In vitro susceptibility study of BMS-284756 against Legionella species

In vitro activity of various antibiotics against clinical strains of Legionella species isolated in Japan

The activities of various antibiotics against 58 clinical isolates of Legionella species were evaluated using two methods, extracellular activity (minimum inhibitory concentration [MIC]) and intracellular activity. Susceptibility testing was performed using BSYEα agar. The minimum extracellular concentration inhibiting intracellular multiplication (MIEC) was determined using a human monocyte-derived cell line, THP-1. The most potent drugs in terms of MICs against clinical isolates were levofloxacin, garenoxacin, and rifampicin with MIC₉₀ values of 0.015 μg/ml. The activities of ciprofloxacin, pazufloxacin, moxifloxacin, clarithromycin, and azithromycin were slightly higher than those of levofloxacin, garenoxacin, and rifampicin with an MIC₉₀ of 0.03-0.06 μg/ml. Minocycline showed the highest activity, with an MIC₉₀ of 1 μg/ml. No resistance against the antibiotics tested was detected. No difference was detected in the MIC distributions of the antibiotics tested between L. pneumophila serogroup 1 and L. pneumophila non-serogroup 1. The MIECs of ciprofloxacin, pazufloxacin, levofloxacin, moxifloxacin, garenoxacin, clarithromycin, and azithromycin were almost the same as their MICs, with MIEC₉₀ values of 0.015-0.06 μg/ml, although the MIEC of minocycline was relatively lower and that of rifampicin was higher than their respective MICs. No difference was detected in the MIEC distributions of the antibiotics tested between L. pneumophila serogroup 1 and L. pneumophila non-serogroup 1. The ratios of MIEC:MIC for rifampicin (8) and pazufloxacin (2) were higher than those for levofloxacin (1), ciprofloxacin (1), moxifloxacin (1), garenoxacin (1), clarithromycin (1), and azithromycin (1). Our study showed that quinolones and macrolides had potent antimicrobial activity against both extracellular and intracellular Legionella species. The present data suggested the possible efficacy of these drugs in treatment of Legionella infections.

Clinical presentation of Legionella pneumonia: Evaluation of clinical scoring systems and therapeutic efficacy

To evaluate scoring systems to predict Legionella pneumonia and therapeutic efficacy against Legionella pneumonia, the Japanese Society of Chemotherapy Legionella committee has collected data on cases of Legionella pneumonia from throughout Japan. We analyzed 176 patients with Legionella pneumonia and compared them with 217 patients with Streptococcus pneumoniae pneumonia and 202 patients with Mycoplasma pneumoniae pneumonia. We evaluated four scoring systems, the Winthrop-University Hospital score, Community-Based Pneumonia Incidence Study Group score, and Japan Respiratory Society score, but they demonstrated limited sensitivity and specificity for predicting Legionella pneumonia. Using six clinical and laboratory parameters (high fever, high C-reactive protein, high lactate dehydrogenase, thrombocytopenia, hyponatremia, and unproductive cough) reported by Fiumefreddo and colleagues, only 6% had Legionnella pneumonia when less than 2 parameters were present. The efficacy rates of antibiotics at the time of termination were 94.6% for intravenous antibiotics, including ciprofloxacin and pazufloxacin, and 95.5% for oral antibiotics, including ciprofloxacin, levofloxacin, garenoxacin, moxifloxacin, and clarithromycin. Our results suggested that the previously reported clinical scoring systems to predict Legionnella pneumonia are not useful, but 6 simple diagnostic score accurately ruled out Legionnella pneumonia, which may help to optimize initial empiric therapy. Quinolones and clarithromycin still showed good clinical efficacy against Legionella pneumonia.

A Review of New Fluoroquinolones : Focus on their Use in Respiratory Tract Infections

The new respiratory fluoroquinolones (gatifloxacin, gemifloxacin, levofloxacin, moxifloxacin, and on the horizon, garenoxacin) offer many improved qualities over older agents such as ciprofloxacin. These include retaining excellent activity against Gram-negative bacilli, with improved Gram-positive activity (including Streptococcus pneumoniae and Staphylococcus aureus). In addition, gatifloxacin, moxifloxacin and garenoxacin all demonstrate increased anaerobic activity (including activity against Bacteroides fragilis). The new fluoroquinolones possess greater bioavailability and longer serum half-lives compared with ciprofloxacin. The new fluoroquinolones allow for once-daily administration, which may improve patient adherence. The high bioavailability allows for rapid step down from intravenous administration to oral therapy, minimizing unnecessary hospitalization, which may decrease costs and improve quality of life of patients. Clinical trials involving the treatment of community-acquired respiratory infections (acute exacerbations of chronic bronchitis, acute sinusitis, and community-acquired pneumonia) demonstrate high bacterial eradication rates and clinical cure rates. In the treatment of community-acquired respiratory tract infections, the various new fluoroquinolones appear to be comparable to each other, but may be more effective than macrolide or cephalosporin-based regimens. However, additional data are required before it can be emphatically stated that the new fluoroquinolones as a class are responsible for better outcomes than comparators in community-acquired respiratory infections. Gemifloxacin (except for higher rates of hypersensitivity), levofloxacin, and moxifloxacin have relatively mild adverse effects that are more or less comparable to ciprofloxacin. In our opinion, gatifloxacin should not be used, due to glucose alterations which may be serious. Although all new fluoroquinolones react with metal ion-containing drugs (antacids), other drug interactions are relatively mild compared with ciprofloxacin. The new fluoroquinolones gatifloxacin, gemifloxacin, levofloxacin, and moxifloxacin have much to offer in terms of bacterial eradication, including activity against resistant respiratory pathogens such as penicillin-resistant, macrolide-resistant, and multidrug-resistant S. pneumoniae. However, ciprofloxacin-resistant organisms, including ciprofloxacin-resistant S. pneumoniae, are becoming more prevalent, thus prudent use must be exercised when prescribing these valuable agents.

Penetration of garenoxacin into lung tissues and bone in subjects undergoing lung biopsy or resection

OBJECTIVE

Concentrations of garenoxacin in plasma and samples of lung parenchyma, bronchial mucosa, and bone were determined following single-dose administration.

RESEARCH DESIGN AND METHODS

Open-label, non-randomized study in which subjects undergoing invasive lung biopsy or resection were given a single 600-mg oral dose of garenoxacin. Lung parenchyma, and, if possible, bronchial mucosa and bone (i.e., flat bone with sinus mucosa or long bone from the lower legs) samples and corresponding plasma samples were obtained 2-4, 4-6, 10-12, or 20-24 h post-dose. Garenoxacin concentrations were measured using validated liquid chromatography with dual mass spectrometry. Safety was also assessed.

RESULTS

Twenty-seven subjects enrolled and completed the study. Garenoxacin plasma concentrations (mean +/- standard deviation) during the 24-h period ranged from 1.9 +/- 1 to 7.4 +/- 3 mug/mL. Garenoxacin concentrations in lung tissue (15.2 +/- 9 mug/g) peaked at 4-6 h and decreased to 3.7 +/- 3 mug/g at 20-24 h. Mean ratios between bronchial mucosa and plasma ranged from 0.82 to 0.99 over a 24-h period. At 12 h, the mean ratio between bone and plasma was 0.56. Garenoxacin concentrations in lung tissue exceeded the MIC(90) for common respiratory pathogens by at least 61-fold. Garenoxacin was safe and well tolerated. Forty-five adverse events were reported by 26 subjects; none were determined to be attributable to garenoxacin by the investigators. Most of the adverse events were mild to moderate in severity.

CONCLUSIONS

Garenoxacin achieved 24-h concentrations in pulmonary tissues that exceeded the MIC(90) for common respiratory pathogens. A controlled study involving a larger number of lung and bone tissue samples is needed to further confirm these findings.

Retrospective analysis of electrocardiographic changes after administration of oral or intravenous garenoxacin in five phase I, placebo-controlled studies in healthy volunteers

BACKGROUND

Certain fluoroquinolones and macrolide antibiotics have been associated with prolongation of the corrected QT (QTc) interval or QT dispersion, leading to cardiac arrhythmias. Garenoxacin is a des-F(6)-quinolone with broad-spectrum antimicrobial activity and a favorable pharmacokinetic/pharmacodynamic profile. Its effects on electrocardiographic (ECG) parameters in healthy volunteers have not been reported.

OBJECTIVE

The cardiac safety profile of garenoxacin was further examined using data from healthy volunteers enrolled in 5 dose-ranging and comparative Phase I clinical studies.

METHODS

This was a retrospective analysis of 5 randomized, double-blind, placebo-controlled studies in which 224 healthy volunteers received oral or intravenous garenoxacin (50-1200 mg/d) for 1 to 28 days' dosing duration (<or=14 days' therapeutic duration). The effects of garenoxacin on the QT interval corrected using Bazett's formula (QTcB) and Fridericia's formula (QTcF) and the PR interval were assessed by counts of outliers, linear regressions, and exposure-response plots. Absence of a concentration-dependent effect of garenoxacin on changes from baseline ECG parameters was concluded if the 95% CI for the linear regression slopes of derived QTc- or PR-interval parameters relative to Cmax and C(avg0-12) (average garenoxacin plasma concentration from 0-12 hours after dosing) values for garenoxacin contained zero.

RESULTS

No clinically relevant changes in the QTc or PR intervals were observed over a range of garenoxacin plasma concentrations (Cmax: 0.5-38.6 microg/mL, oral dose range; 3.36-21.4 microg/mL, intravenous dose range). No volunteer had a prolongation from baseline that exceeded established thresholds for the QTcB or QTcF interval (>450 milliseconds for men, >470 milliseconds for women) or the PR interval (>250 milliseconds). One subject had a change in QTcB of 67 milliseconds 4 hours after administration of garenoxacin 400 mg PO on day 7, but the actual value was 418 milliseconds (baseline, 351 milliseconds); the corresponding change in QTcF was 49 milliseconds (actual, 408 milliseconds; baseline, 359 milliseconds). The means for other derived ECG parameters were generally similar between garenoxacin-treated volunteers and placebo controls.

CONCLUSION

In this retrospective analysis of data from healthy volunteers, garenoxacin had no clinically relevant dose-, route-of-administration-, or concentration-dependent effects on the QTc or PR interval across a dose range from 50 to 1200 mg/d.

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.

In vitro activity of pazufloxacin, tosufloxacin and other quinolones against Legionella species

OBJECTIVES

The activities of pazufloxacin and tosufloxacin against Legionella spp. were evaluated in vitro and compared with those of other quinolones, macrolides and azithromycin.

METHODS

The conventional MICs were determined by the microbroth dilution method. Intracellular activities of drugs were evaluated by a cfu count. The minimal extracellular concentration inhibiting intracellular growth of bacteria (MIEC) was determined by a colorimetric cytopathic assay.

RESULTS

MICs of pazuloxacin and tosufloxacin at which 90% (MIC90) of isolates are inhibited in 76 different Legionella spp. strains (38 ATCC strains and 38 clinical isolates) were 0.032 and 0.016 mg/L, whereas the MIC90s of levofloxacin, ciprofloxacin, garenoxacin, erythromycin, clarithromycin and azithromycin were 0.032, 0.032, 0.032, 2.0, 0.125 and 2.0 mg/L, respectively. Pazufloxacin and tosufloxacin at 4x MIC inhibited intracellular growth of Legionella pneumophila SG1 (80-045 strain), as did other quinolones, clarithromycin and azithromycin, whereas erythromycin at 4x MIC did not. MIECs of pazufloxacin, tosufloxacin, levofloxacin, ciprofloxacin and garenoxacin for the strain were 0.063, 0.004, 0.016, 0.032 and 0.008 mg/L respectively, which were superior to those of macrolides and azithromycin. Pazufloxacin showed potent activity against three additional clinical isolates of L. pneumophila SG1, one clinical isolate each of L. pneumophila SG3 and SG5, as well as Legionella micdadei, Legionella dumoffii and Legionella longbeachae SG1.

CONCLUSIONS

Pazufloxacin and tosufloxacin, as well as other quinolones, were more potent than macrolides and an azalide. Present data warrant further study on the efficacy of these drugs in the treatment of Legionella infections.

Pharmacodynamic studies of moxifloxacin and erythromycin against intracellular Legionella pneumophila in an in vitro kinetic model

BACKGROUND

Newer quinolones are highly active against Legionella pneumophila. Since this pathogen is intracellular, standard in vitro susceptibility tests may not accurately predict clinical efficacy. Few models for studies of intracellular Legionella have been described. In this study, we determined the pharmacodynamic activity of moxifloxacin against intracellular L. pneumophila in comparison with erythromycin.

METHODS

A kinetic model for intracellular studies was constructed in which human pharmacokinetics could be simulated. The model consisted of a glass chamber with two exits and a metal rack fitting cell culture inserts. The inserts had a bottom membrane where cells could be cultured while nutrients and antibiotics passed through. The inserts were prepared with a monolayer of HEp-2 cells, which were exposed to a culture of L. pneumophila. At regular intervals cells were harvested and lysed, viable intracellular bacteria counted and compared with untreated controls.

RESULTS

The MICs were 0.0156 mg/L for moxifloxacin and 0.5 mg/L for erythromycin. The human pharmacokinetics were simulated in the model with a mean initial antibiotic concentration of 2.4 mg/L for moxifloxacin and 8.4 mg/L for erythromycin. The mean half-life was 9 h for moxifloxacin and 3.4 h for erythromycin. At 12 h, a 2 log(10) reduction in bacterial counts was seen in cells treated with moxifloxacin and no regrowth was detected at 24 h. Cells treated with erythromycin showed no reduction in intracellular L. pneumophilia at 12 h or 24 h. In experiments using static concentrations of 9 mg/L of erythromycin, similar results were obtained.

CONCLUSIONS

In this model, moxifloxacin exerts a significantly better antibacterial effect against intracellular L. pneumophila compared with erythromycin.

In vitro activity of garenoxacin against recent clinical isolates of Chlamydia pneumoniae

The in vitro activities of garenoxacin, a novel des-F (6)-quinolone, levofloxacin, moxifloxacin and clarithromycin were tested against 30 recent clinical isolates of Chlamydia pneumoniae. The minimal inhibitory concentration (MIC) at which 90% of the isolates were inhibited and the minimal bactericidal concentration (MBC) at which 90% of the isolates were killed by garenoxacin for C. pneumoniae was 0.03 mg/l (range 0.015-0.03 mg/l).

In vitro susceptibilities to and bactericidal activities of garenoxacin (BMS-284756) and other antimicrobial agents against human mycoplasmas and ureaplasmas

The in vitro susceptibilities to garenoxacin (BMS-284756), an investigational des-fluoroquinolone, and eight other agents were determined for 63 Mycoplasma pneumoniae, 45 Mycoplasma hominis, 15 Mycoplasma fermentans, and 68 Ureaplasma sp. isolates. Garenoxacin was the most active quinolone, inhibiting all isolates at <or=1 microg/ml. The garenoxacin MIC at which 90% of isolates are inhibited (MIC(90)s; <or=0.008 microg/ml) was at least 4-fold less than those of moxifloxacin and clindamycin, 8-fold less than that of sparfloxacin, and 64-fold less than those of levofloxacin and ciprofloxacin for M. pneumoniae. For M. hominis, the garenoxacin MIC(90) (<or=0.008 microg/ml) was 4-fold less than those of clindamycin and moxifloxacin, 8-fold less than that of sparfloxacin, and 64-fold less than those of levofloxacin and ciprofloxacin. All 15 M. fermentans isolates were inhibited by garenoxacin at concentrations <or=0.008 microg/ml, making it the most active drug tested against this organism. For Ureaplasma spp., the garenoxacin MIC(90) (0.25 microg/ml) was equivalent to those of moxifloxacin and doxycycline, 4-fold less than those of levofloxacin and sparfloxacin, 8-fold less than that of azithromycin, and 32-fold less than that of ciprofloxacin. Garenoxacin and the other fluoroquinolones tested were demonstrated to have bactericidal activities against M. pneumoniae and M. hominis by measurement of minimal bactericidal activities and by time-kill studies. Further study of garenoxacin is required, as it has great potential for use in the treatment of infections due to mycoplasmas and ureaplasmas.

Actividad in vitro comparativa de garenoxacino (BMS-284756). Programa SENTRY España (1999-2000)

INTRODUCTION

To evaluate the in vitro activity of the new des-fluoro quinolone, garenoxacin (BMS-284756), compared to activities of ciprofloxacin, levofloxacin, and gatifloxacin in clinical isolates recovered over 1999 and 2000 within the SENTRY antimicrobial surveillance program.

METHODS

Quinolone-MICs were performed using the standard NCCLS microdilution technique in 2599 isolates recovered from Hospital Ramón y Cajal (Madrid), Virgen Macarena (Sevilla), and Bellvitge (Barcelona).

RESULTS

The modal MIC range value exhibited by garenoxacin ( < or = 0.03-0.12 mg/L) for Enterobacteriaceae was similar to that of the other quinolones tested. A total of 70% of Pseudomonas aeruginosa isolates were susceptible to garenoxacin and 85% to ciprofloxacin and levofloxacin. Garenoxacin exhibited the highest activity in Staphylococcus aureus, including both methicillin-susceptible and -resistant isolates, with MIC90 values of < or = 0.03 and 2 mg/L, respectively. All Streptococcus pneumoniae isolates were susceptible to garenoxacin, regardless of their penicillin susceptibility status; in terms of MIC90, garenoxacin was 16 times more active than ciprofloxacin and levofloxacin and 4-8 times more active than gatifloxacin. All 6 ciprofloxacin-resistant S. pneumoniae strains showed garenoxacin MIC values ranging from < or = 0.03 to 0.5 mg/L. In Haemophilus influenzae and Moraxella catarrhalis, garenoxacin displayed excellent in vitro activity (MIC < or = 0.06 mg/L), similar to that of the other quinolones tested.

CONCLUSIONS

Garenoxacin activity was similar to the activity of other quinolones in Enterobacteriaceae, but was lower in P. aeruginosa. Garenoxacin activity was clearly higher than that of other quinolones in gram-positive isolates, including methicillin-resistant S. aureus and S. pneumoniae with reduced penicillin susceptibility.