 mg/L (x ± SEM), 1.6 ± 0.5 h after p. 0. administration of the drug. Elimination half-life ( t112) was 26.8 ± 2.5 h. Peritoneal clearance accounted for 10% of the total body clearance. After 5- h dwell time, ofloxacin concentrations in the dialysate were 1.5 ± 0.2 mg/L, which is above the MIC90 for most bacteria responsible for peritonitis in patients on CAPO. In the multiple dose study, 200 mg ofloxacin were administered twice, with a time interval of 12 h, followed by 200 mg for 9 days every morning. Mean trough serum levels were 2.6 ± 1.0 mg/L, mean peak concentrations were 4.1 ± 1.7 mg/L. Mean ofloxacin concentrations in the peritoneal effluent were 1.9 ± 0.9 mg/L. It is concluded that an oral loading dose of 400 mg on the first day and a maintenance dose of 200 mg ofloxacin/day does not lead to significant accumulation, even though the elimination by the peritoneal route is only small. The proposed dosing regimen could be an adequate therapy of peritonitis and exit-site infections in patients on CAPO since levels reached in the dialysate effluent are bactericidal. The clinical usefulness in the treatment of peritonitis has to be proven in further studies.

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.

Comparative pharmacokinetics and pharmacodynamics of the newer fluoroquinolone antibacterials

A number of new fluoroquinolone antibacterials have been released for clinical use in recent years. These new agents exhibit enhanced activity against Gram-positive organisms while retaining much of the Gram-negative activity of the earlier agents within the same class. The pharmacokinetics of most of these agents are well described including serum pharmacokinetics, tissue and fluid distribution, and pharmacokinetics in renal and hepatic disease. When compared with earlier agents within this class (i.e. ciprofloxacin), the newer agents retain the wide distribution characteristics; however, they exhibit a more prolonged elimination, which, in part, supports single daily administration for these agents. Based on their predominant renal elimination, dosage adjustment is necessary in the presence of renal disease for ciprofloxacin, levofloxacin, gatifloxacin and sitafloxacin. Drug interactions, particularly with multivalent cations (calcium/aluminium-containing antacids and iron products), remain a problem for the newer agents, resulting in reduced absorption requiring separate administration times to maximise bioavailability. However, the newer agents do not appear to interfere significantly with the cytochrome P450 system, thus minimising the potential for interactions with other drugs metabolised by this system. The pharmacodynamic properties of the fluoroquinolones have been well described. The bactericidal activity is maximised when the ratios of peak plasma drug concentration (Cmax): minimum inhibitory concentrations (MIC) or area under the concentration-time curve (AUC): MIC exceed specific threshold values. Knowledge of the pharmacodynamic relationships allows for appropriate drug selection and enables design of dosage regimens to maximise the bactericidal activity. Therapeutic drug monitoring of the fluoroquinolones may provide a means of optimising the dosage regimen in certain clinical situations (that is, meningitis and hospitalised pneumonias) with the goals of achieving a more predictable therapeutic response and minimising the potential for the development of resistance.

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%).

Kinetics of 4-fluoroquinolones permeation into saliva

Following a single oral administration of ciprofloxacin, norfloxacin, pefloxacin and ofloxacin preparations to healthy volunteers simultaneously collected, saliva and plasma 4-fluoroquinolone concentrations were assayed by HPLC. Pharmacokinetic properties were determined by ordinary least squares fitting of the two compartment pharmacokinetic model to the experimental data. A good correlation between plasma and saliva data has been demonstrated. The saliva to venous plasma drug concentration ratio S/P appeared to be time-dependent in the case of norfloxacin and pefloxacin. It was demonstrated that S/P is a function of the quotient of the rate of absorption and venous plasma drug concentration. The calculated S/P ratios with the influence of absorption eliminated, (S/P)(corr) are: ciprofloxacin 0.53+/-0.02, norfloxacin 0.34+/-0.04, ofloxacin 0. 43+/-0.02 and pefloxacin 0.39+/-0.02 (mean+/-S.E.). These values are apparently independent of log D thus making it impossible to predict S/P on the basis of partition principles. The corresponding (S/P)(dif) ratios were calculated on the basis of the assumption that an equilibrium is established across the blood-saliva barrier, which is permeable only for nonionized and nonprotein bound drug fraction. Comparing (S/P)(corr) with the calculated (S/P)(dif) ratios it is evident that 4-fluoroquinolone permeation in saliva cannot be described by passive diffusion based on pH-partition theory.

Levofloxacin and sparfloxacin: new quinolone antibiotics

OBJECTIVE

To discuss the pharmacology, pharmacokinetics, spectrum of activity, clinical trials, and adverse effects of levofloxacin and sparfloxacin, two new fluoroquinolone antibiotics.

DATA SOURCES

Literature was identified by a MEDLINE search from January 1985 to September 1997. Abstracts and presentations were identified by review of program abstracts from the Interscience Conference on Antimicrobial Agents and Chemotherapy from 1988 to 1996.

STUDY SELECTION

Randomized, controlled clinical studies were selected for evaluation; however, uncontrolled studies were included when data were limited for indications approved by the Food and Drug Administration (FDA). In vitro data were selected from comparison trials whenever available. Only in vitro trials that provided data on the minimum inhibitory concentrations required to inhibit 90% of isolates were used. Data from North American studies were selected whenever available.

DATA EXTRACTION

Data were evaluated with respect to in vitro activity, study design, clinical and microbiologic outcomes, and adverse drug reactions.

DATA SYNTHESIS

Levofloxacin and sparfloxacin are active against pathogens frequently involved in community-acquired upper and lower respiratory tract infections, including Streptococcus pneumoniae, Haemophilus influenzae, Moraxella catarrhalis, Mycoplasma pneumoniae, Legionella pneumophila, and Chlamydia pneumoniae. Both compounds have enhanced activity compared with ciprofloxacin against most gram-positive bacteria, including enterococci, streptococci, and staphylococci, and retain good activity against most Enterobacteriaceae and Pseudomonas aeruginosa. Sparfloxacin has greater anaerobic activity than levofloxacin, which is more active than ciprofloxacin or ofloxacin. Although many clinical studies are available only in abstract form, the clinical data demonstrate that these new quinolones are effective for most community-acquired upper and lower respiratory tract infections, urinary tract infections, gonococcal and nongonococcal urethritis, and skin and skin structure infections. FDA-approved indications are limited for both compounds to date.

CONCLUSIONS

Levofloxacin and sparfloxacin have improved gram-positive activity compared with that of older fluoroquinolones, and are administered once daily. Sparfloxacin-associated photosensitivity may limit its therapeutic usefulness. Clinical trials confirm that these agents are as effective as traditional therapies for the management of community-acquired pneumonia, acute exacerbations of chronic bronchitis, sinusitis, urinary tract infections, acute gonococcal and nongonococcal urethritis, and skin and skin structure infections.

Levofloxacin does not alter cyclosporine disposition

Certain fluoroquinolones have been shown to elevate the serum concentrations of the immunosuppressant cyclosporine. It is thus important to investigate the potential interaction between levofloxacin, a new fluoroquinolone antimicrobial agent, and the pharmacokinetics of cyclosporine. Twelve healthy subjects (6 men, 6 women) were enrolled in and completed a placebo-controlled, randomized, double-blind, two-phase crossover study. Subjects were given a single oral 10-mg/kg dose of cyclosporine solution during multiple-dose twice-daily oral treatment with placebo or 500 mg of levofloxacin. Blood cyclosporine concentrations were measured for 48 hours after each cyclosporine dose for pharmacokinetic evaluation. Cyclosporine pharmacokinetic parameters were comparable and not significantly different in the absence and presence of levofloxacin. Results of this study suggest that a clinically important pharmacokinetic interaction between levofloxacin and cyclosporine is unlikely to occur during concurrent therapy.

Intestinal elimination of ofloxacin enantiomers in the rat: evidence of a carrier-mediated process

The aim of this work was to examine the mechanism involved in intestinal elimination of the two optical isomers of ofloxacin in the rat. An intestinal segment was isolated in situ and perfused with saline, while drug solution was administered via the carotid artery. Blood samples and intestinal effluents were collected and analyzed by a high-performance liquid chromatography method. We observed saturable and stereoselective intestinal elimination of the ofloxacin enantiomers. The elimination process favored the R-(+) form of the molecule. After a parenteral dose of 20 mg of racemic ofloxacin per kg of body weight, intestinal clearances were 0.23 +/- 0.03 versus 0.30 +/- 0.03 ml/min for S-(-)- and R-(+)-ofloxacin, respectively. Ciprofloxacin and pefloxacin interfered with ofloxacin elimination and significantly reduced the intestinal clearance of S-(-)- and R-(+)-ofloxacin. With concomitant ciprofloxacin, intestinal clearances became 0.13 +/- 0.02 versus 0.17 +/- 0.03 ml/min and 0.14 +/- 0.01 versus 0.19 +/- 0.05 ml/min with pefloxacin for S-(-)- and R-(+)-ofloxacin, respectively. Those findings argue for the presence of a common transport system in the rat intestine with variable affinities for fluoroquinolones. In addition, verapamil and quinidine, two P-glycoprotein blockers, significantly reduced the intestinal elimination of both ofloxacin isomers (with concomitant verapamil, intestinal clearances were 0.12 +/- 0.02 versus 0.18 +/- 0.03 ml/min for S-(-)- and R-(+)-ofloxacin, respectively, while with concomitant quinidine, values were 0.18 +/- 0.01 versus 0.23 +/- 0.01 ml/min without modifying their areas under the concentration-time curve in serum. Similar results were found with another fluoroquinolone, ciprofloxacin, in previous work. P-glycoprotein appears to be involved in the intestinal elimination of fluoroquinolones in rats. The characterization of fluoroquinolone intestinal elimination has significant clinical relevance for the better evaluation of the influence of this secretory pathway on antibiotic efficacy and selection of resistant bacteria within the intestinal flora.

Ofloxacin versus trimethoprim-sulfamethoxazole in the treatment of patients with acute exacerbation of chronic bronchitis. Study of Ofloxacin in Lower Respiratory Tract Infections Research Group

An open-label, randomized, comparative, parallel-group study of ofloxacin and trimethoprim-sulfamethoxazole was performed in 162 outpatients diagnosed with acute exacerbation of chronic bronchitis. Ofloxacin 400 mg once daily was administered orally; the dose could be increased to 400 mg twice daily if patients had not improved after 72 hours of treatment. The other treatment group received trimethoprim-sulfamethoxazole 960 mg twice daily orally. The duration of treatment was 10 to 14 days for both treatment groups. Successful clinical response (defined as cure or major improvement in symptoms) was achieved in 65 (80.2%) patients in the ofloxacin group and in 42 (51.9%) patients in the trimethoprim-sulfamethoxazole group; the differences between groups were statistically significant. Bacteriologic success (classified as eradication or presumptive eradication of the causative pathogen) was achieved in 27 (50.0%) patients in the ofloxacin group and in 16 (29.1%) patients in the trimethoprim-sulfamethoxazole group; these differences between groups were also statistically significant. Reinfection occurred in 18 (33.3%) and 4 (7.3%) patients treated with ofloxacin and trimethoprim-sulfamethoxazole, respectively. No serious adverse events were reported.

Fluoroquinolones in animal health

The fluoroquinolones are a series of synthetic antibacterial agents that are undergoing extensive investigation for both human and veterinary use in the treatment of a variety of bacterial infections. These agents work through the inhibition of DNA gyrase, interfering with the supercoiling of bacterial chromosomal material. As a result, these agents are rapidly bactericidal primarily against gram-negative bacteria, mycoplasma, and some gram-positive bacteria, with most having little to no activity against group D streptococci and obligate anaerobic bacteria. Resistance develops slowly and is almost always chromosomal and not plasmid-mediated. However, development of resistance to the fluoroquinolones and transfer of that resistance among animal and human pathogens have become a hotly debated issue among microbiologists. The fluoroquinolones are a current antimicrobial class whose use in veterinary medicine is being scrutinized. From a pharmacokinetic perspective, these agents are variably but well absorbed from the gastrointestinal tract and almost completely absorbed from parenteral injection sites, and they are well distributed to various tissues in the body. The fluoroquinolones are metabolized and renally excreted, with many of them having approximately equal excretion by the hepatic and the renal excretory systems. The primary toxicity observed at therapeutic doses involves the gastrointestinal system and phototoxicity, although at higher doses central nervous system toxicity and ocular cataracts are observed. Administration to immature animals may result in erosive arthropathies at weight-bearing joints, and administration of high doses to pregnant animals results in maternotoxicity and occasionally embryonic death. The fluoroquinolones are approved for indications such as urinary tract infections and soft tissue infections in dogs and cats and colibacillosis in poultry. Approval for bovine respiratory disease in the United States is being sought. Other indications for which the fluoroquinolones have been used in animal health include deep-seated infections, prostatitis, and other bacterial infections resistant to standard antimicrobial therapy.

Enoxacin: a reappraisal of its clinical efficacy in the treatment of genitourinary tract infections

Enoxacin is a 6-fluoronaphthyridinone antibacterial agent with good in vitro activity against Neisseria gonorrhoeae and most Gram-negative urinary tract pathogens. It is less active in vitro against Acinetobacter spp., Pseudomonas aeruginosa, and most Gram-positive bacteria, than against Gram-negative organisms. Enoxacin is rapidly absorbed, with a high oral bioavailability (87 to 91%). Of the absorbed dose, 44 to 56% is excreted unchanged in the urine, with peak urinary concentrations (>500 mg/L within 4 hours) remaining high (>100 mg/L) for up to 24 hours, sufficient to inhibit most urinary tract pathogens. Single (400 mg) and multiple oral dose regimens (100 to 600 mg twice or 3 times daily for 5 to 14 days) of enoxacin are as effective for the treatment of patients with complicated or uncomplicated urinary tract infections as other antibacterial agents such as amoxicillin, cefuroxime axetil, cotrimoxazole (trimethoprim-sulfamethoxazole) or trimethoprim. Noncomparative data suggest that enoxacin is also an effective agent for the treatment of prostatitis. Single 400 mgoral doses of enoxacin produce >/- 95% bacteriological cure rates in gonococcal infections, comparable to those produced by single intramuscular doses of ceftriaxone 250 mg. Perioperative doses of oral enoxacin 200 mg provide effective prophylaxis against postoperative bacteriuria after transurethral resection of the prostate. Concomitant administration of enoxacin with a number of commonly used therapeutic agents (e.g. antacids, methylxanthines, warfarin) affects the pharmacokinetic properties of either enoxacin or the coadministered agents. Enoxacin is reasonably well tolerated, with the incidence of adverse experiences ranging from 0 to 24%. Adverse events are mainly gastrointestinal, neurological or dermatological and resolve with minimal intervention. Overall, although enoxacin exhibits a number of clinical characteristics that are similar to those of other agents for the treatment of genitourinary tract infections, the advantages offered by this agent generally do not outweigh those of alternative fluoroquinolone agents. Thus, it is likely to prove to be yet another addition to the list of agents available for the management of these infections.

Antimicrobial prophylaxis in management of urinary tract stones by extracorporeal shock-wave lithotripsy: is it necessary?

OBJECTIVES

In a prospective randomized study, we evaluated the incidence of urinary tract infections following extracorporeal shock-wave lithotripsy (ESWL) and the necessity of prophylactic antibiotic administration in patients treated with this modality.

METHODS

A total of 360 consecutive patients with renal and ureteric stones who had sterile urine before ESWL treatment and did not have any increased risk of infection received either a single dose of 400 mg of ofloxacin or no prophylaxis. Patients were followed by simple urine analysis and urine cultures together, with clinical evaluations.

RESULTS

Only 3 patients (0.8%) had positive urine cultures at 1 week after ESWL. Two of these patients were in the antibiotic prophylaxis group.

CONCLUSIONS

The incidence of urinary tract infections after ESWL is extremely low, provided that patients have sterile urine before ESWL, and prophylactic antibiotics are not required.

Pharmacokinetic studies of CP-74,667, a new quinolone, in laboratory animals

The pharmacokinetics of CP-74,667 (7-(8'-methyl-3',8'-diazabicyclo[3.2.1]oct-3'-yl)-1-cyclopropyl-6- fluoro-1,4-dihydro-4-oxo-3-quinolinecarboxylic acid) were studied following oral or parenteral administration in mice, rats, rabbits, dogs, and cynomolgus monkeys. The mean peak levels of CP-74,667 in serum following a single oral dose of 20 mg/kg of body weight were similar in all species, with a range of 3.7 micrograms/ml in mice to 5.6 micrograms/ml in dogs. In contrast, elimination half-lives were species dependent, with mean values of 2.1, 1.8, 4.5, 7.8, and 13.1 h in mice, rats, rabbits, dogs, and monkeys, respectively. The oral bioavailability of CP-74,667 was 100% in dogs and monkeys, as determined by intravenous-oral crossover experiments. The maximum concentration of drug in serum and area under the concentration-time curve (AUC) of CP-74,667 in dogs were proportional to dose over the range of 5 to 40 mg/kg. Accumulation of drug in serum was observed following the administration of four once-a-day doses of 7.1 mg/kg in monkeys (mimicking a 500-mg human dose), with significant increases in half-life, maximum and minimum concentrations of drug in serum, and AUC. The good tissue penetration of CP-74,667 suggested by a volume of distribution in excess of 2 liters/kg in dogs and monkeys was confirmed by tissue distribution studies with the same species, which demonstrated tissue concentrations (except for those in brain tissue) greater than 1.45 times higher than corresponding levels in serum. The mean urinary recoveries of unchanged drug were 17.7% in rats, 7.8% in monkeys, and 4.9% in dogs. Metabolism studies in dogs, following intravenous dosing, indicated that renal excretion of CP-74,667-related materials accounted for 41.6% of the administered dose, while biliary recoveries accounted for 6.8%. The CP-74,667 N-oxide metabolite was the primary drug-related material eliminated via renal excretion (37.2% of dose). The pharmacokinetics of CP-74,667 describe a quinolone with complete oral absorption, linear pharmacokinetics, a long elimination half-life, and wide distribution into tissues.

Multiple-dose pharmacokinetics of lomefloxacin: rationale for once-a-day dosing

Six dosage regimens of oral lomefloxacin, a new difluorinated quinolone, were given to healthy volunteer subjects for 7 days in a randomized, placebo-controlled trial to evaluate pharmacokinetics and tolerability and to determine the optimum dosage schedule. Single daily doses of lomefloxacin up to 800 mg and multiple doses up to 600 mg twice daily (1,200 mg/day) were well tolerated. At all dose levels and schedules, lomefloxacin was well absorbed and achieved peak plasma concentrations approximately 1 hour after administration. Urine concentrations were approximately 100 times the plasma concentrations. Elimination half-lives of 7-8 hours were found for all dosage regimens. Steady-state was achieved on the second day of dosing. Little accumulation was observed. A 400 mg oral dose provided a mean peak plasma concentration of 3.43 micrograms/mL, and trough concentrations at steady state that were above the minimum inhibitory concentration for 90% (MIC90) of most common Enterobacteriaceae. The 400 mg dose produced a urine concentration of greater than 80 micrograms/mL during the 12- to 24-hour period after the dose, thus exceeding the MIC90 for clinical isolates such as Pseudomonas aeruginosa, Serratia marcescens, and methicillin-susceptible and -resistant Staphylococcus aureus. There was good agreement between the results of this study and previously reported single-dose data. In summary, lomefloxacin's rapid absorption, long half-life, and high sustained plasma and urine concentrations should permit effective once-daily administration in many clinical situations.

Milk and yoghurt do not impair the absorption of ofloxacin

The effects of milk and yoghurt on the oral absorption of ofloxacin were studied in seven healthy volunteers in a randomized cross-over trial. After an overnight fast, 200 mg ofloxacin was given with 300 ml water, milk or yoghurt. Plasma concentrations and urinary excretion of ofloxacin were determined up to 24 h. Values of total plasma AUC and 24 h urinary excretion of ofloxacin were not affected by milk or yoghurt. Plasma ofloxacin concentrations from 0.5 to 1.5 h and the peak concentration were lower (P less than 0.05) after yoghurt than without and the time to peak was prolonged by 1 h (P less than 0.05).

Penetration of ofloxacin into human lung tissue following a single oral dose of 200 milligrams

The penetration of ofloxacin into lung tissue was studied in 10 patients subjected to pulmonary surgery. Samples of blood and lung tissue were obtained 3 to 8 h (mean, 5 h) after oral administration of 200 mg. The mean level in tissue was 2.17 +/- 0.5 micrograms/g, while the mean level in serum was 0.85 +/- 0.23 micrograms/ml. The mean lung tissue/serum concentration ratio was 2.55 +/- 0.30. The achievable levels of ofloxacin in lung tissue are above the MICs for most pulmonary pathogens.

Bioavailability and pharmacokinetics of ofloxacin in healthy volunteers

The pharmacokinetics and bioavailability of ofloxacin in 20 healthy male volunteers were studied in an open-label, randomized, two-way crossover study. Ofloxacin (400 mg) was administered either as a 1-h infusion or as an oral tablet. The mean peak concentration after intravenous infusion was 4.30 +/- 0.69 microgram/ml, and that after oral administration was 3.14 +/- 0.53 microgram/ml, occurring 1.74 +/- 0.57 h after dosing. The bioavailability (F) of the oral dosage form of ofloxacin was virtually identical to that of the intravenous form (F = 105% +/- 7%). This complete bioavailability of ofloxacin is supportive of the use of the oral dosage form for the treatment of infections in hospitalized patients either as a replacement for intravenous ofloxacin therapy or in streamlining therapy from the intravenous to the oral route.

The bioavailability of ofloxacin from several formulations

The bioavailability of ofloxacin after a single dose of one of two tablet formulations (200 or 400 mg) or a liquid formulation (1.67 mg/ml) was investigated in 24 healthy male volunteers in an open randomized, crossover design study with a 5-day wash-out period between doses. Plasma concentrations of ofloxacin were determined at various times after administration by a sensitive and specific High Pressure Liquid Chromatography (HPLC) method. Ofloxacin was well absorbed after each administration, although somewhat more slowly after the tablet formulations than the solution. Mean AUC values of 31.8, 31.3, and 31.3 micrograms.hr/ml were calculated after administration of the solution, 2 x 200 mg tablets and a 400 mg tablet, respectively. Thus, the bioavailability of the tablets was in excess of 98% that of the liquid reference. Mean Cmax values of 4.4, 3.7 and 3.7 micrograms/ml were observed at Tmax values of 0.8, 1.6 and 1.8 hours after administration of the solution, 2 x 200 mg tablets and a 400 mg tablet, respectively. The drug was well tolerated and no adverse effects necessitating subject withdrawal were noted during the study.

High-performance liquid chromatography for the determination of three new fluoroquinolones, fleroxacin, temafloxacin and A-64730, in biological fluids

High-performance liquid chromatographic procedures have been developed for the measurement of three new fluoroquinolones, fleroxacin, temafloxacin and A-64730, in serum, urine and bile. The sample treatment consists of a two-step chemical extraction. The three molecules are chromatographed on a C18 reversed-phase analytical column with spectrofluorimetric detection. At a signal-to-noise ratio of 4, the detection limits in serum are 2.5, 10 and 20 ng/ml, for fleroxacin, temafloxacin and A-64730, respectively. The calibration curves are rectilinear between these detection limits and 20 micrograms/ml. The intra- and inter-assay coefficients of variation are in the ranges 0.8-5.4 and 2.2-7.6%, respectively. These simple and reliable assay procedures will be of great interest for further pharmacokinetic studies and drug monitoring in hospital use.