Antibacterial properties of AM-1155, a new 8-methoxy quinolone

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.

Pharmacokinetics of gatifloxacin in broiler chickens following intravenous and oral administration

1. The pharmacokinetics of gatifloxacin were investigated following intravenous and oral administration of a single dose at a rate of 10 mg/kg body weight in broiler chicks. 2. Drug concentration in plasma was determined using High Performance Liquid Chromatography with ultraviolet detection on samples collected at frequent intervals after drug administration. 3. Following intravenous administration, the drug was rapidly distributed (t(1/2α): 0·33 ± 0·008 h) and eliminated (t(1/2β): 3·62 ± 0·03 h; Cl(B): 0·48 ± 0·002 l/h/kg) from the body. 4. After oral administration, the drug was rapidly absorbed (C (max): 1·74 ± 0·024 µg/mL; T (max): 2 h) and slowly eliminated (t(1/2β): 3·81 ± 0·07 h) from the body. The apparent volume of distribution (V(d(area))), total body clearance (Cl(B)) and mean residence time (MRT) were 3·61 ± 0·04 l/kg, 0·66 ± 0·01 l/h/kg and 7·16 ± 0·08 h, respectively. The oral bioavailability of gatifloxacin was 72·96 ± 1·10 %. 5. Oral administration of gatifloxacin at 10 mg/kg is likely to be highly efficacious against susceptible bacteria in broiler chickens.

Gatifloxacin phase IV surveillance trial (TeqCES study) utilizing 5000 primary care physician practices: report of pathogens isolated and susceptibility patterns in community-acquired respiratory tract infections

Recently FDA-approved fluoroquinolones like gatifloxacin possess enhanced activity against Gram-positive pathogens such as Streptococcus pneumoniae. However, experience with adverse events among previously used fluoroquinolones has led to expanded post-marketing investigations of clinical efficacy and safety. An open-label gatifloxacin trial was initiated in early 2000, using 2795 (>15000 enrolled cases) primary care providers for treatment of community-acquired respiratory tract infections (CARTI) such as community-acquired pneumonia (CAP), acute bacterial exacerbation of chronic bronchitis (ABECB), acute sinusitis. Microbiology specimens and sputum slides were referred to a reference laboratory, pathogens identified and reference antimicrobial susceptibility tests performed. Results were classified by infection site, geographic census region and patient profile/demographics. The most frequent pathogens were: for CAP (n = 384)-S. pneumoniae (37%) > Hemophilus influenzae (31%) > Moraxella catarrhalis (13%); for ABECB (528)-H. influenzae (37%) > M. catarrhalis (26%) > S. pneumoniae (17%); and for sinusitis (2691)-M. catarrhalis (29%) > H. influenzae (24%) > S. pneumoniae (17%). H. parainfluenzae (ABECB) and S. aureus (sinusitis) were also commonly isolated. CAP S. pneumoniae isolates had significantly less high-level resistance (5% at > or =2 micro g/ml) than those isolates from ABECB or sinusitis (13-15%). United States census zone differences in S. pneumoniae resistance were identified (greatest in West or East South Central, South Atlantic). S. pneumoniae macrolide resistance was high (23-33%) and H. influenzae clarithromycin susceptibility was only 56-62%. beta-lactamase rates in H. influenzae and M. catarrhalis were 21-29% and 88-92%, respectively. Only one S. pneumoniae was not susceptible to gatifloxacin, and this new fluoroquinolone was fourfold more potent than levofloxacin (MIC(50,) 0.25 vs. 1 micro g/ml). This Phase IV surveillance trial (TeqCES) confirmed the clinical importance of S. pneumoniae, H. influenzae and M. catarrhalis in CARTI, and high fluoroquinolone potency/spectrum (>97% susceptible). beta-lactams and macrolides continue to be compromised by increasing resistances in pathogens isolated in these monitored primary care settings.

A critical review of the fluoroquinolones: focus on respiratory infections

The new fluoroquinolones (clinafloxacin, gatifloxacin, gemifloxacin, grepafloxacin, levofloxacin, moxifloxacin, sitafloxacin, sparfloxacin and trovafloxacin) offer excellent activity against Gram-negative bacilli and improved Gram-positive activity (e.g. against Streptococcus pneumoniae and Staphylococcus aureus) over ciprofloxacin. Ciprofloxacin still maintains the best in vitro activity against Pseudomonas aeruginosa. Clinafloxacin, gatifloxacin, moxifloxacin, sitafloxacin, sparfloxacin and trovafloxacin display improved activity against anaerobes (e.g. Bacteroides fragilis) versus ciprofloxacin. All of the new fluoroquinolones display excellent bioavailability and have longer serum half-lives than ciprofloxacin allowing for once daily dose administration. Clinical trials comparing the new fluoroquinolones to each other or to standard therapy have demonstrated good efficacy in a variety of community-acquired respiratory infections (e.g. pneumonia, acute exacerbations of chronic bronchitis and acute sinusitis). Limited data suggest that the new fluoroquinolones as a class may lead to better outcomes in community-acquired pneumonia and acute exacerbations of chronic bronchitis versus comparators. Several of these agents have either been withdrawn from the market, had their use severely restricted because of adverse effects (clinafloxacin because of phototoxicity and hypoglycaemia; grepafloxacin because of prolongation of the QTc and resultant torsades de pointes; sparfloxacin because of phototoxicity; and trovafloxacin because of hepatotoxicity), or were discontinued during developmental phases. The remaining fluoroquinolones such as gatifloxacin, gemifloxacin, levofloxacin and moxifloxacin have adverse effect profiles similar to ciprofloxacin. Extensive post-marketing safety surveillance data (as are available with ciprofloxacin and levofloxacin) are required for all new fluoroquinolones before safety can be definitively established. Drug interactions are limited; however, all fluoroquinolones interact with metal ion containing drugs (eg. antacids). The new fluoroquinolones (gatifloxacin, gemifloxacin, levofloxacin and moxifloxacin) offer several advantages over ciprofloxacin and are emerging as important therapeutic agents in the treatment of community-acquired respiratory infections. Their broad spectrum of activity which includes respiratory pathogens such as penicillin and macrolide resistant S. pneumoniae, favourable pharmacokinetic parameters, good bacteriological and clinical efficacy will lead to growing use of these agents in the treatment of community-acquired pneumonia, acute exacerbations of chronic bronchitis and acute sinusitis. These agents may result in cost savings especially in situations where, because of their potent broad-spectrum activity and excellent bioavailability, they may be used orally in place of intravenous antibacterials. Prudent use of the new fluoroquinolones will be required to minimise the development of resistance to these agents.

Genetic analyses of mutations contributing to fluoroquinolone resistance in clinical isolates of Streptococcus pneumoniae

Twenty-one clinical isolates of Streptococcus pneumoniae showing reduced susceptibility or resistance to fluoroquinolones were characterized by serotype, antimicrobial susceptibility, and genetic analyses of the quinolone resistance-determining regions (QRDRs) of gyrA, gyrB, parC, and parE. Five strains were resistant to three or more classes of antimicrobial agents. In susceptibility profiles for gatifloxacin, gemifloxacin, levofloxacin, moxifloxacin, ofloxacin, sparfloxacin, and trovafloxacin, 14 isolates had intermediate- or high-level resistance to all fluoroquinolones tested except gemifloxacin (no breakpoints assigned). Fluoroquinolone resistance was not associated with serotype or with resistance to other antimicrobial agents. Mutations in the QRDRs of these isolates were more heterogeneous than those previously reported for mutants selected in vitro. Eight isolates had amino acid changes at sites other than ParC/S79 and GyrA/S81; several strains contained mutations in gyrB, parE, or both loci. Contributions to fluoroquinolone resistance by individual amino acid changes, including GyrB/E474K, ParE/E474K, and ParC/A63T, were confirmed by genetic transformation of S. pneumoniae R6. Mutations in gyrB were important for resistance to gatifloxacin but not moxifloxacin, and mutation of gyrA was associated with resistance to moxifloxacin but not gatifloxacin, suggesting differences in the drug-target interactions of the two 8-methoxyquinolones. The positions of amino acid changes within the four genes affected resistance more than did the total number of QRDR mutations. However, the effect of a specific mutation varied significantly depending on the agent tested. These data suggest that the heterogeneity of mutations will likely increase as pneumococci are exposed to novel fluoroquinolone structures, complicating the prediction of cross-resistance within this class of antimicrobial agents.

Can antimicrobial susceptibility testing results for ciprofloxacin or levofloxacin predict susceptibility to a newer fluoroquinolone, gatifloxacin?: Report from The SENTRY Antimicrobial Surveillance Program (1997-99)

A serious problem confronting clinical laboratories and hospital formulary practices is the delayed availability of approved, commercially prepared susceptibility test reagents for newer antimicrobials. A current example is gatifloxacin, a new 8-methoxy fluoroquinolone with expanded potency against many Gram-positive pathogens. This study addresses the use of "surrogate marker" fluoroquinolones to predict susceptibility for gatifloxacin. Reference broth microdilution MIC results for 29,632 strains isolated in United States medical centers (SENTRY Antimicrobial Surveillance Program, 1997-99) were used: staphylococci (9,940 strains), enterococci (2,570), Streptococcus pneumoniae (3,784), Enterobacteriaceae (10,670) and Pseudomonas aeruginosa (2,668). Gatifloxacin interpretation categories were compared to those of ciprofloxacin and levofloxacin by regression statistics and error rate bounding analyses. For the Enterobacteriaceae, the absolute categorical agreement was 97.9 to 98.7% (false-susceptible or very-major error [VME], 0.03%-0.1%) for comparisons of both ciprofloxacin and levofloxacin with gatifloxacin. P. aeruginosa testing was more problematic (higher minor error rates), but acceptable at 0.6% to 1.1% VME and a 85.7% to 89.9% overall agreement. Ciprofloxacin results used to predict gatifloxacin in Gram-positive species was almost without VME (0.0%-0.2%) because gatifloxacin was significantly superior against these species, especially for S. pneumoniae, where gatifloxacin (MIC(90,) 0.5 microg/ml) was fourfold more potent than levofloxacin (MIC(90,) 2 microg/ml). The preferred gatifloxacin predictor drug was ciprofloxacin for all species except S. pneumoniae and P. aeruginosa, where levofloxacin results had a slightly greater predictive value. Susceptibility testing results for selected currently available fluoroquinolones can be used to predict susceptibility to gatifloxacin with high confidence. Many Gram-positive cocci, however, will be categorized as false-resistant by this interim method since gatifloxacin has a 11% to 34% wider spectrum of activity compared to ciprofloxacin when testing staphylococci and enterococci. Clinical laboratories can reliably use these suggested "surrogate markers" until reliable tests for gatifloxacin become available.

Activity of gatifloxacin alone or in combination with pyrimethamine or gamma interferon against Toxoplasma gondii

The activity of gatifloxacin against Toxoplasma gondii, either alone or in combination with pyrimethamine or gamma interferon (IFN-gamma), was examined in vitro and in vivo. In vitro, gatifloxacin significantly inhibited intracellular replication of tachyzoites of the RH strain with a 50% inhibitory concentration of 0.21 microg/ml at 48 h after addition of the drug to the cultures. Toxicity for host cells was not observed at this concentration. A synergistic effect (combination indices < 0.5) was demonstrated in vitro following 48 h of treatment with the combination of gatifloxacin and pyrimethamine (1:1 ratio). Doses of gatifloxacin of 100 and 200 mg/kg of body weight/day administered orally to mice for 10 days resulted in significant (P values of 0.056 and <0.0001, respectively) prolongation in time to death following infection with a lethal inoculum of tachyzoites. A dose of 400 mg/kg resulted in 20% survival (P = 0.0001). Mortality was 100% in untreated control mice and in mice treated with 25 or 50 mg/kg/day. Treatment of infected mice with a combination of gatifloxacin at 200 mg/kg/day and pyrimethamine at 12.5 mg/kg/day resulted in 85% survival, whereas 100 and 80% of mice treated with gatifloxacin alone or pyrimethamine alone, respectively, died (P < 0.0001). Moreover, a gatifloxacin dose of 200 mg/kg/day administered orally for 10 days plus 2 microg of recombinant murine IFN-gamma/day administered intraperitoneally for 10 days resulted in significant survival compared with IFN-gamma alone (P < 0.0001) or gatifloxacin alone (P < 0.007).

Gatifloxacin, an advanced 8-methoxy fluoroquinolone

Gatifloxacin is a new 8-methoxy-fluoroquinolone antibiotic approved for use in the United States in December 1999. It has a broad spectrum of activity with potent activity against gram-positive bacteria, including penicillin-resistant Streptococcus pneumoniae, as well as excellent activity against gram-negative and atypical organisms. Gatifloxacin is available in both oral and injectable forms and is administered once/day. Bioavailability is 96%, with a plasma half-life of approximately 8 hours in individuals with normal renal function. Elimination is primarily renal excretion of unchanged drug with no cytochrome P450-mediated metabolism. The drug is distributed extensively into tissues and fluids and has a favorable pharmacodynamic profile against important pathogens. It had excellent efficacy in clinical studies of acute sinusitis, acute bacterial exacerbations of chronic bronchitis, community-acquired pneumonia, complicated and uncomplicated urinary tract infections and pyelonephritis, skin and skin structure infections, and uncomplicated gonococcal infections. The agent is well tolerated, with no evidence of hepatic, cardiac, or phototoxicity noted thus far. Drug interactions are uncommon; however, like other fluoroquinolones, coadministration with multivalent cations should be avoided due to significantly decreased absorption. Gatifloxacin should prove to be a safe and effective agent for a wide variety of infections.

Susceptibility of bacterial isolates to gatifloxacin and ciprofloxacin from clinical trials 1997-1998

MICs of gatifloxacin and ciprofloxacin against 3482 pre-treatment, clinical trial isolates collected during 1997-1998 are reported. These data suggested that gatifloxacin was four- to eight-fold more active than ciprofloxacin against Gram-positive bacteria, with gatifloxacin MIC(90)s < or = 0.33 mg/l against Staphylococcus aureus and Streptococcus pneumoniae, and < or = 1.0 mg/l versus viridans streptococci and Enterococcus faecalis. Both quinolones had similar MIC(90)s versus Enterobacteriaceae (generally < or = 0.38 mg/l, except 0. 7-0.8 mg/l for Citrobacter freundii) and Pseudomonas aeruginosa ( approximately 8 mg/l). A total of 78% P. aeruginosa had gatifloxacin MICs < or = 2 mg/l. Gatifloxacin was more active than ciprofloxacin against Acinetobacter species and non-P. aeruginosa pseudomonads. Both had exceptional activity versus Haemophilus spp, Moraxella catarrhalis and Neisseria gonorrhoeae. In summary, compared to ciprofloxacin, gatifloxacin had improved activity against Gram-positive bacteria and comparable activity against Gram-negative bacteria.

Gatifloxacin

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The future of the quinolones

This review emphasises the advances in the development of newer quinolones: their broader antimicrobial activity particularly their increased activity against Pneumococcus and anaerobes; their longer half-life and tissue penetration including activity in cerebrospinal fluid; and their excellent efficacy in respiratory, intra-abdominal, pelvic, and skin and soft tissue infections. Also, considerable progress has been made in our understanding of the development of bacterial resistance to the newer quinolones. Additional advances in quinolone development are likely to provide better compounds for clinical use.

In vitro activities of gatifloxacin, two other quinolones, and five nonquinolone antimicrobials against obligately anaerobic bacteria

The activity of the new fluoroquinolone gatifloxacin was compared with those of other quinolones and antimicrobial agents of other classes against 294 anaerobes by the broth microdilution technique. For all strains tested, gatifloxacin MICs at which 50 and 90% of the isolates were inhibited were 0.5 and 2 mg/liter, respectively, and were 3 to 4 dilution steps lower than, e.g., ciprofloxacin.

Postantibiotic effects of gatifloxacin against gram-positive and -negative organisms

Gatifloxacin pneumococcal, staphylococcal and enterococcal postantibiotic effects (PAEs) were 0.5 to 4.0 h, respectively. For Escherichia coli and Pseudomonas aeruginosa, PAEs were 2.2 to 4.8 h. Pneumococcal, staphylococcal, and enterococcal postantibiotic sub-MIC effects (PA-SMEs) (four times the MICs) were 3.7 to 8.6, 2.3 to 3.8, and 1.6 h, respectively, and E. coli and P. aeruginosa PA-SMEs were >/=9.6 and 4.4 h, respectively.

Antimicrobial activity evaluations of gatifloxacin, a new fluoroquinolone: contemporary pathogen results from a global antimicrobial resistance surveillance program (SENTRY, 1997)

OBJECTIVE: To investigate the in vitro potency and spectrum of activity of gatifloxacin and five comparator fluoroquinolones tested against over 23 000 clinical isolates from diverse geographic and clinical sources in the Americas. METHODS: Gram-negative, Gram-positive and fastidious bacterial isolates were tested against gatifloxacin, ciprofloxacin, levofloxacin, ofloxacin, sparfloxacin and trovafloxacin using broth microdilution methods recommended by the National Committee for Clinical Laboratory Standards (NCCLS). RESULTS: Gatifloxacin demonstrated a potency and spectrum very similar to those of other new fluoroquinolones such as levofloxacin, sparfloxacin, and trovafloxacin. Gatifloxacin was particularly active against the Enterobacteriaceae (94.8% susceptible at </=2 mg/L), Acinetobacter spp. (77.2%), Stenotrophomonas maltophilia (75.1%), Streptococcus pneumoniae (99.8%), other Streptococcus spp. (>/=98.9%), and various Staphylococcus spp. (79.2-100.0%). Trovafloxacin was the most similar comparison drug overall. CONCLUSIONS: These results indicate a potential therapeutic role for gatifloxacin that would widen the potency or spectrum of fluoroquinolones, particularly against Gram-positive species, when considering its favorable bioavailability.

Antimicrobial activity of gatifloxacin (AM-1155, CG5501), and four other fluoroquinolones tested against 2,284 recent clinical strains of Streptococcus pneumoniae from Europe, Latin America, Canada, and the United States. The SENTRY Antimicrobial Surveillance Group (Americas and Europe)

The newer fluoroquinolones generally have greater potency against Gram-positive cocci including Streptococcus pneumoniae. In this study, we report the activity of gatifloxacin (formerly AM-1155 or CG5501) compared with penicillin, erythromycin, and four other peer drugs, tested against 2284 strains isolated in North America (Canada and United States), Latin America (six nations), and Europe in 1997. Reference broth microdilution methods were used and results were interpreted by consensus standards. Gatifloxacin demonstrated uniform potency against pneumococci across all monitored geographic areas (MIC90, 0.5 microgram/mL; > or = 99.6% of strains inhibited at < or = 1 microgram/mL). This activity was comparable to trovafloxacin (MIC90, 0.5 microgram/mL) and sparfloxacin (MIC90, 0.5 microgram/mL) and two- to four-fold greater than that of ciprofloxacin or levofloxacin. The most resistant strains to the fluoroquinolones had mutations in both par C (Ser 79-->Phe) and gyr A (Ser83-->Lys or Phe). Penicillin resistance (MIC, > or = 0.12 microgram/mL) rates varied from 27.6% in Europe to 55.7% in Latin America. Macrolide resistance was greatest in Europe and the United States. Gatifloxacin appears to be a promising new fluoroquinolone for clinical use in respiratory tract infections commonly caused by S. pneumoniae.

Efficacy of gatifloxacin in experimental Escherichia coli meningitis

The effectiveness of gatifloxacin therapy (15 mg/kg every 5 h [q5h]) was compared with that of meropenem (75 mg/kg q5h) and cefotaxime (75 mg/kg q5h) therapy in experimental meningitis caused by a beta-lactamase-producing strain of Escherichia coli. Gatifloxacin therapy was more rapidly bactericidal than cefotaxime but similar to meropenem therapy (bacterial killing rates at 5 h, 0.83 +/- 0.26, 0. 46 +/- 0.3, and 0.73 +/- 0.17 CFU/ml/h, respectively; P = 0.03 for gatifloxacin versus cefotaxime). At 10 h, seven of eight animals treated with gatifloxacin had <10 CFU/ml in their cerebrospinal fluid, compared with one of seven treated with cefotaxime therapy (P = 0.01). Gatifloxacin was at least as effective as currently available antibiotics in this model of E. coli meningitis.

Activity of gatifloxacin compared to those of five other quinolones versus aerobic and anaerobic isolates from skin and soft tissue samples of human and animal bite wound infections

The activity of gatifloxacin against 308 aerobes and 112 anaerobes isolated from bite wound infections was studied. Gatifloxacin was active at </=0.016 microg/ml against all 148 Pasteurella isolates (eight species and three subspecies) tested and all other aerobes tested, including Actinobacillus-Haemophilus spp., Eikenella corrodens, Neisseria weaveri, Weeksella zoohelcum, staphylococci, and streptococci. Fusobacteria were sometimes resistant. Gatifloxacin MICs at which 90% of the isolates were inhibited were 0. 125 microg/ml against Bacteroides tectum and Prevotella spp., 0.25 microg/ml against Porphyromonas spp., and 0.5 microg/ml against peptostreptococci.

Comparative antimicrobial activity of gatifloxacin tested against Campylobacter jejuni including fluoroquinolone-resistant clinical isolates

Campylobacter jejuni is an important pathogen that causes gastroenteritis, as well as other disease states such as meningitis and septic arthritis. In this study, the Etest (AB BIODISK, Solna, Sweden) results were compared to a reference agar dilution method using gatifloxacin, a new 8-methoxyfluoroquinolone. A total of 53 strains of C. jejuni initially isolated from patients in California and Mexico were tested. Results demonstrated a high correlation (r = 0.88) between the two utilized in vitro dilution methods. In addition, gatifloxacin activity was compared to that of ciprofloxacin, metronidazole, amoxicillin, erythromycin, chloramphenicol, gentamicin, tetracycline, and trimethoprim/sulfamethoxazole using the Etest. Gatifloxacin (MIC90, 4 micrograms/ml) was approximately eight- to 16-fold more potent than ciprofloxacin (Mic90, > 32 micrograms/ml), a commonly used fluoroquinolone for Campylobacter infections. Eight strains highly resistant to ciprofloxacin (MIC90, > 32 micrograms/ml) were tested for cross resistance against the newer fluoroquinolones (gatifloxacin, levofloxacin, trovafloxacin) and the rank order of potency was: gatifloxacin (MIC50, 16 micrograms/ml) > trovafloxacin = levofloxacin (MIC50, > 32 micrograms/mL). However, only 25% ciprofloxacin-resistant strains were inhibited by < or = 1 microgram/mL of gatifloxacin or trovafloxacin. These results for gatifloxacin against C. jejuni strains must be further assessed in the context of in vivo trials before the clinical role of this new fluoroquinolone can be determined. The Etest appears to be a simple and precise susceptibility test method for testing C. jejuni isolates against fluoroquinolones and other alternative therapeutic agents.

Activity of gatifloxacin against Haemophilus influenzae and Moraxella catarrhalis, including susceptibility test development, E-test comparisons, and quality control guidelines for H. influenzae

In vitro antimicrobial activity and susceptibility testing interpretation criteria and quality control were studied for gatifloxacin, a new 8-methoxy fluoroquinolone, tested against Haemophilus influenzae. Moraxella catarrhalis (600 strains) and H. influenzae (1,400 strains) from the SENTRY Antimicrobial Surveillance Program in North America (Canada and the United States) were also tested against gatifloxacin and 12 other antimicrobial agents. Gatifloxacin (MIC at which 90% of the isolates are inhibited [MIC90], </=0.03 microg/ml; 100.0% of strains inhibited at </=2 microg/ml) was the most active agent tested against H. influenzae and was similar to four comparison fluoroquinolones (MICs, </=0.03 to 2 microg/ml) against M. catarrhalis. A subset of 300 recent clinical isolates of H. influenzae were tested by using media (Haemophilus Test Medium agar and broth) and procedures recommended by the National Committee for Clinical Laboratory Standards (NCCLS) and with the E-test (AB BIODISK, Solna, Sweden). Gatifloxacin (MIC50, 0.008 microg/ml) was slightly more active than levofloxacin, and E-test results were generally elevated by 0.5 log2 dilution step compared to reference MICs. The gatifloxacin 5-microg disk test produced zone diameters that were routinely above 30 mm for H. influenzae strains, corresponding to gatifloxacin MICs of 0.008 or 0. 016 microg/ml. The gatifloxacin susceptibility breakpoint proposed for nonfastidious species (</=2 microg/ml; >/=18 mm) was also suggested for H. influenzae testing. No interpretive errors were observed. Quality control guidelines for H. influenzae ATCC 49247 were determined by using the NCCLS M23-T3 (1998) study design. The results from the nine-laboratory protocol suggested the following control ranges: for broth microdilution tests, 0.004 to 0.03 microg/ml; for disk diffusion testing, 33 to 41 mm. Gatifloxacin appears to be a potent anti-Haemophilus fluoroquinolone compound with in vitro testing interpretive criteria that will produce accurate results (disk diffusion, broth microdilution, and E-test).

The new fluoroquinolones: A critical review

OBJECTIVE

This paper reviews the literature available on the new fluoroquinolones - clinafloxacin, gatifloxacin, grepafloxacin, levofloxacin, moxifloxacin, sparfloxacin and trovafloxacin - to compare these agents with each other and contrast them with ciprofloxacin, an older fluoroquinolone.

DATA SELECTION

Published papers used were obtained by searching MEDLINE for articles published between 1994 and 1998, inclusive. References of published papers were also obtained and reviewed. Abstracts from scientific proceedings were reviewed.

DATA EXTRACTION

Due to the limited data available on several of the agents, criteria for study inclusion in the in vitro, pharmacokinetics and in vivo sections were not restrictive.

DATA SYNTHESIS

The new fluoroquinolones offer excellent Gram-negative bacillary activity and improved Gram-positive activity (eg, against Streptococcus pneumoniae and Staphylococcus aureus) over ciprofloxacin. Clinafloxacin, gatifloxacin, moxifloxacin, sparfloxacin and trovafloxacin display improved activity against anaerobes (eg, Bacteriodes fragilis). All of the new fluoroquinolones have a longer serum half-life than ciprofloxacin (allowing for once daily dosing), and several are eliminated predominantly by nonrenal means. No clinical trials are available comparing the new fluoroquinolones with each other. Clinical trials comparing the new fluoroquinolones with standard therapy have demonstrated good efficacy in a variety of infections. Their adverse effect profile is similar to that of ciprofloxacin. Clinafloxacin and sparfloxacin cause a high incidence of phototoxicity (1.5% to 14% and 2% to 11.7%, respectively), grepafloxacin causes a high incidence of taste perversion (9% to 17%) and trovafloxacin causes a high incidence of dizziness (11%). They all interact with metal ion-containing drugs (eg, antacids), and clinafloxacin and grepafloxacin interact with theophylline. The new fluoroquinolones are expensive; however, their use may result in savings in situations where, because of their potent and broad spectrum of activity, they can be used orally in place of intravenous antibiotics.

CONCLUSIONS

The new fluoroquinolones offer advantages over ciprofloxacin in terms of improved in vitro activity and pharmacokinetics. Whether these advantages translate into improved clinical outcomes is presently unknown. The new fluoroquinolones have the potential to emerge as important therapeutic agents in the treatment of respiratory tract and genitourinary tract infections.

Gatifloxacin (AM-1155, CG 5501) susceptibility testing interpretive criteria and quality control guidelines for dilution and disk (5-microgram) diffusion methods. The Quality Control Study Group

Gatifloxacin (formerly AM-1155 and CG5501), a new 8-methoxy fluoroquinolone, has an expanded spectrum of activity against Gram-positive cocci and some anaerobic bacteria. This compound was tested against 600 recent clinical strains of rapidly growing aerobic species to establish susceptibility testing interpretive criteria for the reference broth microdilution and standardized disk (5-microgram) diffusion methods of the National Committee for Clinical Laboratory Standards (NCCLS). These strains included 285 Enterobacteriaceae (17 species), 165 staphylococci, 49 enterococci, and 101 nonfermentative Gram-negative bacilli. Based on achievable serum levels with projected gatifloxacin dosing regimens, MIC break points of < or = 2 micrograms/mL (> or = 18 mm) for susceptibility and > or = 8 micrograms/mL (< or = 14 mm) for resistance were selected. The absolute agreement between tests was 94.3% with no very major false-resistant errors. The quality control ranges (MIC and zone diameters) for the NCCLS recommended strains were determined in a nine-laboratory NCCLS protocol as follows: Escherichia coli ATCC 25922 = 0.008-0.03 microgram/mL and 31-37 mm; Enterococcus faecalis ATCC 29212 = 0.12-1 microgram/mL; Pseudomonas aeruginosa ATCC 27853 = 0.5-2 micrograms/ml and 21-27 mm; Staphylococcus aureus ATCC 25923 = 27-33 mm and S. aureus ATCC 29213 = 0.03-0.12 microgram/mL. Gatifloxacin appears to be a promising new fluoroquinolone with acceptable susceptibility testing methods for routine clinical laboratory use.

Expanded activity and utility of the new fluoroquinolones: a review

In general, the fluoroquinolones developed over the past few years have greater potency, a broader spectrum of antimicrobial activity, greater in vitro efficacy against resistant organisms, and a better safety profile than other antimicrobial agents, including the older quinolones. The present review focuses on 4 new quinolones that are commercially available (levofloxacin, trovafloxacin, grepafloxacin, and sparfloxacin) and 3 that are currently undergoing clinical trials (gatifloxacin, moxifloxacin, and clinafloxacin). Examination of the minimum inhibitory concentrations of these drugs against gram-positive, gram-negative, anaerobic, and atypical organisms demonstrates their increased potency in vitro. The available clinical evidence, although sparse, suggests the potential enhanced efficacy of these drugs in the treatment of various community-acquired and nosocomial infections (eg, respiratory, urinary tract, and skin infections and sexually transmitted diseases). Compared with ciprofloxacin, their pharmacokinetic profiles demonstrate equivalent or greater bioavailability, higher plasma concentrations, and increased tissue penetration, as reflected in greater volume of distribution. Adverse events seen with most quinolones are mild. Serious adverse effects that may occur are phototoxicity (particularly with sparfloxacin) and prolongation of the QTc interval (seen with sparfloxacin and grepafloxacin). Drug interactions are possible between multivalent cation-containing compounds and all quinolones and between theophylline and both ciprofloxacin and grepafloxacin. Drugs that prolong the QTc interval should not be coadministered with sparfloxacin and grepafloxacin. Step-down therapy, a therapeutic and cost-saving advantage possible with gatifloxacin, levofloxacin, and moxifloxacin, allows the switching of patients from intravenous to oral therapy without having to change the dosage regimen or class of antibiotics. In addition to shortening the hospital stay and reducing the risk of venous complications, step-down therapy has been shown to cut hospital drug costs by 40% and hospitalization costs by 20%.

Antimicrobial activity of gatifloxacin tested against 1676 strains of ciprofloxacin-resistant gram-positive cocci isolated from patient infections in North and South America

Gatifloxacin (formerly AM-115) is a new 8-methoxy fluoroquinolone with an expanded spectrum against Gram-positive cocci and some anaerobes. To assess this new agent's activity, a collection of 1,676 Gram-positive cocci were selected for resistance to ciprofloxacin (> or = 4 micrograms/mL) and tested against gatifloxacin and 18 other compounds by reference broth microdilution methods. The strains (approximately 23,000 total isolates from the SENTRY Antimicrobial Surveillance Program) were from significant blood stream, respiratory tract, wound, and urinary tract infections in patients in North (38 hospitals) and South (10 hospitals) America. Against Enterococcus faecalis and E. faecium, gatifloxacin inhibited only 16% and 10% of strains compared with 12% and 5% for recently released trovafloxacin, respectively. Among Staphylococcus aureus (90% oxacillin-resistant) strains, gatifloxacin was more active (67% susceptible at < or = 4 micrograms/mL) than trovafloxacin (59%) or sparfloxacin (4%). Gatifloxacin had a wider spectrum than trovafloxacin against coagulase-negative staphylococci especially S. epidermidis, 2% versus 58% resistance. The glycopeptides, chloramphenicol and rifampin were most active. Against all genus/species groups with more than 100 sample strains (1,566), high-level resistance to gatifloxacin and trovafloxacin (> 4 micrograms/mL) was not significantly different (41.7% versus 39.1%; p > 0.05). Emerging resistance to the fluoroquinolones remains a clinical problem among Gram-positive species, and gatifloxacin seems to be active in vitro against many of these contemporary strains isolated in the Americas.

Pharmacodynamics of gatifloxacin in cerebrospinal fluid in experimental cephalosporin-resistant pneumococcal meningitis

The purpose of this study was to evaluate the cerebrospinal fluid (CSF) pharmacodynamics of a new fluoroquinolone, gatifloxacin (AM-1155), in experimental pneumococcal meningitis. The penetration of gatifloxacin into CSF, calculated as the percentage of the area under the concentration-time curve (AUC) in CSF over the AUC in blood, was 46 to 56%. Gatifloxacin showed linear pharmacokinetics in CSF, and 1 h after intravenous dosages of 7.5, 15, or 30 mg/kg of body weight, peak CSF concentrations were 0.46 +/- 0.08 (mean +/- standard deviation), 0.94 +/- 0.16, and 1.84 +/- 0.5 microg/ml, respectively. The elimination half-life of gatifloxacin in CSF was 3. 8 to 5.6 h (compared with 2.7 to 3.2 h in blood). There was a significant interrelationship among the highest measured values of gatifloxacin in blood and CSF/minimal bactericidal concentration (Cpeak/MBC), the time antibiotic concentrations exceeded the MBC (T > MBC), and AUC/MBC (r = 0.94); in single-dose experiments, each correlated significantly with the bacterial killing rate. Divided-dose regimens, resulting in greater T > MBC values but lower Cpeak/MBC ratios, were more effective in terms of bacterial clearance compared with corresponding single-dose regimens. Gatifloxacin therapy was as effective as currently recommended regimens (e.g., a combination of ceftriaxone and vancomycin) against this highly cephalosporin-resistant pneumococcal strain. The bactericidal activity of gatifloxacin in CSF was closely related to the AUC/MBC ratio, but maximal activity was achieved only when drug concentrations exceeded the MBC for the entire dosing interval.

Activities of gatifloxacin compared to those of seven other agents against anaerobic organisms

The agar dilution MIC was used to compare activities of gatifloxacin with those of ciprofloxacin, sparfloxacin, trovafloxacin, ampicillin, ampicillin-sulbactam, clindamycin, and metronidazole against 351 anaerobes. Overall MICs at which 50% of the isolates are inhibited and MICs at which 90% of the isolates are inhibited (in micrograms per milliliter) were as follows: gatifloxacin, 0.5 and 4; ciprofloxacin, 2 and 32; sparfloxacin, 2 and 8; trovafloxacin, 1 and 4; ampicillin, 1 and 64; ampicillin-sulbactam, 0.5 and 4; clindamycin, 0.125 and 8; and metronidazole, 1 and >16, respectively. Gatifloxacin MICs were similar to those of trovafloxacin in all organism groups.

Antibacterial activity of gatifloxacin (AM-1155, CG5501, BMS-206584), a newly developed fluoroquinolone, against sequentially acquired quinolone-resistant mutants and the norA transformant of Staphylococcus aureus

Alternate mutations in the grlA and gyrA genes were observed through the first- to fourth-step mutants which were obtained from four Staphylococcus aureus strains by sequential selection with several fluoroquinolones. The increases in the MICs of gatifloxacin accompanying those mutational steps suggest that primary targets of gatifloxacin in the wild type and the first-, second-, and third-step mutants are wild-type topoisomerase IV (topo IV), wild-type DNA gyrase, singly mutated topo IV, and singly mutated DNA gyrase, respectively. Gatifloxacin had activity equal to that of tosufloxacin and activity more potent than those of norfloxacin, ofloxacin, ciprofloxacin, and sparfloxacin against the second-step mutants (grlA gyrA; gatifloxacin MIC range, 1.56 to 3.13 microg/ml) and had the most potent activity against the third-step mutants (grlA gyrA grlA; gatifloxacin MIC range, 1.56 to 6.25 microg/ml), suggesting that gatifloxacin possesses the most potent inhibitory activity against singly mutated topo IV and singly mutated DNA gyrase among the quinolones tested. Moreover, gatifloxacin selected resistant mutants from wild-type and the second-step mutants at a low frequency. Gatifloxacin possessed potent activity (MIC, 0.39 microg/ml) against the NorA-overproducing strain S. aureus NY12, the norA transformant, which was slightly lower than that against the parent strain SA113. The increases in the MICs of the quinolones tested against NY12 were negatively correlated with the hydrophobicity of the quinolones (correlation coefficient, -0.93; P < 0.01). Therefore, this slight decrease in the activity of gatifloxacin is attributable to its high hydrophobicity. Those properties of gatifloxacin likely explain its good activity against quinolone-resistant clinical isolates of S. aureus harboring the grlA, gyrA, and/or norA mutations.

In vitro and in vivo activities of AM-1155, a new fluoroquinolone, against Chlamydia spp

The in vitro and in vivo activities of AM-1155, a new quinolone, against Chlamydia spp. were investigated. The MIC of AM-1155 for 10 standard strains of different Chlamydia spp. and 25 wild-type strains of Chlamydia pneumoniae isolated in Japan, which were morphologically different from clinical isolates from the United States, ranged from 0.063 to 0.125 microg/ml. Its activity was almost the same as those of sparfloxacin and tosufloxacin and was 4 and 16 times superior to those of levofloxacin and ciprofloxacin, respectively, but lower than those of clarithromycin and minocycline (range for each, 0.016 to 0.031 microg/ml). The minimal chlamydiacidal concentration of AM-1155 ranged from 0.063 to 0.125 microg/ml, while those of clarithromycin and minocycline ranged from 0.016 to 0.031 microg/ml and 0.016 to 0.063 microg/ml, respectively. The therapeutic effect of a 7-day course of AM-1155 at doses of 5 and 10 mg/kg of body weight administered orally twice daily to mice with experimental Chlamydia psittaci pneumonia was excellent, with a 100% survival rate at 21 days after infection. The efficacy was equal to those of clarithromycin and minocycline and higher than those of ciprofloxacin and ofloxacin.