Fluoroquinolone-resistant Streptococcus pneumoniae in Spain: activities of garenoxacin against clinical isolates including strains with altered topoisomerases

Garenoxacin pharmacokinetics in patients undergoing maintenance hemodialysis

INTRODUCTION

Studies on the pharmacokinetics of the antibiotic garenoxacin (GRNX) in patients with renal insufficiency are lacking. In this study, we attempted to ascertain the appropriate dose of GRNX in patients undergoing maintenance hemodialysis (MH) based on pharmacokinetic parameters and clinical outcomes.

METHODS

Six male patients with infections who were undergoing MH received 200 mg GRNX once daily. Blood samples were taken before and at 1, 2, 4, 6, 12, and 24 hours after GRNX administration. Plasma GRNX concentrations were measured using high-performance liquid chromatography.

FINDINGS

The mean maximum plasma concentration (C_max ) was 3.00 ± 1.12 µg/mL, time to maximum plasma concentration (T_max ) was 3.0 ± 2.0 hours, and area under the curve for 24 hours (AUC_0-24 ) was 40.7 ± 16.7 µg·h/mL. The half-life (T_1/2 ) of GRNX could not be calculated because plasma concentrations remained high 24 hours after administration. C_max was strongly associated with the GRNX dose per kilogram body weight (r = 0.85, P = 0.03). Clinically, fever resolved within 3 days of GRNX administration and C-reactive protein levels returned to normal 14 days after administration. One patient experienced temporary increases in serum transaminase levels.

DISCUSSION

MH patients receiving 200 mg GRNX once daily for infection showed a reduced C_max but similar AUC_0-24 compared with healthy individuals. While this study evaluated the effect of GRNX treatment, further research is needed to assess the accumulation of GRNX and the impact of continuous administration on its pharmacokinetics, as well as to prevent the development of resistant mutants.

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.

In vitro pharmacodynamics of moxifloxacin versus levofloxacin against 4 strains of Streptococcus pneumoniae: 1 wild type, 2 first-step parC mutants, and 1 pump mutant

Levofloxacin binds topoisomerase IV, whereas moxifloxacin preferentially binds DNA gyrase. Most 1st-step pneumococcal mutants have alterations in the parC gene of topoisomerase IV. Because of differential binding affinity, moxifloxacin may have superior activity against 1st-step mutants compared with levofloxacin. The purpose of this work was to compare rates and extent of bacterial killing of genetically characterized Streptococcus pneumoniae with moxifloxacin and levofloxacin. Four strains of S. pneumoniae were used: a wild type, 2 first-step parC mutants, and a pump mutant. Using an in vitro pharmacodynamic model run in duplicate, we exposed bacteria to unbound moxifloxacin and levofloxacin peaks of 2 and 4.5 mg/L, respectively, which emulated clinical dosing. Additional experiments were done in which the area under the curve (AUC)/MIC ratio of 1 agent was matched to the competing drug's clinical dose AUC/MIC ratio. Time kill curves were analyzed for rate and extent of bacterial kill and regrowth. Pre- and postexposure MIC and polymerase chain reaction (PCR) testing were done. Moxifloxacin and levofloxacin displayed similar rates and extent of bacterial kill for the wild type, efflux pump type, and parC mutant 27-1361B. Moxifloxacin initially achieved a faster rate of kill, regardless of the AUC/MIC ratio, against parC mutant 7362 (P < 0.05) but not an advantage in time to 3 log kill. Postexposure MIC values were elevated for strain 7362 in 2 moxifloxacin experiments and 1 levofloxacin experiment. Post-PCR analysis revealed new gyrA mutations for all 3 isolates. Both moxifloxacin and levofloxacin are effective against multiple strains of S. pneumoniae.

Garenoxacin activity against isolates form patients hospitalized with community-acquired pneumonia and multidrug-resistant Streptococcus pneumoniae

Community-acquired pneumonia (CAP) continues to cause significant morbidity worldwide, and the principal bacterial pathogens (Streptococcus pneumoniae and Haemophilus influenzae) have acquired numerous resistance mechanisms over the last few decades. CAP treatment guidelines have suggested the use of broader spectrum agents, such as antipneumococcal fluoroquinolones as the therapy for at-risk patient population. In this report, we studied 3087 CAP isolates from the SENTRY Antimicrobial Surveillance Program (1999-2005) worldwide and all respiratory tract infection (RTI) isolate population of pneumococci (14665 strains) grouped by antibiogram patterns against a new des-F(6)-quinolone, garenoxacin. Results indicated that garenoxacin was highly active against CAP isolates of S. pneumoniae (MIC(90), 0.06 microg/mL) and H. influenzae (MIC(90), < or =0.03 microg/mL). This garenoxacin potency was 8- to 32-fold greater than gatifloxacin, levofloxacin, and ciprofloxacin against the pneumococci and >99.9% of strains were inhibited at < or =1 microg/mL (proposed susceptible breakpoint). Garenoxacin MIC values were not affected by resistances among S. pneumoniae strains to penicillin or erythromycin; however, coresistances were high among the beta-lactams (penicillins and cephalosporins), macrolides, tetracyclines, and trimethoprim/sulfamethoxazole. Analysis of S. pneumoniae isolates with various antimicrobial resistance patterns to 6 drug classes demonstrated that garenoxacin was active against >99.9% (MIC, < or =1 microg/mL) of strains, and the most resistant pneumococci (6-drug resistance, 1051 strains or 7.2% of all isolates) were completely susceptible (100.0% at < or =1 microg/mL) to garenoxacin (MIC(90), 0.06 microg/mL). These results illustrate the high activity of garenoxacin against contemporary CAP isolates and especially against multidrug-resistant (MDR) S. pneumoniae that have created therapeutic dilemmas for all RTI presentations. Garenoxacin appears to be a welcome addition to the CAP treatment options, particularly for the emerging MDR pneumococci strains.

Emergence of a Streptococcus pneumoniae clinical isolate highly resistant to telithromycin and fluoroquinolones

Streptococcus pneumoniae is a major pathogen causing community-acquired pneumonia and acute bronchitis. Macrolides, fluoroquinolones (FQs), and, recently, telithromycin (TEL) constitute primary therapeutic options, and rare cases of resistance have been reported. In this report, we describe the emergence of an S. pneumoniae clinical isolate with high-level TEL resistance (MIC, 256 microg/ml) and simultaneous resistance to FQs. Ongoing studies are oriented to elucidate the precise mechanism of resistance to TEL.

Antimicrobial Resistance amongStreptococcus pneumoniaein the United States: Have We Begun to Turn the Corner on Resistance to Certain Antimicrobial Classes?

BACKGROUND

Antimicrobial resistance has emerged as a major problem in Streptococcus pneumoniae in the United States during the past 15 years. This study was undertaken to elucidate the current scope and magnitude of this problem in the United States and to assess resistance trends since 1994-1995.

METHODS

A total of 1817 S. pneumoniae isolates obtained from patients with community-acquired respiratory tract infections in 44 US medical centers were characterized during the winter of 2002-2003. The activity of 27 antimicrobial agents was assessed. In addition, selected isolates were examined for the presence of mutations in the quinolone-resistance determining regions (QRDRs) of parC and gyrA that resulted in diminished fluoroquinolone activity. The results of this survey were compared with the results of 4 previous surveys conducted in a similar manner since 1994-1995.

RESULTS

Overall rates of resistance (defined as the rate of intermediate resistance plus the rate of resistance) were as follows: penicillin, 34.2%; ceftriaxone, 6.9%; erythromycin, 29.5%; clindamycin, 9.4%; tetracycline, 16.2%; and trimethoprim-sulfamethoxazole (TMP-SMX), 31.9%. No resistance was observed with vancomycin, linezolid, or telithromycin; 22.2% of isolates were multidrug resistant; 2.3% of isolates had ciprofloxacin MICs of >or=4.0 microg/mL. It was estimated that 21.9% of the isolates in this national collection had mutations in the QRDRs of parC and/or gyrA, with parC only mutations occurring most often (in 21% of all isolates). Trend analysis since 1994-1995 indicated that rates of resistance to beta -lactams, macrolides, tetracyclines, TMP-SMX, and multiple drugs have either plateaued or have begun to decrease. Conversely, fluoroquinolone resistance among S. pneumoniae is becoming more prevalent.

CONCLUSION

It appears that, as fluoroquinolone resistance emerges among S. pneumoniae in the United States, resistance to other antimicrobial classes is becoming less common.

Quinolone resistance in bacteria: emphasis on plasmid-mediated mechanisms

Bacterial resistance to quinolones/fluoroquinolones has emerged rapidly and such resistance has traditionally been attributed to the chromosomally mediated mechanisms that alter the quinolone targets (i.e. DNA gyrase and topoisomerase IV) and/or overproduce multidrug resistance efflux pumps. However, the discovery of the plasmid-borne quinolone resistance determinant, named qnr, has substantially broadened our horizon on the molecular mechanisms of quinolone resistance. Several recent reports of Qnr or its homologues encoded by transferable plasmids in Gram-negative bacteria isolated worldwide highlight the significance of the emerging plasmid-mediated mechanism(s). This also alerts us to the potential rapid dissemination of quinolone resistance determinants. Qnr belongs to the pentapeptide repeat family and protects DNA gyrase from the action of quinolone agents including the newer fluoroquinolones. This protection interplays with chromosomal mechanisms to raise significantly the resistance levels. The qnr-bearing strains generate quinolone-resistant mutants at a much higher frequency than those qnr-free strains. Furthermore, the qnr-plasmids are integron-associated and carry multiple resistance determinants providing resistance to several classes of antimicrobials including beta-lactams and aminoglycosides. The high quinolone resistance rates in Escherichia coli are used to address issues of quinolone resistance, and possible strategies for minimising quinolone resistance are discussed.

Risk factors associated with colonization by pneumococci with reduced susceptibility to fluoroquinolones in adult outpatients

We developed a case-control study in order to identify risk factors associated with pharyngeal colonization by Streptococcus pneumoniae with reduced susceptibility to fluoroquinolones (ciprofloxacin MIC, > or =4 microg/ml). A total of 400 patients were studied for colonization by quinolone-nonsusceptible S. pneumoniae (QNSP) isolates and risk factors for this colonization. Isolate susceptibility was determined by the agar dilution method. Forty patients were colonized by QNSP (case patients), and 360 patients were not colonized by QNSP (control patients). The MIC range of ciprofloxacin for QNSP isolates was 4 to 8 microg/ml. No isolates were resistant to levofloxacin and moxifloxacin. Risk factors significantly associated with QNSP colonization, according to univariate analysis, were recent hospitalizations (odds ratio [OR], 3.43; 95% confidence interval [CI], 1.6 to 7.2; P < 0.01) and prior exposure to fluoroquinolones (OR, 6.04; 95% CI, 3.0 to 12.0; P < 0.01). Other factors such as chronic obstructive pulmonary disease (OR, 1.94; 95% CI; 0.7 to 5.0), prior exposure to penicillins (OR, 1,68; 95% CI, 0.8 to 3.3) and prior exposure to macrolides (OR 2; 95% CI, 0.6 to 6.2) were more frequent among patients colonized with QNSP, but there was no statistical significance. Multivariate analysis showed that exposure to fluoroquinolones was the only independent factor associated with colonization by QNSP (OR, 4.2; 95% CI, 1.8 to 9.4; P < 0.01). Throat colonization by QNSP is becoming frequent, though most of these isolates (all the isolates in this case) remain susceptible to newer fluoroquinolones. Previous treatment with fluoroquinolones seems to be the main risk factor associated with colonization by QNSP.

Antibacterial susceptibility testing in the clinical laboratory

This article familiarizes the clinician with the principles of bacterial susceptibility testing and reporting to facilitate communication with the clinical microbiology laboratory. The emergence of resistance in nearly all commonly isolated bacterial organisms has highlighted the need for ongoing dialogue between the laboratory and those who use its services.