In vitro and in vivo antibacterial activities of the fluoroquinolone WIN 49375 (amifloxacin)

Study of acid-base equilibria of fleroxacin

The acid-base equilibria of fleroxacin were studied by means of potentiometry and spectrophotometry. It was established that fleroxacin undergoes a complex acid-base equilibrium due to its zwitterionic nature and two proton-binding sites of similar acidity. The stoichiometric equilibrium constants were determined at 25 degrees C and constant ionic strength 0.1 M (NaCl). The acidity constants pK1 = 5.59 +/- 0.01 and pK2 = 8.08 +/- 0.04 were found by potentiometry, and pK1 = 5.61 +/- 0.03 and pK2 = 8.11 +/- 0.06 by spectrophotometry. The distribution diagram of the corresponding ionic species is given.

In vitro and in vivo antibacterial activities of E-4868, a new fluoroquinolone with a 7-azetidin ring substituent

E-4868, (-)-7-[3-(R)-amino-2-(S)-methyl-1-azetidinyl]-1-(2,4- difluorophenyl)-1,4-dihydro-6-fluoro-4-oxo-3-quinolinecarboxylic acid, is a new fluoroquinolone with an azetidine moiety at the 7 position. The in vitro activity of E-4868 has been compared with those of ciprofloxacin, ofloxacin, and fleroxacin, while the activity of ciprofloxacin was used as reference for in vivo studies. The MICs of E-4868 for 90% of the isolates tested (MIC90s) were 0.06 to 0.5 microgram/ml against gram-positive organisms, including Staphylococcus, Streptococcus, and Enterococcus spp. In general, the in vitro potency of E-4868 against gram-positive bacteria was higher than those of all of the other fluoroquinolones tested. MIC90s against members of the family Enterobacteriaceae between 0.03 and 1 microgram/ml were observed, with the exception of those against Serratia marcescens and Providencia spp., and a MIC90 of 2 micrograms/ml against Pseudomonas aeruginosa was obtained. E-4868 inhibited 90% of the Clostridium spp. and Bacteroides spp. at 2 micrograms/ml and was twofold more active than ciprofloxacin. An increase in the Mg2+ concentration from 1 to 10 mM increased the MIC between two and three times. Human urine caused a significant decrease in activity of E-4868, which was more pronounced at pH 5.5 than at pH 7.2. The presence of serum also decreased the activity of E-4868. Fifty percent effective dose (ED50) values against experimental Escherichia coli HM-42 infections in mice were 3.9 mg/kg of body weight with E-4868 and 3.5 mg/kg of body weight with ciprofloxacin. Corresponding ED50 values against P. aeruginosa HS-116 were 93.2 and 107.8 mg/kg, respectively, and those against Staphylococcus aureus HS-93 were 6.5 and 44.6 mg/kg, respectively. In experimental infections with Streptococcus pneumoniae 84551, the ED50 value of E-4868 was 154.4 mg/kg, while ciprofloxacin proved totally inactive at a dose of 400 mg/kg. When E-4868 was administered orally at a dose of 50 mg/kg in mice, the area under the concentration-time curve (0 to 4 h) value was 28.4 microgram . h/ml, while an area under the concentration-time curve value of 2.3 microgram . h/ml was observed for ciprofloxacin at the same dose. In these studies, levels of the two agents in blood 1 h postadministration were 7.6 and 1.2 microgram/ml, respectively.

Protonation equilibria of quinolone antibacterials

The acid-base properties of seven antibacterial 7-piperazinyl fluoroquinolone derivatives were studied by potentiometry and UV and NMR spectroscopy. These molecules contain two proton-binding sites of similar basicity, namely, the piperazine amino and the carboxylate groups, as proven by 1H NMR spectroscopy. The basicities are quantitated at the molecular level in terms of macroconstants, and also at the submolecular level in terms of microconstants. The microconstants are then used to calculate the concentration of the positive, zwitterionic, neutral, and negatively charged species (microspeciation). The zwitterionic forms always predominate over their neutral protonation isomers, but the zwitterionic:neutral concentration ratio is considerably different for the examined fluoroquinolone derivatives.

Structure-activity relationships in DNA gyrase inhibitors

The review brings the status of research into DNA gyrase inhibitors up to date. Structure-activity relationships in both coumarin antibiotics, like novobiocin or coumermycins, and quinolones are discussed. In the section dealing with the quinolones, promising drugs under further evaluation are pointed out. Recently discovered new types of DNA gyrase inhibitors, i.e. tetramic acid derivatives and biphenyl dicarboxylic acid monoamides, are also briefly mentioned.

In vitro activity of amifloxacin against outer membrane mutants of the family Enterobacteriaceae and frequency of spontaneous resistance

Amifloxacin showed potent inhibitory activity against DNA gyrase of Escherichia coli. The difference in the susceptibilities of lipopolysaccharide-deficient Salmonella typhimurium mutants and their parent strain was less than twofold, and the difference in the susceptibilities of porin-deficient E. coli mutants and their parent strain was less than twofold. There was cross resistance among the quinolone group of agents; however, the decrease in MIC for norB mutants was slightly lower than that of other fluoroquinolones. Cell lysis was induced with combined treatment of amifloxacin and sodium dodecyl sulfate in E. coli. The frequency of mutants spontaneously resistant to amifloxacin was extremely low in all species tested.

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.

Antimicrobial activity and interaction of pefloxacin and its principal metabolites. Collaborative Antimicrobial Susceptibility Testing Group

The in vitro antimicrobial activity of pefloxacin and its major metabolites was determined and the interaction of pefloxacin and N-demethyl pefloxacin (norfloxacin) assessed at the ratio naturally occurring in urine (1:2). Pefloxacin and N-demethyl pefloxacin had approximately the same spectrum but were markedly more active than N-oxide pefloxacin (MIC90s greater than or equal to 64 micrograms/ml) against 867 stock strains. When combined with N-demethyl pefloxacin, pefloxacin had greater potency and a broader spectrum in tests against 5869 fresh clinical organisms. For approximately 10% more strains pefloxacin MICs were less than or equal to 2 micrograms/ml when pefloxacin was combined with 2 parts (4 micrograms/ml) of N-demethyl pefloxacin. The most significant extension of the pefloxacin spectrum was to include non-enteric gram-negative bacilli (inhibition of 67% versus 88%) and enterococci-streptococci (inhibition of 33% versus 86%). These results are similar to those previously noted for enoxacin plus 3-oxo-enoxacin, and potentially achievable with other newer fluoro-quinolones undergoing significant metabolism.

In vitro activities of amifloxacin and two of its metabolites

Amifloxacin and two of its metabolites, N-desmethyl amifloxacin and amifloxacin N-oxide, were evaluated by a microdilution MIC susceptibility test against 500 clinical isolates and compared with ciprofloxacin, lomefloxacin, norfloxacin, aztreonam, and imipenem. Of the Staphylococcus species isolates, 208 were methicillin resistant; the MICs for 78 of the isolates of the family Enterobacteriaceae were greater than or equal to 64 micrograms of cefazolin, ampicillin, piperacillin, and mezlocillin per ml. Based on our results, amifloxacin had activity equivalent to those of norfloxacin and lomefloxacin but was less active than ciprofloxacin. The N-oxide metabolite was the least active; however, for the majority of gram-negative bacteria, N-desmethyl amifloxacin was as active as amifloxacin.

Activity of E-3846, a new fluoroquinolone, in vitro and in experimental cystitis and pyelonephritis in rats

The in vitro antibacterial activity of E-3846, a new fluoroquinolone carboxylic acid derivative with a pyrrol ring substituent at position 7, was evaluated in comparison with norfloxacin and ciprofloxacin. E-3846 was more active than the reference quinolones against Staphylococcus species, including methicillin-resistant strains. E-3846 was similar to ciprofloxacin and more active than norfloxacin against Streptococcus (Enterococcus) faecalis. In general, E-3846 was more active than norfloxacin against members of the family Enterobacteriaceae, but less active than ciprofloxacin. For Pseudomonas aeruginosa, the MICs giving 90% inhibition for E-3846, norfloxacin, and ciprofloxacin were 2, 1, and 0.25 micrograms/ml, respectively. The activity of E-3846 increased at acid pH; in contrast, acid pH caused a pronounced decrease in the activity of norfloxacin and ciprofloxacin. In vivo, E-3846 demonstrated excellent therapeutic efficacy in treating experimental S. faecalis, Escherichia coli, Klebsiella pneumoniae, Proteus mirabilis, and Pseudomonas aeruginosa cystitis and pyelonephritis in rats.

Comparative in vitro activity of amifloxacin and five other fluoroquinolone antimicrobial agents and preliminary criteria for the disk susceptibility test

Amifloxacin is a fluoroquinolone with a spectrum of activity similar to that of ofloxacin, pefloxacin, enoxacin, norfloxacin and ciprofloxacin. For disk susceptibility tests, 10 micrograms amifloxacin disks are recommended with zone size interpretive standards of less than or equal to 16 mm and greater than or equal to 20 mm for the resistant and susceptible categories respectively.

In vitro activity of amifloxacin (WIN 49,375) compared with those of ciprofloxacin and ofloxacin

The in vitro activity of the novel fluoroquinolone derivative, amifloxacin (WIN 49,375), was compared with the activities of ciprofloxacin and ofloxacin. A total of 500 clinical isolates of Gram-negative and Gram-positive bacteria were included, and the minimal inhibitory concentration (MIC) was determined by an agar dilution method. All drugs were highly active against Enterobacteriaceae, but ciprofloxacin showed the highest activity on a weight-for-weight basis (MIC 90% less than or equal to 0.03 mg/l). Ciprofloxacin was the most active agent against Pseudomonas isolates; all isolates being inhibited by 0.25 mg/l or less. The staphylococcal isolates were inhibited by ciprofloxacin and ofloxacin at relatively low concentrations (MIC 100% = 1 mg/l), whereas amifloxacin showed moderate activity against the majority of these isolates. Ciprofloxacin was highly active against enterococci, ofloxacin was moderately active, and amifloxacin was inactive. All Neisseria gonorrhoeae isolates were susceptible to the lowest concentrations of the agents that were employed in the study (0.03 mg/l).

In vitro activity of CI-934, a new quinolone antimicrobial, against gram-positive bacteria

The in vitro activity of CI-934, a new quinolone antimicrobial, was compared with that of ciprofloxacin against selected gram-positive bacteria. Concentrations of CI-934 required to inhibit 90% of strains (MIC90) were twofold to eightfold lower than those of ciprofloxacin. With the exception of Streptococcus faecium, all isolates were inhibited by CI-934 at concentrations less than or equal to 1.0 microgram/ml.

Antimicrobial update

New and soon-to-be introduced antimicrobials are reviewed and compared with agents already in use to determine possible therapeutic and/or cost advantages. Drugs discussed are amdinocillin, ticarcillin/clavulanic acid, ceftriaxone, ceftazidime, imipenem/cilastatin, aztreonam, and quinolones.

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

Quinolones, chemically related to nalidixic acid, have a strong and rapid bactericidal action against Gram-negative bacteria, including Ps. aeruginosa, some Mycobacteria, Legionella and Staphylococci. Streptococci and anaerobic bacteria are usually less sensitive. The quinolones exert their bactericidal action through inhibition of the enzyme DNA gyrase. Quinolones are absorbed for 50-100% from the gastro-intestinal tract, their volume of distribution is generally high (2 l/kg) and high concentrations are reached in almost all organs. The elimination half-lives range from 4 to 14 h. The efficacy of quinolones in urinary tract infections has been shown in many studies. They also seem to be effective in many serious infections. In animal studies their efficacy was generally equal or superior to aminoglycosides. Until now only mild and infrequent side effects have been reported.