Comparative activity of cefepime, alone and in combination, against clinical isolates of Pseudomonas aeruginosa and Pseudomonas cepacia from cystic fibrosis patients

Burkholderia cenocepacia Infections in Cystic Fibrosis Patients: Drug Resistance and Therapeutic Approaches

Burkholderia cenocepacia is an opportunistic pathogen particularly dangerous for cystic fibrosis (CF) patients. It can cause a severe decline in CF lung function possibly developing into a life-threatening systemic infection known as cepacia syndrome. Antibiotic resistance and presence of numerous virulence determinants in the genome make B. cenocepacia extremely difficult to treat. Better understanding of its resistance profiles and mechanisms is crucial to improve management of these infections. Here, we present the clinical distribution of B. cenocepacia described in the last 6 years and methods for identification and classification of epidemic strains. We also detail new antibiotics, clinical trials, and alternative approaches reported in the literature in the last 5 years to tackle B. cenocepacia resistance issue. All together these findings point out the urgent need of new and alternative therapies to improve CF patients’ life expectancy.

Dual beta-lactam therapy for serious Gram-negative infections: is it time to revisit?

We are rapidly approaching a crisis in antibiotic resistance, particularly among Gram-negative pathogens. This, coupled with the slow development of novel antimicrobial agents, underscores the exigency of redeploying existing antimicrobial agents in innovative ways. One therapeutic approach that was heavily studied in the 1980s but abandoned over time is dual beta-lactam therapy. This article reviews the evidence for combination beta-lactam therapy. Overall, in vitro, animal and clinical data are positive and suggest that beta-lactam combinations produce a synergistic effect against Gram-negative pathogens that rivals that of beta-lactam-aminoglycoside or beta-lactam-fluoroquinolone combination therapy. Although the precise mechanism of improved activity is not completely understood, it is likely attributable to an enhanced affinity to the diverse penicillin-binding proteins found among Gram negatives. The collective data indicate that dual beta-lactam therapy should be revisited for serious Gram-negative infections, especially in light of the near availability of potent beta-lactamase inhibitors, which neutralize the effect of problematic beta-lactamases.

Pseudomonas aeruginosa infection in patients with cystic fibrosis: scientific evidence regarding clinical impact, diagnosis, and treatment

Evidence-based techniques have been increasingly used in the creation of clinical guidelines and the development of recommendations for medical practice. The use of levels of evidence allows the reader to identify the quality of scientific information that supports the recommendations made by experts. The objective of this review was to address current concepts related to the clinical impact, diagnosis, and treatment of Pseudomonas aeruginosa infections in patients with cystic fibrosis. For the preparation of this review, the authors defined a group of questions that would be answered in accordance with the principles of PICO-an acronym based on questions regarding the Patients of interest, Intervention being studied, Comparison of the intervention, and Outcome of interest. For each question, a structured review of the literature was performed using the Medline database in order to identify the studies with the methodological design most appropriate to answering the question. The questions were designed so that each of the authors could write a response. A first draft was prepared and discussed by the group. Recommendations were then made on the basis of the level of scientific evidence, in accordance with the classification system devised by the Oxford Centre for Evidence-Based Medicine, as well as the level of agreement among the members of the group.

Inhaled aztreonam for chronic Burkholderia infection in cystic fibrosis: a placebo-controlled trial

BACKGROUND

Individuals with Burkholderia spp. infection have historically been excluded from efficacy trials of inhaled antibiotics, including aztreonam for inhalation solution (AZLI).

METHODS

A double-blind, placebo-controlled, 24-week trial of continuous AZLI/placebo treatment was undertaken in individuals with cystic fibrosis (CF) and chronic Burkholderia spp. infection. All subjects also received usual medical care (determined by their physicians). Additional antibiotic use was not restricted.

RESULTS

Baseline FEV1% predicted values ranged from 15.8% to 114.6%. No significant treatment differences (AZLI vs. placebo) were observed at week 24 for any endpoints, including FEV1% predicted, number of respiratory exacerbations requiring systemic/inhaled antibiotics, or hospitalizations. Continuous AZLI administration was well tolerated. Burkholderia spp. susceptibility to antibiotics commonly used in CF therapy showed little change.

CONCLUSIONS

24-weeks of continuous AZLI treatment did not significantly improve lung function in CF subjects with chronic Burkholderia spp. infection. Non-study antibiotic use may have confounded any potential AZLI effects.

Pulmonary exacerbations in cystic fibrosis

PURPOSE OF REVIEW

The chronic infection and inflammation of cystic fibrosis (CF) lung disease causes a progressive decline of lung function resulting in daily symptoms such as cough and sputum production. There are intermittent episodes of acute worsening of symptoms, more commonly referred to as pulmonary exacerbations. Despite this being a common event, there is still no standardized definition of an exacerbation. A recent set of guidelines from the CF Foundation Pulmonary Therapies Committee on the treatment of exacerbations noted the paucity of data supporting commonly used therapies. This review describes our current understanding of pulmonary exacerbations and the therapies used to treat them.

RECENT FINDINGS

The treatment of an exacerbation is intended to resolve the worsened symptoms and to restore the lung function that is commonly lost in the acute presentation. A most striking finding is the observation that for many patients there is no restoration of lung function, suggesting we either need better therapies to prevent exacerbations or better treatment of exacerbations.

SUMMARY

We have established recommendations on specific treatment of a pulmonary exacerbation and have outlined the areas where we need better information on appropriate therapies. Once we have a standardized definition of an exacerbation, we can proceed with clinical trials of therapies specific for its treatment.

Pharmacodynamics of cefepime alone and in combination with various antimicrobials against methicillin-resistant Staphylococcus aureus in an in vitro pharmacodynamic infection model

Treatment options for gram-positive resistant bacteria are limited; therefore, efforts to evaluate therapy options in the critical care population are warranted. Cefepime has broad-spectrum activity against gram-negative and gram-positive organisms. We have previously demonstrated that the combination of cefepime with vancomycin, linezolid, or quinupristin-dalfopristin had an improved or enhanced effect against methicillin-resistant Staphylococcus aureus (MRSA). We investigated various regimens of cefepime alone and in combination against two clinical MRSA isolates (R2481 and R2484) in an established in vitro pharmacodynamic model. Human pharmacokinetic regimen simulations were as follows: cefepime, 2 g every 8 h (q8h) (C8) and 12 h (C12), continuous-infusion 2-g loading dose followed by 4 g alone or in combination with gentamicin and tobramycin (1.0 or 2.0 [G1 and G2 or TB1 and TB2] mg/kg of body weight q12h and 5.0 [G5 or TB5] mg/kg q24h), arbekacin (ARB) (100 mg q12h), linezolid (LIN) (600 mg q12h), tigecycline (TIG) (100 mg q24h), or daptomycin (DAP) (6 mg/kg q24h) for 48 h. The MICs for cefepime, gentamicin, tobramycin, ARB, LIN, TIG, and DAP for the two clinical MRSA isolates (R2481 and R2484) were 4 and 4, 0.25 and 0.5, 128 and 0.5, 0.5 and 0.125, 2 and 4, 0.25 and 0.25, and 0.0625 and 0.125 microg/ml, respectively. At 48 h, combinations of C12 and C8 plus ARB, G1, or G5 (range, -2.05- to -4.32-log(10) decrease) demonstrated enhanced lethality against R2481 (resistant to tobramycin) (P < 0.05). A similar relationship was demonstrated against R2484 with cefepime plus ARB, gentamicin, or tobramycin (range, -2.05- to -3.63-log(10) decrease) (P < 0.05). A 99.9% kill was achieved with cefepime plus aminoglycoside combinations as early as 2 h and maintained throughout the 48-h period. TIG was antagonistic when combined with C12 against both isolates. DAP alone achieved 99.9% kill for up to 48 h for both isolates and was the most active agent against R2481 and R2484 (-2.89- and -3.61-log(10) decrease at 48 h); therefore, combination therapy did not enhance lethality. Overall, the most potent combinations noted were cefepime in combination with low- and high-dose aminoglycosides. Further investigations with combination therapies are warranted.

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.

Use of the E test to assess synergy of antibiotic combinations against isolates of Burkholderia cepacia-complex from patients with cystic fibrosis

Treatment of Burkholderia cepacia-complex infections in cystic fibrosis patients is problematic, since the microorganism is often resistant to most antimicrobial agents. In this study, the Epsilometer test, or E test, was used to assess the activity of antimicrobial combinations against Burkholderia cepacia-complex. In a preliminary evaluation, the E test was compared to the checkerboard method using 10 test organisms. Synergy testing by the E test was then performed on 131 clinical isolates of Burkholderia cepacia-complex using various combinations of antimicrobial agents. Agreement between the E test and the checkerboard method was 90%. The rate of resistance to individual agents ranged from 48% for meropenem to 100% for tobramycin, chloramphenicol, and rifampin. In 71.6%, 15.6%, and 12.6% of the test evaluations performed, the combinations tested resulted in additivity/indifference, synergism, and antagonism, respectively. The highest rates of synergy were observed with combinations of ciprofloxacin-piperacillin (44%), rifampin-ceftazidime (33%), chloramphenicol-ceftazidime (22%), cotrimoxazole-piperacillin/tazobactam (22%), and ciprofloxacin-ceftazidime (21%). Rates of antagonism for cotrimoxazole and chloramphenicol in combination with beta-lactam agents were higher than those observed for ciprofloxacin plus beta-lactam agents. These results suggest that the E test is a valuable and practical method to be considered for improving the identification of possible therapeutic options in cystic fibrosis patients infected with organisms belonging to the Burkholderia cepacia-complex.

Susceptibility of pseudomonas aeruginosa to cefepime versus ceftazidime in patients with cystic fibrosis

STUDY OBJECTIVES

To compare the susceptibility of respiratory cultures of Pseudomonas aeruginosa obtained from patients with cystic fibrosis to cefepime versus ceftazidime. The pattern of cumulative resistance of P aeruginosa to cefepime in patients who had received at least one treatment course of cefepime between two sputum cultures was also characterized.

DESIGN

Prospective consecutive data collection.

SETTING

University-affiliated cystic fibrosis clinic and medical center.

PATIENTS

Eighty patients with cystic fibrosis who had at least one sputum culture positive for P aeruginosa with reported microbiologic susceptibilities to cefepime and ceftazidime.

INTERVENTION

Patient data was collected and analyzed. Measurements and Main Results. Two hundred and thirty-one P aeruginosa isolates were collected over 6 months. A total of 16.4% and 8.7% of the isolates were nonsusceptible to cefepime and ceftazidime, respectively (p=0.01). In eight patients who had not received cefepime before the study period, nonsusceptibility was 11.8% and 27.2% before and after exposure to cefepime, respectively.

CONCLUSIONS

Susceptibility of P. aeruginosa isolates in patients with cystic fibrosis was lower with cefepime than with ceftazidime. Follow-up surveillance to determine changes in susceptibility of P aeruginosa isolates to cefepime is warranted.

Cefepime-aztreonam: a unique double beta-lactam combination for Pseudomonas aeruginosa

An in vitro pharmacokinetic model was used to determine if aztreonam could enhance the pharmacodynamics of cefepime or ceftazidime against an isogenic panel of Pseudomonas aeruginosa 164, including wild-type (WT), partially derepressed (PD), and fully derepressed (FD) phenotypes. Logarithmic-phase cultures were exposed to peak concentrations achieved in serum with 1- or 2-g intravenous doses, elimination pharmacokinetics were simulated, and viable bacterial counts were measured over three 8-h dosing intervals. In studies with cefepime and cefepime-aztreonam against the PD strain, samples were also filter sterilized, assayed for active cefepime, and assayed for nitrocefin hydrolysis activity before and after overnight dialysis. Against WT strains, the cefepime-aztreonam combination was the most active regimen, but viable counts at 24 h were only 1 log below those in cefepime-treated cultures. Against PD and FD strains, the antibacterial activity of cefepime-aztreonam was significantly enhanced over that of each drug alone, with 3.5 logs of killing by 24 h. Hydrolysis and bioassay studies demonstrated that aztreonam was inhibiting the extracellular cephalosporinase that had accumulated and was thus protecting cefepime in the extracellular environment. In contrast to cefepime-aztreonam, the pharmacodynamics of ceftazidime-aztreonam were not enhanced over those of aztreonam alone. Further pharmacodynamic studies with five other P. aeruginosa strains producing increased levels of cephalosporinase demonstrated that the enhanced pharmacodynamics of cefepime-aztreonam were not unique to the isogenic panel. The results of these studies demonstrate that aztreonam can enhance the antibacterial activity of cefepime against derepressed mutants of P. aeruginosa producing increased levels of cephalosporinase. This positive interaction appears to be due in part to the ability of aztreonam to protect cefepime from extracellular cephalosporinase inactivation. Clinical evaluation of this combination is warranted.

Development and characterization of a murine monoclonal antibody reactive with a 64 kDa somatic antigen of Burkholderia cepacia

Monoclonal antibodies (MAbs) to Burkholderia cepacia were produced from mice immunized with inactivated whole-cell antigen. For screening of resulting MAbs an enzyme-linked immunosorbent assay (ELISA) was used. A stable hybridoma cell line (BC-2) producing specific antibodies to a 64 kDa somatic antigen from B. cepacia was established. In ELISA and immunoblotting analysis the MAb BC-2 recognized all tested strains of B. cepacia whereas no cross-reaction with 32 Pseudomonas aeruginosa strains was found. From a wide range of other bacteria only strains of the species Burkholderia mallei, Burkholderia pseudomallei, and Burkholderia gladioli showed cross-reactions. The MAb BC-2 will be used to develop a diagnostic assay for the identification of B. cepacia and B. gladioli, important agents of nosocomial infections in immunocompromised patients suffering especially from cystic fibrosis (CF).

In vitro activities of antimicrobial agents, alone and in combinations, against Burkholderia cepacia isolated from blood

Burkholderia cepacia is a widespread, environmental gram-negative bacillus that is associated with nosocomial infections. This bacterium is considered to be an important pathogen in immunocompromised patients and is inherently resistant to multiple antimicrobial agents. To compare the activity of different antimicrobial agents and the potential of combinations against invasive strains of B. cepacia, we collected 36 isolates of B. cepacia from blood cultures and checked their susceptibilities to 13 antimicrobials by broth microdilution method. Most strains tested were susceptible to minocycline (94.4%), ceftazidime (86.1%), ciprofloxacin (83.3%), and trimethoprim-sulfamethoxazole (83.3%). All strains were resistant to aminoglycosides, and only some strains were susceptible to imipenem (16.7%), aztreonam (19.4%), moxalactam (25.0%), piperacillin (25.0%), and carbenicillin (47.2%). The effects of combinations of ceftazidime with amikacin, ceftazidime with ciprofloxacin, and ciprofloxacin with amikacin were assayed by checkerboard titration method. Synergistic effect was found in 28 out of 36 tested strains (77.8%), when ceftazidime was combined with amikacin, in 25 out of 36 strains (69.4%) when ceftazidime was combined with ciprofloxacin, and in only 8 out of 36 strains (22.2%) when ciprofloxacin was combined with amikacin.

Bacteriologic and clinical applications of a new extended-spectrum parenteral cephalosporin

Although third-generation cephalosporins have been considered the backbone of antibiotic therapy for the treatment of many kinds of serious infections, including those in hospitalized patients, lack of activity against some important pathogens still exists among currently available drugs. In addition, increasing accounts of antibiotic resistance, particularly in the hospital environment, are of deep concern and have thus led to the need for the development of newer antimicrobial agents. Cefepime is a now parenteral cephalosporin with an extended spectrum of antibacterial activity that includes both aerobic gram-negative and gram-positive bacteria. It is also active against many gram-negative organisms resistant to ceftriaxone and cefotaxime, as well as many strains of Enterobacter and Citrobacter resistant to ceftazidime. Cefepime appears to be less likely to select out resistant organisms, and it may be less likely to change hospital flora than currently available antimicrobials. Cefepime has been shown to be very well tolerated and effective in the treatment of a variety of infections including moderate-to-severe pneumonia (including cases associated with concurrent bacteremia), complicated and uncomplicated urinary tract infections (also including cases associated with concurrent bacteremia), and skin and skin-structure infections. Clinical response rates are > or = 75% for most infections and have been comparable to ceftazidime in comparative trials. In addition, pretreatment susceptibility testing indicates that >94% of organisms isolated in patients enrolled in clinical trials were susceptible to cefepime.

Cefepime

Because of the popularity of some third-generation cephalosporins, emergence of resistant organisms (e.g., selected Enterobacteriaceae) that produce inducible and extended-spectrum beta-lactamases has been a problem. Cefepime's twice-a-day dosage schedule and enhanced activity against Enterobacteriaceae and gram-positive organisms give it several advantages over older drugs. The clinical efficacy of cefepime has been demonstrated in comparative and noncomparative trials in the United States and Europe. Cefepime with twice-daily dosing has been useful in the treatment of lower respiratory tract infections, urinary tract infections, skin and skin structure infections, and in serious infection, including those with associated bacteremia. Cefepime is comparable to ceftazidime in clinical and bacteriologic response rates when both agents are administered three times a day in febrile neutropenic patients. Cefepime is also active against organisms that show resistance to other agents. Several studies have shown that cefepime retains its activity against E. cloacae and E. coli strains resistant to other cephalosporins and against many strains of P. aeruginosa resistant to ceftazidime. Cefepime exhibits a low level of cross-resistance with third-generation cephalosporins and a low propensity for selection of resistant mutants and offers a low potential for the induction of bacterial resistance, which complicates the course of many patients treated with single-agent third-generation therapy. Cefepime should be used in place of ceftazidime based on resistance potential, activity against resistant organisms, and cost.

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

Cefepime is a 'fourth' generation cephalosporin that has a broader spectrum of antibacterial activity than the third generation cephalosporins and is more active in vitro against Gram-positive aerobic bacteria. The fact that cefepime is stable to hydrolysis by many of the common plasmid- and chromosomally-mediated beta-lactamases, and that it is a poor inducer of type I beta-lactamases, indicates that cefepime may be useful for treatment of infections resistant to earlier cephalosporins. In comparative trials, cefepime 1 to 2 g, usually administered intravenously twice daily, was as effective as ceftazidime 1 to 2 g, usually administered 3 times daily, for treatment of bacteraemia and infections of the lower respiratory tract, urinary tract, pelvis and skin and skin structures. Furthermore, cefepime was as effective as ceftazidime and piperacillin or mezlocillin in combination with gentamicin when administered as empirical treatment for fever in patients with neutropenia. A limited number of trials have found cefepime to be as effective as cefotaxime for the treatment of gynaecological and lower respiratory tract infections. Similarly, cefepime 2 g twice daily intravenously (alone or in combination with metronidazole) was as effective as gentamicin in combination with mezlocillin or clindamycin, respectively, for the treatment of intra-abdominal infection. Cefepime has a linear pharmacokinetic profile, an elimination half-life of approximately 2 hours and is primarily excreted by renal mechanisms as unchanged drug. Cefepime has a tolerability profile similar to that of other parenteral cephalosporins; adverse events are primarily gastrointestinal in nature. A total of 1.4 and 2.9% of patients receiving cefepime < or = 2 g/day and > 2 g/day, respectively, required treatment withdrawal as a result of any adverse event. Thus, cefepime has the advantage of an improved spectrum of antibacterial activity, and is less susceptible to hydrolysis by some beta-lactamases, compared with third generation cephalosporins. Despite these advantages, cefepime has not been found to be more effective than ceftazidime and cefotaxime in clinical trials, although most trials selected patients with organisms sensitive in vitro to both comparator agents. Further trials, particularly in areas of widespread bacterial resistance, are required to confirm the positioning of cefepime for treatment of serious infection, and in particular to further explore whether its potential advantages result in clinical benefits.

Effect of sub-MIC antibiotics on the cell surface and extracellular virulence determinants of Pseudomonas cepacia

The effects of sub-MICs of ciprofloxacin and tobramycin on the cell surface characteristics and extracellular virulence factors of Pseudomonas cepacia were evaluated. Cells were grown in batch culture under iron-deficient and iron-replete conditions. At sub-MIC levels that did not affect bacterial growth cell surface hydrophobicity decreased under both iron-replete and iron-depleted conditions with ciprofloxacin, but increased with tobramycin under iron-sufficient conditions. Exopolysaccharide synthesis, lipase production and siderophore production were all significantly increased by the presence of ciprofloxacin under both growth conditions. Outer membrane protein and lipopolysaccharide profiles were not affected by exposure to the two antibiotics.

Pharmacokinetics of cefepime in cystic fibrosis patients

The purposes of this study were to determine and compare the single- and multiple-dose pharmacokinetics of cefepime in patients with and without cystic fibrosis. Twelve patients with cystic fibrosis hospitalized for treatment of acute pulmonary exacerbations were studied. In addition, pharmacokinetic data for seven of the patients with cystic fibrosis were compared with those for seven age-matched control patients. The cefepime dose was 50 mg/kg of body weight (maximum, 2 g) administered as a 30-min intravenous infusion every 8 h for a minimum of 8 days. Serial plasma and urine samples, obtained after the first and last doses, were analyzed for cefepime content by a validated high-pressure liquid chromatographic assay. By standard noncompartmental analysis, the pharmacokinetic parameters ascertained were area under the concentration in plasma-time curve, elimination half-life, total body clearance, renal clearance, and volume of distribution at steady state. In addition, the maximum concentration in plasma was recorded. Mean (+/- standard deviation) results of the first dose analysis in patients with cystic fibrosis were as follows: maximum concentration in plasma, 142.6 (+/- 26.07) micrograms/ml; area under the concentration in plasma-time curve, 265.3 (+/- 114.31) micrograms.h/ml; elimination half-life, 1.8 (+/- 0.53) h; total body clearance, 127.2 (+/- 50.94) ml/min; renal clearance, 91.1 (+/- 38.86) ml/min/kg; volume of distribution at steady state, 14.1 (+/- 4.31) liters. Analysis for the last dose in patients with cystic fibrosis did not vary appreciably from these values, nor did those from the controls. Thus, it appears that the first-dose pharmacokinetics of cefepime are predictive of those at steady state. In order to consistently exceed the MIC for Pseudomonas aeruginosa for the entire dosing interval in patients with cystic fibrosis, a higher dose and/or different dosing interval compared with those used in this study may be necessary.

Advances in the pharmacotherapy of cystic fibrosis

The quality of life and life-span of cystic fibrosis patients have been improved substantially in the last 20 or 30 years. This has been accomplished largely through improved early diagnosis and advances in traditional pharmacotherapy which mainly consists of antibiotic therapy. In the past few years, the basic cellular defect of cystic fibrosis, as well as the gene determining the disease, have been described. These milestones in the quest for knowledge about the disease open the door for other innovative forms of therapy. While corrective gene therapy may be the ultimate result of advances made based upon this new knowledge, we will probably see earlier breakthroughs in the form of immune reaction inhibition and correction of ion flux disturbances. Each of these present and future forms of therapy is explored in this paper.