Spectrum and activity of three contemporary fluoroquinolones tested against Pseudomonas aeruginosa isolates from urinary tract infections in the SENTRY Antimicrobial Surveillance Program (Europe and the Americas; 2000): more alike than different!

Correlation between antibiotic consumption and resistance of Pseudomonas aeruginosa in a teaching hospital implementing an antimicrobial stewardship program: A longitudinal observational study

BACKGROUND/PURPOSE

The rapid emergence of Pseudomonas aeruginosa resistance made selecting antibiotics more challenge. Antimicrobial stewardship programs (ASPs) are urging to implant to control the P. aeruginosa resistance. The purpose of this study is to evaluate the relationship between antimicrobial consumption and P. aeruginosa resistance, the impact of ASPs implemented during the 14-year study period.

METHODS

A total 14,852 P. aeruginosa isolates were included in our study. The resistant rate and antimicrobial consumption were investigated every six months. Linear regression analysis was conducted to examine the trends in antibiotics consumption and antimicrobial resistance over time. The relationship between P. aeruginosa resistance and antimicrobial consumption were using Pearson correlation coefficient to analysis. The trend of resistance before and after ASPs implanted is evaluated by segment regression analysis.

RESULTS

P. aeruginosa resistance to ceftazidime, gentamicin, amikacin, ciprofloxacin and levofloxacin significantly decreased during the study period; piperacillin/tazobactam (PTZ), cefepime, imipenem/cilastatin and meropenem remained stable. The P. aeruginosa resistance to ciprofloxacin and levofloxacin increasing initial then decreased after strictly controlled the use of levofloxacin since 2007. As the first choice antibiotic to treat P. aeruginosa, the consumption and resistance to PTZ increase yearly and resistance became stable since extended-infusion therapy policy implant in 2009.

CONCLUSION

Our ASP intervention strategy, which included extended infusion of PTZ and restrict use of levofloxacin, may be used to control antimicrobial resistance of P. aeruginosa in medical practice.

Synthesis and spectrum of the neoglycoside ACHN-490

ACHN-490 is a neoglycoside, or "next-generation" aminoglycoside (AG), that has been identified as a potentially useful agent to combat drug-resistant bacteria emerging in hospitals and health care facilities around the world. A focused medicinal chemistry campaign produced a collection of over 400 sisomicin analogs from which ACHN-490 was selected. We tested ACHN-490 against two panels of Gram-negative and Gram-positive pathogens, many of which harbored AG resistance mechanisms. Unlike legacy AGs, ACHN-490 was active against strains expressing known AG-modifying enzymes, including the three most common such enzymes found in Enterobacteriaceae. ACHN-490 inhibited the growth of AG-resistant Enterobacteriaceae (MIC(90), ≤4 μg/ml), with the exception of Proteus mirabilis and indole-positive Proteae (MIC(90), 8 μg/ml and 16 μg/ml, respectively). ACHN-490 was more active alone in vitro against Pseudomonas aeruginosa and Acinetobacter baumannii isolates with AG-modifying enzymes than against those with altered permeability/efflux. The MIC(90) of ACHN-490 against AG-resistant staphylococci was 2 μg/ml. Due to its promising in vitro and in vivo profiles, ACHN-490 has been advanced into clinical development as a new antibacterial agent.

Intravenous doripenem at 500 milligrams versus levofloxacin at 250 milligrams, with an option to switch to oral therapy, for treatment of complicated lower urinary tract infection and pyelonephritis

The prospective, multicenter, double-blind study presented in this report evaluated whether or not intravenous (IV) administration of doripenem, a carbapenem with bactericidal activity against gram-negative and gram-positive uropathogens, is inferior to IV administration of levofloxacin in the treatment of complicated urinary tract infection (cUTI). Patients (n = 753) with complicated lower UTI or pyelonephritis were randomly assigned to receive IV doripenem at 500 mg every 8 h (q8h) or IV levofloxacin at 250 mg q24h. Patients in both treatment arms were eligible to switch to oral levofloxacin after 3 days of IV therapy to complete a 10-day treatment course if they demonstrated significant clinical and microbiological improvements. The microbiological cure rate (primary end point) was determined at the test-of-cure (TOC) visit occurring 5 to 11 days after the last dose of antibiotic. For the microbiologically evaluable patients (n = 545), the microbiological cure rates were 82.1% and 83.4% for doripenem and levofloxacin, respectively (95% confidence interval [CI] for the difference, -8.0 to 5.5%); in the microbiological modified intent-to-treat cohort (n = 648), the cure rates were 79.2% and 78.2%, respectively. Clinical cure rates at the TOC visit were 95.1% in the doripenem arm and 90.2% in the levofloxacin arm (95% CI around the difference in cure rates [doripenem cure rate minus levofloxacin cure rate], 0.2% to 9.6%). Both treatment regimens were generally well tolerated. Doripenem was found not to be inferior to levofloxacin in terms of therapeutics and is now approved for use in the United States and Europe for the treatment of adults with cUTI, including pyelonephritis. As fluoroquinolone resistance increases, doripenem may become a more important option for successful treatment of cUTIs, including treatment of pyelonephritis.

Bloodstream infections in febrile neutropenic patients at a tertiary care center in Lebanon: a view of the past decade

OBJECTIVES

Previous studies from Lebanon have shown Gram-negative organisms to be the predominant agents in febrile neutropenic patients. The objective of this study was to evaluate the most current epidemiological trends among patients with neutropenic fever.

METHODS

This prospective observational cohort study, the largest to date in the country, was conducted at the American University of Beirut Medical Center between January 2001 and December 2003, with the objective of describing the characteristics of patients with neutropenic fever and to assess temporal trends.

RESULTS

We included 177 episodes of neutropenic fever. The most common underlying malignancy was lymphoma (42.4%). Gastrointestinal and abdominal infections were predominant (31.6%) and 23.7% of cases represented fever of unknown origin. Gram-negative organisms were responsible for 78.8% (26/33) of bloodstream infections compared to 33.3% (11/33) with Gram-positive organisms. The in-hospital mortality rate in this study (12.1%) was considerably lower than in previous years.

CONCLUSIONS

Gram-negative organisms are persistently predominant in our center. In a developing country like Lebanon with limited resources, lower mortality rates commensurate with worldwide reports were successfully achieved in this high-risk patient population. Protocols and guidelines should be adapted to the characteristics of individual institutions to ensure delivery of appropriate care to febrile neutropenic patients.

Levofloxacin-imipenem combination prevents the emergence of resistance among clinical isolates of Pseudomonas aeruginosa

A 2-compartment in vitro pharmacokinetic model (IVPM) was used to assess the potential of a levofloxacin-imipenem combination to prevent the emergence of resistance during treatment of Pseudomonas aeruginosa infection. Log-phase cultures (10(8) cfu/mL) of 3 clinical isolates were inoculated into the peripheral compartment of the IVPMs and were treated with simulated human doses of levofloxacin (750 mg) and imipenem (250 mg). Pharmacodynamics and the emergence of resistance were evaluated over the course of 24 h. Resistant mutants were evaluated for transcriptional expression of specific efflux pumps. Initially, rapid killing was observed in association with each regimen. However, with levofloxacin and imipenem alone, rapid regrowth was observed as a result of the selection of resistant subpopulations. Analysis of mutants selected by levofloxacin demonstrated that mexEF-oprN-overexpressing subpopulations resistant to both levofloxacin and imipenem were selected from cultures of all 3 strains. Nevertheless, the levofloxacin-imipenem combination rapidly eradicated all 3 P. aeruginosa strains. These data suggest that levofloxacin-imipenem may be an effective combination for preventing the emergence of resistance among P. aeruginosa strains, even when subpopulations resistant to both drugs are present. Further studies are warranted to evaluate the use of this combination against strains with established resistance to either or both drugs.

Current challenges in the treatment of complicated urinary tract infections and prostatitis

Serious urinary tract infections (UTIs) and acute bacterial prostatitis in adults cause significant morbidity and economic burden. Chronic bacterial prostatitis is a rather rare condition seen in urological practice, however, in certain occasions difficult to treat. In this paper, we review the bacterial etiologies and the resistance patterns found in adults with serious UTIs and bacterial prostatitis, and discuss considerations for selecting optimal antimicrobial therapy. The role of fluoroquinolones as targeted therapy for serious UTIs is highlighted. The use of effective antimicrobial therapy is the foundation of management of serious UTIs and bacterial prostatitis. Selection of the optimal antimicrobial agent must take into account patient-specific factors; infection characteristics (e.g., severity, community- vs. institutional- or hospital-acquired, need for IV agent, UTI, prostatitis); local resistance pattern; pharmacokinetic and pharmacodynamic principles; and cost. Fluoroquinolones are among the alternatives for empirical antibiotic treatment of serious UTIs and acute bacterial prostatitis. In serious UTIs activity of the antimicrobial agent against Pseudomonas aeruginosa needs to be taken into account. In chronic bacterial prostatitis fluoroquinolones are the first choice because of their favourable pharmacokinetic properties at the site of infection. Targeted antimicrobial therapy--emphasising the correct antibacterial spectrum and correct dosage--is likely to provide important benefits, such as reduced morbidity and associated costs, reduced emergence of resistance and maintenance of class efficacy.

Emergence of antibiotic resistance amongst hospital-acquired urinary tract infections and pharmacokinetic/pharmacodynamic considerations

Bacterial urinary tract infections (UTIs) are frequent infections in the nosocomial setting. Nosocomial UTIs are almost exclusively complicated UTIs, although the complicating factors may be very heterogenous. The bacterial spectrum of nosocomial UTIs is broad and antibiotic resistance is common. The results of international and national surveillance studies on the bacterial spectrum and antibiotic resistance of nosocomial uropathogens are provided. The treatment of nosocomial UTIs encompasses treatment of the complicating factors as well as antimicrobial chemotherapy. At least in serious UTIs, adequate initial antibiotic therapy results in lower mortality. Therefore, the initial antibiotic regimen must provide sufficient antibiotic cover. However, this can only be achieved if the bacterial spectrum and antibiotic resistance patterns of uropathogens in the institution are followed continuously. Provisional microbiological findings, such as reports on Gram stain or certain biochemical results, can lead to early stratification of pathogens and allow more tailored empiric antibiotic therapy. Antibiotic therapy of nosocomial UTIs has to consider two different aspects: (1) therapeutic success in the individual patient; and (2) prevention of emergence of antibiotic-resistant mutants. The emergence of resistance can possibly be lowered by adequate drug selection and dosing. Increasing antibiotic resistance requires more prudent use of antimicrobial drugs.

Treatment and control of severe infections caused by multiresistant Pseudomonas aeruginosa

Pseudomonas aeruginosa is one of the leading causes of nosocomial infections. Severe infections, such as pneumonia or bacteraemia, are associated with high mortality rates and are often difficult to treat, as the repertoire of useful anti-pseudomonal agents is limited (some beta-lactams, fluoroquinolones and aminoglycosides, and the polymyxins as last-resort drugs); moreover, P. aeruginosa exhibits remarkable ability to acquire resistance to these agents. Acquired resistance arises by mutation or acquisition of exogenous resistance determinants and can be mediated by several mechanisms (degrading enzymes, reduced permeability, active efflux and target modification). Overall, resistance rates are on the increase, and may be different in different settings, so that surveillance of P. aeruginosa susceptibility is essential for the definition of empirical regimens. Multidrug resistance is frequent, and clinical isolates resistant to virtually all anti-pseudomonal agents are increasingly being reported. Monotherapy is usually recommended for uncomplicated urinary tract infections, while combination therapy is normally recommended for severe infections, such as bacteraemia and pneumonia, although, at least in some cases, the advantage of combination therapy remains a matter of debate. Antimicrobial use is a risk factor for P. aeruginosa resistance, especially with some agents (fluoroquinolones and carbapenems), and interventions based on antimicrobial rotation and restriction of certain agents can be useful to control the spread of resistance. Similar measures, together with the prudent use of antibiotics and compliance with infection control measures, are essential to preserve the efficacy of the currently available anti-pseudomonal agents, in view of the dearth, in the near future, of new options against multidrug-resistant P. aeruginosa strains.

Stable Antimicrobial Susceptibility Rates for Clinical Isolates of Pseudomonas aeruginosa from the 2001–2003 Tracking Resistance in the United States Today Surveillance Studies

From 2001 to 2003, rates of susceptibility to piperacillin-tazobactam (86%), ceftazidime (80%), ciprofloxacin (68%), and levofloxacin (67%) did not decrease or decreased by <1.5%, whereas the rate of susceptibility to gentamicin decreased by 3.2% (from 75.5% to 72.3%) and the rate of susceptibility to imipenem decreased by 5.6% (from 84.4% to 78.8%), for 2394 clinical isolates of Pseudomonas aeruginosa collected in the Tracking Resistance in the United States Today surveillance studies. Rates of multidrug resistance (i.e., resistance to > or =3 antimicrobial agents) increased from 7.2% in 2001 to 9.9% in 2003 and were significantly higher for isolates from the East North Central and Mid-Atlantic regions of the United States than for isolates from other regions. Analysis of minimum inhibitory concentrations (MICs) suggested that combining an antipseudomonal beta -lactam with ciprofloxacin or levofloxacin would yield a 3.4%-7.1% increase in the percentage of isolates susceptible to the combination, compared with the beta -lactam alone. Ratios of the area under the serum concentration-time curve values for free drug to modal MICs for ciprofloxacin and levofloxacin were similar and were >125 (target ratio), whereas those ratios for gatifloxacin and moxifloxacin were significantly lower. Ongoing surveillance of P. aeruginosa is essential.

Role of fluoroquinolones in the treatment of serious bacterial urinary tract infections

Serious urinary tract infections (UTIs) in adults--defined as acute complicated UTIs or pyelonephritis requiring initial intravenous antimicrobials and/or hospitalisation and nosocomial infections--cause significant morbidity and economic burden. In the US, UTIs are responsible for nearly 7 million outpatient physician office visits, 1 million emergency room visits and over 100 000 hospital admissions annually. Complicated UTIs often affect patients with underlying functional, metabolic or anatomical defects of the urinary tract, whereas most nosocomial UTIs (~80%) are related to short- or long-term catheterisation. Serious UTIs are often difficult to treat because infection involves a diverse array of Gram-negative and Gram-positive bacteria, coupled with increasing antimicrobial resistance in some uropathogens, and a higher rate of recurrent infections. Although Escherichia coli remains a common aetiology (< or =60%), other Enterobacteriaceae, Gram-negative bacilli (e.g. Pseudomonas aeruginosa), and Gram-positive bacteria (e.g. Staphylococcus aureus) are frequently isolated. Patients with long-term catheterisation have UTIs typically caused by organisms that produce biofilms making eradication even more difficult. Overall, aetiology and resistance patterns are not predictable for those with serious UTIs, necessitating confirmation by culture and susceptibility testing.Numerous intravenous and oral antimicrobial treatment options are available and the majority of patients with serious UTIs will need initial intravenous therapy because of the possibility of bacteraemia/sepsis or impaired gastrointestinal absorption. Many experts concur that empirical therapy for the institutionalised or hospitalised patient with a serious UTI should include an intravenous antipseudomonal agent because of an increased risk of urosepsis. While state-of-the-art treatment guidelines are lacking for these infections, targeted therapy should be initiated once susceptibility data are known. The use of targeted therapy--emphasising the "correct antibacterial spectrum" and pharmacodynamic superiority--is likely to provide important benefits (e.g. reduced morbidity and associated costs, reduced emergence of resistance). Agents commonly prescribed include aminoglycosides, beta-lactam/beta-lactamase inhibitor combinations, imipenem, advanced-generation cephalosporins and fluoroquinolones. Fluoroquinolones are often recommended when conventional agents have failed or are less desirable (e.g. toxicity/hypersensitivity concerns), or when resistance is high. Several pivotal clinical trials support the use of fluoroquinolones for serious UTIs with most experience garnered with ciprofloxacin, including a new once-daily extended-release tablet formulation.Treatment of patients with serious UTIs remains challenging. Physicians should choose empirical therapy based on patient demographics/medical history, presumed aetiology and local resistance patterns until more definitive guidelines become available.

Changes in the etiology of bacteremia in febrile neutropenic patients and the susceptibilities of the currently isolated pathogens

The etiology of bacteremia in febrile neutropenic patients in the past few decades has shifted from gram-negative to gram-positive organisms. Potential reasons include the use of indwelling catheters, local environmental conditions, and the administration of specific antibiotic agents, especially as prophylaxis. Other factors may emerge from new studies, such as the categorization of febrile neutropenic patients into groups at low risk and at high risk of developing serious complications, continuing changes in resistance in the community, the use of antibiotic-coated catheters, and future changes in cytotoxic chemotherapy or antineoplastic therapy. In addition, there has been a drift in susceptibility patterns, with resistance issues seen in the general population of hospitalized patients now emerging in febrile neutropenic patients, as well as some issues specific to these patients. These changes affect empirical therapy as it was practiced a decade ago. Among the most commonly used agents, cefepime and carbapenems continue to show the highest rates of in vitro susceptibility, providing coverage against most gram-positive and gram-negative organisms and reducing the need for glycopeptides. Older agents continue to show degradation of their effectiveness. Among Pseudomonas aeruginosa strains, susceptibility to all agents continues to decline.

Pathogen of occurrence and susceptibility patterns associated with pneumonia in hospitalized patients in North America: results of the SENTRY Antimicrobial Surveillance Study (2000)

Antimicrobial selection for patients diagnosed with pneumonia is a major therapeutic challenge and dilemma to the clinical practitioner. In the community setting, patients usually receive empiric oral therapy based upon multiple patient risk factors and locally prevalent pathogen susceptibilities. For patients admitted to the hospital with pneumonia, or who acquire pneumonia while in the hospital, therapy can be initially empiric and then become directed once culture and susceptibility results are known. The SENTRY Antimicrobial Surveillance Program since 1997, has monitored pathogen frequency and antimicrobial susceptibilities in hospitalized patients with pneumonia in North America. In this Study 2,712 pathogens were studied from 30 medical centers (25 in the United States and 5 in Canada). Over 30 species of organisms were recovered with Staphylococcus aureus comprising 28.0% of all isolates and with four other species (Pseudomonas aeruginosa 20.0%, Streptococcus pneumoniae 9.1%, Klebsiella spp. 7.5% and Haemophilus influenzae 7.3%) constituted 71.9% of isolates submitted. Methicillin (oxacillin)-resistant S. aureus accounted for 43.7% of all S. aureus isolates. Antimicrobials demonstrating significant (>80%) activity against S. aureus were: chloramphenicol (81.6%), tetracycline (91.4%), rifampin (96.4%) and quinupristin/dalfopristin (99.7%); and no isolate was resistant to glycopeptides or linezolid. North American isolates of P. aeruginosa were most susceptible to amikacin (93.7%) > tobramycin (90.2%) > meropenem (89.1%) > imipenem = piperacillin/tazobactam (85.6%) > piperacillin (82.1%) > cefepime (80.5%). Overall, 32.1% of S. pneumoniae were penicillin non-susceptible while erythromycin susceptibility was only 74.8%. Fluoroquinolones and recent generation cephalosporins retained excellent activity (gatifloxacin [99.2%] > levofloxacin = cefepime [98.8%] > ceftriaxone [97.2%]) against S. pneumoniae. Klebsiella spp. were 100.0% susceptible to the carbapenems (meropenem and imipenem) but extended spectrum beta-lactamases were detected at a rate of 5.4%. The beta-lactamase-positive rate in H. influenzae was 28.6% in North America (71.4% ampicillin-susceptible). The SENTRY Antimicrobial Surveillance Program continues to identify important North American patterns of pathogen frequency and resistance. Additionally, the provision of multi-year longitudinal data and associated reports allow for comparisons, which function as critical tools for effective patient management and antimicrobial interventions.

Levofloxacin

Levofloxacin is the L-form of the fluoroquinolone antibacterial agent, ofloxacin. In in vitro studies, levofloxacin demonstrated a broad range of activity against Gram-positive and -negative organisms and anaerobes. The drug is more active against Gram-positive organisms than ciprofloxacin, but less active than newer fluoroquinolones such as gatifloxacin. Its activity against Streptococcus pneumoniae is unaffected by the presence of penicillin resistance. In several randomised controlled trails, 5 to 14 days' treatment with intravenous and/or oral levofloxacin proved an effective therapy for upper and lower respiratory tract infections. In patients with mild to severe community-acquired pneumonia (CAP), intravenous and/or oral levofloxacin 500mg once or twice daily was as effective as intravenous and/or oral gatifloxacin, clarithromycin, azithromycin or amoxicillin/clavulanic acid. Overall, clinical response rates with levofloxacin ranged from 86 to 95% versus 88 to 96% with comparator agents; bacteriological response rates were 88 to 95% and 86 to 98%, respectively. Sequential (intravenous +/- oral switch) therapy with levofloxacin 750mg once daily was as effective as intravenous imipenem/cilastatin (+/- oral switch to ciprofloxacin) in patients with severe nosocomial pneumonia. Generally, oral levofloxacin 250 or 500mg once daily was at least as effective as oral cefaclor, cefuroxime axetil, clarithromycin or moxifloxacin in patients with acute exacerbations of chronic bronchitis as assessed by either clinical or bacteriological response rates. This approach also provided similar efficacy to amoxicillin/ clavulanic acid or clarithromycin in patients with acute sinusitis. Sequential therapy with levofloxacin 500mg twice daily for 7 to 14 days' was as effective as intravenous imipenem/cilastatin in patients with suspected bacteraemia. Oral levofloxacin 500mg once daily for 7 to 10 days was also an effective treatment in patients with uncomplicated skin and skin structure infections, and in those with complicated urinary tract infections. A higher dosage of sequential levofloxacin 750mg once daily proved as effective as intravenous ticarcillin/clavulanic acid (+/- oral switch to amoxicillin/clavulanic acid) in the treatment of complicated skin and skin structure infections. Pharmacoeconomic studies suggest that levofloxacin may be cost-saving in comparison to conventional therapies.

CONCLUSIONS

Levofloxacin continues to demonstrate good clinical efficacy in the treatment of a range of infections, including those in which S. pneumoniae is a potential pathogen. Importantly, it has efficacy in CAP similar to that of gatifloxacin and at least as good as that of the third generation cephalosporins. Extensive clinical data confirm the good tolerability profile of this agent without the phototoxicity, hepatic and cardiac events evident with some of the other newer fluoroquinolone agents. Levofloxacin therefore offers a unique combination of documented efficacy and tolerability, and provides an important option for the treatment of bacterial infections.