Fluorinated quinolones. A review of their mode of action, antimicrobial activity, pharmacokinetics and clinical efficacy

CAPD Peritonitis and Fluoroquinolones: A Review

Fluoroquinolones are potentially useful agents in the treatment of CAPD peritonitis, due to their wide spectrum of antimicrobial activity, favourable pharmacokinetics, oral availability and their relatively low toxicity.

The microbiological, pharmacokinetic, and clinical aspects of these drugs in CAPD are reviewed.

Ciprofloxacin showed superior in-vitro activity in comparison with various beta lactam agents; gentamicin and vancomycin against staphylococci and particularly against Gram-negative bacteria. Its activity against streptococci is low. The in vitro activity of fiuoroquinolones is reduced in peritoneal dialysis fluid.

A limited rise in serum levels is observed with daily administration of fiuoroquinolones in CAPD patients during 5–15 days. Effective dialysate levels are reached in most patients after oral dosing, but these levels are highly variable and low levels are often observed during the first day, an d with short dwell times. Concurrent administration with phosphate binding antacids should be avoided.

Initial clinical experience shows that ciprofloxacin and ofloxacin may be effective agents to treat CAPD peritonitis via the oral route. They are usually well tolerated, although convulsions have been observed. The relative efficacy in comparison with “standard therapies” will have to be shown in comparative studies.

Comparative Evaluation of Efficacy and Safety of Ciprofloxacin and Norfloxacin Ophthalmic Solutions

The efficacy and safety of ciprofloxacin ophthalmic solution 0.3% and norfloxacin ophthalmic solution 0.3% in the treatment of bacterial conjunctivitis and blepharitis were compared in a double masked randomised study. A total of 131 patients, 65 treated with ciprofloxacin (42 with conjunctivitis and 23 with blepharitis) and 66 treated with norfloxacin (39 with conjunctivitis and 27 with blepharitis) were enrolled in the study at five centres in France. In the efficacy population, pathogens were eradicated or reduced in 96% (24/25) of patients in the ciprofloxacin group and 89% (24/27) in the norfloxacin group. There was no difference between treatments with regard to eradication of particular pathogens. In the efficacy population, clinical cure or improvement was seen in 96% of the patients (24/25 in the ciprofloxacin group and 26/27 in the norfloxacin group). There were no significant differences between ciprofloxacin and norfloxacin with respect to improvements in four symptoms or ten clinical signs. No serious treatment-related adverse events were reported and both ciprofloxacin and norfloxacin were well tolerated.

An overview of phenylcyclopropylamine derivatives: biochemical and biological significance and recent developments

trans-2-Phencylcyclopropylamine (2-PCPA), a potent, clinically used antidepressant, affects monoamine neurotransmitter levels by inhibiting the main metabolizing enzymes, monoamine oxidases (MAOs). However, the antidepressant action of this compound was not fully explained by its effects on MAOs due to its wide variety of biological effects. 2-PCPA also affects depression-associated pathophysiological pathways, and linked with increased levels of trace amines in brain, upregulation of GABAB receptors (where GABA is gamma amino butyric acid), modulation of phospholipid metabolism, and interference with various cytochrome P450 (CYP) enzymes. Consequently, despite its adverse effects and limited clinical applicability, 2-PCPA has attracted interest as a structural scaffold for the development of mechanism-based inhibitors of various enzymes, including lysine-specific demethylase 1 (LSD1), which is a possible target for cancer chemotherapy. In the recent years, many reports have appeared in the literature based on 2-PCPA scaffold and their potential medicinal implications. This review mainly focuses on the medicinal chemistry aspects including drug design, structure-activity relationships (SAR), biological and biochemical properties, and mechanism of actions of 2-PCPA and its derivatives. Furthermore, we also highlight recent advance in this area and discuss their future applications for beneficial therapeutic effects.

Effect of Fenbufen on the Entry of New Quinolones, Norfloxacin and Ofloxacin, into the Central Nervous System in Rats

The entry of two new quinolone antibacterial agents, norfloxacin and ofloxacin, into the central nervous system (CNS) of rats, and the effect of fenbufen on this was investigated. At various times after the administration of a bolus intravenous dose of norfloxacin or ofloxacin (10 mg kg−1) with or without fenbufen (20 mg kg−1), serum and cerebrospinal fluid (CSF) samples and whole brain were collected from the rats and the concentration of norfloxacin or ofloxacin in each sample was determined. Serum concentrations of both quinolones declined biexponentially with time and were significantly elevated by coadministration with fenbufen at the terminal phase. The fractions of these quinolones bound to serum protein were not altered by coadministration with fenbufen. Coadministered fenbufen raised the brain concentrations of both quinolones but did not affect their brain to serum unbound concentration ratios. In contrast, CSF to serum unbound concentration ratios as well as CSF concentrations of norfloxacin and ofloxacin were elevated by coadministration with fenbufen. Apparent diffusional clearances between blood and CSF of norfloxacin and ofloxacin estimated by the physiological model analysis increased by 1·9 and 2·6 times, respectively, after coadministration with fenbufen. These findings suggest that coadministered fenbufen may facilitate the entry of norfloxacin and ofloxacin into the CNS.

Clinical role of protein binding of quinolones

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

Glycosylation of fluoroquinolones through direct and oxygenated polymethylene linkages as a sugar-mediated active transport system for antimicrobials

We report herein the synthesis and biological testing of several glycosylated derivatives of some fluoroquinolone antibiotics. In particular, we have prepared several glycosylated derivatives of ciprofloxacin (2) in which the carbohydrate units are linked to the free secondary amine of the piperazine unit by: (a) no linker (e.g., a glycosylamine), (b) a beta-oxyethyl linker, and (c) a gamma-oxypropyl linker. Both glucose and galactose were used as carbohydrates so that six compounds of this type were prepared, e.g., no linker 4a,b, oxyethyl linker 5a,b, and oxypropyl linker 6a,b. In addition the aryl glycosides of glucose and galactose (7a,b) were prepared from the active 1-(4-hydroxyphenyl)fluoroquinolone (3.) The syntheses of the glycosylamines 4a,b involved the direct condensation of glucose and galactose with the hydrochloride salt of ciprofloxacin (2). For the oxyalkyl-linked compounds, we first prepared the peracetylated omega-bromoalkyl glycopyranosides 14a,b and 15a,b and then coupled them to the allyl ester of ciprofloxacin (11) to give, after saponification to remove all of the esters, the desired fluoroquinolone carbohydrates 5a,b and 6a,b. The final series was prepared from 2,4,5-trifluorobenzoyl chloride (22) which gave 3 in four precedented steps. Coupling of 3 with the peracetylated glucosyl and galactosyl halides 12a,b and 26 afforded, after saponification, the desired aryl glycosides 7a,b. Six of these derivatives of ciprofloxacin-4a,b, 5a,b, and 6a,b-were subjected to microbiological screening. Of the six, compound 6a showed the highest activity. Since 6a would give the hydroxypropyl-substituted ciprofloxacin on hydrolysis and its activity is approximately 4-8 times less than that of ciprofloxacin (2), this implies that compound 6a is probably being actively transported. Thus preliminary results suggest that some of the compounds are stable in culture conditions and may be differentially transported by multiple resistant organisms. In some cases, the addition of a linker and a carbohydrate to ciprofloxacin lessens, but does not eliminate, antimicrobial activity.

Pharmacokinetic-pharmacodynamic contributions to the convulsant activity of fluoroquinolones in rats

The in vivo convulsant activities in rats of five representative fluoroquinolones (FQs), norfloxacin, enoxacin, sparfloxacin, fleroxacin, and pefloxacin, were compared. The experimental approach allowed distinction between the drugs' ability to reach the pharmacological receptors at the level of the central nervous system (pharmacokinetic contribution) and their ability to interact with these receptors (pharmacodynamic contribution). The presence of a methyl group on the piperazine moiety decreased the pharmacodynamic contribution to the convulsant activity by severalfold, and the ratios of concentrations of the FQs in cerebrospinal fluid (CSF) to concentrations of unbound FQs in plasma varied from about 5 to 75% as a function of lipophilicity. Interestingly, FQs with the highest intrinsic convulsant activities had the lowest levels of diffusion in CSF and vice versa. This in vivo approach provides information complementary to that of in vitro experiments and should be recommended for early preclinical assessment of a new FQ's epileptogenic risk.

Distribution of ciprofloxacin into the central nervous system in rats with acute renal or hepatic failure

Pharmacokinetic changes of various drugs have been reported in renal or hepatic failure. The present study employed ciprofloxacin, a quinolone antibiotic having neurotoxic side effects, to assess the influence of these diseases on distribution of ciprofloxacin into the central nervous system (CNS). After intravenous dosing of ciprofloxacin (10-30 mg kg(-1)), ciprofloxacin levels in plasma and brain were measured in normal rats (Wistar, male, 10-week-old) and those with acute renal and hepatic injuries which were induced by uranyl nitrate and carbon tetrachloride (CCl4), respectively. In the uranyl nitrate-treated rats, the plasma elimination half-life of ciprofloxacin was prolonged and the total body clearance was reduced when compared with those in the normal rats. Similar but smaller changes were observed in the CCl4-treated group. Brain levels of ciprofloxacin were significantly increased by both uranyl nitrate and CCl4 treatments. A proportional correlation between serum unbound levels and brain levels of ciprofloxacin was observed in the normal group. However, brain-to-serum unbound concentration ratios of ciprofloxacin were reduced in the rats with renal or hepatic failure. These results suggest that renal failure as well as hepatic failure retards elimination of ciprofloxacin from the blood, leading to elevation of the CNS level, and also that ciprofloxacin distribution in the brain is reduced in these disease states.

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.

Tremendous high plasma lipopolysaccharide concentrations in a patient with Legionella pneumophila pneumonia

We describe a patient suffering from nosocomial Legionella pneumophila pneumonia with extremely high lipopolysaccharide (LPS) concentrations (peak concentration = 725 EU/ml). This unexpectedly high LPS load led to an exaggerated response of the cytokine network. Although immediate treatment with macrolides was instituted, the patient developed an adult respiratory distress syndrome. Despite application of nitric oxide and porcine natural surfactant factor, the patient died 5 days after admission to the ICU. Because of this dramatic case, we emphasize physicians to be aware of L. pneumophila and to include this organism into the diagnosis and antibiotic therapy in patients with nosocomial pneumonia.

Antibiotic treatment of ophthalmic infection: new developments

The introduction of quinolones has dramatically altered antibiotic therapy for serious ophthalmic infections. The newer cephalosporins are also playing a more significant role. The recently introduced macrolides, particularly azithromycin, have great potential for treating not only serious infections, but also some of the less serious ones. These new developments are discussed, and the cost implications of new antibiotic treatment on ophthalmology is described.

Effects of some quinolones on imipenem-induced seizures in DBA/2 mice

1. The behavioural and convulsant effects of imipenem, a carbapenem derivative, were studied after i.p. administration in DBA/2 mice, a strain genetically susceptible to sound-induced seizures and in Swiss mice. 2. It was found that DBA/2 mice were more susceptible to seizures induced by imipenem than Swiss mice. 3. The proconvulsant effects of some quinolones were also evaluated in DBA/2 mice on seizures evoked by means of i.p. administration of imipenem. The present study demonstrated that the order of proconvulsant activity in our epileptic model was pefloxacin > enoxacin > ofloxacin > nalidixic acid > rufloxacin > norfloxacin > ciprofloxacin > cinoxacin > temafloxacin. 4. The relationship between the chemical structure and the proconvulsant activity of quinolone derivatives was studied. The relationship between the lipophilicity and the proconvulsant activity was also investigated. 5. Although the main mechanism for seizure potentiation cannot be easily determined potential drug interactions exist. It has been reported that imipenem and quinolones are all believed to increase excitation of the central nervous system by inhibition of GABA binding to receptors. 6. A slow clearance from the central nervous system and from the kidney may also occur following the concomitant administration of some quinolones and imipenem.

High-performance liquid chromatographic determination of nalidixic acid in rat serum, brain and cerebrospinal fluid

A high-performance liquid chromatographic method for the determination of nalidixic acid (NA) in rat serum, brain and cerebrospinal fluid (CSF) was developed. NA in rat serum and brain homogenate was extracted and injected onto a reversed-phase column. CSF was directly analysed without extraction procedure. The limits of detection were 0.05 microgram ml-1 for serum, 0.07 microgram g-1 for brain and 0.02 microgram ml-1 for CSF, respectively. Calibration curves were linear over the concentration ranges 0.1-50 micrograms ml-1 for serum, 0.12-9 micrograms g-1 for brain and 0.05-10 micrograms ml-1 for CSF, respectively. The reproducibility of NA assay in rat biological media ranged from 1 to 4% relative standard deviations (RSD). The recoveries of NA added to serum and brain were higher than 96% with an RSD of less than 4%. The present method was found to be applicable to pharmacokinetic study of NA in rat serum, brain and CSF.

Feline neonatal sepsis

When bacterial infections exceed or overcome the ability of a kitten's immune system to provide protection, life-threatening illnesses such as neonatal sepsis often occur. Many kittens with neonatal sepsis show unusual presentations or a wide variety of clinical presentations that may not be immediately recognized as being associated with sepsis. Because neonatal sepsis causes unexpected sudden death, kittens suspected of having sepsis should be treated immediately. In most instances, initial antimicrobial therapy is selected empirically. Kittens are treated by giving intravenous or intraosseous fluids for dehydration, oxygen to counter tissue hypoxemia, and glucose if hypoglycemia is present. The beta-lactam antimicrobial agents such as the penicillins, cephalosporins, and the combination of beta-lactam antimicrobials and beta-lactamase inhibitors are considered to be the first choice in the treatment of any septicemic kittens.

The proconvulsive activity of quinolone antibiotics in an animal model

The side-effect profile of quinolone antibiotics in man includes CNS disturbances such as dizziness, insomnia and convulsions. Although it has been suggested that the proconvulsive liability of quinolones involves an interaction with GABA receptors in the central nervous system, no animal model has been described to evaluate or confirm the mechanism of this effect. The proconvulsive activity of the quinolone antibiotics, nalidixic (NAL) and oxolinic (OXO) acid were tested in male mice following oral doses of 10-100 mg/kg utilizing the convulsive stimuli pentylenetetrazole (PTZ), picrotoxin, strychnine or electroshock. While NAL and OXO did not alter the threshold for convulsions induced by PTZ, strychnine or picrotoxin, both agents lowered the threshold for electroshock-induced seizures. Furthermore, the proconvulsive actions of NAL and OXO were completely blocked by the excitatory amino acid receptor antagonists, MK-801 and 2-amino-4-phosphonobutyric acid (AP-4). These data indicate that the mechanism of convulsive liability of quinolone antibiotics does not involve GABA receptor interactions as previously thought, but appears to involve activation of excitatory amino acid (EAA) receptors, possibly located in the optic region of the central nervous system.

The effect of ofloxacin and ciprofloxacin on pentylenetetrazol-induced convulsions in mice

There have been several reports that convulsions, although rare, occur in patients who received fluoroquinolones. In this study, conducted for the evaluation of the convulsant action of fluoroquinolones, the effect of ofloxacin and ciprofloxacin on pentylenetetrazol-induced convulsions were investigated in mice. Mice were pretreated intraperitoneally (IP) with saline, ofloxacin (20 or 80 mg/kg) or ciprofloxacin (20 or 80 mg/kg) 30 minutes before subcutaneous (SC) administration of pentylenetetrazol (40 or 60 mg/kg). In another experiment, diazepam (5 mg/kg) was injected (IP) in mice alone or in combination with ofloxacin (80 mg/kg) 30 minutes before pentylenetetrazol (40 mg/kg) administration (SC). In each experiment mice were observed over the following hour for the incidence and onset of clonic convulsions. Results showed that both doses of ofloxacin increased the incidence of clonic convulsions induced by 40 mg/kg pentylenetetrazol. This effect, however was only significant in the higher dose and inhibited by diazepam. On the other hand, a similar proconvulsant effect by ciprofloxacin could not be demonstrated.

Fluoroquinolones. New miracle drugs?

Fluoroquinolones are the newest antibiotics for treatment of some infections caused by highly resistant bacteria (eg, Pseudomonas aeruginosa). Clinically sound indications for these drugs include resistant infections of the urinary, intestinal, and respiratory tracts; otitis externa; osteomyelitis; foot infections in diabetic patients; and late infections complicating burns. Fluoroquinolone therapy is not indicated in children younger than 12 years old and patients with foreign bodies, abscesses, pelvic inflammatory disease, or infections requiring a prophylactic antibiotic. Drug interactions with antacids or theophylline may occur.

In vitro activity of flumequine in comparison with several other antimicrobial agents against five pathogens isolated in calves in The Netherlands

The in vitro activity of flumequine in comparison with several other drugs was tested against 17 P. multocida, 16 P. haemolytica, 21 S. dublin, 21 S. typhimurium and 21 E. coli strains, isolated in (veal) calves in the Netherlands. The MIC50 of flumequine for the respective pasteurellas was 0.25 and 1 microgram/ml, for the salmonellas and E. coli 0.5 micrograms/ml. In comparison with flumequine, enrofloxacin and ciprofloxacin showed higher in vitro activity, with MIC50 less than or equal to 0.008 micrograms/ml for ciprofloxacin. Decreased susceptibility of the pasteurellas was found for kanamycin, neomycin, streptomycin, gentamicin, oxytetracycline and doxycycline. The MIC50 of minocycline for P. multocida was 0.5 micrograms/ml and there was no cross resistance with the other tetracyclines. P. multocida was very susceptible to ampicillin (MIC50 less than or equal to 0.03 micrograms/ml), P. haemolytica, however, was 100% resistant to this drug. Both pasteurellas were susceptible to cephalothin and approximately 50% of the strains of both bacteria were resistant to chloramphenicol. The MIC50 of either spiramycin or tylosin was greater than or equal to their respective breakpoint-MIC values. Both pasteurellas were susceptible to the combination of trimethoprim and sulphamethoxazole. However, for P. multocida, the addition of sulphamethoxazole to trimethoprim had no synergistic effect on its MIC. In comparison with trimethorpim, aditoprim was less potent. Therefore only P. multocida was susceptible to aditoprim.

A review of the antimicrobial activity of the fluoroquinolones

The evolution of the fluoroquinolones is described, and structure-activity relationships outlined. The in-vitro antimicrobial activities of ciprofloxacin, enoxacin, norfloxacin, ofloxacin and pefloxacin against a wide range of organisms are critically reviewed. In-vitro factors influencing fluoroquinolone activity are discussed. Reports of the acquisition of resistance to the fluoroquinolones are evaluated. Finally, possible future directions for this group of antibiotics are discussed.

Ciprofloxacin absorption in different regions of the human gastrointestinal tract. Investigations with the hf-capsule

1. The absorption of ciprofloxacin from different regions of the human gastrointestinal tract was investigated in four healthy males using a remote-controlled drug delivery device (hf-capsule). 2. Significant differences in AUC were observed in the control study (oral administration of ciprofloxacin solution without the hf-capsule = 100%) and after release of ciprofloxacin in the jejunum (geometric mean: 37%), the ileum (mean: 23%), the ascending colon (mean: 7%) and the descending colon (mean: 5%), whereas tmax showed no difference for any of the absorption sites. Ciprofloxacin release in the stomach resulted in the greatest AUC (mean: 140%). Thus, it is concluded that the main absorption site of ciprofloxacin is the upper gastrointestinal tract, up to the jejunum. 3. Differences in presystemic metabolism of known drug metabolites along the gut could be excluded, as the pattern of urinary recovery of desethylene-, sulpho-, and oxo-ciprofloxacin and the parent compound was similar for all drug release sites.

Pharmacokinetics, metabolism and renal clearance of flumequine in veal calves

The pharmacokinetics of flumequine was studied in 1-, 5- and 18-week-old veal calves. A two-compartment model was used to fit the plasma concentration-time curve of flumequine after the intravenous injection of 10 mg/kg of a 10% solution. The elimination half-life (t1/2 beta) of the drug ranged from 6 to 7 h. The Vd beta and ClB of 1-week-old calves (1.07 l/kg, 1.78 ml/min/kg) were significantly lower than those of 5-week-old (1.89 l/kg, 3.23 ml/min/kg) and 18-week-old calves (1.57 l/kg, 3.10 ml/min/kg). After the oral administration of 10 mg/kg of a 2% flumequine formulation mixed with milk replacer, the Cmax was highest in 1-week-old (9.27 micrograms/ml) and lowest in 18-week-old calves (4.47 micrograms/ml). The absorption was rapid (Tmax of approximately 3 h) and complete. When flumequine itself and a formulation containing 2% flumequine and 20 X 10(6) iu of colistin sulphate were mixed with milk replacer and administered at the same dose rate, absorption was incomplete and Cmax was lower. The main urinary metabolite of flumequine was the glucuronide conjugate (approximately 40% recovery within 48 h of intravenous injection) and the second most important metabolite was 7-hydroxy-flumequine (approximately 3% recovery within 12 h of intravenous injection). Only 3.2-6.5% was excreted in the urine unchanged. After oral administration a 'first-pass' effect was observed, with a significant increase in the excretion of conjugated drug. For 1-week-old calves it is recommended that the 2% formulation should be administered at a dose rate of 8 mg/kg every 24 h or 4 mg/kg every 12 h; for calves over 6 weeks old, the dose should be increased to 15 mg/kg every 24 h or 7.5 mg/kg every 12 h. The formulation containing colistin sulphate should be administered to 1-week-old calves at a flumequine dose of 12 mg/kg every 24 h or 6 mg/kg every 12 h.

Microbial DNA topoisomerases and their inhibition by antibiotics

Supercoiling of bacterial DNA is regulated by topoisomerases and influences most of the metabolic processes involving DNA. The present review is devoted to a brief outline of the supercoiled state of DNA in bacteria and to all microbial topoisomerases hitherto described. Recent studies on topoisomerases of archaebacteria led to the discovery of a so-called reverse gyrase, the properties of which are also discussed. Special emphasis is given to a selective treatment of the effects of those antibiotics which act as gyrase inhibitors.

The fluoroquinolone antibacterial agents

In summary, the last decade has been a highly fertile and productive period in quinolone medicinal chemistry, resulting in major improvements in potency, antibacterial spectra, oral absorption and pharmacokinetic properties as well as an increased knowledge of the molecular features important to conferring these various properties. Very recent discoveries concerning replacements for the 3-carboxylic acid moiety, previously thought to be uniquely essential for activity, to give highly potent antibacterials such as (83) illustrate the potential for new breakthroughs in this field. Among the major goals for future research remains the understanding of the potential cartilage toxicity associated with this class of agents, such that an agent useful for pediatric indications may be developed. Future studies can also be expected to further enhance and refine the level of current insight into the manner by which these agents inhibit the target enzyme on a molecular level.

Oral absorption and bioavailability of flumequine in veal calves

The oral absorption and bioavailability of flumequine was studied in 1-, 5- and 18-week-old calves following intravenous and oral administration of different formulations of flumequine (Flumix, Flumix C and pure flumequine). Increasing age had a negative influence on the Cmax after the administration of Flumix, based on a larger VD in the older calves. The Cmax decreased from 5.02 +/- 1.46 micrograms/ml in the first week to 3.28 +/- 0.42 micrograms/ml in the 18th week. Adding colistin sulfate to the flumequine formulation and administring pure flumequine mixed with milk replacer had a negative effect on the Cmax of flumequine after oral administration of 5 and 10 mg/kg body weight. The bioavailability of the orally administered flumequine formulations was 100% in all cases except after the administration of Flumix C, for which it was 75.9 +/- 18.2%. The urinary recovery of flumequine after intravenous injection of a 10% solution varied from 35.2 +/- 2.3% for Group B, to 41.2 +/- 6.3% for Group C. The dosage of 5 mg/kg body weight Flumix twice daily in 1-week-old veal calves is sufficient to reach therapeutic plasma concentrations, based on a MIC value of 0.8 micrograms/ml of the target bacteria. In older calves it is advisable to increase the dosage 7.5 or 10 mg/kg body weight every 12 hours. In combination with colistin sulfate it is also advisable to increase the dosage slightly because of the negative effect of the colistin sulfate on the Cmax of flumequine.

Absence of pharmacokinetic interaction between ofloxacin and fenbufen in rats

The possible pharmacokinetic interaction between a new quinolone and fenbufen was investigated by comparing the plasma concentration-time profiles and serum protein binding of ofloxacin, fenbufen and its active metabolite, felbinac, in rats. The rats were administered intravenous doses of ofloxacin (5 mg kg-1), fenbufen (10 mg kg-1) alone or concomitantly. The plasma elimination half-lives were about 55 min in both groups. A slight elevation of plasma concentration of ofloxacin and a small decrease of its total body clearance were observed after its coadministration with fenbufen. The extent of ofloxacin binding to rat serum tended to be slightly reduced by fenbufen which coexisted at relatively high concentrations. Plasma concentration-time curves, pharmacokinetic parameters and serum protein binding of fenbufen and felbinac were not affected by the coadministration with ofloxacin. These results suggest that any substantive pharmacokinetic interaction may be unlikely after the concomitant administration of ofloxacin and fenbufen.

In vitro activity of five tetracyclines and some other antimicrobial agents against four porcine respiratory tract pathogens

The minimal inhibitory concentrations (MIC) of five tetracyclines and ten other antimicrobial agents were determined for four porcine bacterial respiratory tract pathogens by the agar dilution method. For the following oxytetracycline-susceptible strains, the MIC50 ranges of the tetracyclines were: P. multocida (n = 17) 0.25-0.5 micrograms/ml; B. bronchiseptica (n = 20) 0.25-1.0 micrograms/ml; H. pleuropneumoniae (n = 20) 0.25-0.5 micrograms/ml; S. suis Type 2 (n = 20) 0.06-0.25 micrograms/ml. For 19 oxytetracycline-resistant P. multocida strains the MIC50 of the tetracyclines varied from 64 micrograms/ml for oxytetracycline to 0.5 micrograms/ml for minocycline. Strikingly, minocycline showed no cross-resistance with oxytetracycline, tetracycline, chlortetracycline and doxycycline in P. multocida and in H. pleuropneumoniae. Moreover, in susceptible strains minocycline showed the highest in vitro activity followed by doxycycline. Low MIC50 values were observed for chloramphenicol, ampicillin, flumequine, ofloxacin and ciprofloxacin against P. multocida and H. pleuropneumoniae. B. bronchiseptica was moderately susceptible or resistant to these compounds. As expected tiamulin, lincomycin, tylosin and spiramycin were not active against H. pleuropneumoniae. Except for flumequine, the MIC50 values of nine antimicrobial agents were low for S. suis Type 2. Six strains of this species showed resistance to the macrolides and lincomycin.

Oral pharmacokinetics and ascitic fluid penetration of ofloxacin in cirrhosis

Plasma and ascitic fluid concentrations of ofloxacin were determined in 12 cirrhotic patients after a single dose and repeated 200 mg oral doses. The single dose kinetics were compared to those obtained in 12 healthy volunteers. Mean plasma elimination half-life was 11.6 h in cirrhotics and 7.0 h in controls. Mean total clearance was 2.3 times lower in patients than in controls, due to a significant decrease of renal clearance of the drug, unrelated to creatinine clearance. Mean apparent volume of distribution was 1.2 l/kg in patients and 1.8 l/kg in controls. Estimated by the ratio of AUC in peritoneal fluid and plasma, ascitic fluid penetration was 80% after the first oral dose. Ascitic fluid concentrations equaled corresponding plasma concentrations after 10 h, without pronounced accumulation of ofloxacin in ascites. We may conclude that, in cirrhotic patients with normal serum creatinine, a significant impairment of renal tubular handling of ofloxacin could be observed and led to a delayed elimination half-life of the drug. Because of its broad spectrum of activity, low side-effect profile, and large ascitic fluid penetration after oral administration, ofloxacin appears to be a new therapeutic approach of severe infections in cirrhotic patients, in particular spontaneous bacterial peritonitis.

Simultaneous determination of ofloxacin, fenbufen and felbinac in rat plasma by high-performance liquid chromatography

Ofloxacin, fenbufen and its active metabolite, felbinac, were simultaneously extracted from 50 microliters of rat plasma and analysed by high-performance liquid chromatography on a reversed-phase column. Quantitative and reproducible determinations were possible for ofloxacin, fenbufen and felbinac over the concentration ranges 0.15-40, 0.3-80 and 0.45-45 micrograms/ml, respectively. The detection limits for all the drugs were lower than those reported previously. The recovery of ofloxacin, fenbufen and felbinac added to plasma was nearly 100% with a coefficient of variation of less than 3.0%. This method was found to be applicable to pharmacokinetic studies of each drug after the concomitant administration of ofloxacin and fenbufen.

The absorption and disposition of enoxacin in healthy subjects

Enoxacin is a new orally active, synthetic broad-spectrum antibacterial drug of the fluorinated quinolone class. The pharmacokinetics and renal handling of this drug have not been thoroughly investigated, in particular, with specific analytical methodology. Sixteen healthy, young subjects received a single 400-mg oral dose of enoxacin after an overnight fast and multiple blood samples and all urine were collected for 33 hours. Enoxacin in plasma and urine and oxo-enoxacin in urine were determined by a high-performance liquid chromatographic method. Enoxacin was absorbed rapidly, with tmax values ranging from 0.5 to 2.5 hours. The variability in the AUC values of 35% was reduced to 23% when variations in body weight were taken into consideration. The terminal half-life ranged from 4.2 to 6.8 hours and the unbound fraction in plasma was 0.33 +/- 0.07. In urine, 44 +/- 9% of the dose was recovered as unchanged enoxacin and 5.4 +/- 3.9% as oxo-enoxacin; there was no evidence of conjugates of enoxacin in urine. Renal clearance of enoxacin was 230 +/- 92 mL/min, with 17 +/- 8% of this being due to glomerular filtration and 83 +/- 8% being due to tubular secretion. These data indicate that the major potential drug interactions affecting enoxacin disposition are likely with drugs competing for renal proximal tubular secretion and hepatic elimination. These conclusions regarding enoxacin are likely to be applicable to the fluorinated quinolones in general.

A double-blind comparative trial of short-term orally administered enoxacin in the prevention of urinary infection after elective transurethral prostatectomy: a clinical and pharmacokinetic study

A double-blind randomized comparative study was done to investigate the efficacy of enoxacin in the prevention of urinary infection after elective transurethral prostatectomy, as well as its ability to penetrate the prostate. A total of 40 patients received 200 mg. enoxacin and 40 received a placebo, given orally the night before the operation, 2 to 4 hours preoperatively and every 12 hours postoperatively for 36 hours. Urine samples for bacterial culture were obtained within 1 week preoperatively, at operation and at 48 hours, 5 days, and 2 and 6 weeks postoperatively. Samples of the serum and prostate were taken at operation and assayed for enoxacin levels. Of the placebo patients 15 had a urinary infection postoperatively (38 per cent) compared to 3 enoxacin patients (8 per cent) (p less than 0.01). Enoxacin penetrated well into prostatic tissue; the mean levels in tissue and serum were 3.1 +/- 1.8 mg. per kg. (standard deviation) and 1.26 +/- 0.48 mg. per l., respectively, with a mean tissue-to-serum ratio of 2.53 +/- 1.8.

Quinolones: a new class of antimicrobial agents with wide potential uses

Quinolone antibiotics provide potentially important therapy for many infections that heretofore required extensive hospitalization. Improper use of these agents rapidly can lead to resistance and thereby remove them from the physician's arsenal of antimicrobial compounds. It also is possible that with more extensive use, these drugs will demonstrate adverse reactions that to date are unknown. Attention to how the agents are used can simultaneously avoid the problems of resistance and toxicity.

Clinical pharmacokinetics of the newer antibacterial 4-quinolones

Structural modification of the so-called 'first-generation' or 'urinary' quinolones has led to a considerable increase in their intrinsic antibacterial activity, together with marked changes in the pharmacokinetic properties. Tissue penetration is the most notable change, and the newer quinolones are comparable with the newer broad spectrum beta-lactams in their clinical spectrum of activity. Marketed compounds in the 4-quinolones group include pefloxacin, ofloxacin, enoxacin, ciprofloxacin and norfloxacin; many more compounds are in various stages of research and development. The 4-quinolones act by inhibition of bacterial DNA gyrase, a process which is pH and concentration dependent. The bactericidal activity can be partly abolished if protein synthesis is inhibited by chloramphenicol, or if RNA synthesis is inhibited by rifampicin (rifampin). The antibacterial spectrum of activity includes methicillin- and gentamicin-resistant staphylococci, multiresistant non-fermenters, all Enterobacteriaceae, Legionella, Neisseria species, Branhamella and Haemophilus influenzae. With the exception of norfloxacin, which is only 30 to 40% bioavailable from the oral route, the 4-quinolones are 80 to 100% bioavailable, absorption occurring within 1 to 3 hours. Food does not significantly alter Cmax, AUC or elimination half-life, although tmax, may be increased. The 4-quinolones are widely distributed throughout the body, with volumes of distribution greater than 1.5 L/kg. Protein binding is less than 30% in most cases. Penetration into most tissues is good. With the exception of ofloxacin and lomefloxacin (NY 198), which are metabolically stable, metabolism of the 4-quinolones occurs primarily at the C7 position in the piperazinyl ring. Biotransformation is extensive (85%) with pefloxacin, medium (25 to 40%) with ciprofloxacin and enoxacin, and low (less than 20%) with norfloxacin. Elimination half-lives vary between 3 and 5 hours (ciprofloxacin) and 8 to 14 hours (pefloxacin). Biliary concentrations of the 4-quinolones are 2 to 10 times greater than those in serum or plasma, with several compounds undergoing enterohepatic circulation. There is some evidence that ciprofloxacin, norfloxacin, ofloxacin and enoxacin have an active renal tubular excretion pathway. In impaired renal function, reduction of the glomerular filtration rate below 30 ml/min (1.8 L/h) is associated with an increase in elimination half-life and AUC, and a decrease in renal and total clearance of the 4-quinolones, and a decrease in 24-hour urinary recovery.(ABSTRACT TRUNCATED AT 400 WORDS)

4-quinolones inhibit biotransformation of caffeine

The pharmacokinetics of caffeine, including formation of its major metabolite paraxanthine in plasma, has been investigated in 12 healthy males (age 20-40 years) alone and during co-administration of the 4-quinolones ofloxacin, norfloxacin, pipemidic acid, ciprofloxacin, and enoxacin; ciprofloxacin and enoxacin were given in 3 different dose levels. The naphthyridine derivative enoxacin and the pyrido-pyrimidine derivative pipemidic acid had caused marked inhibition of caffeine and paraxanthine metabolism, whereas the genuine quinolone derivatives norfloxacin and ciprofloxacin had little effect, and the pyrido-benzoxacine derivative ofloxacin had no detectable effect. The different molecular and spatial structures of the compounds appear to be responsible for the differences in inhibitory potency.

Pharmacokinetics of ciprofloxacin

The fluorination of piperazinyl substituted quinolones has led to an interesting development of a series of new broad spectrum antibacterial agents that may be administered orally as well as parenterally and are well tolerated. Norfloxacin was an early compound, later followed by ciprofloxacin, enoxacin, ofloxacin and pefloxacin. In this overview the emphasis will be on the most extensively studied compound including comparisons, where data are available, with norfloxacin and ofloxacin. Enoxacin and pefloxacin will be omitted due to their pattern of side effects, which at present curtail their therapeutic use. More recent substances such as fleroxacin and defloxacin have not been sufficiently investigated to be considered in this context.

Ofloxacin. A review of its antibacterial activity, pharmacokinetic properties and therapeutic use

Ofloxacin is one of a new generation of fluorinated quinolones structurally related to nalidixic acid. It is an orally administered broad spectrum antibacterial drug active against most Gram-negative bacteria, many Gram-positive bacteria and some anaerobes. Ciprofloxacin is the only other quinolone with superior in vitro antibacterial activity. However, the pharmacokinetic profile of ofloxacin is superior to that of ciprofloxacin, with more rapid absorption and a peak serum concentration several times higher. Moreover, ofloxacin achieves high concentrations in most tissues and body fluids. The results of clinical trials with ofloxacin have confirmed the potential for use in a wide range of infections, which was indicated by its in vitro antibacterial and pharmacokinetic profiles. It has proven effective against a high percentage of infections caused by Gram-negative organisms, slightly less effective against Gram-positive infections, and effective against some anaerobic infections. Clinical efficacy has also been confirmed in a variety of systemic infections as well as in acute and chronic urinary tract infections, and ofloxacin has generally appeared to be at least as effective as alternative orally administered antibacterial drugs. Ofloxacin is well tolerated and, although experience with the drug in clinical practice to date is limited, bacterial resistance does not appear to develop readily. Thus, ofloxacin is an orally active drug which offers a valuable alternative to other broad spectrum antibacterial drugs.

Effect of food on enoxacin absorption

Fifteen subjects received a single 400-mg oral dose of enoxacin in the fasting state and after carbohydrate and high-fat meals. The carbohydrate meal delayed the time to peak enoxacin concentration in plasma by an average of 0.92 h. The extent of enoxacin absorption was not altered by food.

Steady-state kinetics of the quinolone derivatives ofloxacin, enoxacin, ciprofloxacin and pefloxacin during maintenance treatment with theophylline

Some of the new quinolone derivatives may be of value in the treatment of respiratory tract infections. It has been demonstrated that enoxacin, pefloxacin and ciprofloxacin, but not ofloxacin, decreased the metabolic clearance of the bronchodilator theophylline. This resulted in elevated plasma theophylline concentrations and, in some of the patients, theophylline toxicity. When the pharmacokinetic parameters of enoxacin, pefloxacin, ciprofloxacin and ofloxacin obtained in the present study were compared with those obtained from other studies in healthy volunteers not given concomitant theophylline, there was no evidence of theophylline influencing the clearance of the investigated quinolones.