TEXT

Top Abstract Text References

Y-688 [(S)-(+)-7-(3-aminomethyl-3-fluoromethyl-1-pyrrolidi- ny)-1-cyclopropyl-6-fluoro-1,4-dihydro8-methoxy-4-oxo-3-qui- nolinecarboxylic acid] is a new 7-substituted fluoroquinolone (Fig. 1) (7). Little work has so far been published on its in vitro activity against anaerobes, although Y-688 is known to have good activity against gram-positive strains, including strains of staphylococci and enterococci resistant to ofloxacin, tosufloxacin, or sparfloxacin (17). In this study the in vitro activity of Y-688 was compared to those of the fluoroquinolone levofloxacin, the napthyridone compound trovafloxacin (4), the carbapenem meropenem, and the nitroimidazole metronidazole against 317 nonduplicate anaerobic clinical isolates.

View larger version (8K): [in this window] [in a new window]   FIG. 1.   Structure of Y-688.

The anaerobic bacteria studied were from the collection held at Southmead Hospital. Most were recent clinical isolates from the hospital, but strains were also provided by Bristol Dental Hospital, the Public Health Laboratory Service Anaerobic Reference Unit, Cardiff, United Kingdom, Zeneca Pharma, Alderley Park, United Kingdom, and D. A. Murdoch of this department. Strains were identified by standard criteria (10, 13). The following control strains were used: Bacteroides fragilis ATCC 25285, Clostridium perfringens NCTC 1129, Peptostreptococcus magnus ATCC 14956, Staphylococcus aureus ATCC 9144, and Escherichia coli ATCC 10536. The antimicrobials used were obtained from their manufacturers. They included levofloxacin (Hoechst-Marion-Roussel, Middlesex, United Kingdom), trovafloxacin (Pfizer, Sandwich, United Kingdom), meropenem (Zeneca Pharma, Cheshire, United Kingdom), and metronidazole (P.M.U. South Devon Healthcare, Devon, United Kingdom). Susceptibilities were determined by the standard agar incorporation dilution method recommended by the British Society for Antimicrobial Chemotherapy (3). Wilkins Chalgren agar (CM619; Unipath) supplemented with 5% lysed horse blood was used, and the antimicrobials were incorporated into the medium in a log₂ dilution series starting from 1 mg/liter. Inocula were prepared by diluting bacterial suspensions equivalent in turbidity to McFarland 0.5 standard 1 in 10 in saline, resulting in approximately 10⁴ CFU per spot when the inocula were applied by a multipoint inoculator (Denley Instruments, Billingshurst, United Kingdom). The plates were incubated anaerobically in an atmosphere of 80% N₂, 10% H₂, and 10% CO₂ at 37°C for 40 h in an anaerobic cabinet (Don Whitley, Shipley, United Kingdom). The MIC was read by eye and was defined as the lowest concentration of drug to inhibit macroscopically visible colonies.

For the purposes of analysis strains were grouped into either a species or a genus with 5 representatives, and MIC ranges, MICs at which 50% of the isolates were inhibited (MIC₅₀), and MIC₉₀s were calculated. If there were 10 strains in a particular group the percentages of strains with MIC values of 0.5, 1, 2, and 4 mg/liter were calculated for the quinolones.

Y-688 and trovafloxacin were the most active fluoroquinolones tested against these anaerobic bacteria: the MIC₉₀ of Y-688 was 1.0 mg/liter, compared to 8, 1, 1, and >128 mg/liter for levofloxacin, trovafloxacin, meropenem, and metronidazole, respectively (Tables 1 and 2). The high MIC₉₀ of metronidazole was related to the numbers of Actinomyces spp., Lactobacillus spp., and Propionibacterium acnes isolates tested rather than to any changes in metronidazole susceptibility in other anaerobe species. However, Y-688 was two- to fourfold less active than trovafloxacin against members of the B. fragilis group but four to eight times more active than trovafloxacin against other gram-negative rods such as Fusobacterium and Prevotella spp. (Table 1). Y-688 had activity similar to those of trovafloxacin, meropenem, and metronidazole against gram-positive anaerobic cocci (Table 2). Similarly, for either spore-forming or non-spore-forming gram-positive bacilli Y-688 was equipotent to trovafloxacin and meropenem (Table 2).

The MIC₅₀s for Bacteroides spp. B. distasonis, B. ovatus, B. thetaiotaomicron, B. uniformis, and B. vulgatus and for a Bifidobacterium species were the highest, namely, 1 mg/liter, while those for P. magnus, Peptostreptococcus micros, and Prevotella intermedia were the lowest, namely, 0.015 mg/liter. The MICs of Y-688 against those genera or species for which fewer than five representatives were tested, B. caccae (1), B. eggerthii (3), B. ureolyticus (3), Fusobacterium necrophorum (1), Fusobacterium sp. (1), Peptostreptococcus prevoti (2), Porphyromonas asaccharolytica (1), Porphyromonas gingivalis (1), Prevotella buccae (4), Prevotella loescheii (2), and a Propionibacterium sp. (2) (the numbers in parentheses are the numbers of isolates) were <1 mg/liter except for a single isolate of P. buccae (MIC, 4 mg/liter). The MICs for single strains of Clostridium paraputrificum and Clostridium clostridioforme of quinolones were high, and the C. paraputrificum isolate was also resistant to metronidazole (MIC, 32 mg/liter; Table 1). The meropenem MICs for all strains tested were <4 mg/liter except for single strains of Actinomyces meyeri (MIC, 4 mg/liter) and Actinomyces viscosus (MIC, 8 mg/liter) and three strains of Lactobacillus spp. (MICs, 8, 16, and 16 mg/liter). As expected, metronidazole MICs of 8 mg/liter were noted among Actinomyces spp. Lactobacillus spp., and Propionibacterium spp.

There are at present a number of fluoroquinolone derivatives with greater in vitro activity against anaerobic bacteria than ciprofloxacin and ofloxacin (8). Perhaps the most active thus far described is E5068, with a MIC₅₀ and a MIC₉₀ of 0.03 and 0.25 mg/liter, respectively, against the B. fragilis group (1). Clinafloxacin (CI960, PD 127391), DU 6859a, and Bay y3118 have MIC₉₀s of 0.12 to 0.5 mg/liter for these bacteria (6, 12, 15, 16), while WIN 57273 and clinafloxacin inhibited >95% of 300 mixed anaerobe strains (5) at 2 mg/liter. Bay y3118 and DU 6859a also have excellent activities against a wide range of anaerobes (11, 14, 16). However, WIN 57273 and Bay y 3118 are not being developed because of toxicity problems.

Other fluoroquinolones are not quite as active; for example, trovafloxacin had an MIC₉₀ of 1 mg/liter against 400 mixed anaerobes but is more active than CI990 (95% of strains inhibited by 16 mg/liter), sparfloxacin, or temafloxacin (2, 5). All of the above are more active than levofloxacin. Y-688 has an MIC₉₀ of 1 mg/liter, indicating that it has activity similar to those of trovafloxacin and also Bay 12-8039 (9). However, Y-688 is two- to fourfold less active than trovafloxacin or Bay 12-8039 against the B. fragilis group, which is of concern in view of their importance as human pathogens. Besides the in vitro activity against anaerobes, bactericidal activity, inoculum effect, postantibiotic effect, toxicology, and performance in in vitro and animal models and human pharmacokinetics will have to be taken into account prior to deciding doses and frequency of dosing for human treatment studies and the further development of Y-688.