Longitudinal assessment of antipneumococcal susceptibility in the United States

Use of the respiratory fluoroquinolones for the outpatient management of community-acquired pneumonia

BACKGROUND

Approximately 4 million cases of community-acquired pneumonia (CAP) occur in the United States each year, with the majority treated on an outpatient basis. The first fluoroquinolones (eg, ciprofloxacin) were used with caution for respiratory tract infections due to limited in vitro activity against common gram-positive pathogens. With the availability of levofloxacin, followed by gatifloxacin and moxifloxacin hydrochloride, which exhibited increased activity against gram-positive organisms, the fluoroquinolones have become a practical choice for the treatment of CAP.

OBJECTIVE

The aim of this review was to compare the respiratory fluoroquinolones in the outpatient management of CAP.

METHODS

We conducted a search for English-language articles (key terms: fluoroquinolone, levofloxacin, gatifloxacin, moxifloxacin, and pneumonia; years: 1996-2004). Data from published literature were reviewed regarding clinical and microbiologic efficacy and tolerability; pharmacokinetic and pharmacodynamic properties; and drug costs of levofloxacin, gatifloxacin, and moxifloxacin.

RESULTS

The 3 fluoroquinolones reviewed showed comparable clinical and microbiologic efficacy for the treatment of CAP. In general, the fluoroquinolones were well tolerated, although some differences have been reported, including higher rates of gastrointestinal and other adverse events for gatifloxacin and moxifloxacin. Gatifloxacin and moxifloxacin exhibited greater in vitro potency than levofloxacin against Streptococcus pneumoniae. However, levofloxacin achieved a higher serum drug concentration than the other agents, allowing similar attainment of pharmacokinetic and pharmacodynamic targets required for effective treatment.

CONCLUSIONS

The respiratory fluoroquinolones provided appropriate first line treatment in select patients with CAP on the basis of their microbiologic and clinical efficacy and their safety profiles.

Predicting the Clinical Efficacy of Generic Formulations of Ceftriaxone

Time above MIC (T>MIC) is regarded as the best pharmacokinetic/pharmacodynamic (PK/PD) parameter for predicting the clinical efficacy of cephalosporins. The concentration of non-protein-bound proprietary ceftriaxone (Rocephin, Roche) in body fluids exceeds this PK/PD criterion for the treatment of Streptococcus pneumoniae respiratory infections. However, the pharmaceutical quality of several generic products may be inferior to Rocephin. We have calculated the variations in fluid concentrations of 34 generic formulations of ceftriaxone and, by mathematical modelling, the implications for attainment of recommended PK/PD criteria, specifically: Treatment of S. pneumoniae infections based on the time that non-protein-bound ceftriaxone concentration in pleural fluid exceeds the CLSI (NCCLS) breakpoint of 4 mg/L for identification of resistant isolates. Impact upon Monte Carlo simulations in plasma for the treatment of S. pneumoniae infections based on T>MIC for 50% dosing interval. Rocephin exceeded the required PK/PD parameters at the mean and two standard deviation levels in both investigations. In contrast, most generic products failed to achieve required PK/PD levels in both investigations. As a consequence, some generic formulations of ceftriaxone may increase risks of clinical failure and/or emergence of resistant isolates.

Global fluoroquinolone resistance epidemiology and implictions for clinical use

This paper on the fluoroquinolone resistance epidemiology stratifies the data according to the different prescription patterns by either primary or tertiary caregivers and by indication. Global surveillance studies demonstrate that fluoroquinolone resistance rates increased in the past years in almost all bacterial species except S. pneumoniae and H. influenzae, causing community-acquired respiratory tract infections. However, 10 to 30% of these isolates harbored first-step mutations conferring low level fluoroquinolone resistance. Fluoroquinolone resistance increased in Enterobacteriaceae causing community acquired or healthcare associated urinary tract infections and intraabdominal infections, exceeding 50% in some parts of the world, particularly in Asia. One to two-thirds of Enterobacteriaceae producing extended spectrum β-lactamases were fluoroquinolone resistant too. Furthermore, fluoroquinolones select for methicillin resistance in Staphylococci. Neisseria gonorrhoeae acquired fluoroquinolone resistance rapidly; actual resistance rates are highly variable and can be as high as almost 100%, particularly in Asia, whereas resistance rates in Europe and North America range from <10% in rural areas to >30% in established sexual networks. In general, the continued increase in fluoroquinolone resistance affects patient management and necessitates changes in some guidelines, for example, treatment of urinary tract, intra-abdominal, skin and skin structure infections, and traveller's diarrhea, or even precludes the use in indications like sexually transmitted diseases and enteric fever.

Antibiotic resistance in sputum isolates of Streptococcus pneumoniae in chronic obstructive pulmonary disease is related to antibiotic exposure

Streptococcus pneumoniae (S. pneumoniae) is recovered from sputum of patients with chronic obstructive pulmonary disease (COPD) during stable disease and exacerbations. In patients with community acquired pneumonia, antibiotic exposure in the prior 3-6 months is associated with recovery of antibiotic resistant isolates of S. pneumoniae. Whether the same relationship is seen in COPD is not known. From April 1994 to June 2004, 127 adults with COPD were enrolled in a prospective longitudinal study. Sputum isolates of S. pneumoniae were characterized with susceptibility testing and pulsed-field gel electrophoresis (PFGE). The relationship between antibiotic use in the previous 3 and 6 months with either new acquisition of a resistant pneumococcal isolate or development of resistance (4-fold increase in MIC) in a pre-existing colonizing pneumococcal strain was determined. A total of 194 pneumococcal isolates were recovered from 38 patients. Among 71 newly acquired and 4 resistance-emergent strains analyzed further, rates of resistance to penicillin (MIC ≥2), erythromycin (MIC ≥1), tetracycline (MIC ≥8) and trimethoprim/sulfamethoxazole (MIC ≥4) were 8%, 24%, 17% and 16% respectively. Flouroquinolone resistance was not seen. Among strains isolated from patients exposed to a macrolide within 6 months, 53.6% displayed erythromycin resistance vs. 14% of strains without such exposure (p = 0.00085). Similar associations were not seen for other antibiotics. Macrolide use in the previous 6 months is associated with macrolide resistance in sputum isolates of S. pneumoniae. Recent antibiotic exposure may help in determining appropriate antibiotic treatment in these patients.

National and regional assessment of antimicrobial resistance among community-acquired respiratory tract pathogens identified in a 2005-2006 U.S. Faropenem surveillance study

Surveillance studies conducted in the United States over the last decade have revealed increasing resistance among community-acquired respiratory pathogens, especially Streptococcus pneumoniae, that may limit future options for empirical therapy. The objective of this study was to assess the scope and magnitude of the problem at the national and regional levels during the 2005-2006 respiratory season (the season when community-acquired respiratory pathogens are prevalent) in the United States. Also, since faropenem is an oral penem being developed for the treatment of community-acquired respiratory tract infections, another study objective was to provide baseline data to benchmark changes in the susceptibility of U.S. respiratory pathogens to the drug in the future. The in vitro activities of faropenem and other agents were determined against 1,543 S. pneumoniae isolates, 978 Haemophilus influenzae isolates, and 489 Moraxella catarrhalis isolates collected from 104 U.S. laboratories across six geographic regions during the 2005-2006 respiratory season. Among S. pneumoniae isolates, the rates of resistance to penicillin, amoxicillin-clavulanate, and cefdinir were 16, 6.4, and 19.2%, respectively. The least effective agents were trimethoprim-sulfamethoxazole (SXT) and azithromycin, with resistance rates of 23.5 and 34%, respectively. Penicillin resistance rates for S. pneumoniae varied by region (from 8.7 to 22.5%), as did multidrug resistance rates for S. pneumoniae (from 8.8 to 24.9%). Resistance to beta-lactams, azithromycin, and SXT was higher among S. pneumoniae isolates from children than those from adults. beta-Lactamase production rates among H. influenzae and M. catarrhalis isolates were 27.4 and 91.6%, respectively. Faropenem MICs at which 90% of isolates are inhibited were 0.5 mug/ml for S. pneumoniae, 1 mug/ml for H. influenzae, and 0.5 mug/ml for M. catarrhalis, suggesting that faropenem shows promise as a treatment option for respiratory infections caused by contemporary resistant phenotypes.

Geographically-based evaluation of multidrug resistance trends among Streptococcus pneumoniae in the USA: findings of the FAST surveillance initiative (2003–2004)

Surveillance initiatives to track Streptococcus pneumoniae resistance trends are important for understanding the current in vitro effectiveness of available antimicrobial agents. The antimicrobial susceptibility profiles of S. pneumoniae (n=1479 isolates) collected from 17 geographical areas across the USA (2003-2004) were analysed; 36.8% of isolates were resistant to one or more agents (24.4% were multidrug-resistant, i.e. resistant to two or more antimicrobial classes). Multidrug resistance involved resistance to beta-lactams, macrolides, tetracycline and trimethoprim/sulphamethoxazole, but rarely fluoroquinolones (>96% of multidrug-resistant isolates were fluoroquinolone-susceptible). Multidrug resistance rates were prominent regardless of the geographical region surveyed. As this trend continues, the empirical therapeutic options for S. pneumoniae infections will diminish and there will be an ongoing need to evaluate the effectiveness of potent fluoroquinolones such as gemifloxacin.

Treating acute exacerbations of chronic bronchitis and community-acquired pneumonia: how effective are respiratory fluoroquinolones?

OBJECTIVE

To provide family physicians with a review of evidence supporting fluoroquinolone therapy for defined patient populations with acute exacerbations of chronic bronchitis (AECB) and community-acquired pneumonia (CAP).

QUALITY OF EVIDENCE

A MEDLINE search found surveillance studies, randomized controlled trials, outcome studies, and expert consensus opinion. Descriptions of patient populations for which fluoroquinolone therapy is recommended are based on level I and level III evidence.

MAIN MESSAGE

A growing body of evidence supports fluoroquinolones as first-choice agents for treatment of AECB or CAP patients with comorbidity or a recent history of antibiotic use. Judicious and targeted therapy using fluoroquinolones among patients at risk of infections of the lower respiratory tract should contribute to improved clinical outcomes and broader health care savings.

CONCLUSION

Current data show clinical utility and cost-effectiveness of fluoroquinolones in lower respiratory tract infections. The most recently issued AECB and CAP guidelines now recommend these antimicrobial agents as first-choice agents for specific patient populations.

Severe sepsis and septic shock: review of the literature and emergency department management guidelines

Severe sepsis and septic shock are as common and lethal as other acute life-threatening conditions that emergency physicians routinely confront such as acute myocardial infarction, stroke, and trauma. Recent studies have led to a better understanding of the pathogenic mechanisms and the development of new or newly applied therapies. These therapies place early and aggressive management of severe sepsis and septic shock as integral to improving outcome. This independent review of the literature examines the recent pathogenic, diagnostic, and therapeutic advances in severe sepsis and septic shock for adults, with particular relevance to emergency practice. Recommendations are provided for therapies that have been shown to improve outcomes, including early goal-directed therapy, early and appropriate antimicrobials, source control, recombinant human activated protein C, corticosteroids, and low tidal volume mechanical ventilation.

Efficacy of moxifloxacin for treatment of penicillin-, macrolide- and multidrug-resistant Streptococcus pneumoniae in community-acquired pneumonia

This pooled analysis of six prospective, multicentre trials aimed to determine the efficacy of moxifloxacin in community-acquired pneumonia (CAP) due to penicillin-, macrolide- and multidrug-resistant Streptococcus pneumoniae (MDRSP). At a central laboratory, isolates were identified and antimicrobial susceptibility determined (microbroth dilution). MDRSP was defined as resistance > or =3 drug classes. Patients received oral or sequential intravenous/oral 400 mg moxifloxacin once daily for 7-14 days. The primary endpoint was clinical success at test-of-cure for efficacy-valid patients with proven pretherapy S. pneumoniae infection. Of 140 S. pneumoniae isolated (112 respiratory, 28 blood), 23 (16.4%) were penicillin resistant, 26 (18.6%) macrolide resistant and 31 (22.1%) MDRSP. The moxifloxacin MIC90 was 0.25 microg/ml. Clinical cure with moxifloxacin was 95.4% (125/131) overall, and 100% (21/21) for penicillin-, 95.7% (22/23) for macrolide- and 96.4% (27/28) for multidrug-resistant strains. Moxifloxacin provided excellent clinical and bacteriological cure rates in CAP due to drug-resistant pneumococci.

Current management of acute bacterial rhinosinusitis and the role of moxifloxacin

Episodes of acute rhinosinusitis are common among adults and are associated with a significant amount of morbidity. The symptoms of rhinosinusitis are nasal drainage, congestion, and sinus pressure. A bacterial sinus infection is more likely if these symptoms worsen after 5-7 days or do not improve after 10-14 days. The majority of bacterial episodes have been associated with Streptococcus pneumoniae and Haemophilus influenzae. In the current era of increasing resistance to beta -lactams and macrolides, treatment guidelines have been formulated worldwide to assist clinicians in the selection of antibacterials. According to one model, the following antibacterials are most likely to provide desired outcomes (90%-92% predicted clinical efficacy) for adults: respiratory fluoroquinolones (i.e., moxifloxacin, gatifloxacin, and levofloxacin), ceftriaxone, and high-dose amoxicillin-clavulanate (4 g of amoxicillin/day and 250 mg of clavulanate/day). Although the role of the fluoroquinolones in the treatment of this condition is evolving, fluoroquinolones are often recommended as second-line therapy or as first-line therapy for selected patients (e.g., those who received antibacterials in the previous 4-6 weeks or adults with moderate-to-severe disease).

High genetic diversity of ciprofloxacin-nonsusceptible isolates of Streptococcus pneumoniae in Poland

We have analyzed the susceptibility to ciprofloxacin of 697 pneumococcal isolates collected in 1998-2002 in Poland from patients with respiratory tract diseases. Thirty-one ciprofloxacin-nonsusceptible isolates (MICs, > or =4 microg/ml) were identified, of which two were resistant to levofloxacin (MIC, 8 microg/ml). Serotyping, pulsed-field gel electrophoresis, multilocus sequence typing, and the analysis of resistance determinants showed their great genetic diversity.

Role of efflux mechanisms on fluoroquinolone resistance in Streptococcus pneumoniae and Pseudomonas aeruginosa

Prokaryotic efflux mechanisms can effectively increase the intrinsic resistance of bacteria by actively transporting antibiotics out of cells, thus reducing the effective concentration of these agents. The fluoroquinolones, similar to most other antimicrobial classes, are susceptible to efflux mechanisms, particularly in Gram-negative organisms, such as Pseudomonas aeruginosa. Resistant P. aeruginosa clones isolated after fluoroquinolone therapy frequently over express at least one of the multiple efflux pump mechanisms found in this organism. Gram-positive bacteria, such as Streptococcus pneumoniae, also possess efflux mechanisms, though their effect on fluoroquinolone resistance seems to be more limited and selective. In the future, efflux pump inhibitors may offer effective adjunctive therapy to antibiotics for the treatment of difficult infections by efflux mutants. In the meantime, appropriate antibiotic selection and optimal dosing strategies should aim to eradicate the causative pathogen before a resistant efflux mutant can emerge.

Quinolone resistance mechanisms in pneumococci

Quinolones are widely used in the treatment of respiratory infections, in large part because of their activity against Streptococcus pneumoniae and other commonly encountered respiratory tract pathogens. Pneumococcal isolates that are resistant to these "respiratory quinolones" have now begun to emerge. Resistance is attributable to mutations affecting the intracellular targets of these drugs, topoisomerase IV and DNA gyrase; drug efflux contributes to quinolone resistance in some isolates. Most commonly, strains fully resistant to the newer quinolones have one or more mutations affecting DNA gyrase and topoisomerase IV. Although various agents of this class exhibit selectivity in primarily targeting one or the other of these enzymes, the passage of isolates in the presence of any agent can result in selection of mutations affecting both enzymes. Quinolone resistance in S. pneumoniae has arisen in heterogeneous genetic backgrounds but, ominously, has now appeared in strains that are well adapted for regional and global transmission.

Mutant selection window in levofloxacin and moxifloxacin treatments of experimental pneumococcal pneumonia in a rabbit model of human therapy

For some pneumococci the fluoroquinolone MICs are low but the mutant prevention concentrations (MPCs) are high; this difference defines in vitro the mutant selection window (MSW). We investigated in vivo the bacterial reduction and the occurrence of resistant mutants with moxifloxacin (MFX; 400 mg once daily) or levofloxacin (LVX; 500 mg twice daily) in treatments similar to those in humans with experimental pneumonia due to pneumococci (expPP) exhibiting various MICs and MPCs. The MIC/MPC for MFX and LVX and genotypes were as follows: strain 16089, 0.125/0.125 and 0.5/0.5 (wild type); strain MS1A, 0.25/0.25 and 1/2 (efflux); strain MS2A, 0.25/4 and 1.75/28 (parC79); strain MR3B4, 0.25/4 and 2/32 (parC79); strain M16, 0.5/2 and 8/32 (parC83); strain Gyr-1207, 1.5/3 and 8/16 (gyrA); and strain MQ3A, 4/4 and 16/64 (parC and gyrA). Both drugs were efficient with wild type-expPP, but only MFX was efficient with efflux-expPP. No bacterial reduction was observed for parC-expPPs due to mutants observed in 18 to 100% of animals, depending on the strain and the drug tested. These mutants showed unbound area under the concentration-time curve and MICs of from 50 to 164 for MFX. The in vivo pharmacodynamic boundaries of the MSW were different for MFX and LVX. We conclude that, after LVX or MFX treatment, mutants occur in vivo if there is a preexisting parC mutation, since the drug concentrations fall below the MPCs of these strains. Since the MPC determination cannot be routinely determined, these phenotypes or genotypes should be detected by simple tests to guide the therapeutic options.

Who defines resistance? the clinical and economic impact of antimicrobial susceptibility testing breakpoints

Antimicrobial susceptibility test breakpoints are necessary for the correct clinical interpretation of quantitative or qualitative susceptibility test values of antibacterial agents. Breakpoints are selected by regulatory bodies or professional groups (eg, the National Committee for Clinical Laboratory Standards) based on an extensive review of the microbiological, pharmacokinetic, and clinical data applicable to each drug. No precise formula for selection of optimal breakpoints has been established. Instead, the process involves a review of all existing data and is influenced by the perspectives of the individuals charged with selecting the breakpoints. The interpretive breakpoints may differ somewhat by country with some antibiotics because of regional or national decisions on dosing regimens. Breakpoints also influence the selection of empiric therapy and development of local, regional, or national treatment guidelines by classifying the percentage of previously tested organisms that were susceptible to various antibiotics. Thus, antibiotic breakpoints affect the care of individual patients and provide epidemiologists and policy makers with data regarding trends in antibiotic resistance.

In vitro and in vivo antibacterial activities of DK-507k, a novel fluoroquinolone

The antibacterial activities of DK-507k, a novel quinolone, were compared with those of other quinolones: ciprofloxacin, gatifloxacin, levofloxacin, moxifloxacin, sitafloxacin, and garenoxacin (BMS284756). DK-507k was as active as sitafloxacin and was as active as or up to eightfold more active than gatifloxacin, moxifloxacin, and garenoxacin against Streptococcus pneumoniae, methicillin-susceptible and methicillin-resistant Staphylococcus aureus, and coagulase-negative staphylococci. DK-507k was as active as or 4-fold more active than garenoxacin and 2- to 16-fold more active than gatifloxacin and moxifloxacin against ciprofloxacin-resistant strains of S. pneumoniae, including clinical isolates and in vitro-selected mutants with known mutations. DK-507k inhibited all ciprofloxacin-resistant strains of S. pneumoniae at 1 microg/ml. A time-kill assay with S. pneumoniae showed that DK-507k was more bactericidal than gatifloxacin and moxifloxacin. The activities of DK-507k against most members of the family Enterobacteriaceae were comparable to those of ciprofloxacin and equal to or up to 32-fold higher than those of gatifloxacin, levofloxacin, moxifloxacin, and garenoxacin. DK-507k was fourfold less active than sitafloxacin and ciprofloxacin against Pseudomonas aeruginosa, while it was two to four times more potent than levofloxacin, gatifloxacin, moxifloxacin, and garenoxacin against P. aeruginosa. In vivo, intravenous treatment with DK-507k was more effective than that with gatifloxacin and moxifloxacin against systemic infections caused by S. aureus, S. pneumoniae, and P. aeruginosa in mice. In a mouse model of pneumonia due to penicillin-resistant S. pneumoniae, DK-507k administered subcutaneously showed dose-dependent efficacy and eliminated the bacteria from the lungs, whereas gatifloxacin and moxifloxacin had no significant efficacy. Oral treatment with DK-507k was slightly more effective than that with ciprofloxacin in a rat model of foreign body-associated urinary tract infection caused by a P. aeruginosa isolate for which the MIC of DK-507k was fourfold higher than that of ciprofloxacin. Oral administration of DK-507k to rats achieved higher peak concentrations in serum and higher concentrations in cumulative urine than those achieved with ciprofloxacin. These data indicate the potential advantages of DK-507k over other quinolones for the treatment of a wide range of community-acquired infections.

Antimicrobial susceptibility breakpoints and first-step parC mutations in Streptococcus pneumoniae: redefining fluoroquinolone resistance

Clinical antimicrobial susceptibility breakpoints are used to predict the clinical outcome of antimicrobial treatment. In contrast, microbiologic breakpoints are used to identify isolates that may be categorized as susceptible when applying clinical breakpoints but harbor resistance mechanisms that result in their reduced susceptibility to the agent being tested. Currently, the National Committee for Clinical Laboratory Standards (NCCLS) guidelines utilize clinical breakpoints to characterize the activity of the fluoroquinolones against Streptococcus pneumoniae. To determine whether levofloxacin breakpoints can identify isolates that harbor recognized resistance mechanisms, we examined 115 S. pneumoniae isolates with a levofloxacin MIC of >2 mg/mL for first-step parC mutations. A total of 48 (59%) of 82 isolates with a levofloxacin MIC of 2 mg/mL, a level considered susceptible by NCCLS criteria, had a first-step mutation in parC. Whether surveillance programs that use levofloxacin data can effectively detect emerging resistance and whether fluoroquinolones can effectively treat infections caused by such isolates should be evaluated.