Timed killing kinetic studies of the interaction between ciprofloxacin and beta-lactams against gram-negative bacilli

Synthesis and Biological Evaluation of Novel Fusidic Acid Derivatives as Two-in-One Agent with Potent Antibacterial and Anti-Inflammatory Activity

Fusidic acid (FA), a narrow-spectrum antibiotics, is highly sensitive to various Gram-positive cocci associated with skin infections. It has outstanding antibacterial effects against certain Gram-positive bacteria whilst no cross-resistance with other antibiotics. Two series of FA derivatives were synthesized and their antibacterial activities were tested. A new aromatic side-chain analog, FA-15 exhibited good antibacterial activity with MIC values in the range of 0.781–1.563 µM against three strains of Staphylococcus spp. Furthermore, through the assessment by the kinetic assay, similar characteristics of bacteriostasis by FA and its aromatic derivatives were observed. In addition, anti-inflammatory activities of FA and its aromatic derivatives were evaluated by using a 12-O-tetradecanoylphorbol-13-acetate (TPA) induced mouse ear edema model. The results also indicated that FA and its aromatic derivatives effectively reduced TPA-induced ear edema in a dose-dependent manner. Following, multiform computerized simulation, including homology modeling, molecular docking, molecular dynamic simulation and QSAR was conducted to clarify the mechanism and regularity of activities. Overall, the present work gave vital clues about structural modifications and has profound significance in deeply scouting for bioactive potentials of FA and its derivatives.

Empiric antimicrobial therapy in severe sepsis and septic shock: optimizing pathogen clearance

Mortality and morbidity in severe sepsis and septic shock remain high despite significant advances in critical care. Efforts to improve outcome in septic conditions have focused on targeted, quantitative resuscitation strategies utilizing intravenous fluids, vasopressors, inotropes, and blood transfusions to correct disease-associated circulatory dysfunction driven by immune-mediated systemic inflammation. This review explores an alternate paradigm of septic shock in which microbial burden is identified as the key driver of mortality and progression to irreversible shock. We propose that clinical outcomes in severe sepsis and septic shock hinge upon the optimized selection, dosing, and delivery of highly potent antimicrobial therapy.

Antibiotic-resistant Pseudomonas aeruginosa: focus on care in patients receiving assisted ventilation

ABSTRACT: 

This article discusses ventilator-associated pneumonia caused by Pseudomonas aeruginosa. Ventilator-associated pneumonia caused by P. aeruginosa is one of the leading causes of morbidity and mortality in the intensive care unit, and nowadays it represents a major concern due to the increasing resistance rate of the pathogen to different classes of antibiotics. Here, the choice between a combination therapy and a monotherapy in the empirical setting is analyzed and discussed, by focusing on the recommendations of different published guidelines. Pros and cons of the different possible associations are analyzed and suggestions are given in light of the emergence of multidrug-resistant strains. Route of administration is also discussed, with an emphasis on the use of nebulized antibiotics. Optimal duration of treatment is an additional point of discussion, and explanations are provided for the suggested longer course compared with that of other etiologies.

An alternate pathophysiologic paradigm of sepsis and septic shock: implications for optimizing antimicrobial therapy

The advent of modern antimicrobial therapy following the discovery of penicillin during the 1940s yielded remarkable improvements in case fatality rate of serious infections including septic shock. Since then, pathogens have continuously evolved under selective antimicrobial pressure resulting in a lack of significant improvement in clinical effectiveness in the antimicrobial therapy of septic shock despite ever more broad-spectrum and potent drugs. In addition, although substantial effort and money has been expended on the development novel non-antimicrobial therapies of sepsis in the past 30 years, clinical progress in this regard has been limited. This review explores the possibility that the current pathophysiologic paradigm of septic shock fails to appropriately consider the primacy of the microbial burden of infection as the primary driver of septic organ dysfunction. An alternate paradigm is offered that suggests that has substantial implications for optimizing antimicrobial therapy in septic shock. This model of disease progression suggests the key to significant improvement in the outcome of septic shock may lie, in great part, with improvements in delivery of existing antimicrobials and other anti-infectious strategies. Recognition of the role of delays in administration of antimicrobial therapy in the poor outcomes of septic shock is central to this effort. However, therapeutic strategies that improve the degree of antimicrobial cidality likely also have a crucial role.

In Vitro Activity of β-Lactam Antimicrobial Agents in Combination with Aztreonam Tested Against Metallob-β-Lactamase-Producing Pseudomonas aeruginosa and Acinetobacter baumannii

We evaluate the antimicrobial interactions between aztreonam and selected beta-lactams when tested against metallo-beta-lactamase (MbetaL)-producing clinical strains. Ten Pseudomonsa aeruginosa strains, including nine MbetaL-producers (IMP-1, -2, -13, -16, VIM-1, -2, -7, SPM-1 and GIM-1) and five Acinetobacter baumannii strains, including three MbetaL-producers (IMP-1 and -2) were tested using time kill/bactericidal activity methods. Aztreonam at 4, 8 and 16 mg/L was combined with four other beta-lactam antimicrobials (cefepime, ceftazidime, meropenem and piperacillin/tazobactam or ampicillin/sulbactam), each tested at the recognized susceptible breakpoint concentration. Enhanced activity (synergism or additive effect) was observed with four P. aeruginosa strains (IMP-16, VIM-2, SPM-1 and GIM-1 containing strains) and four A. baumannii strains, while antagonism was observed with two P. aeruginosa (IMP-16 and SPM-1-producing strains) and one A. baumannii (non-MbetaL) strain. All other strains showed indifferent interaction (variation of +/- 1 log10 CFU/ml) with any combination evaluated.

Combination therapy for treatment of infections with gram-negative bacteria

Combination antibiotic therapy for invasive infections with Gram-negative bacteria is employed in many health care facilities, especially for certain subgroups of patients, including those with neutropenia, those with infections caused by Pseudomonas aeruginosa, those with ventilator-associated pneumonia, and the severely ill. An argument can be made for empiric combination therapy, as we are witnessing a rise in infections caused by multidrug-resistant Gram-negative organisms. The wisdom of continued combination therapy after an organism is isolated and antimicrobial susceptibility data are known, however, is more controversial. The available evidence suggests that the greatest benefit of combination antibiotic therapy stems from the increased likelihood of choosing an effective agent during empiric therapy, rather than exploitation of in vitro synergy or the prevention of resistance during definitive treatment. In this review, we summarize the available data comparing monotherapy versus combination antimicrobial therapy for the treatment of infections with Gram-negative bacteria.

Early combination antibiotic therapy yields improved survival compared with monotherapy in septic shock: a propensity-matched analysis

BACKGROUND

Septic shock represents the major cause of infection-associated mortality in the intensive care unit. The possibility that combination antibiotic therapy of bacterial septic shock improves outcome is controversial. Current guidelines do not recommend combination therapy except for the express purpose of broadening coverage when resistant pathogens are a concern.

OBJECTIVE

To evaluate the therapeutic benefit of early combination therapy comprising at least two antibiotics of different mechanisms with in vitro activity for the isolated pathogen in patients with bacterial septic shock.

DESIGN

Retrospective, propensity matched, multicenter, cohort study.

SETTING

Intensive care units of 28 academic and community hospitals in three countries between 1996 and 2007.

SUBJECTS

A total of 4662 eligible cases of culture-positive, bacterial septic shock treated with combination or monotherapy from which 1223 propensity-matched pairs were generated.

MEASUREMENTS AND MAIN RESULTS

The primary outcome of study was 28-day mortality. Using a Cox proportional hazards model, combination therapy was associated with decreased 28-day mortality (444 of 1223 [36.3%] vs. 355 of 1223 [29.0%]; hazard ratio, 0.77; 95% confidence interval, 0.67-0.88; p = .0002). The beneficial impact of combination therapy applied to both Gram-positive and Gram-negative infections but was restricted to patients treated with beta-lactams in combination with aminoglycosides, fluoroquinolones, or macrolides/clindamycin. Combination therapy was also associated with significant reductions in intensive care unit (437 of 1223 [35.7%] vs. 352 of 1223 [28.8%]; odds ratio, 0.75; 95% confidence interval, 0.63-0.92; p = .0006) and hospital mortality (584 of 1223 [47.8%] vs. 457 of 1223 [37.4%]; odds ratio, 0.69; 95% confidence interval, 0.59-0.81; p < .0001). The use of combination therapy was associated with increased ventilator (median and [interquartile range], 10 [0-25] vs. 17 [0-26]; p = .008) and pressor/inotrope-free days (median and [interquartile range], 23 [0-28] vs. 25 [0-28]; p = .007) up to 30 days.

CONCLUSION

Early combination antibiotic therapy is associated with decreased mortality in septic shock. Prospective randomized trials are needed.

A survival benefit of combination antibiotic therapy for serious infections associated with sepsis and septic shock is contingent only on the risk of death: a meta-analytic/meta-regression study

OBJECTIVE

To assess whether a potential benefit with combination antibiotic therapy is restricted to the most critically ill subset of patients, particularly those with septic shock.

DATA SOURCES

OVID MEDLINE (1950-October 2009), EMBASE (1980-October 2009), the Cochrane Central Register of Controlled Trials (to third quarter 2009), the ClinicalTrial.gov database, and the SCOPUS database.

STUDY SELECTION

Randomized or observational studies of antimicrobial therapy of serious bacterial infections potentially associated with sepsis or septic shock. Fifty studies met entry criteria.

DATA EXTRACTION

Study design, mortality/clinical response, and other variables were extracted independently by two reviewers. When possible, study datasets were split into mutually exclusive groups with and without shock or critical illness.

DATA SYNTHESIS

Although a pooled odds ratio indicated no overall mortality/clinical response benefit with combination therapy (odds ratio, 0.856; 95% confidence interval, 0.71-1.03; p = .0943; I = 45.1%), stratification of datasets by monotherapy mortality risk demonstrated substantial benefit in the most severely ill subset (monotherapy risk of death >25%; odds ratio of death, 0.51; 95% confidence interval, 0.41-0.64; I = 8.6%). Of those datasets that could be stratified by the presence of shock/critical illness, the more severely ill group consistently demonstrated increased efficacy of a combination therapy strategy (odds ratio, 0.49; 95% confidence interval, 0.35-0.70; p < .0001; I = 0%). An increased risk of death was found in low-risk patients (risk of death <or=15% in the monotherapy arm) exposed to combination therapy (odds ratio, 1.53; 95% confidence interval, 1.16-2.03; p = .003; I = 8.2%). Meta-regression indicated that efficacy of combination therapy was dependent only on the risk of death in the monotherapy group.

CONCLUSION

Combination antibiotic therapy improves survival and clinical response of high-risk, life-threatening infections, particularly those associated with septic shock but may be detrimental to low-risk patients.

In vitro activities of antibiotic combinations against clincal isolates of Pseudomonas aeruginosa

Combination therapy has been recommended to treat Pseudomonas aeruginosa infections worldwide. The purpose of the present study was to determine the in vitro activities of piperacillin, cefepime, aztreonam, amikacin, and ciprofloxacin alone and in combination against 100 clinical isolates of P. aeruginosa from one medical center in southern Taiwan. The combination susceptibility assay was performed using the checkerboard technique. The percentage of resistance of P. aeruginosa to single agents in our study was relatively high for the Asia-Pacific area, except to aztreonam. Piperacillin plus amikacin exhibited the highest potential for synergy (59/100) in this study. Moreover, a high percentage of synergism was also noted with amikacin combined with cefepime (7/100) or aztreonam (16/100). The combination of two beta-lactams, such as cefepime with piperacillin, and aztreonam with cefepime or piperacillin, showed synergistic effects against some P. aeruginosa isolates. Although ciprofloxacin is a good anti-pseudomonal agent, a very low potential for synergy with other antibiotics was demonstrated in this study. No antagonism was exhibited by any combination in our study. Among piperacillin-resistant strains, there was synergy with a beta-lactam plus amikacin, including the combination of piperacillin and amikacin. However, the combination of two beta-lactams, such as piperacillin and cefepime or aztreonam, did not have any synergistic activity against these strains. In summary, the combinations of amikacin with the tested beta-lactams (piperacillin, aztreonam, cefepime) had a greater synergistic effect against P. aeruginosa, even piperacillin-resistant strains, than other combinations. Understanding the synergistic effect on clinical strains may help clinicians choose better empirical therapy in an area with high prevalence of multidrug-resistant P. aeruginosa.

Does combination antimicrobial therapy reduce mortality in Gram-negative bacteraemia? A meta-analysis

The use of combination antimicrobial therapy for bacteraemia caused by Gram-negative bacilli is controversial. We did a meta-analysis of published studies to determine whether a combination of two or more antimicrobials reduces mortality in patients with Gram-negative bacteraemia. Criteria for inclusion were: analytic studies of patients with documented Gram-negative bacteraemia that included patients receiving a single antibiotic (monotherapy) and patients receiving two or more antibiotics (combination therapy). Data on mortality (outcome) had to be provided. A pooled odds ratio was calculated with the random effects model of DerSimonian and Laird. Assessment of heterogeneity was done with the Breslow-Day test and reasons for heterogeneity were explored. 17 studies met the inclusion criteria, five prospective cohort studies, two prospective randomised trials, and ten retrospective cohort studies. Most studies used beta-lactams or aminoglycosides alone and in combination. The summary odds ratio was 0.96 (95% CI 0.70-1.32), indicating no mortality benefit with combination therapy. Subgroup analyses adjusting for year of publication, study design, and severity of illness did not change the results. Considerable heterogeneity was present in the main analyses. Analysis of only Pseudomonas aeruginosa bacteraemias showed a significant mortality benefit (OR 0.50, 95% CI 0.30-0.79). Our analysis does not support the routine use of combination antimicrobial therapy for Gram-negative bacteraemia, beyond settings where infection by P aeruginosa is strongly suspected or more than one drug would be desirable to assure in-vitro efficacy.

Contemporary in vitro synergy rates for aztreonam combined with newer fluoroquinolones and beta-lactams tested against gram-negative bacilli

Aztreonam has been commonly used in various combinations to enhance antimicrobial spectrum of co-drugs and produce potential synergistic activity. Although well studied in vitro over 10 years ago, aztreonam combination testing has been poorly documented with newer or commonly used agents against contemporary isolates. All MIC tests (alone or in combination) used in this experiment were reference broth microdilution methods in checkerboard tray designs. Aztreonam was combined with ciprofloxacin, gatifloxacin, levofloxacin, cefepime, ceftazidime and imipenem at clinically relevant concentrations. Interaction categories were defined by established criteria. Forty strains each of Pseudomonas aeruginosa and Enterobacteriaceae (12 species; aztreonam MIC, 1-16 microg/ml) were tested for each antimicrobial combination (480 total determinations). No antagonism or indeterminate interactions were identified. The overall rates of synergy or partial synergy for aztreonam with fluoroquinolone combinations was 63.4% versus P. aeruginosa, greatest for aztreonam with gatifloxacin (67.5%). Interaction categories varied greatly among aztreonam with beta-lactam combinations. Aztreonam with ceftazidime or cefepime versus P. aeruginosa had 75.0 - 85.0% partial or complete synergy rates, but aztreonam with imipenem showed dominant indifference (65.0%). In contrast, aztreonam with imipenem was more likely to exhibit synergy (32.5%) when tested against Enterobacteriaceae. Aztreonam, often used as an aminoglycoside substitute in antimicrobial combinations, continues to demonstrate enhanced, but variable drug activity interactions for contemporary antimicrobial combinations when tested against recent (2002) clinical isolates.

In vitro evaluation of the activity of two doses of Levofloxacin alone and in combination with other agents against Pseudomonas aeruginosa

P. aeruginosa is one of the most difficult to treat pathogens that generally requires combination therapy to prevent the development of resistance. This study evaluated the in vitro activity of two concentrations of levofloxacin (modeled for the 500 mg and 750 mg daily dose) in combination with ceftazidime, cefepime, piperacillin/tazobactam, imipenem, and tobramycin against P. aeruginosa. MICs and time-kill studies were performed against 12 non-duplicate clinical isolates of P. aeruginosa. The percent susceptible for levofloxacin, ceftazidime, cefepime, piperacillin/tazobactam, imipenem, and tobramycin were 67%, 58%, 58%, 67%, 75%, and 100%, respectively. Tobramycin was the most active single agent, killing and maintaining > or =99.9% killing over a 24 h period against all isolates. Levofloxacin 4 microg/mL(750 mg/day) alone reached 99.9% killing and maintain this killing over the time period more often than levofloxacin 2 microg/mL (500 mg/day). No combination was antagonistic and all combinations with tobramycin were indifferent. Overall, levofloxacin 2 microg/mL plus a beta-lactam was synergistic (65%) more often than levofloxacin 4 microg/mL combinations (46%). This was not unexpected due to the increased activity of levofloxacin 4 microg/mL. However, levofloxacin 4 microg/mL combinations maintained a > or =99.9% killing over the entire 24 h period more often than levofloxacin 2 microg/mL combinations (94% vs 83%). The findings from this work suggest that levofloxacin 750 mg/day in combination with another agent active against P. aeruginosa may prove to be clinically beneficial and superior to combinations using lower doses of levofloxacin. In vivo studies are needed to evaluate the clinical significance of these findings.

In vitro synergy studies using aztreonam and fluoroquinolone combinations against six species of Gram-negative bacilli

BACKGROUND

Combination antimicrobial therapy is often necessary to eradicate infections caused by gram-negative bacteria.

METHODS

To evaluate the potential benefit of aztreonam and fluoroquinolone combination therapy, the activity of aztreonam in combination with ciprofloxacin, gatifloxacin, levofloxacin and moxifloxacin was assessed using checkerboard testing for four clinical isolates of each of Escherichia coli, Klebsiella pneumoniae, Proteus mirabilis, Enterobacter cloacae, Burkholderia cepacia and Pseudomanas aeruginosa.

RESULTS

All aztreonam and fluoroquinolone combinations demonstrated additive activity [fractional inhibitory concentration (FIC) index >0.5-4] or synergy (FIC index <or=0.5) for all 24 isolates tested. Aztreonam plus ciprofloxacin was the most effective combination, demonstrating synergy against 16.7% of isolates (2 P. mirabilis, 1 E. cloacae, 1 B. cepacia). Aztreonam in combination with moxifloxacin was synergistic against 2 isolates (P. mirabilis, E. cloacae), and in combination with gatifloxacin against 1 isolate (E. cloacae). Aztreonam and levofloxacin demonstrated only additive activity.

CONCLUSION

Additive activity was observed for the majority of the aztreonam and fluoroquinolone combinations tested against six species of gram-negative bacilli. Synergy involving aztreonam and fluoroquinolone combinations was less common than additive activity and was isolate dependent. Although in vivo clinical successes have been documented using aztreonam in combination with other agents, confirmation by laboratory techniques requires further investigation.

In vitro activity of beta-lactams in combination with other antimicrobial agents against resistant strains of Pseudomonas aeruginosa

Using the chequerboard titration method, the activity in combination of beta-lactams, fluoroquinolones and aminoglycosides was investigated against 24 Pseudomonas aeruginosa isolates resistant to these antibiotics. Synergy was detected with one or more antimicrobial combinations against 15 of 24 (63%) isolates and partial synergy was detected with one or more combinations against all 24 isolates. No antagonism was seen with any combination. Ceftazidime and cefepime with aztreonam, amikacin and isepamicin showed synergy or partial synergy against 12-20 (50-80%) isolates. Imipenem and meropenem with amikacin and isepamicin showed synergy or partial synergy against eight to 12 (33-50%) isolates. The results of this study indicate that against P. aeruginosa, synergy may occur between beta-lactams, fluoroquinolones and aminoglycosides although the strains are resistant to the individual antibiotics.

Activity of piperacillin/tazobactam in combination with amikacin, ciprofloxacin, and trovafloxacin against Pseudomonas aeruginosa by time-kill

Pseudomonal infections have a high rate of morbidity and mortality, thus combination therapy is often recommended. We compared the activity of piperacillin/tazobactam in combination with amikacin, ciprofloxacin, or trovafloxacin at different concentrations against P. aeruginosa using time-kill methodology. MICs were determined for 4 clinical isolates of P. aeruginosa. Time-kill studies were conducted over 24 h. Each drug was tested alone and in combination using the following concentrations: 2 and 1/4, 1/4 and 2, and 1/4 and 1/4xMIC of piperacillin/tazobactam and amikacin, ciprofloxacin, or trovafloxacin. Combinations were classified as synergistic, indifferent, or antagonistic. Synergy was defined as > or = 2-log(10) decrease in CFU/mL at 24 h with the combination when compared to the most active single agent and the number of surviving organisms for the antimicrobial combination was > or =2-log(10) less than the initial inoculum. The MICs for piperacillin/tazobactam, amikacin, ciprofloxacin, and trovafloxacin, ranged from 4/4-512/4, 0.5-4, 0.125-4, and 0.5-8 microg/mL, respectively. Fifty eight percent of the combinations using concentrations of 1/4xMIC of piperacillin/tazobactam and 2xMIC of amikacin, ciprofloxacin, and trovafloxacin or 2xMIC of piperacillin/tazobactam and 1/4xMIC of amikacin, ciprofloxacin, and trovafloxacin were synergistic. Although no differences existed in synergistic activity between the two combinations, the 1/4 and 2xMIC maintained colony counts below the limit of quantification for 24 h for a significantly greater percentage of isolates than the 2 and 1/4xMIC combinations (75 and 25%, respectively; p = 0.04). Overall, synergy was most frequently (42%) noted with the piperacillin/tazobactam and amikacin combinations followed by 33 and 8% of the piperacillin/tazobactam and trovafloxacin and ciprofloxacin combinations. No combination demonstrated antagonism. Further more extensive studies are necessary to determine clinical significance.