Comparative chemotherapeutic activity of new fluorinated 4-quinolones and standard agents against a variety of bacteria in a mouse infection model

In vitro and in vivo activities of PD 0305970 and PD 0326448, new bacterial gyrase/topoisomerase inhibitors with potent antibacterial activities versus multidrug-resistant gram-positive and fastidious organism groups

PD 0305970 and PD 0326448 are new bacterial gyrase and topoisomerase inhibitors (quinazoline-2,4-diones) that possess outstanding in vitro and in vivo activities against a wide spectrum of bacterial species including quinolone- and multidrug-resistant gram-positive and fastidious organism groups. The respective MICs (microg/ml) for PD 0305970 capable of inhibiting>or=90% of bacterial strains tested ranged from 0.125 to 0.5 versus staphylococci, 0.03 to 0.06 versus streptococci, 0.25 to 2 versus enterococci, and 0.25 to 0.5 versus Moraxella catarrhalis, Haemophilus influenzae, Listeria monocytogenes, Legionella pneumophila, and Neisseria spp. PD 0326448 MIC90s were generally twofold higher versus these same organism groups. Comparative quinolone MIC90 values were 4- to 512-fold higher than those of PD 0305970. In testing for frequency of resistance, PD 0305970 and levofloxacin showed low levels of development of spontaneous resistant mutants versus both Staphylococcus aureus and Streptococcus pneumoniae. Unlike quinolones, which target primarily gyrA and parC, analysis of resistant mutants in S. pneumoniae indicates that the likely targets of PD 0305970 are gyrB and parE. PD 0305970 demonstrated rapid bactericidal activity by in vitro time-kill testing versus streptococci. This bactericidal activity carried over to in vivo testing, where PD 0305970 and PD 0326448 displayed outstanding Streptococcus pyogenes 50% protective doses (PD50s) (oral dosing) of 0.7 and 3.6 mg/kg, respectively (ciprofloxacin and levofloxacin PD50s were>100 and 17.7 mg/kg, respectively). PD 0305970 was also potent in a pneumococcal pneumonia mouse infection model (PD50=3.2 mg/kg) and was 22-fold more potent than levofloxacin.

In vivo therapeutic efficacies of PD 138312 and PD 140248, two novel fluoronaphthyridines with outstanding gram-positive potency

PD 138312 and PD 140248 are novel broad-spectrum 7-pyrrolidinyl fluoronaphthyridines with a cyclopropyl or a difluorophenyl substitution at the 1 positions, respectively. They have been demonstrated to have excellent in vitro activity against gram-positive organisms. These compounds were evaluated for their in vivo potencies against acute systemic infections in mice and in a mouse pneumococcal pneumonia model. They were very effective by both the oral and subcutaneous routes of administration. Most remarkable were their comparative median protective values against methicillin-resistant Staphylococcus aureus, Streptococcus pneumoniae, and Streptococcus pyogenes. In general, these compounds were 28- to 100-fold more active than ciprofloxacin against these clinically significant organisms when the drugs were given orally and 10- to 38-fold more active when the drugs were given parenterally. Average ratios of drug concentrations in mice after drug administration by the oral route to that after administration by the subcutaneous route indicate 34 to 44% greater bioavailabilities of PD 138312 and PD 140248 compared with that of ciprofloxacin. In a multidose pneumococcal mouse pneumonia model these new quinolones were extremely effective, with median curative doses of 2 to 2.8 mg/kg of body weight per dose. Ciprofloxacin was ineffective (median curative dose, >100 mg/kg per dose) in this model. Comparative pharmacokinetic studies in mice revealed a relative superiority of PD 140248. Peak levels of PD 140248 in blood after the administration of a single oral 50-mg/kg dose were twice those of PD 138312 and ciprofloxacin, with PD 140248 having a substantially longer half-life. These results indicate that PD 138312 and PD 140248 have excellent therapeutic potential against clinically important gram-positive pathogens when the drugs are administered both orally and parenterally.

Failure of beta-lactam antibiotics and marked efficacy of fluoroquinolones in treatment of murine Yersinia pseudotuberculosis infection

The treatment of yersiniosis by beta-lactams is questionable considering the proven failure of newer beta-lactams for treating murine Yersinia enterocolitica infection. Another modality of experimental treatment was performed with a virulent strain of Y. pseudotuberculosis (nonproducer of beta-lactamase) highly susceptible (in terms of MICs) to amoxicillin, cefotaxime, ceftriaxone, imipenem, doxycycline, gentamicin, and ofloxacin. The in vivo comparative efficacy of these drugs was evaluated in a standardized and reproducible mouse model of systemic infection. Each single antibiotic was injected intravenously once, at 30 h after intravenous inoculation of the infective strain, and then repeatedly (at 30, 52, and 76 h postinfection). In vivo results were measured by counting the viable bacteria recovered from the whole spleens of mice sacrificed at selected times. Cefotaxime, even at high doses (250 mg/kg of body weight), was totally ineffective. Amoxicillin and imipenem at high doses (200 and 100 mg/kg, respectively) and ceftriaxone at usual doses (20 mg/kg) were active only in stopping bacterial proliferation to a more or less slight degree. Ceftriaxone was able to reduce viable counts in the spleen only at high doses (200 mg/kg), as were gentamicin (20 mg/kg) and doxycycline (125 mg/kg). Ofloxacin at the low dose of 5 mg/kg was demonstrated to be very effective by the very significant decrease observed in bacterial numbers from 10(6) to 10(3) CFU per spleen. The pharmacological parameters do not in themselves explain all the discrepancies between the in vitro and in vivo activities of beta-lactams on yersiniae. No emergence of beta-lactam-resistant organisms, which could explain the failure of beta-lactams, was detected. Thus, their use should be delayed in the therapy of human yersinosis until further investigations are carried out. The fluoroquinolone appeared more active and rapid than reference drugs in the treatment of murine yersinosis, which confirms initial clinical results.

Antimicrobial activity evaluations of two new quinolones, PD127391 (CI-960 and AM-1091) and PD131628

The in vitro activities of PD127391 and the new fluorinated-4-quinolone, PD131628, were compared with each other and with five similar fluoroquinolones (ciprofloxacin, enoxacin, fleroxacin, norfloxacin, and ofloxacin). A total of 844 isolates mainly from recent clinical bacteremias and additional stock strains with well-characterized resistance mechanisms were tested. PD127391 had slightly more activity than PD131628 (90% minimum inhibitory concentration (MIC90)] 0.008-0.12) against the Enterobacteriaceae, but both were two- to fourfold more potent than ciprofloxacin. PD131628 activity was equal to or greater than PD127391 when tested against Pseudomonas aeruginosa. PD127391 showed greatest activity against Bacteroides fragilis group strains (MIC90, 2 micrograms/ml) when compared with PD131628 (MIC90 greater than 8 micrograms/ml). Both PD127391 (MIC90s, 0.015-1.0 micrograms/ml) and PD131628 (MIC90s, 0.03 - greater than 8 micrograms/ml) were more active than ciprofloxacin against Gram-positive organisms. Altering the medium pH, adding divalent cations (magnesium), and increasing the inoculum concentration to 10(6) colony-forming units per spot adversely effected the activity of both PD127391 and PD131628. Resistance selection and mutational rates to resistance were identical to previously studied drugs in their class.

In vitro antibacterial activities of the fluoroquinolones PD 117596, PD 124816, and PD 127391

Three new aminopyrrolidine-substituted fluorocyclopropyl quinolones--PD 117596, PD 124816, and PD 127391--were tested for in vitro antibacterial activity against 349 bacterial strains, which are primarily clinical isolates. The minimum inhibitory concentrations (MIC) in micrograms/ml required for greater than or equal to 90% of strains were 0.03-0.06 for staphylococci (26 strains); 0.06-0.25 for Streptococcus pyogenes, S. agalactiae, S. pneumoniae, and Enterococcus faecalis (80); less than or equal to 0.015 for Branhamella catarrhalis, Haemophilus influenzae, and Neisseria gonorrhoeae (42); 0.06 for Enterobacteriaceae (97); 0.125-0.25 for Acinetobacter spp. (14); 0.5 for Pseudomonas aeruginosa (20); 0.125-1.0 for Bacteroides fragilis (13); and 0.25-0.5 for anaerobic cocci (11). These activities were generally superior to that of ciprofloxacin, imipenem, ampicillin, penicillin G, oxacillin, cefazolin, ceftazidime, cefoxitin, cefsulodin, aztreonam, piperacillin, amikacin, spectinomycin, doxycycline, erythomycin, clindamycin, metronidazole, and vancomycin. The activities of the new quinolones were generally unchanged with light, 50% human serum, aerobic/anaerobic atmosphere, 5% sodium choate, cation supplementation, and 100-fold increased or decreased inoculum; as with other quinolones, potency was measurably diminished with decreasing pH (pH less than or equal to 6.0) and in 100% urine.

Newly documented antimicrobial activity of quinolones

The improved antimicrobial activity of newer fluoroquinolones and novel applications recently found for the drugs already marketed are reviewed. Several new compounds are more active against gram-positive bacteria than the presently marketed fluoroquinolones. WIN 57273, the most potent compound in vitro on a weight basis, is 16 to 128 times more active than ciprofloxacin against various staphylococci, streptococci, Enterococcus spp., Corynebacterium spp., Listeria monocytogenes and Bacillus spp. BMY 40062, PD 117558, PD 127391, sparfloxacin, temafloxacin and tosufloxacin also show enhanced in vitro efficacy against these species. These drugs also possess increased activity against various anaerobes, notably Clostridium perfringens, Clostridium difficile and the Bacteroides fragilis group. Mycobacterium tuberculosis, rapidly growing mycobacteria other than Mycobacterium chelonae, and Mycobacterium leprae are often susceptible to quinolones displaying bactericidal activity which is potentially useful for curing difficult-to-treat mycobacteriosis. In addition, a number of new products, notably those containing a cyclopropyl group, are more active than reference fluoroquinolones against Mycobacterium leprae. Sparfloxacin, BMY 40062 and WIN 57273 compare favorably with older fluoroquinolones in the killing of intracellular Legionella spp., and several of the newer compounds have greater antichlamydial potency. Improved antibacterial activity has also been found against Mycoplasma hominis, Ureaplasma urealyticum, Acinetobacter spp. and Pseudomonas maltophilia. By contrast, the newer quinolones have similar or less activity against Pseudomonas aeruginosa and Enterobacteriaceae. Recently, pefloxacin, ofloxacin and ciprofloxacin were found to be active against protozoa, including Plasmodium spp., Trypanosoma cruzi and Leishmania donovani, but not against Toxoplasma gondii. In the near future, more specific research testing unusual pathogens may lead to the identification of quinolones with more selective activity.