Laboratory evaluation of enoxacin: comparison with norfloxacin and nalidixic acid

Combining molecular modeling with experimental methodologies: mechanism of membrane permeation and accumulation of ofloxacin

The interaction between ofloxacin, as a model drug of the fluoroquinolone class, and biomembranes was examined as the possible initial step in a transmembrane diffusion process. Dipalmitoylphosphatidylcholine was used for the preparation of biomembrane models. The influence of environmental conditions and protonation on molecular physicochemical behavior, and hence on the membrane interaction, was investigated by differential scanning calorimetry (DSC). This technique has been shown to be very effective in the interpretation of interactions of drug microspeciations with biomembranes. These findings suggest that the interaction occurred owing to ionic and hydrophobic forces showing how the passage through the membrane is mainly favored in the pH interval 6-7.4. It was demonstrated that a pH gradient through model membranes may be responsible for a poorly homogeneous distribution of ofloxacin (or other related fluoroquinolones), which justifies the in vivo accumulation properties of this drug. DSC experiments, which are in agreement with computational data, also showed that the complexing capability of ofloxacin with regard to Mg(++) or Ca(++) may govern the drug entrance into bacterial cells before the DNA Girase inhibition and could ensure the formation of hydrophobic and more fluid phospholipid domains on the surface of the model membrane. These regions are more permeable with regard to various solutes, as well as ofloxacin, allowing a so-called 'self-promoted entrance pathway'. The combination of experimental methodologies with computational data allowed a further rationalization of the results and opened new perspectives into the mechanism of action of ofloxacin, namely its interaction with lipid bilayers and drug-divalent cation complex formation, which might be extended to the entire fluoroquinolone class. Ofloxacin accumulation within Escherichia coli ATCC 25922 was measured as a function of time. Also in this example, the environmental conditions influenced ofloxacin penetration and accumulation. The in vitro experiments, reported here, show that a suitable balance of hydrophilic and hydrophobic fluoroquinolone properties needs to occur for there to be increased drug permeation.

Dental health and viridans streptococcal bacteremia in allogeneic hematopoietic stem cell transplant recipients

Viridans streptococci were the most common cause of bacteremia in 61 consecutive myeloablative allogeneic hematopoietic stem cell transplant (HSCT) recipients, occurring in 19 of 31 bacteremic patients (61%) during the period of post-transplant neutropenia. Seven of the 19 had more than one viridans streptococcus in the same blood culture. Twenty isolates from 15 patients were Streptococcus mitis. Most viridans streptococci were resistant to norfloxacin, used routinely for prophylaxis. Comparison of the 19 patients with viridans streptococcal bacteremia with a contemporaneous group of 23 allogeneic HSCT recipients with fever and neutropenia but no identified focus of infection found that patients with viridans streptococcal bacteremia were more likely to have severe intraoral pathology while neutropenic (26% vs 0%) and slightly shorter interval between the last dental procedure and the onset of neutropenia (11 vs 14 days). Poor underlying dental health and the use of norfloxacin thus appear to predispose to viridans streptococcal bacteremia.

Complexes of ciprofloxacin with metal ions contained in antacid drugs

Simultaneous administration of antacids containing magnesium or aluminium and ciprofloxacin or other quinolones decreases the gastrointestinal absorption of those antibacterial agents. Current speculation about the mechanism of this interaction has focused on drug-cation chelation. The present study was designed to detect the protonation in solutions and the formation of the complex species at the pH levels typical of the gastrointestinal tract. It involves the study of ciprofloxacin in aqueous solutions containing Al3+ and (or) Mg2+ by combining the results of potentiometric and spectroscopic (1H nuclear magnetic resonance) techniques. Calculations were only performed for data in the range 4.5 < pH < 5.5 (pH levels typical of gastrointestinal tract) and the results of both methods are made self-consistent, assuming an equilibrium model including complex species MHL, MLOH (where H2L denotes ciprofloxacin and M is Al3+ or Mg2+); their formation constants are given.

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.

Studies on the emergence of resistance to lomefloxacin in vitro

The emergence of resistance to lomefloxacin, norfloxacin and ciprofloxacin was investigated in nalidixic acid sensitive and resistant urinary isolates by continuous turbidimetry. A decline in susceptibility was observed after a single exposure to each of the drugs, and further increments of resistance occurred during three sequential passages. Variants resistant to one quinolone were cross-resistant to the others. The level of resistance selected by norfloxacin in three of the five test strains was greater than that observed with lomefloxacin or ciprofloxacin. In experiments in a model of the treatment of bacterial cystitis, concentrations of lomefloxacin well within those readily achievable in urine suppressed growth of nalidixic acid sensitive and resistant strains for more than 20 h without causing any decline in susceptibility of surviving bacteria.

Review of the 4-quinolones

Improvements in antimicrobial activity and pharmacokinetics have moved the 4-quinolones into the forefront of antibiotic research. The 4-quinolones are analogues of nalidixic acid, and there are presently at least six agents in this group under investigation in the United States. It is difficult to generalize their clinical usefulness, since these agents exhibit different pharmacokinetic profiles, antimicrobial activity (with varied minimum inhibitory concentrations among similar organisms), and dosage regimens. The 4-quinolones are potential therapeutic alternatives for infections caused by a variety of organisms. They include: Neisseria gonorrhoeae; Pseudomonas aeruginosa; Haemophilus influenzae; Staphylococcus aureus; common enteric pathogens (salmonella, shigella, campylobacter, etc); and intracellular bacteria (legionella, chlamydia, mycobacteria, etc). Clinical efficacy has been demonstrated in urinary tract infections, respiratory tract infections, and sexually transmitted diseases. Future studies will undoubtedly demonstrate effectiveness in numerous additional infectious processes. The purpose of this article is to compare the 4-quinolones in regards to pharmacokinetics and spectrum of activity and review the clinical studies involving these agents.

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.

Comparative activity of ofloxacin and seven other antimicrobials against urea-splitting microorganisms

Urinary tract infections caused by urea-splitting bacteria are severe clinical conditions and very difficult to treat due to their association with calculi, and because such bacteria form ammonium hydroxide raising the urinary pH and thereby creating an unfavourable condition for the action of most antimicrobials. We tested ofloxacin, norfloxacin, nalidixic acid, amoxicillin, amoxicillin-clavulanic acid, gentamicin, co-trimoxazole and nitrofurantoin against 143 gram-negative and 99 gram-positive bacteria, all urea-splitting, isolated from patients with urinary tract infections. All drugs were tested using media at two different pHs (pH 7.4 and PH 8.5) and two inoculum sizes (10(4) and 10(6) cfu). Although ofloxacin and norfloxacin had a similar spectrum of activity, ofloxacin had somewhat greater intrinsic activity against gram-positive organisms. MICs of ofloxacin for 90% of Proteus mirabilis, indole-positive Proteus spp., Klebsiella pneumoniae, Staphylococcus aureus, coagulase-negative staphylococci and the Corynebacterium group D2 were greater than or equal to 4 mg/l. The activity of the other drugs varied, but there were many strains resistant to these antimicrobials. The pH and inoculum size did not significantly affect the activity of ofloxacin so that this drug should be useful for the treatment of urinary tract infections caused by the commonest urea-splitting bacteria involved in such infections.