ANTIMICROBIAL AGENTS AND CHEMOTHERAPY, Sept. 1988, p. 1336-1340 0066-4804/88/091336-05$02.00/0 Copyright C 1988, American Society for Microbiology Vol. 32, No. 9 In Vitro Activity of, an Optically Active TSUTOMU UNE,* TERUO FUJIMOTO, KENICHI SATO, AND YASUAKI OSADA Research Institute, Daiichi Seiyaku Co., Ltd., 1-16-13, Kitakasai, Edogawa, Tokyo 134, Japan Received 10 March 1988/Accepted 14 June 1988, the S-(-)-isomer of ofloxacin, was generally twice as potent as ofloxacin against a variety of gram-positive and gram-negative pathogens, and its action was bactericidal. The compound was characterized by having the highest level of activity against staphylococci, Bacteroides fragilis, and Peptococcus spp. of the fluorinated quinolones tested, including ofloxacin, ciprofloxacin, fleroxacin, and. The activity of was not affected by different media, inoculum size, or human serum, but decreased under acidic conditions at ph 5.0 or in human urine. During the past decade, the development of fluorinated quinolones such as norfloxacin (6), ofloxacin (10), ciprofloxacin (12), fleroxacin (3), and (4) has been aimed mainly at enhancing activity against gram-negative and gram-positive pathogens. Among these compounds, ofloxacin (10) is characterized chemically by a tricyclic structure with a methyl group at the C-3 position in the oxazine ring, thus providing an asymmetric center at this position (Fig. 1). In the course of studies on the structure-activity relationships between stereochemistry and activity, two optically active isomers of ofloxacin, i.e., [S-(-)-ofloxacin] and DR-3354 [R-(+)-ofloxacin], were prepared successfully by use of their optically resolved synthetic intermediates (Fig. 1) (2). A preliminary study of the spectrum of activity of these isomers against selected laboratory strains revealed that was 8 to 128 times more potent than DR-3354 and approximately twice as active as ofloxacin (2). In this paper we describe the in vitro activity of, relative to other fluorinated quinolones, against a large number of clinical isolates. MATERIALS AND METHODS Compounds. and ofloxacin were synthesized at the Research Institute, Daiichi Seiyaku Co., Ltd., Tokyo, Japan, as were ciprofloxacin, fleroxacin, and. sodium (Banyu Pharmaceutical Co., Ltd., Tokyo, Japan) and clindamycin phosphate (Japan Upjohn Ltd., Tokyo, Japan) were commercial products. Organisms. Each strain we used was a fresh clinical isolate. The isolates were obtained from patients in geographically separate medical centers in Japan (one isolate per patient). Determination of MICs. The MICs were determined by standard agar dilution techniques (8) with Mueller-Hinton agar (Difco Laboratories, Detroit, Mich.). Chocolate agar was used for streptococci and Haemophilus influenzae. GC agar (Difco) supplemented with 1% hemoglobin and 1% IsoVitaleX (BBL Microbiology Systems, Cockeysville, Md.), GAM agar (Nissui Seiyaku Co., Ltd., Tokyo, Japan), and GAM agar supplemented with 5% defibrinated horse blood were used for Neisseria gonorrhoeae, Bacteroides fragilis, and Peptococcus spp., respectively. One loopful (5 RI) of an inoculum corresponding to about 105 CFU was applied per compound-containing agar plate, and the plates were incubated for 20 h at 37 C, except for B. fragilis and * Corresponding author. 1336 Peptococcus spp., which were incubated for 48 h. H. influenzae and N. gonorrhoeae were incubated in a candle jar. B. fragilis and Peptococcus spp. were incubated in an anaerobic cabinet. The MIC was defined as the lowest drug concentration which prevented visible growth of bacteria. Determination of MBCs. The bactericidal test was performed by the method described by Taylor et al. (11) with an inoculum of 5 x 105 CFU/ml and a subculture volume of 10,lI. The MBCs were defined as the lowest drug concentrations that produced 99.9% or greater killing of the initial inoculum (9). RESULTS Antibacterial activity. The overall activity of compared with that of reference drugs is shown in Table 1. The MICs of at which 90% of the isolates were inhibited (MIC%0s) were,, and,ug/ml against methicillin-susceptible strains of Staphylococcus aureus, Staphylococcus epidermidis, and Staphylococcus saprophyticus, respectively; i.e., the MICs were,ug or less of methicillin per ml. Thus, was 2 to 8 times more potent than ofloxacin, ciprofloxacin, fleroxacin, and NY- 198. was also active against methicillin-resistant staphylococci at concentrations almost equal to those for activity against methicillin-susceptible strains. Against Streptococcus pneumoniae, Streptococcus pyogenes, and Enterococcus faecalis, the MIC%0s of ranged from 0 F 9 OCOOH N ~~N4 3 ~~~~~2 : R = - CH3 : R='NCH3 DR-3354: R=-auICH3 FIG. 1. Chemical structure of ofloxacin and its optical isomers [S-(-)-ofloxacin] and DR-3354 [R-(+)-ofloxacin]., the racemic mixture of S and R isomers at a 1:1 ratio, is an anhydrous compound, whereas each isomer is a hemihydrate.
VOL. 32, 1988 ACTIVITY OF OPTICALLY ACTIVE OFLOXACIN 1337 TABLE 1. Antibacterial activities of and other drugs against fresh clinical isolatesa Drug MIC (kg/mil) Staphylococcus aureus (42) - - - - - - Staphylococcus epidermidis (40) Staphylococcus saprophyticus (13) -resistant staphylococci (42)b Streptococcus pneumoniae (54) Streptococcus pyogenes (41) Enterococcus faecalis (50) Escherichia coli (50) - - - - - - - - - - - - - -> -> -> -> -> - - - - - - - - -> -> - - - -> -> 0.013-0.0-0.006- - - > 0.0 0.013 > 0.013 Klebsiella spp. (60)C 0.013-0.0-> -0.003-0.0-> 0.0-> Proteus spp. (49)d 0.013- - 0.013- - - 0.0 Continued on following page
1338 UNE ET AL. ANTIMICROB. AGENTS CHEMOTHER. TABLE 1-Continued Drug MIC (,ug/ml) MorQanella moreanii (19) 1J^-111 J-. IVJ"1,5L4rMltL9 fr9"1,5e4ff9l k.l-lj - - 0.013-0.0 - - Providencia spp. (18)' Enterobacter spp. (33)f Citrobacterfreundii (20) Serratia marcescens (50) Pseudomonas aeruginosa (50) Xanthomonas maltophilia (24) Alcaligenes faecalis () Haemophilus influenzae (22) Neisseria gonorrhoeae () Bacteroides fragilis (41) Clindamycin 0.0- - 0.006- - - 0.013-0.0-0.006- - - - - 0.013- - - - -> - -> -> - - - - - - -> - - -> 0.0-> -> 0.0-> -> -> 0.0-0.013- - 0.013-0.013-0.006-0.0-0.0- - -> -> -> -> 0. 19->100 0.0 0.0 0.0 0.0 0.0 0.0 50 > > > > > 0.0 0.0 >100 Continued on following page
VOL. 32, 1988 ACTIVITY OF OPTICALLY ACTIVE OFLOXACIN 1339 TABLE 1-Continued Drug MIC (vg/ml) Peptococcus spp. ()8 - - - - - Clindamycin ->100 >100 Agar dilution; 105 CFU. b Includes 28 S. aureus and 14 S. epidermidis strains. ' Includes 40 K. pneumoniae and 20 K. oxytoca strains. d Includes 40 P. mirabilis and 9 P. vulgaris strains. eincludes 10 P. rettgeri and 8 P. stuartii strains. f Includes 18 E. cloacae and 15 E. aerogenes strains. g Includes 18 P. magnus, 6 P. asacc-harolyticus, and 1 P. prevotii strains. to p.g/ml; its activity was roughly comparable to that of ciprofloxacin and 2 to 8 times higher than those of ofloxacin, fleroxacin, and. Against various members of the family Enterobacteriaceae, the activity of was equal to or slightly less than that of ciprofloxacin and 2 to 4 times higher than those of ofloxacin, fleroxacin, and. inhibited most isolates (90%) of Escherichia coli, Klebsiella spp., Proteus spp., Morganella morganii, Providencia spp., Enterobacter spp., Citrobacter freuindii, and Serratia marcescens at,,,,,,, and,ug/ml, respectively. Glucosenonfermenting gram-negative bacteria, including Pseudomonas aeruginosa, Xanthomonas maltophilia, and Alcaligenes faecalis, were less susceptible to than were members of the family Enterobacteriaceae. Against P. aeruginosa, inhibited 50% and 90% of the isolates at concentrations of and 50,ug/ml, respectively; its activity was inferior to that of ciprofloxacin but superior to those of ofloxacin, fleroxacin, and. The activity of against X. maltophilia and A. faecalis was twice as high as those of the reference quinolones tested, with MICs against 50% of isolates (MIC50s) of and,uglml, respectively. H. influenzae and N. gonorrhoeae were highly susceptible to, which had MIC90s of 0.0 and,ug/ ml, respectively. was more than 2 to 8 times as active as ofloxacin, ciprofloxacin, fleroxacin, and against B. fragilis and Peptococcus spp., including those resistant to clindamycin. Factors affecting the activity. The activity of against S. aureus 209P, E. coli NIHJ, and P. aeruginosa 32104 was the same or varied by one dilution when five different media (Mueller-Hinton, nutrient, brain heart infusion, heart infusion, and tryptose blood agars) were used (data not shown). Varying the ph of Mueller-Hinton agar between 6.0 and 8.0, adding 50% human serum to the medium, or increasing the inoculum size from 103 to 107 TABLE 2. Bactericidal activity of against fresh clinical isolates MIC (,±g/ml)a MBC (1gIml)b 50% 90% 50% 90% Staphylococcus aureus (50) Escherichia coli (47) Pseudomonas aeruginosa (50) 100 100 a Broth dilution; 5 x 105 CFU/ml. b.99.9% killing. CFU had no significant effect on the activity of against each strain (data not shown). However, its activity decreased 4- to 16-fold under acidic conditions at ph 5.0 or in human urine, as did that of ofloxacin and ciprofloxacin (data not shown). Bactericidal activity. The bactericidal activity of against 47 or 50 isolates each of S. aureus, E. coli, and P. aeruginosa is shown in Table 2. The MBCs at which 50% and 90% of isolates were killed (MBC50 and MBC90, respectively) of against each species were identical to the M'C50 and MIC90, respectively, indicating that is highly bactericidal. Although data are not shown, both ofloxacin and ciprofloxacin were also verified to be bactericidal. DISCUSSION is an interesting new quinolone with a broad spectrum of activity, and its action was bactericidal. The compound was characterized by its high level of activity against staphylococci and anaerobes, including those resistant to methicillin and clindamycin, respectively; however, it exhibited slightly less activity than ciprofloxacin against gram-negative pathogens, including P. aeruginosa. was generally twice as potent as ofloxacin, and no isolates showed higher susceptibility to ofloxacin than to. The difference in activity between these two compounds has been shown to be largely attributed to their anti-dna gyrase activity (5, 7, 13). Gerster et al. (1) reported that the S-isomer of the tricyclic quinolone analog fused with a piperidine ring was also much more active than the R-isomer and tended to be twice as active as the racemic mixture. After peroral administration to laboratory animals, DR- 3355 was well absorbed, was distributed rapidly to various tissues, and was excreted efficiently in the urine as an unchanged form, and no chiral inversion from to DR-3354 occurred in vivo (H. Tachizawa, 0. Okazaki, T. Kurata, K. Mitsugi, and Y. Ezumi, Program Abstr. 27th Intersci. Conf. Antimicrob. Agents Chemother., abstr. no. 260, 1987). Interestingly, and DR-3354 were 10 times more soluble in water than ofloxacin, although the reason has not been clarified (T. Une, T. Fujimoto, and Y. Osada, 27th ICAAC, abstr. no. 9, 1987). These favorable pharmacokinetic and physicochemical properties of DR- 3355, coupled with its excellent in vitro potency, indicate that the compound might prove to be a useful quinolone as both oral and parenteral formulations.
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