S377 Patterns of Susceptibility to Fluoroquinolones Among Anaerobic Bacterial Isolates in the United States Ellie J. C. Goldstein From R. M. Alden Research Laboratory, Santa Monica Hospital Medical Center, Santa Monica; and UCLA School of Medicine, Los Angeles, California The activity of the fluoroquinolone antibiotics against anaerobic bacteria has generally been moderate to poor. Nalidixic acid and cinoxacin show poor activity against almost all anaerobes. and enoxacin exhibit poor anaerobic activity (MIC 90, 8 >256 tig/ml) except against Clostridium perfringens, Bacteroides ureolyticus, and some eubacteria. is slightly more active than enoxacin against some Bacteroides species. While ciprofloxacin is more active than earlier fluoroquinolones against anaerobes such as Bacteroides fragilis (MIC 90, 4-16 tig/ml), fusobacteria, and peptostreptococci, its activity is often variable and its MIC 90 is frequently close to the maximal level attainable in serum. is active against B. fragilis (MIC90, 4-8 gg/ml) but not against other species of the B. fragilis group (MIC90, 8-32 Ag/mL); other anaerobes (e.g., peptostreptococci and fusobacteria) are generally susceptible to <8 Ag of ofloxacin/ml. Several newer quinolones exhibit improved anaerobic activity (although the studies yielding relevant data have often used diverse methods, small numbers and varieties of isolates, and different breakpoints). and inhibit 95% of strains tested at <2 Ag/mL., sparfloxacin, and temafloxacin inhibit most anaerobes at <2 gg/ml, but clustering around the breakpoint and strain variability have been noted. is active against more than 85% of B. fragilis strains (MIC90, 4 Ag/mL), but other species of the B. fragilis group often require >4 gg/ml for inhibition; Prevotella bivia, Fusobacterium varium, and Fusobacterium ulcerans are usually resistant. inhibits more than 75% of B. fragilis isolates but fewer than 50% of other B. fragilis group isolates at <2 p.g/ml. With the exact figure depending on the breakpoint chosen, temafloxacin is active against more than 85% of all B. fragilis group species at 4 itg/ml. The fluoroquinolones are an expanding group of synthetic compounds that are increasingly used for a variety of clinical indications. While their activity against aerobic bacteria is excellent and has been well studied, their activity against anaerobic bacteria has generally been moderate to poor. Consequently, attempts to synthesize new compounds with improved anaerobic activity continue. This paper reviews the activity of several quinolones against anaerobic bacteria in various stages of development, as detailed in some of the reports generated from centers in the United States (table 1). Nalidixic Acid and the Early Quinolones In 1962, Lesher et al. [14] noted the synthesis of 1,8- naphthyridine derivatives, including nalidixic acid, but did not report on the activity of these compounds against anaerobic bacteria. In 1973, Wick et al. [15] tested nalidixic acid against three strains of Bacteroides species and one strain of Fusobacterium species by agar dilution (using brain-heart infusion agar supplemented with 5% defibrinated rabbit blood) Reprints or correspondence: Dr. Ellie J. C. Goldstein, 2021 Santa Monica Boulevard, Suite 640E, Santa Monica, California 90404. Clinical Infectious Diseases 1993;16(Suppl 4):S377-81 1993 by The University of Chicago. All rights reserved. 1058-4838/93/1606-0038$02.00 and found MICs of 256 tig/ml. The same authors also tested three strains of Clostridium perfringens and one of Clostridium tetani and documented MICs of 32 and 8 p,g of nalidixic acid/ml, respectively. Most other studies of the activity of nalidixic acid against anaerobic bacteria were published more than 20 years after the initial work by Lesher and associates. These studies compared nalidixic acid with the first fluoroquinolone, norfloxacin [3]; a number of the studies were conducted in European or Japanese laboratories (see below) [16-18, 22]. In general, researchers noted the poor activity of nalidixic acid against anaerobic bacteria. In 1968, Turner et al. [19] reported the synthesis of the first quinolone, oxolinic acid, but did not test the drug against anaerobic bacteria. Wick et al. [15] reported the activity of cinoxacin and nalidixic acid against the eight anaerobic strains noted above and found that the two agents had similarly poor activity. In 1980, Ito et al. [1] introduced the first of the fluoroquinolones, norfloxacin, and documented its expanded spectrum of activity against aerobic bacteria. In 1987, a review of the literature on studies of in vitro susceptibility to norfloxacin noted the drug's activity to be generally poor against anaerobes [16]. The authors used different methodologies and failed to identify their anaerobic isolates to the species level. In general, MICs of norfloxacin were tig/ml for Bacter-
S378 Goldstein CID 1993;16 (Suppi 4) Table 1. Summary of selected published studies of the in vitro activity of various fluoroquinolones against anaerobic bacteria. Organism, quinolone, no. of strains tested MIC (pg/ml) MIC50 MIC90 Maximum MIC Reference Organism, quinolone, no. of strains tested MIC (gg/ml) MIC50 MIC 90 Maximum MIC Reference Bacteroides fragilis 25 12 12 12 [1] 51 32 64 >64 [2] 15 16 32 32 [3] 51 4 16 >64 [2] 23 4 8 >128 [4] 73 8 16 >32 [5] 30 8 16 >16 [6] 11 4 4 8 [7] 15 4 16 16 [8] 20 4 8 16 [9] 15 2 4 4 [3] 51 4 4 >64 [2] 23 2 8 64 [4] 15 2 8 8 [8] 11 2 4 8 [10] 23 1 4 16 [4] 73 2 4 4 [5] 30 2 2 2 [6] 15 2 2 2 [8] 23 1 4 32 [4] 22 2 4 16 [5] 11 1 2 4 [7] 30 0.5 1 1 [6] 23 0.1 0.5 2 [4] 23 2 4 16 [4] 23 0.2 0.5 2 [4] 24 0.5 2 2 [5] 20 0.2 0.2 0.2 [9] B. fragilis group 20 128 256 >256 [3] 122 8 32 256 [11] 45 16 32 64 [5] 30 16 >16 >16 [6] 10 (B. distasonis) 2 8 64 [ 10] 14 (B. thetaiotaomicron) 16 16 256 [ 10] 12 (B. ovatus) 16 32 32 [10] 12 (B. vulgates) 4 8 16 [ 10] 81 4 4 16 [5] 30 2 4 16 [6] 45 4 8 32 [5] 30 1 2 8 [6] 32 0.2 0.5 0.5 [12] 45 0.5 1 2 [5] Clostridium perfringens 12 0.5 0.5 0.5 [4] 10 0.1 0.5 2 [8] 12 0.5 0.5 0.5 [7] 11 2 4 16 [5] 10 0.5 1 1 [10] 12 0.5 0.5 1 [4] 10 0.5 0.5 2 [8] 12 0.2 0.5 0.5 [4] 10 0.1 0.5 1 [8] 11 1 2 8 [5] 12 0.2 0.5 0.5 [4] 12 0.2 0.2 0.5 [7] 12 0.06 0.1 0.1 [4] 12 0.1 0.2 0.2 [4] 12 0.01 0.03 0.06 [4] Peptostreptococcus 15 4 8 16 [3] 15 1 2 4 [3] 11 0.5 2 2 [13] 22 1 4 8 [4] 10 0.5 2 8 [9] 15 0.5 4 4 [6] 22 1 4 8 [5] 83 1 8 16 [11.] 8 0.5 8 8 [2] 20 0.5 8 16 [10] 22 0.2 1 16 [4] 8 0.5 4 4 [2] 22 0.2 1 4 [4] 15 0.5 1 2 [6] 22 1 2 8 [5] 22 0.2 2 2 [4] 17 1 2 2 [7] 10 1 1 8 [5] 15 0.5 2 4 [6] 22 0.3 0.5 0.5 [4] 22 0.2 2 2 [4] (PD131628) 15 0.2 1 1 [13] 17 1 2 2 [7] 22 0.3 0.1 0.2 [4] 10 0.3 0.1 0.5 [9]
CID 1993;16 (Suppl 4) Fluoroquinolones vs. Anaerobes S379 oides fragilis, and MIC90 values were >128 µg/ml for other species of the B. fragilis group. Except for Bacteroides ureolyticus, C. perfringens, and some Eubacterium species, the majority of other anaerobes were resistant to norfloxacin (MIC90 > 16 µg/ml). Neu and Labthavikul [20] noted norfloxacin MICs of 12.5 µg/ml for all of the 25 strains of B. fragilis tested. Goldstein and Citron [3], using the Wadsworth agar dilution method, studied the activity of enoxacin against 118 anaerobes and found it to be similar to (often within one dilution of) that of norfloxacin. was slightly more active than enoxacin against some Bacteroides species. was more active than earlier compounds against B. fragilis, fusobacteria, C. perfringens, and peptostreptococci [1-7, 9, 10, 14, 19, 21, 23]. However, its activity was often variable; moreover, the level of activity differed among studies, and the MIC 90 was often close to the maximal levels attainable in serum [21]. Phillips and King [22] reviewed the activities of ciprofloxacin and eight other 4- quinolones against anaerobic bacteria and found modest results at best. Since ciprofloxacin is widely used clinically, many recent studies of new fluoroquinolones have used it as a reference agent [2, 4-9, 12, 13] and again have found its activity to be modest. B. fragilis species are generally more susceptible to ciprofloxacin and to all other fluoroquinolones than are other members of the B. fragilis group. possesses an oxazine ring that results in slightly improved anaerobic activity [2, 10, 23, 24]. Fuchs [23] summarized information on the activity of ofloxacin against anaerobes; against the B. fragilis group, MIC 90 values "were categorized as intermediate and resistant," but the drug was active against C. perfringens (MIC 90, 1 µg/ml). In a study of the activity of ofloxacin alone and in combination with metronidazole against 177 anaerobes isolated from intraabdominal infections, Goldstein and Citron [10] found that some strains of B. fragilis were susceptible to ofloxacin (MIC90, 4 µg/ml) but that most other species of the B. fragilis group especially Bacteroides thetaiotaomicron (MIC 90, 16 µg/ml) and Bacteroides ovatus (MIC90, 32 pg/ml) were resistant to this agent. All strains of Fusobacterium nucleatum and Fusobacterium necrophorum, some strains of Fusobacterium mortiferum and Fusobacterium varium, all C. perfringens strains, all Eubacterium species, and most peptostreptococci were susceptible to ofloxacin (MIC, ml). In combination, ofloxacin and metronidazole generally exhibited indifference; no antagonism was found. Isolates associated with disease of the female genital tract (Prevotella intermedia, Prevotella melaninogenica, Prevotella bivia, Porphyromonas asaccharolytica, and peptostreptococci) were generally susceptible to ofloxacin. Chin et al. [8] noted MIC90 values of 8 µg/ml for 15 strains of B. fragilis and 0.5 µg/ml for 10 strains of C. perfringens tested against ofloxacin. (1-cyclopropy1-7-[2,6-dimethy1-4-pyridiny1]- 6-fluoro-1,4-dihydro-4-oxo-3-quinoloncarbylic acid) appears to be quite active against almost all anaerobic bacteria, including members of the B. fragilis group, with MIC 90 values of µg/ml [4, 5, 9, 12]. Occasional strains of Clostridium limosum, Fusobacterium gonidiaformans, the F. mortiferum-varium group, and P. melananinogenica are resistant. Jones and Barry [12] found, unlike other quinolones, to have increased activity at a low ph but also noted some solubility problems. (PD 127391 and AM 1091) (7-[3-amino-l-pyrrolidinyl] 8-chloro- 1 -cyclopropy1-6-fluoro- 1, 4- dihydro-4-oxo -3-quinolinecarboxylic acid) is also exceedingly active against almost all genera of anaerobic bacteria, with MIC 90 values of µg/ml [4]. Peptostreptococci, Propionibacterium species, nonpigmented Prevotella species, P. bivia, fusobacteria, Actinomyces, and C. perfringens are highly susceptible to. Only occasional strains of Bacteroides caccae, Clostridium ramosum, and P. melaninogenica have MICs of >4 pg of /ml. While all B. fragilis group species are very susceptible to, strains of B. thetaiotaomicron are the least susceptible, with an MIC 90 of 2µg/mL. (PD 131628) ([S]-7-[3-amino-l-pyrrolidiny1]-1- cyclopropy1-6-fluoro- 1, 4-dihydro-4-oxo-1, 8-naphthyridine -3-carboxylic acid) is active against all peptostreptococci and against 87% of B. fragilis strains at s 2 µg/ml [4]. While many strains of the B. fragilis group are susceptible (MIC 50, 2 µg/ml), some strains of B. thetaiotaomicron and B. vulgatus are more resistant, with an MIC 90 of 16 µg/ml. This more resistant subgroup results in an overall rate of resistance of 28% among B. fragilis group species. Almost all strains of P. bivia require >4 lig of /ml for inhibition; moreover, strains of F. varium and Fusobacterium ulcerans often have MICs of 2-4 µg/ml. Cohen et al. [13] tested PD 131628, the active metabolite of the prodrug L-analyl aminde PD 131112 (), and found an MIC 90 of µg/ml for B. fragilis group species.
S380 Goldstein CID 1993;16 (Suppl 4) inhibited most of the 290 anaerobic strains tested by Goldstein and Citron [4] at <2 ps/ml. At 4 ii.g/ml the drug was active against more than 90% of B. fragilis strains and against more than 85% of other B. fragilis group species [4, 5, 7]. For many non perfringens Clostridium species, non-spore-forming gram-positive bacilli, F. varium, F. mortiferum, and F. ulcerans, temafloxacin concentrations of >4 p,g/ml are required for inhibition. This drug is active against C. perfringens, B. ureolyticus, peptostreptococci, nonpigmented Prevotella species, and propionibacteria, with MICs of <2 Ag/mL. had been released in the United States for a number of indications and was undergoing clinical trials for anaerobic activity when it was withdrawn from the market because of safety considerations. has been tested against diverse inocula of anaerobic bacteria by a variety of methods [4-6, 8]. In general, sparfloxacin inhibits most anaerobes at <2 p.g/ml [4]. Variation in the susceptibility of the various members of the B. fragilis group has been noted [4], with MIC 90 values of 4,ug/mL for B. fragilis, B. caccae, Bacteroides distasonis, and B. ovatus; 2 Ag/mL for Bacteroides vulgatus; and 8 Ag/mL for B. thetaiotaomicron. While almost all isolates of C. perfringens are susceptible to sparfloxacin (MICs, <0.5 AgimL), other clostridia are often more resistant, with MIC90 values of 8-32 Ag/mL [4-6]. Against P. bivia, F. varium, F. ulcerans, and P. melaninogenica, sparfloxacin concentrations of 8-16 Ag/mL are often required for inhibition. Wexler et al. [5] noted lower susceptibility of their anaerobic bacterial isolates to sparfloxacin but used a breakpoint of 2 ttg/ml rather than the 4 i/g/ml used by other researchers. In one study [4], sparfloxacin was active against all strains of Actinomyces, B. ureolyticus, peptostreptococci, Prevotella buccae, Prevotella oris, and propionibacteria tested. was studied by Barry and Fuchs [6] against a limited number of anaerobes. The following MIC 90 values were noted: B. fragilis, 1 ttg/ml, other B. fragilis group species, 2 Ag/mL; Clostridium species, 0.5 Ag/mL; and peptostreptococci, 2 zg/ml. These authors also speculated that low serum levels of this drug seen in an experimental animal model might diminish the clinical importance of its apparently enhanced anaerobic potency in humans. Other Fluoroquinolones Numerous other fluoroquinolone agents, including amifloxacin, difloxacin, fleroxacin, lomefloxacin, pefloxacin, A-56620, Bay 3118, CI-934, and OPC-17116, have been subjected to even more limited in vitro testing against anaerobes and are not considered here. The search for new fluoroquinolone agents with improved anaerobic activity continues. 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