Fluoroquinolone-resistant Moraxella catarrhalis in a patient with pneumonia: report from the SENTRY Antimicrobial Surveillance Program (1998)

Alternations in DNA gyrase genes in low-level fluoroquinolone-resistant Moraxella catarrhalis strains isolated in Poland

PURPOSE

The purpose of this study was to investigate the molecular mechanisms of fluoroquinolone resistance in Moraxella catarrhalis clinical strains isolated in Lublin, Poland.

MATERIALS AND METHODS

A total of 150 non-duplicate clinical strains of M. catarrhalis were obtained from individuals with signs of upper respiratory tract infection. Bacterial identification was corroborated on the basis of phenotypic and biochemical characteristics as well as with the use of molecular tests. The antimicrobial susceptibility of M. catarrhalis isolates was determined using the disk diffusion method and Etest. Mutations in the gyrase (gyrA and gyrB) and topoisomerase (parC and parE) genes were determined by polymerase chain reaction and sequencing.

RESULTS

It was observed that 16.7% of the studied isolates were drug resistant. Resistance to tetracycline was detected for 12% of the strains. Resistance to nalidixic acid, moxifloxacin, and levofloxacin was exhibited by 2.7% of the strains; 1.3% of the strains were resistant to trimethoprim/sulfamethoxazole and 0.7% to erythromycin. Minimum inhibitory concentration values of the four strains demonstrating fluoroquinolone resistance were: 6-12 mg/L for nalidixic acid, 1-1.5 mg/L for levofloxacin, 1 mg/L for moxifloxacin, and 0.25-0.5 mg/L for ciprofloxacin. The research resulted in the detection of mutations in 4 strains, in gyrase gyrA and gyrB genes. In gyrA gene, there occurred mutation G412C as well as four silent transition mutations. Within gyrB gene, there occurred mutation, substitution A1481G, as well as two identical silent mutations.

CONCLUSION

Our findings reveal that resistance to fluoroquinolones in M. catarrhalis is connected with amino acid substitutions in gyrA and gyrB genes. To our knowledge, this work is the first description of fluoroquinolone-resistant clinical strains of M. catarrhalis with described mutations in gyrA and gyrB genes isolated in Poland and in Europe.

Development and validation of UV spectrophotometric method for orbifloxacin assay and dissolution studies

New, simple and cost effective UV-spectrophotometric method was developed for the estimation of orbifloxacin in pharmaceutical formulation. Orbifloxacin was estimated at 290 nm in 0.5 M hydrochloric acid. Linearity range was found to be 1.0-6.0 μg mL-1. The method was tested and validated for various parameters according to main guidelines. The proposed method was successfully applied for the determination of orbifloxacin in tablets. The results demonstrated that the procedure is accurate, precise and reproducible, while being simple, economical and less time consuming. It can be suitably applied for the estimation of orbifloxacin in routine quality control and dissolution studies.

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.

Resistance surveillance studies: a multifaceted problem--the fluoroquinolone example

INTRODUCTION

This review summarizes data on the fluoroquinolone resistance epidemiology published in the previous 5 years.

MATERIALS AND METHODS

The data reviewed are stratified according to the different prescription patterns by either primary- or tertiary-care givers and by indication. Global surveillance studies demonstrate that fluoroquinolone- resistance rates increased in the past several years in almost all bacterial species except Staphylococcus pneumoniae and Haemophilus influenzae causing community-acquired respiratory tract infections (CARTIs), as well as Enterobacteriaceae causing community-acquired urinary tract infections. Geographically and quantitatively varying fluoroquinolone resistance rates were recorded among Gram-positive and Gram-negative pathogens causing healthcare-associated respiratory tract infections. One- to two-thirds of Enterobacteriaceae producing extended-spectrum β-lactamases (ESBLs) were fluoroquinolone resistant too, thus, limiting the fluoroquinolone use in the treatment of community- as well as healthcare-acquired urinary tract and intra-abdominal infections. The remaining ESBL-producing or plasmid-mediated quinolone resistance mechanisms harboring Enterobacteriaceae were low-level quinolone resistant. Furthermore, 10-30 % of H. influenzae and S. pneumoniae causing CARTIs harbored first-step quinolone resistance determining region (QRDR) mutations. These mutants pass susceptibility testing unnoticed and are primed to acquire high-level fluoroquinolone resistance rapidly, thus, putting the patient at risk. The continued increase in fluoroquinolone resistance affects patient management and necessitates changes in some current guidelines for the treatment of intra-abdominal infections or even precludes the use of fluoroquinolones in certain indications like gonorrhea and pelvic inflammatory diseases in those geographic areas in which fluoroquinolone resistance rates and/or ESBL production is high. Fluoroquinolone resistance has been selected among the commensal flora colonizing the gut, nose, oropharynx, and skin, so that horizontal gene transfer between the commensal flora and the offending pathogen as well as inter- and intraspecies recombinations contribute to the emergence and spread of fluoroquinolone resistance among pathogenic streptococci. Although interspecies recombinations are not yet the major cause for the emergence of fluoroquinolone resistance, its existence indicates that a large reservoir of fluoroquinolone resistance exists. Thus, a scenario resembling that of a worldwide spread of β-lactam resistance in pneumococci is conceivable. However, many resistance surveillance studies suffer from inaccuracies like the sampling of a selected patient population, restricted geographical sampling, and undefined requirements of the user, so that the results are biased. The number of national centers is most often limited with one to two participating laboratories, so that such studies are point prevalence but not surveillance studies. Selected samples are analyzed predominantly as either hospitalized patients or patients at risk or those in whom therapy failed are sampled; however, fluoroquinolones are most frequently prescribed by the general practitioner. Selected sampling results in a significant over-estimation of fluoroquinolone resistance in outpatients. Furthermore, the requirements of the users are often not met; the prescribing physician, the microbiologist, the infection control specialist, public health and regulatory authorities, and the pharmaceutical industry have diverse interests, which, however, are not addressed by different designs of a surveillance study. Tools should be developed to provide customer-specific datasets.

CONCLUSION

Consequently, most surveillance studies suffer from well recognized but uncorrected biases or inaccuracies. Nevertheless, they provide important information that allows the identification of trends in pathogen incidence and antimicrobial resistance.

Development and validation of a microbiological agar assay for determination of orbifloxacin in pharmaceutical preparations

Orbifloxacin is a fluoroquinolone with broad-spectrum antimicrobial activity, and belongs to the third generation of quinolones. Regarding the quality control of medicines, a validated microbiological assay for determination of orbifloxacin in pharmaceutical formulations has not as yet been reported. For this purpose, this paper reports the development and validation of a simple, sensitive, accurate and reproducible agar diffusion method to quantify orbifloxacin in tablet formulations. The assay is based on the inhibitory effect of orbifloxacin upon the strain of Staphylococcus aureus ATCC 25923 used as test microorganism. The results were treated statistically by analysis of variance and were found to be linear (r = 0.9992) in the selected range of 16.0–64.0 μg/mL, precise with relative standard deviation (RSD) of repeatability intraday = 2.88%, intermediate precision RSD = 3.33%, and accurate (100.31%). The results demonstrated the validity of the proposed bioassay, which allows reliable orbifloxacin quantitation in pharmaceutical samples and therefore can be used as a useful alternative methodology for the routine quality control of this medicine.

Susceptibility trends of haemophilus influenzae and Moraxella catarrhalis against orally administered antimicrobial agents: five-year report from the SENTRY Antimicrobial Surveillance Program

The assessment of orally administered antimicrobial susceptibilities of common pathogens that cause community-acquired respiratory tract infections (CARTI) has become exceedingly important due to the number of office visits for this indication. Numerous local, regional and global studies have documented the susceptibilities of Haemophilus influenzae, Streptococcus pneumoniae, and Moraxella catarrhalis, the most common CARTI pathogens. SENTRY Antimicrobial Surveillance Program sites in North and Latin America, and Europe were requested to send a combined total of 100 isolates of these pathogens to the local monitor for reference broth microdilution testing (1997-2001). This study compared the susceptibility profiles of H. influenzae and M. catarrhalis isolates (13,370 strains) from the three geographic regions over a five year period. beta-lactamase mediated ampicillin resistance among H. influenzae was highest among North American isolates (27.9%) compared to Latin America and Europe (16.2 to 16.3%), although it was noted that during the five year study period, ampicillin resistance was steadily increasing in the latter two regions. Cefprozil (84.3% susceptible) and clarithromycin (81.1% susceptible) were also less active against North American H. influenzae isolates. Latin American isolates were much less susceptible to trimethoprim/sulfamethoxazole (T/S; 59.3%) compared to the other regions (75.8 to 78.6%). M. catarrhalis isolates were also significantly less susceptible to T/S in Latin America (10.5% resistance). The production of beta-lactamase enzymes among the M. catarrhalis isolates exceeded >95% in all three regions during the five year period. The fluoroquinolones (FQ) remained very active against these two respiratory pathogens with rare isolates with elevated FQ MIC results. It is apparent from this investigation that many commonly prescribed empiric treatments remain viable therapeutic options for CARTI caused by these two Gram-negative respiratory tract pathogens.

Emergence of levofloxacin-resistant pneumococci in immunocompromised adults after therapy for community-acquired pneumonia

We describe 4 patients infected with levofloxacin-resistant pneumococci after therapy for community-acquired pneumonia (CAP). The 4 patients had 15 episodes of CAP; Streptococcus pneumoniae was isolated from blood or sputum samples obtained during 14 of the episodes. The underlying medical condition was Bruton agammaglobulinemia in 3 patients and chronic lymphoid leukemia in the other. The initial episode of CAP in each patient was due to a levofloxacin-susceptible strain. One of 4 reinfections and 5 of 6 relapses were due to levofloxacin-resistant strains. All of these strains had amino acid substitutions in the quinolone-resistance-determining region of the genes parC and gyrA. The time between episodes of pneumonia varied from 1 to 4 months. In immunocompromised patients with suspected or proven pneumococcal infection, it may be prudent not to use fluoroquinolone monotherapy empirically when the patient has a history of fluoroquinolone therapy in at least the past 4 months.

Five-year analysis of Haemophilus influenzae isolates with reduced susceptibility to fluoroquinolones: prevalence results from the SENTRY antimicrobial surveillance program

The appearance of resistance or reduced susceptibility to fluoroquinolones among Hemophilus influenzae has been documented for nearly a decade. Over this time, the use of fluoroquinolones for the treatment of respiratory infections including commonly isolated bacterial causes of community-acquired infections has markedly increased. The documentation of resistance to fluoroquinolones among Streptococcus pneumoniae and H. influenzae has also become more prevalent as measured by peer-reviewed publications. During 1997-2001, a total of 11,355 H. influenzae isolates were tested by reference broth microdilution methods from strains collected by the SENTRY Antimicrobial Surveillance Program (American and European medical centers). Strains with reduced susceptibility to fluoroquinolones (RSF) were detected during all five study years at an overall rate of 0.15%. Among the tested compounds, sitafloxacin (MIC(50,) 0.03 microg/ml) was the most potent agent against the RSF strains, followed by gemifloxacin (0.12 microg/ml) > garenoxacin = grepafloxacin = levofloxacin = moxifloxacin = trovafloxacin (0.5 microg/ml) > ciprofloxacin = sparfloxacin (1 microg/ml). Gene sequencing of the quinolone resistance determining region and epidemiologic typing of 30 RSF isolates showed diverse mutational events in gyr A and par C and multiple pulsed-field gel electrophoresis (PFGE) patterns among strains that was not consistent with clonal dissemination. Continued surveillance by global or national networks should continue to monitor for H. influenzae isolates that are refractory to fluoroquinolone therapy.

Comparative activity of garenoxacin (BMS 284756), a novel desfluoroquinolone, tested against 8,331 isolates from community-acquired respiratory tract infections: North American results from the SENTRY Antimicrobial Surveillance Program (1999-2001)

Emerging resistances to orally administered antimicrobials have escalated among bacteria causing community-acquired respiratory infections (CARTI). The spectrum and potency of garenoxacin, (formerly BMS 284756) was assessed against a collection of CARTI isolates from North American medical centers during a longitudinal surveillance study, the SENTRY Antimicrobial Surveillance Program (1999-2001). A total of 8,331 strains of Hemophilus influenzae, Moraxella catarrhalis, and Streptococcus pneumoniae were tested by reference methods and compared to numerous other marketed antimicrobials. Nearly all (95.1%) M. catarrhalis were penicillin-resistant, 27.9% of H. influenzae were ampicillin-resistant and 35.0% of S. pneumoniae had MICs at > or = 0.12 microg/ml for penicillin. Garenoxacin was very active against the three monitored species with MIC(90) values of < or =0.06 microg/ml. Garenoxacin and other quinolones were equally active against the Gram-negative pathogens (except moxifloxacin which was at least twofold less potent versus M. catarrhalis). However, against pneumococci the rank order of potency (MIC(50) in microg/ml) was: gemifloxacin (0.015) > garenoxacin (0.06) > trovafloxacin = moxifloxacin (0.12) > gatifloxacin (0.25) > levofloxacin = ciprofloxacin (1). A trend toward greater resistance worldwide was observed for ciprofloxacin (MIC, > or = 4 microg/ml), increasing from 1.5% in 1999 to 6.8% in 2001. The highest quinolone resistance rate was observed in North America. Garenoxacin, a new desfluoro(6)quinolone, was documented to be very active in vitro (MIC, < or =2 microg/ml) against > 99.9% of all CARTI isolates in the SENTRY Program. Evolving resistances to other antimicrobial classes or among currently used quinolones appear to position this investigational desfluoro(6)quinolone as a potential treatment option for future clinical use in ambulatory patients.

In vitro assessment of gatifloxacin spectrum and potency tested against Haemophilus influenzae, Moraxella catarrhalis, and Streptococcus pneumoniae isolates from the Asia-Western Pacific component of the SENTRY antimicrobial surveillance program (1998-1999)

Fluoroquinolones, especially the newer agents, have an increased role in the management of respiratory tract infections worldwide. In the SENTRY Antimicrobial Surveillance Program for the Asia-Pacific Region for 1998 and 1999, 630 Streptococcus pneumoniae, 583 Hemophilus influenzae and 274 Moraxella catarrhalis isolates were examined to determine the comparative activity of the new fluoroquinolone, gatifloxacin, compared with those of ciprofloxacin, levofloxacin and trovafloxacin. Gatifloxacin was highly active against all three species. Decreased susceptibility (MIC >/=2 microg/mL) to gatifloxacin was noted in only seven strains of S. pneumoniae (3 of which were resistant); in three strains of H. influenzae (MIC >/= 0.12 microg/mL), and 2 M. catarrhalis (MIC > 2 microg/mL).

Evaluation of in vitro susceptibility testing criteria for gemifloxacin when tested against Haemophilus influenzae strains with reduced susceptibility to ciprofloxacin and ofloxacin

Although Hemophilus influenzae resistance to fluoroquinolones is low, it is important to monitor the development of populations with decreased susceptibility to this class of antimicrobials. The activity of gemifloxacin, a new fluoroquinolone, was measured against a collection of susceptible wild-type strains (MIC(90,) 0.008 microg/ml for both beta-lactamase-negative and -positive strains) and strains less susceptible to quinolones (MIC(90,) 1 microg/ml). Using a 5microg disk, the gemifloxacin-susceptible strains had MIC results ranging from </= 0.004 to 0.25 microg/ml (the proposed breakpoint), corresponding to zone diameters of 20 to 39 mm. However, some H. influenzae strains having multiple QRDR mutations were less susceptible to gemifloxacin (MIC range, 0.016-2 microg/ml), although gemifloxacin remained active against 57.1% of strains. In vitro testing, using these selected resistant strains, defined the categorical interpretive criteria for routine clinical laboratory use.

Apparent plateau in beta-lactamase production among clinical isolates of Haemophilus influenzae and Moraxella catarrhalis in the United States: results from the LIBRA Surveillance initiative

Haemophilus influenzae (n=2791) and Moraxella catarrhalis (n=1249) isolated from patient specimens during 1999 were collected from 290 laboratories participating in a moxifloxacin surveillance study as part of the LIBRA Surveillance initiative. Isolates were tested for in vitro susceptibility to a panel of agents suitable for the treatment of respiratory tract infections. beta-Lactamase production was identified in 32.2% of H. influenzae and 94.2% of M. catarrhalis. These percentages differed by less than 1.5% from results of a study conducted in 1997-1998 and were similar to results from other recent US surveillance studies. Resistance among H. influenzae to trimethoprim-sulphamethoxazole increased considerably, from 2% in the 1997-1998 study (n=6588 H. influenzae) to 15.5% in the current study. One isolate of H. influenzae had an MIC of 8 mg/l to both levofloxacin and moxifloxacin; all other isolates had MICs of < or =0.5 mg/l and < or =0.25 mg/l, respectively. beta-Lactamase production was found to confer ampicillin resistance in nearly all isolates. For M. catarrhalis, beta-lactamase-negative isolates had MICs < or =0.12-0.25 mg/l for ampicillin and < or =0.03-0.12 mg/l for ceftriaxone. In contrast, beta-lactamase production resulted in MICs of < or = 0.12->16 mg/l for ampicillin and < or = 0.03-4 mg/l for ceftriaxone. All M. catarrhalis had MICs < or =0.12 mg/l for moxifloxacin and < or =1 mg/l for levofloxacin. In summary, antimicrobial susceptibilities and the prevalence of beta-lactamase production in H. influenzae and M. catarrhalis in the United States has remained essentially unchanged from 1997-1998 to 1999.

Antimicrobial drug use and resistance among respiratory pathogens in the community

There is substantial evidence that the overuse of antibiotics is a major cause for the emergence of resistance in respiratory pathogens in the community. However, it is also recognized that the mechanisms of resistance, the cost of resistance to the fitness of the organism, and the ability of the resistant strain to disseminate are all important contributors to this problem. Therefore, when developing strategies to control and/or prevent the emergence of resistance, health care professionals must take each of these factors into consideration. As we enter a new era in the use of fluoroquinolones for the treatment of respiratory tract infections, we have an opportunity to apply such lessons learned in the past to minimize or prevent the development of resistance to this class of antimicrobial drugs in the future.

Integration of molecular characterization of microorganisms in a global antimicrobial resistance surveillance program

The SENTRY Antimicrobial Surveillance Program has incorporated molecular strain typing and resistance genotyping as a means of providing additional information that may be useful for understanding pathogenic microorganisms worldwide. Resistance phenotypes of interest include multidrug-resistant pathogens, extended-spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae, methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant enterococci, and fluoroquinolone-resistant (FQR) strains of gram-negative bacilli and Streptococcus pneumoniae. Clusters of > or =2 isolates within a given resistance profile that are linked temporally and by hospital location are flagged for DNA fingerprinting. Further characterization of organisms with respect to resistance genotype is accomplished with use of polymerase chain reaction and DNA sequencing. This process has been highly successful in identifying clonal spread within clusters of multiresistant pathogens. Between 50% and 90% of MRSA clusters identified by phenotypic screening contained evidence of clonal spread. Among the Enterobacteriaceae, ESBL-producing strains of Escherichia coli and Klebsiella pneumoniae are the most common pathogens causing clusters of infection, and approximately 50% of recognized clusters demonstrate clonal spread. Clusters of Pseudomonas aeruginosa, Acinetobacter species, and Stenotrophomonas maltophilia have been noted with clonal spread among patients with urinary tract, respiratory, and bloodstream infections. Characterization of mutations in the FQR-determining region of phenotypically susceptible isolates of E. coli and S. pneumoniae has identified first-stage mutants among as many as 40% of isolates. The ability to characterize organisms phenotypically and genotypically is extremely powerful and provides unique information that is important in a global antimicrobial surveillance program.

Worldwide prevalence of antimicrobial resistance in Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis in the SENTRY Antimicrobial Surveillance Program, 1997-1999

The in vitro activities of numerous antimicrobials against clinical isolates of Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis from patients with bloodstream and respiratory tract infections in the United States, Canada, Europe, Latin America, and the Asia-Pacific region were studied in the SENTRY Antimicrobial Surveillance Program. Penicillin resistance (minimum inhibitory concentration, > or =2 microg/mL) was noted in all 5 geographic regions, and a high and increasing rate of macrolide resistance among S. pneumoniae isolates was observed. Elevated rates of resistance to clindamycin, trimethoprim-sulfamethoxazole, chloramphenicol, and tetracycline were seen. beta-Lactamase-mediated resistance in H. influenzae to amoxicillin and variable trimethoprim-sulfamethoxazole resistance by region were documented. Resistance to several drugs continues to emerge among pneumococci worldwide, but more stable resistance patterns have been noted for H. influenzae and M. catarrhalis. Continued surveillance of this pathogen group appears to be prudent.

Activity of BMS284756 against 2,681 recent clinical isolates of Haemophilus influenzae and Moraxella catarrhalis: Report from The SENTRY Antimicrobial Surveillance Program (2000) in Europe, Canada and the United States

Although the isolation and detection of fluoroquinolone-resistant Haemophilus influenzae and Moraxella catarrhalis has been a very rare occurrence, newer agents in the quinolone class must be evaluated to determine their comparative potencies and to develop in vitro testing methods. BMS284756 is an investigational desfluoro(6)-quinolone with a spectrum of activity most similar to recently introduced agents such as gatifloxacin and trovafloxacin. This compound was compared to levofloxacin, gatifloxacin, ciprofloxacin and moxifloxacin, as well as other orally administered antimicrobials against 1,872 H. influenzae and 810 M. catarrhalis isolates. Two Canadian H. influenzae strains had ciprofloxacin MICs elevated above the normal wild type susceptible MIC population (> 0.06 microg/mL). All other strains of H. influenzae and M catarrhalis were highly susceptible to the tested quinolones (MIC(90,) < or = 0.016 or 0.03 microg/mL). For the two H. influenzae isolates with elevated quinolone MICs the potency rank order was: gatifloxacin and BMS284756 (MICs, 0.25 and 1 microg/mL) > levofloxacin and moxifloxacin > ciprofloxacin (MICs, 0.5 and > 2 microg/mL). The comparison of Etest (AB BIODISK, Solna, Sweden) and disk diffusion results to the reference broth microdilution values produced acceptable intermethod accuracy when applied to BMS284756. This novel desfluoro compound possesses promising activity against fastidious Gram-negative respiratory tract pathogens and further clinical development is underway.

Clinical perspectives on new antimicrobials: focus on fluoroquinolones

Respiratory tract infections are the most common infectious presentation in the community and hospital settings and are a major cause of morbidity and mortality worldwide. Recently, newer fluoroquinolones have been recommended for the treatment of these infections. Among them, moxifloxacin shows improved activity against gram-positive pathogens, has maintained potency against gram-negative organisms, and shows activity against atypical pathogens and anaerobes. Moxifloxacin also has excellent in vitro activity against strains resistant to penicillin, erythromycin, and other fluoroquinolones, such as levofloxacin. Moxifloxacin has demonstrated clinical efficacy rates of 90%-95% in clinical trials in community-acquired pneumonia, acute exacerbations of chronic bronchitis, and acute sinusitis. In these trials, moxifloxacin demonstrated no serious or unexpected adverse effects. Development of resistance appears to be slower for moxifloxacin than for several other fluoroquinolones, making moxifloxacin a good treatment choice. The pharmacodynamics of moxifloxacin support once-daily oral therapy of short duration, providing convenience, compliance, and safety advantages.

Clinical utility of the new fluoroquinolones for treating respiratory and urinary tract infections

Increasing antimicrobial resistance among most common urinary and respiratory tract pathogens has been the catalyst for the development of fluoroquinolones that are effective against these prevalent resistant organisms. Important attributes of the newly developed fluoroquinolones include once-daily dosing, maintained extensive tissue penetration and high oral bioavailability added to targeted antibacterial activities, all pharmacodynamic characteristics that may reduce the need for parenteral therapy or prevent patients being hospitalised. Some fluoroquinolones also offer same-dose bioequivalency between iv. and oral formulations, a feature that allows iv.-to-oral dosing (step-down or 'switch' therapy) without the need for dosage adjustments. These features suggest that the newer fluoroquinolones may be near-ideal agents for the empirical treatment of many common infections. This review discusses the efficacy and clinically relevant antimicrobial and pharmacokinetic qualities of the fluoroquinolones in comparison with other agents traditionally used to treat patients with urinary and respiratory tract infections.

In vitro activity of newer fluoroquinolones for respiratory tract infections and emerging patterns of antimicrobial resistance: data from the SENTRY antimicrobial surveillance program

In 1997, an international surveillance program, SENTRY Antimicrobial Surveillance Program, was initiated with the aim of tracking the emergence of antimicrobial resistance worldwide. Results from reference antimicrobial susceptibility testing of bacterial pathogens (from bloodstream, inpatient and outpatient lower respiratory tract, urinary tract, and skin and soft-tissue infections) were included in an extensive database used to define antimicrobial resistance patterns throughout the world. On the basis of 1997-1999 test results from the Americas, fluoroquinolones continue to demonstrate potent in vitro activity against Enterobacteriaceae and important pathogens (Haemophilus influenzae, Moraxella catarrhalis, Streptococcus pneumoniae, and atypicals) that cause community-acquired respiratory tract infections. At published breakpoint concentrations, gatifloxacin, levofloxacin, sparfloxacin, grepafloxacin, trovafloxacin, and ciprofloxacin inhibited approximately 100% of H. influenzae isolates, including those that demonstrated resistance to beta-lactams and macrolides. Fluoroquinolones were also active against numerous other gram-negative bacilli and demonstrated high activity against S. pneumoniae and beta-hemolytic or viridans group streptococci. New fluoroquinolones maintain activity against penicillin-resistant strains of S. pneumoniae, with a low overall resistance in this species, even among the most recent (1999) clinical isolates. The SENTRY Antimicrobial Surveillance Program will continue to monitor the antibacterial activity of these newer agents throughout the world, to identify emerging resistant strains and to facilitate possible intervention strategies as these newer compounds are used in the clinic setting.

Antimicrobial activity of advanced-spectrum fluoroquinolones tested against more than 2000 contemporary bacterial isolates of species causing community-acquired respiratory tract infections in the United States (1999)

In vitro activity of four newer fluoroquinolones (clinafloxacin, gemifloxacin, moxifloxacin, sitafloxacin) and an equal number control drugs in the same class (ciprofloxacin, grepafloxacin, levofloxacin, trovafloxacin) was determined by reference dilution tests against 2156 recent United States clinical isolates of Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis. All the fluoroquinolones demonstrated excellent in vitro activity against these pathogens. Streptococcus pneumoniae isolates were fully susceptible to clinafloxacin, sitafloxacin, and gemifloxacin at 0.5 microg/ml, and over 98% of sampled strains had MICs of </=1 microg/ml for grepafloxacin, moxifloxacin and trovafloxacin. Penicillin resistance did not influence the potency of the tested fluoroquinolones. All the isolates of H. influenzae and M. catarrhalis were inhibited by the investigational, as well as comparator fluoroquinolones at </=0.5 microg/ml, irrespective of their beta-lactamase producing abilities. In conclusion, the investigational fluoroquinolones demonstrated excellent activity against these major respiratory tract pathogens isolated in 1999, and some remain safe candidates for empiric therapy of community-acquired respiratory tract infections and selected infections in hospitalized patients.

Fluoroquinolone-resistant Haemophilus influenzae: frequency of occurrence and analysis of confirmed strains in the SENTRY antimicrobial surveillance program (North and Latin America)

The incidence of fluoroquinolone-resistant (FQR) Haemophilus influenzae and Moraxella catarrhalis isolated from clinical specimens remains very rare, and the identification of such strains has been previously limited to case reports from diverse geographic locations. During the 1997 through 1998 SENTRY Antimicrobial Surveillance Program, four FQR-H. influenzae (0.13% of all strains) and one FQR-M. catarrhalis strains were identified and confirmed as having elevated MICs to > or =5 FQ class drugs. Among H. influenzae strains, MICs to marketed FQs were > or =0.12 microg/ml with ciprofloxacin MIC results > or =8-fold higher than wild type susceptible strains. The FQR-H. influenzae isolates were then compared with two previously reported strains that were determined to be identical using ribotyping and other molecular methods. In contrast, the SENTRY isolates were all genetically distinct and had mutations in parC and/or gyrA. Isolates having the lowest MIC elevations had a single mutation in gyrA, while isolates with higher MICs had at least one mutation in both studied genes. In general, the single gyr A mutations involved the same position but differed in the amino acid substitution (Ser84Leu or Phe or Ala). The isolates reported outside the SENTRY Program (controls) had an unusual mutation in par C (Gly82Asp) and two mutations in gyr A; producing the highest recorded FQR MICs. The FQR-M. catarrhalis strain was discovered in late 1997 and has been reported before. Although detection of these FQR isolates remains at <1% of all contemporary H. influenzae and M. catarrhalis isolates, surveillance programs will be an important detection method to determine the extent of emerging novel resistance patterns among clinically prevalent fastidious pathogens.

A review of clinical trials with fluoroquinolones with an emphasis on new agents

This review aims to provide a comparison between the antimicrobial spectra, pharmacokinetics and clinical efficacy of the newer fluoroquinolones with older agents in this class, as well as other antibiotics used to treat lower respiratory and urinary tract infections (LRTIs and UTIs) respectively. Increasing antimicrobial resistance among common uro- and respiratory pathogens has focused attention on the development of fluoroquinolones, which have a broad spectrum of activity and improved tissue penetration. The new and developmental quinolones can be administered on a once-daily basis and exhibit high oral bioavailability, which reduces the need for parenteral therapy in hospitalised patients and may therefore potentially reduce the need for hospitalisation. These attributes, coupled with their expanded spectrum suggest that the newer fluoroquinolones are so far the most ideal agents for the empirical treatment of many common infections.