In vitro and in vivo evaluations of LB20304, a new fluoronaphthyridone

Pharmacokinetics and tolerability of gemifloxacin (SB-265805) after administration of single oral doses to healthy volunteers

Gemifloxacin (known as SB-265805 or LB-20304) is a potent, novel fluoroquinolone compound with a broad spectrum of antibacterial activity. The pharmacokinetics and tolerability of oral gemifloxacin were characterized in healthy male volunteers after a single dose of 20, 40, 80, 160, 320, 600, or 800 mg. Multiple serum and urine samples were collected and analyzed for gemifloxacin using high-performance liquid chromatography with fluorescence detection. Safety assessments included vital signs, 12-lead electrocardiogram readings, hematology, clinical chemistry, urinalysis, and adverse-experience monitoring. Gemifloxacin was rapidly absorbed after all doses. Maximum concentrations of gemifloxacin in serum (C(max)) were achieved approximately 1 h after dosing, after which concentrations in serum declined in a biexponential manner. Values of C(max) and the area under the concentration-time curve in serum from 0 h to infinity (serum AUC(0-infinity)) increased linearly with dose. Serum AUC(0-infinity) values (mean +/- standard deviation) were 0.65+/-0.01, 1.28+/-0.22, 2.54+/-0.31, 5.48+/-1.24, 9.82+/-2.70, 24.4+/-7.1, and 31.4+/-7.6 microg. h/ml following 20-, 40-, 80-, 160-, 320-, 600-, and 800-mg doses, respectively. The terminal phase elimination half-life was independent of dose, with an overall mean of 7.4+/-2.0 h. The profiles indicated that the pharmacokinetic profile is suitable for a once-daily dosing regimen. Approximately 25 to 40% of the administered dose was excreted unchanged in the urine, and renal clearance (ca. 150 ml/min) was independent of dose. There were no significant changes in clinical chemistry, hematology, or urinalysis parameters, vital signs, or 12-lead electrocardiogram readings in subjects, irrespective of dose. The results of these studies support the further investigation of once-daily administration of gemifloxacin.

Direct liquid chromatographic enantiomer separation of new fluoroquinolones including gemifloxacin

The enantiomers of gemifloxacin mesylate (formerly LB20304a), a new fluoroquinolone compound with potent in vitro and in vivo antibacterial profile were resolved on a commercially available Crownpak CR chiral stationary phase (CSP). All of the fluoroquinolones, including gemifloxacin used in this study, were well enantioseparated on Crownpak CR(+) column. These results are the first reported for the direct separation of the enantiomers of quinolones on chiral crown ether coated Crownpak CR CSP. The behavior of chromatographic parameters by the change of mobile phase additives for the resolution of gemifloxacin was investigated. Also, the effect of structural change of gemifloxacin on chiral recognition was described.

Activity of gemifloxacin, a new broad-spectrum quinolone, against 200 pneumococci by four different susceptibility testing methods

Agar and microdilution (in air), Etest (in air and CO(2)) and disc diffusion (in air and CO(2)) susceptibility testing methods were used to investigate the activity of gemifloxacin against 200 pneumococci. MIC(50)s were 0.016-0.03 mg/L and MIC(90)s 0.125-0.25 mg/L for all methods. With agar dilution as reference, 187/200 strains gave essential agreement with microdilution and 196 with Etest (air and CO(2)). Disc zones were a few millimetres narrower in CO(2) than in air. With discs in CO(2), all ciprofloxacin-susceptible strains yielded zone diameters 26 mm; values in air were 28 mm. Zones for ciprofloxacin-resistant strains in CO(2) were mostly 21-26 mm; zones in air were a few millimetres wider, but mostly <31 mm.

Activities and postantibiotic effects of gemifloxacin compared to those of 11 other agents against Haemophilus influenzae and Moraxella catarrhalis

The activity of gemifloxacin against Haemophilus influenzae and Moraxella catarrhalis was compared to those of 11 other agents. All quinolones were very active (MICs, </=0.125 microgram/ml) against 248 quinolone-susceptible H. influenzae isolates (40.7% of which were beta-lactamase positive); cefixime (MICs, </=0.125 microgram/ml) and amoxicillin-clavulanate (MICs </=4.0 microgram/ml) were active, followed by cefuroxime (MICs, </=16.0 microgram/ml); azithromycin MICs were </=4.0 microg/ml. For nine H. influenzae isolates with reduced quinolone susceptibilities, the MICs at which 50% of isolates are inhibited (MIC(50)s) were 0.25 microgram/ml for gemifloxacin and 1.0 microgram/ml for the other quinolones tested. All strains had mutations in GyrA (Ser84, Asp88); most also had mutations in ParC (Asp83, Ser84, Glu88) and ParE (Asp420, Ser458), and only one had a mutation in GyrB (Gln468). All quinolones tested were equally active (MICs, </=0.06 microgram/ml) against 50 M. catarrhalis strains; amoxicillin-clavulanate, cefixime, cefuroxime, and azithromycin were very active. Against 10 H. influenzae strains gemifloxacin, levofloxacin, sparfloxacin, and trovafloxacin at 2x the MIC and ciprofloxacin at 4x the MIC were uniformly bactericidal after 24 h, and against 9 of 10 strains grepafloxacin at 2x the MIC was bactericidal after 24 h. After 24 h bactericidal activity was seen with amoxicillin-clavulanate at 2x the MIC for all strains, cefixime at 2x the MIC for 9 of 10 strains, cefuroxime at 4x the MIC for all strains, and azithromycin at 2x the MIC for all strains. All quinolones except grepafloxacin (which was bactericidal against four of five strains) and all ss-lactams at 2x to 4x the MIC were bactericidal against five M. catarrhalis strains after 24 h; azithromycin at the MIC was bactericidal against all strains after 24 h. The postantibiotic effects (PAEs) against four quinolone-susceptible H. influenzae strains were as follows: gemifloxacin, 0.3 to 2.3 h; ciprofloxacin, 1.3 to 4.2 h; levofloxacin, 2.8 to 6.2 h; sparfloxacin, 0.6 to 3.0 h; grepafloxacin, 0 to 2.1 h; trovafloxacin, 0.8 to 2.8 h. At 10x the MIC, no quinolone PAEs were found against the strain for which quinolone MICs were increased. Azithromycin PAEs were 3.7 to 7.3 h.

Antipneumococcal activities of gemifloxacin compared to those of nine other agents

The activities of gemifloxacin compared to those of nine other agents was tested against a range of penicillin-susceptible and -resistant pneumococci by agar dilution, microdilution, time-kill, and post-antibiotic effect (PAE) methods. Against 64 penicillin-susceptible, 68 penicillin-intermediate, and 75 penicillin-resistant pneumococci (all quinolone susceptible), agar dilution MIC(50)s (MICs at which 50% of isolates are inhibited)/MIC(90)s (in micrograms per milliliter) were as follows: gemifloxacin, 0.03/0.06; ciprofloxacin, 1.0/4.0; levofloxacin, 1.0/2. 0; sparfloxacin, 0.5/1.0; grepafloxacin, 0.125/0.5; trovafloxacin, 0. 125/0.25; amoxicillin, 0.016/0.06 (penicillin-susceptible isolates), 0.125/1.0 (penicillin-intermediate isolates), and 2.0/4.0 (penicillin-resistant isolates); cefuroxime, 0.03/0.25 (penicillin-susceptible isolates), 0.5/2.0 (penicillin-intermediate isolates), and 8.0/16.0 (penicillin-resistant isolates); azithromycin, 0.125/0.5 (penicillin-susceptible isolates), 0. 125/>128.0 (penicillin-intermediate isolates), and 4.0/>128.0 (penicillin-resistant isolates); and clarithromycin, 0.03/0.06 (penicillin-susceptible isolates), 0.03/32.0 (penicillin-intermediate isolates), and 2.0/>128.0 (penicillin-resistant isolates). Against 28 strains with ciprofloxacin MICs of >/=8 microg/ml, gemifloxacin had the lowest MICs (0.03 to 1.0 microg/ml; MIC(90), 0.5 microg/ml), compared with MICs ranging between 0.25 and >32.0 microg/ml (MIC(90)s of 4.0 to >32.0 microg/ml) for other quinolones. Resistance in these 28 strains was associated with mutations in parC, gyrA, parE, and/or gyrB or efflux, with some strains having multiple resistance mechanisms. For 12 penicillin-susceptible and -resistant pneumococcal strains (2 quinolone resistant), time-kill results showed that levofloxacin at the MIC, gemifloxacin and sparfloxacin at two times the MIC, and ciprofloxacin, grepafloxacin, and trovafloxacin at four times the MIC were bactericidal for all strains after 24 h. Gemifloxacin was uniformly bactericidal after 24 h at </=0.5 microg/ml. Various degrees of 90 and 99% killing by all quinolones were detected after 3 h. Gemifloxacin and trovafloxacin were both bactericidal at two times the MIC for the two quinolone-resistant pneumococci. Amoxicillin at two times the MIC and cefuroxime at four times the MIC were uniformly bactericidal after 24 h, with some degree of killing at earlier time points. Macrolides gave slower killing against the seven susceptible strains tested, with 99.9% killing of all strains at two to four times the MIC after 24 h. PAEs for five quinolone-susceptible strains were similar (0.3 to 3.0 h) for all quinolones, and significant quinolone PAEs were found for the quinolone-resistant strain.

Pharmacokinetics and pharmacodynamics of fluoroquinolones

The fluoroquinolones have moderate to excellent bioavailability, moderate to long elimination half-lives (50 to 98%) and volumes of distribution >1.5 L/kg. There is considerable variation in elimination pattern between fluoroquinolone agents, ranging from predominant renal excretion to extensive hepatic metabolism. Protein binding also varies between agents. Tissue concentrations often exceed plasma concentrations, while concentrations in CSF are modest in the presence of inflammation. Fluoroquinolones show concentration-dependent killing in vitro, and animal models have demonstrated the 24-hour AUC/MIC (area under the concentration-time curve/minimum inhibitory concentration) ratio to be the best predictor of bacterial killing in vivo, with the peak plasma concentration (Cmax)/MIC ratio being important for some bacteria, to prevent the emergence of resistance during treatment. Animal models and human studies with ciprofloxacin, grepafloxacin and levofloxacin show that a 24-hour AUC/MIC ratio of about 100, or a Cmax/MIC ratio of about 10 gives maximum clinical and bacteriological efficacy. These values can be used to predict the efficacy of different agents against different pathogens, and to define pharmacodynamic 'breakpoints'.

Activity of newer fluoroquinolones in vitro against gram-positive bacteria

Several newer fluoroquinolones, which have been recently introduced or are under investigation, display substantially greater potency against gram-positive organisms than the older generation agents of this class. Nevertheless, for problem organisms including methicillin-resistant strains of Staphylococcus aureus and many Enterococcus faecium, concentrations of newer antimicrobials required to inhibit 90% of organisms in the collections studied remain above those that are projected to be achievable with clinical use. Nevertheless, enhanced potency of several newer quinolones may result in a favourable pharmacodynamic profile leading to improved outcomes against gram-positive infections and possibly to the delayed or diminished emergence of resistance to these agents.

Activity of gemifloxacin against penicillin- and ciprofloxacin-resistant Streptococcus pneumoniae displaying topoisomerase- and efflux-mediated resistance mechanisms

Nine penicillin-resistant Streptococcus pneumoniae clinical isolates from Northern Ireland, resistant to ciprofloxacin (MICs, 2 to 64 microg/ml) through topoisomerase- and/or reserpine-sensitive efflux mechanisms, were highly susceptible to gemifloxacin (MICs, 0.03 to 0. 12 microg/ml). Two strains (requiring a ciprofloxacin MIC of 64 microg/ml) carried known quinolone resistance mutations in parC, parE, and gyrB, resulting in S79F, D435V, and E474K changes, respectively. Thus, gemifloxacin is active against clinical strains exhibiting altered topoisomerase and efflux phenotypes.

Activities of gemifloxacin (SB 265805, LB20304) compared to those of other oral antimicrobial agents against unusual anaerobes

The activities of gemifloxacin (SB 265805, LB20304) and comparator agents were determined by an agar dilution method against 419 clinical strains of less-commonly identified species of anaerobes. Gemifloxacin was generally more active than trovafloxacin against gram-positive strains by one to two dilutions. Peptostreptococci (Peptostreptococcus asaccharolyticus, Peptostreptococcus magnus, Peptostreptococcus micros, and Peptostreptococcus prevotii) and Porphyromonas spp. (Porphyromonas asaccharolytica, Porphyromonas canoris, Porphyromonas gingivalis, and Porphyromonas macacae) were all susceptible to </=0.25 microgram of gemifloxacin per ml. The MICs of gemifloxacin at which 90% of the following strains were inhibited (MIC(90)s) were </=2 microgram/ml: Actinomyces israelii, Actinomyces odontolyticus, Clostridium innocuum, Clostridium clostridioforme, Anaerobiospirillum spp., Bacteroides tectum, Bacteroides ureolyticus, Bacteroides gracilis (now Campylobacter gracilis), Prevotella intermedia, Prevotella heparinolytica, and the Prevotella oris-buccae group. Fusobacterium naviforme and Fusobacterium necrophorum were also susceptible to </=2 microgram of gemifloxacin per ml, while Fusobacterium varium strains exhibited a bimodal pattern; the other Fusobacterium species, such as Fusobacterium ulcerans and Fusobacterium russii, as well as Veillonella spp., the Prevotella melaninogenica group, Prevotella bivia, Clostridium difficile, and Bilophila wadsworthia were relatively resistant to gemifloxacin (MIC(90)s, >/=4 microgram/ml).

In vitro activities of gemifloxacin (SB 265805, LB20304) against recent clinical isolates of Chlamydia pneumoniae

We compared the in vitro activity of gemifloxacin, a new quinolone antibiotic, to the activities of levofloxacin, moxifloxacin, trovafloxacin, erythromycin, and doxycycline against 20 isolates of Chlamydia pneumoniae. Gemifloxacin was the most active quinolone tested, with a MIC at which 90% of the isolates are inhibited and a minimal bactericidal concentration at which 90% of strains tested are killed of 0.25 microg/ml, but this activity was less than those of doxycycline and erythromycin.

The in-vitro activity and tentative breakpoint of gemifloxacin, a new fluoroquinolone

The in-vitro activity of gemifloxacin, a new fluoroquinolone, against a wide range (c. 700) of recent clinical isolates, was compared with that of three other fluoroquinolones and other relevant agents. Gemifloxacin inhibited 90% of the Enterobacteriaceae strains at 0.5 mg/L or less, exceptions being Serratia spp. (MIC(90) 1 mg/L) and strains possessing a putative mechanism of resistance to fluoroquinolones. Ninety per cent of Pseudomonas aeruginosa were inhibited by 4 mg/L. Gemifloxacin had good activity against respiratory pathogens, with 90% of Streptococcus pneumoniae, Haemophilus influenzae and Moraxella catarrhalis being inhibited by 0.06 mg/L or less. Staphylococcus aureus (MSSA) were highly susceptible (MIC(90) 0.06 mg/L) but MRSA less susceptible (MIC(90) 8 mg/L) to gemifloxacin. Enterococcus spp. were markedly more susceptible to the study agent than to ciprofloxacin. Gemifloxacin showed good activity against Bacteroides fragilis (MIC(90) 0.5 mg/L) and anaerobic cocci. A tentative in-vitro breakpoint of 0.5 mg/L was studied using a 1 microg disc content for all genera except Pseudomonas where a 5 microg disc content was employed. The false sensitivity reporting rate was 0.5% and false resistance rate was 6.0%, which was considered acceptable. In conclusion, gemifloxacin is a highly active fluoroquinolone that should prove clinically useful in the treatment of a wide range of infections. Susceptibility testing criteria have been developed that should prove robust in a clinical laboratory.

Development of in vitro susceptibility testing methods for gemifloxacin (formerly LB20304a or SB-265805), an investigational fluoronaphthyridone

Potent investigational fluoroquinolones require convenient, but accurate, diagnostic tests for initially applied clinical trials. For this purpose, gemifloxacin (formerly SB-265805, LB20304a) was tested by the reference dilution tests and standardized disk diffusion methods of the National Committee for Clinical Laboratory Standards (NCCLS) to establish interpretive criteria. For rapid-growing pathogens, 986 organisms were tested by broth microdilution MIC, and 5- and 10-microgram disk diffusion tests. Correlation (r) between 5- and 10-microgram disk zone diameters was 0.99 (y = -0.12 to 0.99x) and the preferred 5-microgram disk zone/MIC scattergram produced a regression of y = 14.8 to 0.41x (r = 0.93). At potential pharmacodynamics (Cmax = 1.3 micrograms/mL for 320 mg dose) validated breakpoints of < or = 0.5 microgram/mL for susceptible and > or = 2 micrograms/mL for resistant, correlate zones of > or = 17 mm and < or = 13 mm produced rare serious interpretive errors (0.1%) and 96.7% absolute categorical agreement. For 304 Streptococcus pneumoniae and 305 strains of other streptococci, the same breakpoints produced 100 and 99.1% categorical accuracy even when testing levofloxacin-resistant (MIC, > or = 4 micrograms/mL) strains. Interpretive breakpoints were proposed for Hemophilus influenzae (300 strains tested), with complete correlation between tests. Etest (AB BIODISK, Solna, Sweden) was compared in all experiments with the fastidious species and showed a trend toward higher values (twofold). Gemifloxacin in vitro susceptibility test methods seem to be accurate and with very acceptable intermethod agreement, supported by previously reported functional quality control guidelines.

In vitro activity of gemifloxacin (SB 265805) against anaerobes

Gemifloxacin mesylate (SB 265805), a new fluoronaphthyridone, was tested against 359 recent clinical anaerobic isolates by the National Committee for Clinical Laboratory Standards reference agar dilution method with supplemented brucella blood agar and an inoculum of 10(5) CFU/spot. Comparative antimicrobials tested included trovafloxacin, levofloxacin, grepafloxacin, sparfloxacin, sitafloxacin (DU-6859a), penicillin G, amoxicillin clavulanate, imipenem, cefoxitin, clindamycin, and metronidazole. The MIC(50) and MIC(90) (MICs at which 50 and 90% of the isolates were inhibited) of gemifloxacin against various organisms (with the number of strains tested in parentheses) were as follows (in micrograms per milliliter): for Bacteroides fragilis (28), 0.5 and 2; for Bacteroides thetaiotaomicron (24), 1 and 16; for Bacteroides caccae (12), 1 and 16; for Bacteroides distasonis (12), 8 and >16; for Bacteroides ovatus (12), 4 and >16; for Bacteroides stercoris (12), 0.5 and 0.5; for Bacteroides uniformis (12), 1 and 4; for Bacteroides vulgatus (11), 4 and 4; for Clostridium clostridioforme (15), 0.5 and 0.5; for Clostridium difficile (15), 1 and >16; for Clostridium innocuum (13), 0.125 and 2; for Clostridium perfringens (13), 0.06 and 0.06; for Clostridium ramosum (14), 0.25 and 8; for Fusobacterium nucleatum (12), 0.125 and 0.25; for Fusobacterium necrophorum (11), 0.25 and 0.5; for Fusobacterium varium (13), 0.5 and 1; for Fusobacterium spp. (12), 1 and 2; for Peptostreptococcus anaerobius (13), 0.06 and 0.06; for Peptostreptococcus asaccharolyticus (13), 0.125 and 0.125; for Peptostreptococcus magnus (14), 0.03 and 0.03; for Peptostreptococcus micros (12), 0.06 and 0.06; for Peptostreptococcus prevotii (14), 0.06 and 0.25; for Porphyromonas asaccharolytica (11), 0.125 and 0.125; for Prevotella bivia (10), 8 and 16; for Prevotella buccae (10), 2 and 2; for Prevotella intermedia (10), 0.5 and 0.5; and for Prevotella melaninogenica (11), 1 and 1. Gemifloxacin mesylate (SB 265805) was 1 to 4 dilutions more active than trovafloxacin against fusobacteria and peptostreptococci, and the two drugs were equivalent against clostridia and P. asaccharolytica. Gemifloxacin was equivalent to sitafloxacin (DU 6859a) against peptostreptococci, C. perfringens, and C. ramosum, and sitafloxacin was 2 to 3 dilutions more active against fusobacteria. Sparfloxacin, grepafloxacin, and levofloxacin were generally less active than gemifloxacin against all anaerobes.

Anti-streptococcal activity of SB-265805 (LB20304), a novel fluoronaphthyridone, compared with five other compounds, including quality control guidelines

SB-265805 (formerly LB20304) is a novel C-7 pyrrolidine-substituted naphthyridone that has a broad spectrum of activity, especially against Gram-positive cocci. SB-265805 activity was compared with ciprofloxacin, grepafloxacin, moxifloxacin, sparfloxacin, and penicillin against 599 Streptococcus spp. isolated recently from more than 30 medical centers in North and South America. These included 70 isolates with decreased susceptibility to recently released fluoroquinolones (levofloxacin MIC, > or = 4 micrograms/mL). All strains were tested by reference microdilution methods in lysed horse blood-supplemented Mueller-Hinton broth. Sixteen percent of 148 beta-haemolytic streptococci (strains of gr. B and C) were not susceptible to penicillin, whereas 38% and 42% of viridans group streptococci and Streptococcus pneumoniae were resistant to penicillin, respectively. SB-265805 potency against 301 pneumococci (MIC90, 0.06 microgram/mL) was fourfold more active than moxifloxacin and was > or = eightfold more potent than other quinolones. Against beta-haemolytic streptococci, SB-265805 and moxifloxacin were the most active (MIC90, 0.06 and 0.25 microgram/mL, respectively), whereas sparfloxacin, grepafloxacin, and ciprofloxacin (MIC90, 0.5-1 microgram/mL) were less potent. SB-265805 MICs versus viridans group streptococci (MIC90, 0.12 microgram/mL) were fourfold lower than sparfloxacin or grepafloxacin, and twofold more active than moxifloxacin. A nine-laboratory quality control (QC) protocol conforming to NCCLS M23-T3 guidelines demonstrated a modal SB-265805 MIC of 0.016 microgram/mL for S. pneumoniae ATCC 49619 (proposed QC range, 0.008 to 0.03 microgram/mL). The SB-265805 disk (5-microgram) QC range was 28-34 mm (97.3% of qualifying results). In general, SB-265805 in vitro activity against Streptococcus species was superior to sparfloxacin, grepafloxacin, and moxifloxacin and markedly greater than ciprofloxacin. This degree of antimicrobial potency warrants further investigation of this newer drug for its potential human clinical application against streptococcal infections.

Clinical trial of ototopical ofloxacin for treatment of chronic suppurative otitis media

A multicenter, open-label prospective trial was performed to determine the clinical and microbiologic efficacy of ofloxacin (OFLX) otic solution in the treatment of subjects > or =12 years with chronic suppurative otitis media (CSOM) and a chronically perforated tympanic membrane in the infected ear(s). A total of 207 patients at 27 centers in the United States and Central America received OFLX 0.5 mL instilled ototopically twice daily for 14 consecutive days. The primary clinical end point was cure (dry ear) or failure (not dry ear). The primary microbiologic end point was eradication of baseline pathogens. Because there was no comparator and there were few data in the literature regarding clinical efficacy in patients treated with other regimens, the efficacy of OFLX was compared with data recorded in the clinical records of historical-practice control (HPC) or current-practice control (CPC) subjects. The incidence of clinical cure in clinically evaluable OFLX-treated patients (91%; 148 of 162 subjects) was significantly higher than in HPC subjects (67%; 124 of 185 subjects) or CPC subjects (70%; 38 of 54 subjects). OFLX eradicated all baseline pathogens isolated in microbiologically evaluable subjects. These pathogens were predominantly Staphylococcus aureus, Pseudomonas aeruginosa, and Proteus mirabilis. The most common treatment-related adverse event, bitter taste, occurred in 17% (35 of 207) of OFLX-treated subjects. Thus OFLX 0.5 mL administered twice daily for 14 days was effective in resolving the signs and symptoms of CSOM in subjects > or =12 years, was significantly more effective than therapies used to treat HPC or CPC subjects, and was well tolerated.

Antimicrobial activity and spectrum of LB20304, a novel fluoronaphthyridone

Compound LB20304 is a fluoronaphthyridone carboxylic acid with a novel pyrrolidine substituent. This drug was compared with ciprofloxacin, levofloxacin, ofloxacin, and trovafloxacin against over 800 pathogens, most from blood stream infections, by National Committee for Clinical Laboratory Standards reference methods. LB20304 was the most active agent against gram-positive species including strains observed to be resistant to other fluoroquinolones and glycopeptides. The potency of LB20304 (MIC50, 0.03 micrograms/ml) against the Enterobacteriaceae was exceeded only by that of ciprofloxacin (0.015 micrograms/ml). It has limited activity against gram-negative anaerobes.