In vitro activity of ciprofloxacin combined with azlocillin

In vitro antibacterial activity of enrofloxacin and ciprofloxacin in combination against Escherichia coli and staphylococcal clinical isolates from dogs

The objective of the study was to determine the in vitro interaction between enrofloxacin and ciprofloxacin against Escherichia coli and staphylococcal isolates from dogs. The microdilution checkerboard assay was used to determine the interaction of the drugs against 50 E. coli and 50 beta-haemolytic staphylococcal clinical isolates. The checkerboard assay revealed that the activity of enrofloxacin and ciprofloxacin was additive against E. coli and staphylococcal clinical isolates. It was concluded that for bacterial species against which ciprofloxacin is more potent than enrofloxacin, the in vivo transformation of enrofloxacin to ciprofloxacin may enhance the efficacy of enrofloxacin, if additivity of the drugs is confirmed in vivo.

Bactericidal effect of pefloxacin and fosfomycin against Pseudomonas aeruginosa in a rabbit endocarditis model with pharmacokinetics of pefloxacin in humans simulated in vivo

The bactericidal activity of pefloxacin and fosfomycin alone and in combination against Pseudomonas aeruginosa was evaluated in an experimental rabbit endocarditis model after 24 h of treatment. Two strains with intermediate susceptibility to pefloxacin and good susceptibility to fosfomycin were tested. The serum kinetics obtained during administration of 400 mg every 12 h in humans were simulated in the animals using computer-controlled variable-flow infusion. Fosfomycin was administered as a continuous infusion at a constant flow, allowing a steady-state concentration of 47.4 +/- 11.9 mg/ml to be reached in serum. In valvular vegetations, pefloxacin was less bactericidal than fosfomycin, and in combination treatment, it reduced (but did not abolish) the bactericidal effect of fosfomycin. The duration of the pretreatment interval (12-48 h) had a negative effect on the bactericidal activity of both drugs, especially that of fosfomycin.

Assessment of the synergistic interactions of levofloxacin and ampicillin against Enterococcus faecium by the checkerboard agar dilution and time-kill methods

Multidrug-resistant enterococci have become increasingly difficult to eradicate in a growing number of nosocomial infections. With the emergence of vancomycin-resistant enterococci, the use of synergistic antibiotic combinations has become one of the only remaining therapeutic options. Levofloxacin, the active l-isomer of ofloxacin, is a new oral and intravenous fluoroquinolone with a broad spectrum of activity against numerous Gram-positive, Gram-negative, and atypical organisms. The in vitro activity of levofloxacin, alone and in combination with ampicillin, against recent clinical isolates of Enterococcus faecium was assessed for synergistic interactions using the checkerboard agar dilution technique and time-kill methodology. Against all strains, the static technique of checkerboard agar dilution demonstrated indifferent or additive effects for the ampicillin + levofloxacin combination. With the dynamic time-kill technique, synergy was demonstrated for ampicillin (16 micrograms/ml) + levofloxacin (2 micrograms/ml) combination against three levofloxacin-sensitive, ampicillin-resistant isolates. At 24 h, the combination yielded a > or = 2-log10 decrease in CFU/ml compared to levofloxacin alone, while ampicillin had negligible effects. Against both a levofloxacin-intermediate, ampicillin-resistant isolate, and a highly levofloxacin-resistant, ampicillin-resistant isolate, none of the ampicillin+levofloxacin combinations tested demonstrated a synergistic interaction. The time-kill method suggested synergy for the ampicillin+levofloxacin combination against some strains of E. faecium.

Bactericidal activity of the fluoroquinolone DU-6859a alone and in combination with other antimicrobial agents against multiresistant enterococci

The in vitro activity of DU-6859a (DU) alone and in combination with various antimicrobials was evaluated against multiresistant enterococci including some isolates with defined gyrA mutations. DU produced rapid in vitro killing against most enterococci that lacked resistance to ciprofloxacin, but it was not bactericidal against strains with MICs of ciprofloxacin of > or = 8 micrograms/ml, or against one of four strains with an MIC of ciprofloxacin of 4 micrograms/ml. The combination of DU with rifampin was antagonistic against two of two isolates tested. Combinations of DU and novobiocin, gentamicin, or a beta-lactam (amoxicillin, ampicillin-sulbactam, or amoxicillin-clavulanate) were generally indifferent. When different beta-lactams were used together, with or without DU, bactericidal activity was observed against some isolates. Despite the absence of synergistic interactions with other agents, DU is a promising fluoroquinolone for use against enterococci, although prior development of resistance to currently available fluoroquinolones diminishes some of its effect.

Current perspectives on glycopeptide resistance

In the last 5 years, clinical isolates of gram-positive bacteria with intrinsic or acquired resistance to glycopeptide antibiotics have been encountered increasingly. In many of these isolates, resistance arises from an alteration of the antibiotic target site, with the terminal D-alanyl-D-alanine moiety of peptidoglycan precursors being replaced by groups that do not bind glycopeptides. Although the criteria for defining resistance have been revised frequently, the reliable detection of low-level glycopeptide resistance remains problematic and is influenced by the method chosen. Glycopeptide-resistant enterococci have emerged as a particular problem in hospitals, where in addition to sporadic cases, clusters of infections with evidence of interpatient spread have occurred. Studies using molecular typing methods have implicated colonization of patients, staff carriage, and environmental contamination in the dissemination of these bacteria. Choice of antimicrobial therapy for infections caused by glycopeptide-resistant bacteria may be complicated by resistance to other antibiotics. Severe therapeutic difficulties are being encountered among patients infected with enterococci, with some infections being untreatable with currently available antibiotics.

Bactericidal activity of the fluoroquinolone WIN 57273 against high-level gentamicin-resistant Enterococcus faecalis

The fluoroquinolone WIN 57273 showed identical bactericidal activities (MBC for 90% of the strains = 0.25 micrograms/ml) for bacteremic strains of Enterococcus faecalis with and without high-level gentamicin resistance. WIN 57273 was bactericidal in time-kill measurements with highly gentamicin-resistant, ciprofloxacin-susceptible strains of E. faecalis. However, WIN 57273 was indifferent with penicillin for gentamicin-resistant E. faecalis and was not bactericidal for ciprofloxacin-resistant E. faecalis.

Novel antibiotic regimens against Enterococcus faecium resistant to ampicillin, vancomycin, and gentamicin

Enterococci have emerged as significant nosocomial pathogens. Enterococci with resistance to commonly used antibiotics are appearing more frequently. We encountered at our institution several infections caused by Enterococcus faecium with high-level resistance to ampicillin, vancomycin, and gentamicin. The optimal antibiotic therapy for serious infections with unusually resistant enterococci has not been established. Using time-kill studies, we tested the effectiveness of various antibiotic combinations against 15 isolates of multidrug-resistant enterococci. No antibiotic was consistently effective when used alone. The combination of ampicillin plus ciprofloxacin was bactericidal for the 12 isolates for which the ciprofloxacin MIC was < or = 8 micrograms/ml. The combination of ciprofloxacin plus novobiocin also demonstrated activity against these isolates. No combination was found to be bactericidal for the remaining three isolates, which were highly ciprofloxacin resistant. These antibiotic combinations may be important for the future treatment of serious infections caused by these resistant pathogens.

Synergy and antagonism of fluoroquinolones with other classes of antimicrobial agents

In an attempt to overcome some of the gaps in their antibacterial spectrum, e.g. some Gram-positive bacteria (notably streptococci and Streptococcus pneumoniae) and anaerobes, the fluoroquinolones have been combined with other bactericidal and bacteriostatic agents. In general, the fluoroquinolones rarely show either synergy or antagonism when used in combination with other antimicrobial agents against most bacteria. Therefore, in infections where the fluoroquinolones do not provide cover against all potential organisms, combined treatment with an appropriate agent may be considered. Current data suggest that the fluoroquinolones are not antagonistic with beta-lactams, macrolides, clindamycin and the imidazoles. Aminoglycosides in combination with the fluoroquinolones do not show synergy. Antipseudomonal penicillins, ceftazidime or imipenem in combination with the fluoroquinolones are synergistic and may be useful for treating infections in immunocompromised patients. Rifampicin in combination with a fluoroquinolone for the treatment of staphylococcal endocarditis or osteomyelitis may be useful, although in vitro and in vivo results do not always coincide.

In vitro interactions of aminoglycosides with imipenem or ciprofloxacin against aminoglycoside resistant Acinetobacter baumannii

The in vitro interactions between gentamicin, tobramycin, netilmicin and amikacin with imipenem and ciprofloxacin were evaluated by the killing curve technique against 20 clinical isolates of Acinetobacter baumannii highly resistant to aminoglycosides which were susceptible or moderately susceptible to imipenem and resistant or moderately susceptible to ciprofloxacin. Imipenem enhanced killing by gentamicin, tobramycin, netilmicin and amikacin in tests with 9, 12, 10 and 15 strains (45-75%) while ciprofloxacin with 3, 7, 5 and 6 strains (15-35%) respectively. Interaction results were influenced by the height of aminoglycoside minimum bactericidal concentrations (MBCs) but were independent of imipenem or ciprofloxacin MBCs and the presence of aminoglycoside modifying enzymes. It is concluded that enhanced killing after aminoglycoside interaction with imipenem or ciprofloxacin versus A. baumannii cannot be predicted but it should be carefully tested in vitro. The in vivo significance of the reported findings mandates clinical studies in humans.

Synergy and antagonism of combinations with quinolones

Combinations of fluoroquinolones with other antimicrobial agents have been extensively investigated. Combinations of fluoroquinolones with aminoglycosides, beta-lactams, imidazoles, macrolides and clindamycin infrequently show synergy against Enterobacteriaceae and gram-positive bacteria. These combinations rarely show antagonism. Combinations of rifampin with fluoroquinolones tested against Staphylococcus aureus have been reported to show synergy and antagonism, and in vitro results have not correlated with results of animal infection experiments. Against Pseudomonas aeruginosa combinations of antipseudomonas penicillins or imipenem with fluoroquinolones are synergistic for 20% to 50% of isolates in vitro and also are synergistic in animal models of infection, whereas combinations of aminoglycosides with fluoroquinolones rarely show synergy against Pseudomonas aeruginosa. Against anaerobic species such as Bacteroides fragilis combinations of fluoroquinolones with clindamycin, anti-anaerobic penicillins, cephalosporins or imidazoles are occasionally synergistic but usually indifferent. Ciprofloxacin and ofloxacin combined with antituberculosis agents have activity against Mycobacterium tuberculosis and atypical mycobacteria. In general, fluoroquinolones should be combined with other agents not to achieve synergy, which is extremely variable, but to provide activity against bacteria inadequately inhibited by the fluoroquinolones.

Synergism between ciprofloxacin and fosfomycin against gram-negative bacteria in vitro

A combination of ciprofloxacin and fosfomycin was evaluated for synergism employing time-kill experiments. A total of 59 clinical isolates of gram-negative bacteria was examined. All organisms were moderately sensitive or resistant to ciprofloxacin; 72.9% also showed moderate sensitivity or resistance to fosfomycin. After 24 h, synergism was seen in 22% of the strains, i.e. less than reported by other authors. There was no correlation between synergistic action and sensitivity to ciprofloxacin and fosfomycin, respectively.

Ciprofloxacin in combination with other antimicrobials

Combinations of ciprofloxacin with aminoglycosides or beta-lactams are infrequently synergistic and only rarely antagonistic against Enterobacteriaceae or gram-positive bacteria. Against Pseudomonas aeruginosa, combinations of ciprofloxacin with an aminoglycoside are synergistic for a minority of isolates, whereas rates of synergistic interactions between ciprofloxacin and beta-lactams against this group of organisms vary over a wide range.

Use of ciprofloxacin in cystic fibrosis patients

In order to evaluate the clinical efficacy and safety of oral ciprofloxacin in the treatment of acute pulmonary exacerbations of cystic fibrosis and trace the possible development of resistance over time, three trials were conducted. In an open-label, uncontrolled trial, 25 courses of ciprofloxacin were administered to 16 patients. Efficacy and safety were assessed based on changes in short-term clinical scores, white blood cell counts, Pseudomonas aeruginosa counts in sputum, pulmonary function tests, and standard serum chemistries and urinalysis that were performed before therapy, weekly during therapy, at the end of therapy, and at a seven-day follow-up visit after therapy. In an open-label, randomized, controlled study, the efficacy and tolerance of oral ciprofloxacin were compared with those of intravenous tobramycin and azlocillin. In another study, the rate of susceptibility of P. aeruginosa isolated from cystic fibrosis patients during more than two years of clinical use was determined. In the uncontrolled trial, ciprofloxacin therapy was associated with clinical improvement in most cases with changes in short-term clinical score and forced expiratory volume in one second being statistically significant (p less than 0.05). Twenty-five patients were entered in the controlled trial with 12 patients in each treatment group being evaluable. The groups were comparable based on admitting demographic and disease characteristics, and no differences in therapeutic response or side effects were noted between the two treatments (p greater than 0.5). Bacterial susceptibility to ciprofloxacin has remained relatively stable over time. Based on these results as well as those from similar evaluations, ciprofloxacin appears to be efficacious in the treatment of acute pulmonary exacerbations in adults with cystic fibrosis, producing responses similar to those observed with standard intravenous antibiotic therapy.

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.

In vitro activities of quinolones against enterococci resistant to penicillin-aminoglycoside synergy

The MICs and MBCs of CI-934, ciprofloxacin, difloxacin (A-56619), A-56620, norfloxacin, enoxacin, amifloxacin, and coumermycin were determined for 43 clinical isolates of Enterococcus faecalis known to be resistant to penicillin-aminoglycoside synergy. Results were compared with those obtained for 37 synergy-susceptible E. faecalis and 22 Enterococcus faecium strains. Although no substantial differences in quinolone activities were observed between synergy-resistant and -susceptible E. faecalis strains, CI-934 and ciprofloxacin were the drugs that demonstrated the greatest bactericidal activity against both types of E. faecalis. The MBCs of the other quinolones were generally within a single twofold dilution of the MICs, but their antienterococcal activity did not approach that of CI-934 or ciprofloxacin. The MBCs for 90% of the isolates of CI-934 for synergy-resistant and -susceptible E. faecalis strains were 1 and less than or equal to 0.5 microgram/ml, respectively. The ciprofloxacin MBC for 90% of the E. faecalis strains tested was 1 microgram/ml. For E. faecium isolates the CI-934 and ciprofloxacin MBCs for 90% of the isolates were 8 and 4 micrograms/ml, respectively. Time-kill assays performed with synergy-susceptible enterococcal strains showed that the bactericidal activities of both CI-934 and ciprofloxacin were less than those of the penicillin-aminoglycoside combinations tested. However, against synergy-resistant isolates the activities of these two quinolones were comparable with and sometimes greater than those of penicillin-aminoglycoside combinations.

In vitro synergy studies with ciprofloxacin and selected beta-lactam agents and aminoglycosides against multidrug-resistant Pseudomonas aeruginosa

In order to determine the effect of combining ciprofloxacin with beta-lactam and aminoglycoside agents against multidrug-resistant P. aeruginosa, ciprofloxacin was tested in vitro with the checkerboard broth microdilution technique with various current beta-lactam and aminoglycoside agents. In both inhibitory and bactericidal testing, the combination of ciprofloxacin with a beta-lactam agent (ceftazidime, piperacillin, mezlocillin, azlocillin, or imipenem) was more likely to show a synergistic effect or additive effect and lack of antagonism (96.5% of all inhibitory and cidal tests) than was a combination of ciprofloxacin with an aminoglycoside [(amikacin, tobramycin, or gentamicin), 90% of all inhibitory and cidal tests]. Finding of antagonism in some testing, especially with aminoglycosides, indicates that results are unpredictable. These results may influence selection of agents for selection in clinical situations.

Fluoroquinolone antibiotics. Microbiology, pharmacokinetics and clinical use

The newer fluoroquinolones are a major advance in antimicrobial chemotherapy. They inhibit the supercoiling activity of the DNA gyrase enzyme, thus exerting their antibacterial action on DNA and RNA synthesis, resulting in a biphasic response and killing of susceptible organisms. The newer fluoroquinolones have an extended antimicrobial spectrum compared to their older congeners, and are highly active against most Gram-negative pathogens including the Enterobacteriaceae and Pseudomonas aeruginosa. While Staphylococcus aureus and coagulase-negative staphylococci are usually susceptible to the fluoroquinolones, streptococci are generally more resistant and enterococci are resistant. All of the newer fluoroquinolones may be administered orally and most of them have been administered parenterally. They are widely distributed in the body, attaining therapeutic concentrations in most tissues. All of the fluoroquinolones have long half-lives and may be administered once or twice daily. The fluoroquinolones have proved effective in many infections, including uncomplicated or complicated urinary tract infections, respiratory tract infections, gonorrhoea, bacterial gastroenteritis, and soft tissue infections due to Gram-negative organisms. In general, success has been notable in the management of Gram-negative infections but less so with Gram-positive infections. Resistance has occurred and is proving a problem with P. aeruginosa in some cystic fibrosis patients, but as yet no plasmid-mediated resistance has developed. Cross-resistance occurs between the quinolones but only rarely with other classes of antibacterial drugs. The fluoroquinolones have an excellent safety record and their adverse effects, which include hypersensitivity reactions, dizziness, headache, gastrointestinal disturbance and minor haematological abnormalities are usually mild and transient. However, the fluoroquinolones have been found to damage juvenile weight-bearing joints in animals and are therefore only to be used with caution in children; transient arthralgia has been reported in a cystic fibrotic teenager on long term ciprofloxacin therapy. All of the fluoroquinolones except ofloxacin are associated with a variable increase in the serum concentration of theophylline, warfarin and caffeine. Thus, the fluoroquinolones are an attractive option in the management of many infections. Cost and possible resistance, however, should counsel caution in their use, and may limit them to situations where a cheaper antimicrobial of equivalent efficacy is not available.

Ciprofloxacin interactions with imipenem and amikacin against multiresistant Pseudomonas aeruginosa

In vitro interactions of ciprofloxacin with imipenem and amikacin were evaluated by the killing-curve technique against 26 Pseudomonas aeruginosa strains resistant to amikacin and resistant or moderately susceptible to ciprofloxacin and imipenem. Imipenem enhanced killing by ciprofloxacin in tests with 11 strains, whereas amikacin enhanced killing in tests with only 4 strains.

Analysis of the interaction between piperacillin and ciprofloxacin or tobramycin against thirteen strains of Pseudomonas aeruginosa, using killing curves

Time-kill studies were made with thirteen strains of Pseudomonas aeruginosa, comparing the activity of ciprofloxacin plus piperacillin with the combination of tobramycin and piperacillin. Synergism was demonstrated in an equal number of strains with both combinations. No antagonism was demonstrated. The reproducibility of the killing-curve method suggests that at least two different concentrations should be used and that a decrease in viable counts below 2 log10 after 24 hours does not exclude a synergistic action.