norfloxacin, a fluoroquinolone antibacterial agent

Norfloxacin, a Fluoroquinolone Antibacterial Agent

Classification, Mechanism of Action, and in Vitro Activity

ELLIE J.C. GOLDSTEIN, M.D. Los Angeles, California

Norfloxacin is an orally absorbed fluoroquinolone antibacterial with a fluorine at position 6 and a piperazine ring at position 7. These changes have resulted in a marked enhancement (compared with that of the older quinolones) of in vitro antibacterial activity. Specifi- cally, the antibacterial spectrum of norfloxacin fncludes Pseudomo- nas aeruginosa, as well as enteric pathogens. Norfloxacin is also active against both penicillin-susceptibfe and penicillfn-resistant strains of Neisseria gonorrhoeae. Relative to its activity against gram-negative bacteria, norfloxacin is somewhat less active against gram-positive cocci. In general, the staphylococci are more suscep tibte to the drug than are the streptococci. As with all fluoroquinolones, norfloxacins activity against anaerobic bacteria is poor. For urinary tract bacterial isolates, the following Bauer-Kirby disk diffusion zone-size breakpoints have been proposed: greater than or equal to 17 mm, susceptible; 13 to 16 mm, intermediate; less than or equal to 12 mm, resistant. Bacteria with minimal inhibitory concentrations (WCs) less than or equal to 16 pg/ml are considered susceptible; those with WCs greater than or equal to 32 pgirnl are considered resistant to norfloxacfn. The mechanism of action of norfloxacin involves inhibition of the A subunit of the important bacterial enzyme DNA gyrase, which is essential for DNA replication. Plasmid-mediated resistance to the fluoroquinolones is not encountered. Further, although some cross-resistance within the fluoroquinolone class has occurred, there is little cross-resistance between norfloxacin and antibiotics of other classes.

The new fluoroquinolone class of antibacterials has received increasing clinical attention in recent years [1,2]. The infectious disease community has viewed these orally absorbed, synthetically derived agents with special interest, despite the recent development of numerous beta-lactam antibiotics (including penicillins, cephalosporins, carbapenems, and mon- obactams). The newer drugs have a broad antibacterial spectrum that includes gentamicin-susceptible and gentamicin-resistant strains of Pseudomonas aeruginosa; other multi-resistant, gram-negative rods; gram-positive cocci; and beta-lactamase-producing bacteria [3-291. Fur- thermore, their mechanism of antimicrobial activity differs from that of other well-known antibiotics. The fluoroquinolones inhibit the activity of DNA gyrase, an essential bacterial enzyme involved in DNA replication [30-321; consequently, plasmid-mediated resistance to the fluoroquinolones is not encountered [l].

Norfloxacin, one of these fluoroquinolone antibacterials, was originally

From the R.M. Alden Research Laboratory, Los Angeles, California, and Santa Monica Hospital Medical Center, Santa Monica, California. Re- quests for reprints should be addressed to Dr. Ellie J.C. Goldstein, R.M. Alden Research Laboratory, 11980 San Vicente Boulevard, Suite 103, Los An- geles, California, 90049. synthesized in 1980 by the Japanese, who were the first to document its

June 26, 1967 The American Journal of Medicine Volume 62 (suppl 6B) 3

SYMPOSIUM ON NORFLOXACIN-GOLDSTEIN

Parent Nucleus

A. Carboxylic acid ring B _ Pyridine ring X . Carbon or nitrogen R - Side chain

Naphthyridine Quinolone Cinnoline Pyrido-Pyrimidine

Derivatives Enoxacin Nalidixic acid

Derivatives Ciprofloxacin Flumequine Norfloxacin Oxolinic acid Pefloxacin

Derivatives Cinoxacin

Derivatives Pipemidic acid

Norfloxacin

Igun, 1. Structure of norfloxacin and other quinolone derivatives.

broad spectrum of antibacterial activity [33]. A quinolone carboxylic acid derivative, norfloxacin (1 -ethyl6-fluoro- 1,4-dihydro-4-0x0-7-(1 -piperazinyl)S-quinoline carboxylic acid) is characterized by the addition of a fluorine at position 6 and a piperazine ring at position 7 (Figure 1). These structural changes have resulted in a marked enhancement (compared with the older quinolones) of its antibacterial spectrum.

This article reviews (1) the classification of norfloxacin and other fluoroquinolones; (2) the proposed mechanism of action of the fluoroquinolones; and (3) published reports in the international literature of the in vitro antibacterial activity of norfloxacin.

CLASSIFICATION

In a study of new antibacterial agents, Lesher and associates [34] prepared a number of 1 ,&naphthyridine carboxylic acid derivatives; nalidixic acid was considered the outstanding compound in this series. As can be seen in

Figure 1, it has a bicyclic, heteroaromatic system made up of a carboxylic acid ring (A) and a substituted pyridine nucleus (6) with nitrogen atoms at positions 1 and 6. The prototype naphthyridine antibacterial, nalidixic acid, has pronounced activity against gram-negative bacteria (ex- cluding P. aeruginosa) and relatively modest activity against gram-positive organisms. Thus, in 1963, this agent was introduced in the United States for the treatment of urinary tract infections.

In 1966, Turner et al [35] reported the synthesis of oxolinic acid, which has an antibacterial spectrum similar to that of nalidixic acid. It became commercially available in 1972. By substituting a carbon for nitrogen at position 8 (Figure l), oxolinic acid became the first quinolone and the prototype for this class of antibacterials. Unlike the naphthyridine derivatives, which have two nitrogen atoms (position 1 of ring A and position 8 of ring B), true quinolone antibacterials have only a single nitrogen atom at position 1 (ring A).

Cinoxacin, released in 1975, was reported by Wick et al

4 June 28, 1987 The American Journal of Medicine Volume 82 (suppl8B)

[36] to have equivalent antibacterial activity along with superior pharmacological properties compared with nalidixic acid. It differed from oxolinic acid in the substitution of nitrogen at position 2, thereby forming the cinnoline ring [37]. Some researchers consider cinoxacin the prototype cinnoline; others consider it a nalidixic acid analogue (naphthyridine family) with a cinnoline system [37].

Subsequently, researchers throughout the world modified these two six-membered rings and, by 1977, more than 1,000 variants had been created [371. In current usage, the term quinolone is often loosely applied and used generically to refer to all members of the naphthyridine (nalidixic acid), quinolone (oxolinic acid), cinnoline (cinoxacin), and pyrido-pyrimidine (pipemidic acid) classes of antibacterials.

Norfloxacin was recently synthesized by attaching a fluorine at position 6 and a piperazine ring at position 7 to the quinolone nucleus [33]. Other fluorinated, piperazinyl analogues of the naphthyridine and quinolone families have also been synthesized and several of these are currently in clinical development [36].

The relationship between structural substitutions and antibacterial activity has previously been reviewed [37, 361. Any substitution on the quinolone nucleus is an important determinant of a quinolones in vitro activity. The A ring is considered responsible for the intrinsic effect of all analogues and most substitutions within this ring result in a loss of activity [37]. One exception is the substitution of a nitrogen at position 2, as in cinoxacin, which resulted in improved pharmacokinetics with little change in antibacterial activity [36]. Most quinolones have a methyl- substituted pyridine nucleus for ring B. However, this may be replaced by a variety of other aromatic and heterocy- clic rings without losing antibacterial activity [37]. Substitu- tions with nitrogen at positions 5, 6, 7, or 6 of the pyridine B ring will, however, decrease or abolish the activity of these compounds [36]. For example, the 6/8-dinitrogen in pipemidic acid decreases antibacterial activity but en- hances absorption. Hence, the basic structure of nalidixic acid, the quinolones, and related compounds is a bicyclic, heteroaromatic ring (A-B) system, with one of these having the characteristics of the A ring.

In addition to substitutions within the ring, numerous al- terations of the ring itself have been attempted and have produced varying degrees of activity. Most compounds, including norfloxacin, have an ethyl (C2Hs) substituent at position 1. This moiety appears to be essential for good antibacterial activity. For example, ciprofloxacin has a three-membered ring, spatially constructed to form a similar configuration as an ethyl group at position 1. Another, as-yet-to-be-named quinolone has a 4-fluorophenol group at position 1. Both have maintained antibacterial activity [38]. Modification at position 2, however, does not appear to be beneficial, and, consequently, very few such compounds have been studied. A carboxylic acid (COOH) and a ketone moiety are usually attached to positions 3 and 4,


respectively. These positions are rarely modified, as the link between the carboxylic acid and the ketone moiety seems to be necessary for binding of these compounds to DNA gyrase, [38] and, therefore, for the antibacterial activity of these agents.

Whereas modification at position 5 does not seem to improve antibacterial efficacy, substitutions at positions 6 and 7 do result in marked enhancement of such activity. For example, the norfloxacin nucleus has a fluorine at position 6 and a piperazinyl ring at position 7. Other halo- gens (e.g., chlorine, bromine, and iodine) have been substituted at position 6. However, only the fluorine atom has produced a dramatic increase in general antibacterial activity [38], while the piperazine ring at position 7 confers antipseudomonal activity on norfloxacin and other similar compounds. Finally, modifications at position 8 (with either fluorine or short one- to three-atom chains) appear to alter, and possibly enhance, activity against gram-positive and anaerobic organisms [38].

MECHANISM OF ACTION

The fluoroquinolone antibacterials in general, and norfloxacin in particular, are bactericidal. These agents are thought to specifically inhibit the A subunit of the enzyme DNA gyrase, a type II topoisomerase [30,31], which appears to be essential for DNA replication. However, the exact mechanism by which the fluoroquinolones cause cell death remains to be demonstrated [30].

DNA gyrases have been found in numerous bacteria and have been studied in Escherichia coli, Micrococcus luteus, P. aeruginosa, and Bacillus subtilis [Sl]. The enzyme is composed of two A subunits (with a molecular weight of 100,000 to 150,000 daltons each) and two B subunits (with a molecular weight of 90,000 to 95,000 daltons each). It has equal amounts of each subunit and requires all four entities of both types to be active. Whereas novobiocin and coumermycin Al inhibit the activity of the B subunit, the fluoroquinolones inhibit the A subunit. Since this enzyme is multifunctional, there are several alternative theories regarding the mechanism of action of these agents [31,39].

Cozzarelli [40] and Gellert [41] have reviewed the activities of DNA gyrase and have found the functions of this enzyme to include the following: (1) Supercoiling of DNA. This process involves the sign inversion model (i.e., the breaking and resealing of DNA strands) and is coupled with energy transduction. Although both novobiocin and the fluoroquinolones inhibit supercoiling, each interferes at a different sequence in the process [31]. (2) Binding of gyrase to DNA. This is site specific and is not inhibited by either novobiocin or the fluoroquinolones. (3) Relaxation of supercoiled DNA. This activity is inhibited by the fluoroquinolones but not by novobiocin. (4) Cleavage of DNA. Neither the fluoroquinolones nor novobiocin interferes with this step in the sequence. (5) Hydrolysis of adenosine triphosphate (ATP) (to adenosine diphosphate [ADP]) and

June 26, 1987 The American Journal of Medicine Volume 82 (suppl 6B) 5


Norfloxacin (1.0 mg/L)

.I I AZ E c?T

0 1 2 3 4 5 6

Time (Hours)

the associated release of energy. This step is inhibited by novobiocin, but not by the fluoroquinolones. (6) Catena- tion and decatenation of DNA. Catenation refers to the interlocking of duplex DNA rings and the resolution of these rings into component circles. This step is inhibited by both the fluoroquinolones and novobiocin. Thus, in general, the fiuoroquinolones inhibit those reactions- e.g., supercoiling, relaxation, catenation, and decatenation-that require the breaking and reuniting of DNA strands.

DNA was recognized as a constituent of chromosomes more than 70 years ago. However, it was not until Watson and Crick elucidated the double-helix structure of DNA that the field of molecular biology and microbial genetics was revolutionized [42]. This technologic advance made it possible to analyze the antibacterial activity of the fluoroquinolones on a molecular level, knowledge of which since 1952 has come primarily from work with E. coli [42].

As the repository of genetic information, DNA directs the manufacture of cellular proteins. Information from DNA is transcribed by messenger RNA (mRNA) and car- ried to the ribosomes where it is translated, with the assistance of transfer RNA (tRNA), into specific proteins. DNA exists as two long slender strands of covalently bonded polymers, which are composed of four nucleotide bases: adenine, guanine, thymidine, and cytosine. These two polymers are twisted about each other into a right- handed helix and held together by weak hydrogen bonds linking complementary base pairs. The double helix makes a complete turn every 34 angstroms and is capa- ble of assuming many forms and reacting in many ways [43]. The topographic supercoiled state of DNA, which is controlled by topoisomerase enzymes such as DNA gyrase, is the natural state of bacterial genetic material. Thus, the supercoiling of DNA is an important element in the process of DNA replication, transcription, and genetic recombination [41].

Figure 2. The effects of norfloxacin upon DNA, RNA, arid protein synthesis were monitored by measuring the incorpora- tion of rtilthymidine, rH]uridine, or r5S]methionine administered in five- minute pulses at the times indicated after commencement of treatment with norfloxacin at 7.0 mglliter. l = RNA; 0 = protein; 0 = DNA. Reproduced with permission from PO].

E. coli have one chromosome composed of doubie- stranded DNA in a circular shape [42]. Ttiis chromosome is long and large and, in order to fit within the confines of the cell nucleus, it must twist the helix upon itself, i.e., become sup&coiled. The DNA gyrase enzyme pro- motes the energy-dependent supercoiling and uncoiling of DNA; the A and B subunits of DNA gyrase are involved in different steps of the supercoiling process [31].

In the simple bacterial cell, mRNA sequentially copies various regions of DNA. For DNA replication to occur, breaks must be present in the circular strands of DNA and each strand must act as a template for itself. There must also be exposure of the two single DNA strands in order for mRNA to gain access to the parent DNA strand and form a complementary strand. This is accomplished by relaxation of the supercoiled strands, which are coiled in a direction opposite from that of the double helix itself [31]. Replication also requires separation of the complementary parent DNA strands: these functions are accomplished by DNA gyrase. Once replication is completed, there must be separation of catenated (intertwined) rings for distribution of genetic material to daughter cells. DNA gyrase also helps accomplish this.

Wolfson and Hooper [44] have recently published a minireview of the mechanisms of action of the fluoroquinolones, i.e., as inhibitors of DNA gyrase. Alternative theories regarding the mechanism of antibacterial action of the fluoroquinolones have also been postulated. For example, Zweerink and Edison [32] studied the activity of 11 of the fluoroquinolones, including norfloxacin, on M. luteus DNA gyrase. They noted that the potency of the fluoroquinolones as DNA gyrase inhibitors did not always correlate with their antimicrobial potency [32]. This suggested that other factors, such as penetration of the drug into the bacterial cell, were important for fluoroquinolone activity. Conversely, Wright and associates (391 suggested that the fluoroquinolones might exert their antibac-

6 June 26, 1967 The American Journal of Medicine Volume 62 (suppl 6B)


terial effect by inhibiting another class of enzymes, the . tRNA synthetases.

Crumplin and associates [30], who examined the effects of norfloxacin on E. coli K12 and mutant derivatives, noted that the agent was bactericidal, specifically inhibited DNA gyrase activity, and precipitated a range of meta- bolic sequelae. They suggested that the death of norfloxacin-treated E. coli required competent RNA activity and protein synthesis (Figure 2). In fact, the addition of protein inhibitors, e.g., rifampicin or chloramphenicol, to norfloxacin-treated E. coli in vitro prevented bacterial killing in their study (Figure 3). This phenomenon has also been observed with several of the other fluoroquinolones [30,31]. Whether this observation has any in vivo clinical relevance remains to be seen, however. Crumplin et al [30] also reported that norfloxacin-treated E. coli had less enterotoxin in the periplasmic space; since local entero- toxins probably produce tissue inflammation, this may reduce patient symptoms prior to ceil death.

IN VITRO ANTIBACTERIAL ACTIVITY

Since 1980, numerous publications and literature reviews have compared the in vitro activity of norfloxacin with that of other quinolones, beta-lactams, and aminoglycosides [3-38,44,45]. These studies have used a variety of media, test conditions, and methodologies. The susceptibility of clinical isolates in general, and of pathogens isolated from specifically infected sites (e.g., the urinary tract [10,22- 251, the gastrointestinal tract [26-291, the ocular area [20], and sites affected by venereal diseases [8,13]), have been reported. In many of these studies, isolates were chosen that were resistant to multiple other antibiotics, including nalidixic acid.

The activity of norfloxacin against a wide spectrum of bacterial pathogens (more than 9,500 strains) has been reported in these studies and is shown in Tables I through VI. Additionally, several authors have published multiple reports on the comparative in vitro activity of norfloxacin; when it was not possible to discern whether entirely different isolates had been included in a report, only one of that authors (or groups) reports is cited.

In general, norfloxacin was active against a wide variety of aerobic gram-positive and gram-negative bacteria. Fur- thermore, there was little cross-resistance between norfloxacin and agents of other antibiotic classes. Nalidixic acid-resistant strains remained susceptible to norfloxacin, but were significantly less susceptible than nalidixic acid- susceptible strains [4,33,44]. The minimal inhibitory concentration of norfloxacin against 90 percent (MI&) of 1,282 strains of E. coli was less than 0.02 @ml. Addition- ally, norfloxacin was active against all the Enterobacteria- ceae and other gram-negative rods, with MI&,-, values as follows: Klebsiella species, 2 pglml (696 strains); Entero- batter species, 0.5 pg/ml (556 strains); Proteus mirabilis, 0.1 pg/ml (571 strains); and other Proteus species, 0.4 pg/ml (421 strains).

L f

1 E. co/i KU6 + Norfloxacin (2.5 mg/L)

(b) RNA 10 (a) Protein

\ b

I

30 60 90

Time (Minutes)

Vgura 3. Logarithmic phase cultures of E. co/i strain KL76 were treated with norfloxacin at 2.5 mglliter and incubated at 37%. At the times indicated, either chloramphenicol or rifampicin were added to sample cultures. Samples were re- moved at 1 B-minute intervals for viable counting. l = RNA; Cl = protein. Reproduced with permission from [30].

Norfloxacin was also active (MI& of 2 pg/ml) against 1,325 gentamicin-susceptible strains of P. aeruginosa. Against 97 gentamicin-resistant strains, norfloxacin had a MI&, of 1 w/ml and a Ml& of 8 &ml [9,16,22]. It ap peared to be active against Citrobacter species, Serratia marcescens, Morganella species, and Providencia species. Some Providencia species, non-aeruginosa Pseu- domonas species (including Pseudomonas maltophilia and Pseudomonas cepacia), and Acinetobacter calcoace- ticus var. anitratus had higher MIC& values. Occasionally, these organisms were resistant to norfloxacin.

A variety of enteric pathogens were also susceptible to norfloxacin; these included Salmonella species, Shigella species, toxogenic E. coli, Campylobacter fetus species jejuni, Vibrio cholerae, Yersinia enterocolitica, Aeromonas species, and Plesiomonas shigelloides. The agent had poor activity against Clostridium difficile, however.

One study found strains of Listeria monocytogenes to be relatively resistant to norfloxacin [6]. Other studies, however, found the agent to be active against both penicillin-susceptible and penicillin-resistant strains of Neisse- ria gonorrhoeae [7,8,13]. In fact, Crider et al [B] noted that 98 percent of the gonococci isolated from servicemen in the Philippines were inhibited by 0.125 &ml of norfloxa- tin. They did not detect a difference in susceptibility to norfloxacin between penicillinase-producing and non- penicillinase-producing strains of N. gonorrhoeae.

June 26,1987 The American Journal of Medlclne Volume 82 (euppl6B) 7

SYMPOSIUM ON NOAFLOMCIN-GOLDSTEIN

TABLE I Summary of Published in Vitro Activity of Norfloxacin against Gram-Positive Cocci

Number of MK50 MN& Maximal strains bwml) MW) MIC Reference

Staphylococcus aureus Methicillin susceptible (or not specified)

Methicillin-resistant

Staphylococcus (coagulase negative)

Staphylococcus saprophyticus Streptococcus agalaqtiae

Streptococcus bovis Enterococci

Streptococcus faecalis

Not specified

Streptococcus pneumoniae Penicillin susceptible

Penicillin resistant

Streptococcus pyogenes

Streptococcus viridans

50 115

26 16 22 30 35 15 20

100 14 34 30

25 25 30 15 16 50

9 13 20 20 50 15 20

9 10 25 10 15

26 125

20 52 50 30 25 50 20 19 16 20

10 16 20 20 10 10 20 16 20 22

1 2 4 [31 1 2 4 [41 0.6 6.3 6.3 PI 2 4 4 1161 1 4 6 (241 2 2 4 v41 2 2 2 PaI 1 1 2 1101 0.2 0.5 0.5 [71 1.6 3.1 6.3 [191 1 2 4 [41 2 4 32 171 0.5 1 1 131

0.5 1 2 131 1 1 4 [41 0.5 1 1 171 0.2 0.5 1 1101 1.6 3.1 12.5 PI 1 2 6 1241 1 1 2 v41 1 2 4 1161 2 4 4 (171 1 2 2 1181 1 3.1 12.5 1191 2 2 2 1101 4 6 6 [31 1.6 6.3 6.3 PI 2 2 4 [lOI 2 4 4 P41 4 4 4 1181 2 16 16 1101

4 4 a [31 4 a 16 [41 3.1 12.5 12.5 P31 6 6 16 1161 3.1 6.2 6.2 1191 1 2 2 [71 2 4 4 DOI 4 a 6 1241 2 4 4 1141 2 4 4 1181 2 a 16 PI 2 4 4 [171

2 4 4 6 16 16 2 6 16 4 16 32 4 4 6 2 2 4 2 32 32 1.6 6.3 6.3 4 4 32 6 25 25

[!I [lf4 [31 [41

13: El 1181 WI

8 June 26,1987 The American Journal of Medlclne Volume 82 (suppl6B)

TABLE II Summary of Published in Vitro Activity of NorfIoxacin against Qram-Negative Bacilli

Acinetobacter species A. anitratus

A. lwoffi Not specified

Citrobacter species

Escherichia coli

Nalidixic acid susceptible Nalidixic resistant Ampicillin susceptible Ampicillin resistant

Hemophilus influenzae

Klebsiella species

Natidixic acid susceptible Nalidixic resistant

15 2 4 4 60 4 6 32 16 3.1 12.5 12.5 23 1 4 4 35 1 4 4

5 4 8 8 46 1.6 6.3 50 20 ~0.06 0.25 1.0 45 0.06 0.2 2 11 0.06 2 2 33 0.1 0.4 0.8

6

SYMPOSlUMON NORFLOXACIN-GOLDSTEIN

TABLE II Summary of Published in Vitro Activity of Norfloxacin against Gram-Negative Bacilli (continued)

Number of Strains MGAI Wml) Mb0 bmU Maximal MIC Reference

K. pneumoniae K. oxytoca

Listeria monocytogenes Morganella species

Proteus mirabilis

Naiidixic acid susceptible Natidixic resistant

Other Proteus species

Providencia species Natidixic acid susceptible Natidixic resistant

Pseudomonas aeruginosa Gentamicin susceptible

Gentamicin resistant

Gentamicin susceptibility not noted

(Table II Is continued on page 11)

38 13 38 53

100 20

100 19 22 44 31 10 40 20 18 10 61 25 31

125 20 18 40 50 36 20 20 98 60 24 10 10

9 70 53 25 20 20

181 9

14

24 12 31 22 20 11 59

18 56 31 25 54 18 50

424 67 40

100 100

50 48

120

0.1 0.1 0.1 0.1 0.5 0.1 0.1 0.1 0.2 0.5 6.3 0.1 0.06 0.05 0.1

co.1 0.1

~0.06 0.06 0.01 0.1 0.5 0.03 0.2

~0.06 0.1 0.06 0.5 0.1 0.06

10.06 0.06 0.1 0.03

50.06 0.1 0.06 0.06 0.05 0.3

so.1

0.03 0.2 1 [41 8 16 16 141 0.4 3.1 6.3 PI 0.06 0.5 0.5 171

so.1 0.5 2 [lOI 0.1 0.5 2 1161 0.2 4 4 1251

0.5 0.5 0.5

4 0.5 0.5 0.8 0.5 0.1 0.5

2 2

0.4 0.4 2

2

0.2 0.5 0.5 2

12.5 0.2 0.06 0.2 0.5

10.1 0.2 0.1 0.1 0.06

0.1 0.1 0.2 0.1 2 0.1 0.2 0.2 0.1 0.1 0.06 0.4 0.06

~0.06 0.5 0.1 0.06 0.4 0.3

so.1

2 2 4 8 8 2 2 3.1 2 0.8 4 2 4

16

0.8 1.6 4 2 8 4 1.6 0.5 0.5 8

12.5 2 2 0.4 0.5 1 2 0.2 0.1 0.5 2 0.1 0.1 2 4 2 0.1 0.4 2 1 0.2 0.1 0.4 0.25 0.1 8 0.1 0.1 3.1 0.6

so.1

161 PI 1211 1161 I241 [I71 [191 [181 [2,51 PO1 PI 131 141 PI

[\!I 12,51

131 [51 [41 [41 PI (71

1241 [161 1171 [181 1191

[2,51 WI [31 [51 El 141

[161 1241 1171 1181 1191 PI [lOI

1 [=I 32 PI

8 P61 8 P21

r32 PI 8 1161 4 [31

>32 141 100 El

4 [71 10 [231 32 DOI

2 iI41 16 1241 32 t151

10 June 26, 1987 The American Journal of Medicine Volume 82 (suppl 66)


TABLE II Summary of Published in Vitro Activity of Norfloxacin against Gram-Negative Bacilli (conf~nuedj

Number of Strains M&0 b.aW MICgo MVml) Maximal MIC Reference

20 0.5 5 a v71 106 0.8 1.6 6.3 [191

59 2 4 4 P51 16 0.2 0.5 2 (1 ai 26 0.5 - 2 WI

Pseudomonas cepacia 5 12.5 12.5 25 PI Pseudomonas maltophilia 19 6.3 12.5 12.5 PI

10 ,128 2128 >12a [71 Pseudomonas species (not specified) 31 0.2 16 32 [31

93 0.5 2 16 [51 19 2 16 32 [lOI 39 1 16 32 t141

4 12.5 12.5 12.5 PI Serrafia marcescens 25 0.1 0.5 2 t31

Nalidixic acid susceptible 32 0.1 0.2 1 141 Nalidixic acid resistant 5 4 4 4 141

38 0.4 0.8 6.3 1'31 Gentamicin susceptible 33 2 4 4 P21

40 0.1 0.5 2 171 6 2 4 4 1101

14 0.1 0.1 0.5 1161 10 0.2 2 2 1241

100 0.4 3.1 10 j231 20 so.1 0.1 2 11 ai

100 0.8 12.5 100 1191 Serratia species (not specified) 20 0.1 0.1 0.2 [51

TABLE Ill Summarv of Published in Vitro Activity of Norfloxacin against Enteric Pathogens

Number of Strains Maxlinal MIC Reference

Aeromonas species

Campylobacter fetus species jejuni

Clostridium difficile Escherichia coli (toxogenic)

Plesiomonas shigelloides

Salmonella species

Shigella species

Vibrio cholerae

Vibrio parahaemolyticus

Vibrio vulnificus Yersinia enterocolitica

5 0.05 0.02 0.2 al 50.06 0.1 0.5

6 so.5 so.5 so.5 30 so.5 1 2 36 0.06 0.2 0.5 28 0.25 0.5 1 11 64 128 128 50 SO.05 so.05 1 28 0.004 0.00s 0.01

4 so.5 co.5 SO.5 17 ~0.06 ~0.06 ~0.06

7 0.06 1 1 50 co.5 so.5 1 19 0.05 0.1 0.2 27 0.01 0.06 0.06 ia 0.1 1 1 20 0.06 0.06 0.1 27 0.06 0.1 1 a0 so.5 co.5 1 21 0.05 0.1 0.2 40 0.01 0.06 0.1 20 0.03 0.03 0.03 25 0.01 0.03 0.03 40 0.01 0.01 0.25 26 0.008 0.01 0.01 22 0.1 0.2 0.2 10 0.66 0.06 0.2

9 co.05 SO.05 SO.05 19 0.06 0.06 0.25 14 co.5 so.5 so.5 la ~0.06 ~0.06 ~0.06 25 0.06 0.03 0.03

PI wi WI WY 171 w PI 1261 P91

[El [51 WI El

[!ii] [la] BJI P4 PI

[!I P91 VI WI WI WI [=I (271 [=I V61 1291

June 26,1967 The American Journal of Medicine Volume 62 (suppl 66) 11


TABLE IV Summary of Published in Vitro Activity of Norfloxacin against Anaerobic Bacteria

Number of MN& mll Maximal Strains ho/ml) bo/mU MIC RefefOllC@

Bacteroides fragilis group

Other Bacteroides species

Clostridium perfringens Other Clostridium species

(Non-perfringens, nondiiicile)

Fusobacterium species

Peptostreptococcus species

24 13 20 1st 10 12 12 26 17 17

17 9

18 13

6 10

2

6.3 25 >lOO PI 32 32 128 WI

128 256 512 1121 16 32 32 1121 16 128 128 1141 32 128 128 1181 25 >lOO >lOO WI

8 128 512 WI 8 64 128 P41 1.6 1.6 12.5 WI

16 32 32 128 32 128

8 32 8 16 2 16 2 4

64 2128

128 128

16 128 -

P21 1141 Ifs1 P21 1141 1141 US1

Other 8. fragilis group. +B. fragilis group.

TABLE V Summary of Published in Vitro Activity of Norfloxacin against Neisserla gonorrhoeaa

Number ot ma wa Maximal Streins bo/mU Wml) MC Reference

Neisseria gonorrhoeae Beta-lactamase negative (or not specified)

Beta-lactamase positive

50 SO.06 SO.06 ~0.06 14 0.05 0.1 0.1

5 0.03 0.06 0.06 52 0.03 0.1 0.1 56 0.15 so.1 0.3 48 0.01 0.01 0.01 17 0.01 0.03 0.03 48 0.05 1.0 1.0 58 0.06 0.1 0.5 16 so.1 0.3 0.3

131 PI

Is: 1131 P41 WI WI PI

1131

TABLE VI Summary of Published in Vitro Activity of Notfloxacin against Mycobacteria

Number of MlCp Mb0 Maximal Ntrainr Wml) bolml) MtC Reference

Mycobacterium tuberculosis 20 4 8 8 1471 Mycobacterium fortuitum 20 0.5 2 >16 1471 Mycobacterium avium complex 20 16 >16 >16 [47l Mycobacterium chelonas 20 16 >16 >16 [47l Mycobacterium kansasii 20 16 >16 >16 [47l

Whereas norfloxacin is extremely active against gram- agulase-negative staphylococci, are susceptible to nor- negative pathogens, it is relatively less active against floxacin. In general, staphylococci are more susceptible to gram-positive cocci. However, Staphylococcus species, norfloxacin than are streptococci. For example, the MIC& including methicillin-susceptible and methicillin-resistant of norfloxacin for enterococci, including many Streptococ- S. aureus, Staphylococcus saprophyticus, and other co- cus faecalis, is 8 m/ml, and, in a multicenter study, enter-

12 June 26,19S7 The American Journal of Mdlclne Volume 82 (suppl6B)


TABLE Vii Quality Control Limits, Proposed interpretive Zone Standards,* and MiCs for Susceptibility Testing with Norfioxacin against Urinary Bacterial isolates

Organism ATCC Number Ouality Control limits (mm)

Escherichia coli Staphylococcus aureus Pseudomonas aeruginosa

Susceptible Moderately susceptible Resistant

25922 25923 27853

Zone 47 mm

13-16 mm 512 mm

28-36 17-28 22-29

MC 516 pg/ml

232 pglml

ATCC = American Type Culture Collection. *10-w disk standards derived from [46,48].

ococci and group D non-enterococci accounted for a large percentage of the norfloxacin-resistant strains [46].

The activity of ail fluoroquinoione antibacteriais against anaerobic bacteria is poor [6,12,14,18,19]. Most studies have not differentiated between Bacteroides fragilis and other members of the B. fragiiis group (e.g., Bacteroides distasonis, Bacteroides vuigatus, and Bacteroides thetaiotaomicron, among others); Goldstein and Citron [12], however, did speciate anaerobic isolates. They noted that B. fragilis strains were somewhat more susceptible to norfloxacin than were other B. fragilis group strains [12]. With the exception of Bacteroides ureolyticus, Cios- tridium perfringens, and some Eubacterium species, the majority of anaerobes (including gram-positive cocci and rods and gram-negative rods) were relatively resistant to norfioxacin. Some variation in results from study to study may be related to methodoiogic and technical considera- tions, as well as to the lack of anaerobic speciation in many of the trials.

Gay and associates [47] studied the activity of norfloxa- tin against 100 isolates of mycobacteria. They noted that the range of MiCs for individual isolates of each species varied widely. isolates of Mycobacterium tuberculosis and Mycobacterium fortuitum were usually more susceptible to norfloxacin (MI&, values of 8 pg/ml and 2 pg/ml, respectively) than were isolates of Mycobacterium avium complex, Mycobacterium kansasii, and Mycobacterium cheionei (MI&-, values greater than 16 pg/mi) [47].

Preliminary studies have found norfioxacin to be active against isolates of Campyiobacter pyioridis. it was not active against Chlamydia trachomatis [48-501. However, Meier-Ewert et al [49] tested norfioxacin against five strains of C. trachomatis and found that although 5 pg/ml reduced iodine-stainable inclusions by at least 50 percent, 20 pg/mi was required for inhibition of replication.

The proposed quality control limits and interpretive standards for disk diffusion testing and determination of MiCs for norfioxacin are shown in Table Vii. Using a lo-pg disk, Shungu et al [46,51] proposed the following

June 26,1987

interpretive zone-size breakpoints for urinary tract bacterial isolates: greater than or equal to 17 mm, susceptible; 13 to 16 mm, moderately susceptible (intermediate): less than or equal to 12 mm, resistant. Because of differences in antibacterial spectra and pharmacokinetic properties, the use of a class disk for the fluoroquinolones seems inappropriate. it has been proposed, however, that isolates with MlCs less than or equal to 16 pg/ml be considered susceptible, whereas those with MlCs greater than or equal to 32 pg/ml be considered resistant to norfloxa- tin. (When reconstituting norfioxacin from standard laboratory powder, it must first be soiubilized in O.lN sodium hydroxide and then diluted in sterile water or broth. if a steers-type replicator is used, one must be careful of drug carryover. Additionally, the head should be changed between runs.)

A number of studies have evaluated the effect of different environmental test conditions on the activity of norfloxacin [6,14,17,44,52-551. in general, these findings apply to all members of the fluoroquinolone class of antibacterials [44].

Tolerance (minimal bactericidal concentration (MBC)/ MIC ratio greater than or equal to 32 mglml) does not seem to occur with norfioxacin. Furthermore, studies have shown that for norfloxacin, MiCs are similar to MBCs [14,52]. Although the MiCs of aerobic bacteria are not markedly affected by inoculum size [4,17,44,52], an inoculum effect is observed with some anaerobic bacteria [56].

Similarly, early studies suggested that pH and the com- position of the testing media had little or no effect on the activity of norfioxacin [44,52]. For example, Shah et al [53] compared the activity of nalidixic acid, cinoxacin, and norfloxacin against 302 urinary tract pathogens in DST (Oxoid) agar and pooled human urine agar (pH 5.4 to 5.8) [53]. They found that all three compounds lost activity in urine agar, an effect confirmed by other investigators [4]. They suggested that this finding was due to low urinary pH, especially if the level was less than 5.0 [45,54,55]. However, Greenwood and associates [54], using a dy-

The American Journal of Medicine Volume 82 (suppl 8B) 13


A

Y

l A

l

l A

i

A

v tf

Proteus Hafnia + Serratia E. coli

Acinetobacter + Klebsiella

namic bladder model to simulate clinical cystitis, noted that this effect has little clinical relevance since the urine concentrations of norfloxacin still greatly exceed those necessary to inhibit growth even under the most unfavora- ble conditions. Lacey et al [55] noted a similar decrease in the activity of norfloxatiin in urine having an acid pH. Despite this, when comparing norfloxacin with other antibiotics, the rate of killing of cultures in urine was second only to gentamicin.

Lacey et al [55] also reported a reduction in the activity of norfloxacin at high, as opposed to low, urine concentrations (90 pg/ml), a phenomenon called the paradoxical

Figure 4. Frequency (x 10-9 of appearance of resistant variants at M/C x 4 concentrations of antibiotic. l = nalidixic acid; A = noifloxacin. Repro- duced with permission from [Sl].

or %agle effect. They postulated that this effect was produced by reduced drug solubility at low pH and not by the pH level itself. Although a paradoxical effect has been observed with nalidixic acid [57,58], preliminary probe experiments with E. boli suggest that it does not octiur with norfloxacin [59].

Neu [80] has recently reviewed the effect of cations upon the activity of fluoroquinolones, and suggested that alteration of norfloxa+s activity in urine and Laceys [55] reported paradoxical effect might be related to the higher concentrations of magnesium in urine as opposed to broth or agar media. For the fluoroquinolones, increased mag-



r >105

105-

101.

103.

102-

10'.

O-

Figure 5. Frequency (x 70-3 of appearance of resistant variants at M/C x 16 concentrations of antibiotic. l = nalidixic acid; A = norfloxacin. Repro- duced with permission from [Sl].

i i i

l

l

.

l

l

l

l

l

i

Q

Pseudomonas Citrobacter + Serratia

Acinetobacter + Klebsiella

l

l

i i

Proteus Hafnia E. coli

nesium concentrations do alter MI&, but increased cal- cium concentrations do not. It is speculated that magnesium may increase MIC values by impeding ATPase activity or by interfering with the interaction between DNA and the fluoroquinolones.

Whereas nalidixic acid has been limited in its clinical usefulness because of the development of bacterial resistance during therapy [61], studies on the frequency, selection, and development of in vitro resistance to norfloxacin have produced conflicting results regarding the latters clinical applications [53,54,61-641. Tenney et al [62] were able to produce resistant strains of E. coli and P.

aeruginosa by serial passage with subinhibitory concentrations of norfloxacin. Greenwood et al [54] have also been able to induce resistance. They noted, however, that the level of resistance remains within therapeutically achievable limits. Duckworth and Williams [62] reported that resistance developed less frequently with norfloxacin than with nalidixic acid (Figures 4 and 5); they also found nonfermenting gram-negative bacteria more likely to de- velop resistance than were enterobacteria. Sanders et al [63] reported that nalidixic acid was likely to select resistant mutants, but notfloxacin was no more likely to select for resistant mutants than amikacin. They estimated the

June 29,1987 The American Journal of Medicine Volume 92 (suppl 66) 15


mutational frequency to be as low as 1 Oe7 to 1 Ov8. Cross- resistance within the fluoroquinolone class has occurred, however, although it has not developed between fluoroquinolones and other classes of antibiotics, e.g., the beta- lactams. One exception is a K. pneumoniae strain that developed cross-resistance. This unique change sug- gests an alteration in outer membrane proteins and, hence, permeability barriers [65,66].

COMMENTS

In conclusion, norfloxacin is an interesting new fluoroquinolone antibacterial agent. As a consequence of structural modifications of the quinolone nucleus, it has a broader spectrum of in vitro antibacterial activity than does nalidixic acid. This spectrum includes aerobic gram- positive and gram-negative organisms; multi-antibiotic- resistant, gram-negative rods; aminoglycoside-resistant P. aeruginosa; and beta-lactamase-producing organisms.

1. Editorial: The quinolones. Lancet 1984; I: 24-25. 2. Fass FtJ: The quinolones. Ann Intern Med 1985; 102: 400-402. 3. Barry AL, Jones RN, Thornsberry C, et al: Antibacterial activities 14.

of ciprofloxacin, norfloxacin, oxolinic acid, cinoxacin and nalidixic acid. Antimicrob Agents Chemother 1984; 25: 633-637.

4. Bauernfeind A, Ullmann U: In-vitro activity of enoxacin, ofloxa- 15. tin, norfloxacin and nalidixic acid. J Antimicrob Chemother 1984; 14 (SUPPI c): 33-37.

5. Body BA, Fromtling RA, Shadomy S, Shadomy HJ: In vitro anti- 16. bacterial activity of norfloxacin compared with eight other antimicrobial agents. Eur J Clin Microbial 1983; 2: 230-234.

6. Chin NX, Neu HC: In vitro activity of enoxacin, a quinolone carboxylic acid, compared with those of norfloxacin, new beta- 17. lactams, aminoglycosides, and trimethoprim. Antimicrob Agents Chemother 1983; 24: 754-763. ia.

7. Corrado ML, Cherubin CE, Shulman M: The comparative activity of norfloxacin with other antimicrobial agents against gram- positive and gram-negative bacteria. J Antimicrob Chemother 1963; 11: 369-376. 19.

a. Crider SR, Colby SD, Miller LK, et al: Treatment of penicillin- resistant Neisseria gonorrhoeae with oral norfloxacin. N Engl J Med 1984; 311: 137-140. 20.

9. Forward KR, Harding GKM, Gray GJ, et al: Comparative activities of norfloxacin and fifteen other antipseudomonal agents against gentamicin-susceptible and -resistant Pseudomonas 21. aeruginosa strains. Antimicrob Agents Chemother 1983; 24: 602-604.

10. Hasse D, Urias B, Harding G, Ronald A: Comparative in vitro activity of norfloxacin against urinary tract pathogens. Eur J 22. Clin Microbial 1983; 2: 235-241.

11. Gombert ME, Aulicino TM: Susceptibility of multiply antibiotic- resistant pneumococci to the new quinolone antibiotics, nalidixic acid, coumermycin, and novobiocin. Antimicrob Agents Chemother 1964; 26: 933-934. 23.

12. Goldstein EJC, Citron DM: Comparative activity of the quinolones against anaerobic bacteria isolated at community hospi- tals. Antimicrob Agents Chemother 1985; 27: 657-659.

13. Khan MY, Siddiqui Y, Gruninger RP: Comparative in vitro activ- 24. ity of MK-0366 and other selected oral antimicrobial agents

The class of fluoroquinolones as a whole is also bactericidal. The mechanism of action of these drugs involves inhibition of bacterial DNA gyrase, an essential enzyme involved in DNA replication. The incidence of cross-resistance within the fluoroquinolone class and between norfloxacin and other antibiotic classes (e.g., penicillins, cephalosporins, and aminoglycosides) is very low. The exploration of the in vitro, antibacterial, and pharmaco- logic properties of norfloxacin has provided a sound ra- tionale for its use as treatment for a number of important infectious disease syndromes.

ACKNOWLEDGMENT

I would like to thank the following people for various forms of assistance: Alice E. Vagvolgyi, Judee H. Knight, Diane M. Citron, Ronald Grun, Gregory Fergueson, and Richard D. Meyer.

REFERENCES

against Neisseria gonorrhoeae. Antimicrob Agents Chemo- ther 1981; 20: 265-266.

King A, Warren C, Shannon K, Phillips I: In vitro antibacterial activity of norfloxacin (MK-0366). Antimicrob Agents Chemo- ther 1982; 21: 604-607.

Marone P, Concia E, Michelone G, et al: In vitro antibacterial activity of norfloxacin against Pseudomonas aeruginosa. Eur J Chemother Antibiotics 1963; 3: 15-16.

Muytjens HL, van de Repe J, van Veldhuizen GL: Comparative activities of ciprofloxacin (Bay 0 9867), norfloxacin, pipemidic acid, and nalidixic acid. Antimicrob Agents Chemother 1983; 24: 302-304.

Norrby SR, Jonsson M: Antibacterial activity of norfloxacin. An- timicrob Agents Chemother 1983; 23: 15-18.

Reeves DS, Bywater MJ, Holt HA: The activity of enoxacin against clinical bacterial isolates in comparison with that of five other agents, and factors affecting that activity. J An- timicrob Chemother 1984; 14 (suppl C): 7-17.

Sato K, Matsuura Y, lnoue M, et al: In vitro and in vivo activity of DL-8280, a new oxazine derivative. Antimicrob Agents Che- mother 1982; 22: 546-553.

Shungu DL, Tutlane VK, Weinberg E, Gadesbusch HH: In vitro antibacterial activity of norfloxacin and other agents against ocular pathogens. Chemotherapy 1985; 31: 112-l 18.

Van Caekenberghe DL, Pattyn SR: In vitro activity of ciprofloxa- tin compared with those of other new fluorinated piperazinyl- substituted quinolone derivatives. Antimicrob Agents Chemo- ther 1984; 25: 518-521.

Corigliano BE, Appleman MD, Heseltine PNR, Leedom JM: Comparative in vitro activities of norfloxacin (MK-0366) and six commonly used antimicrobial agents against 199 urinary isolates showing various degrees of antibiotic resistance. Diagn Microbial Infect Dis 1984; 2: 101-106.

Downs J, Andrfole VT, Ryan JL: In vitro activity of MK-0366 against clinical urinary pathogens including gentamicin-resistant Pseudomonas aeruginosa. Antimicrob Agents Chemo- ther 1982; 21: 670-672.

Khan MY, Gruninger RP, Nelson SM, Klicker RE: Comparative in vitro activity of norfloxacin (MK-0366) and ten other oral



25.

26.

27.

28.

29.

30.

31.

32.

33.

34.

35.

36.

37.

38.

39.

40.

41.

42.

43. 44.

45.

46.

antimicrobial agents against urinary bacterial isolates. An- timicrob Agents Chemother 1982; 21: 848-851.

Tenney JH, Warren JW: Bactericidal activity of norfloxacin and nine other urinary tract antibiotics against gram-negative bacilli causing bacteriuria in chronically catheterized patients. J Antimicrob Chemother 1983; 11: 287-290.

Carlson JR, Thornton SA, DuPont HL, et al: Comparative in vitro activity of ten antimicrobial agents against bacterial entero- pathogens. Antimicrob Agents Chemother 1983; 24: 509- 513.

Morris JG, Tenney JH, Drusano GL: In vitro susceptibility of pathogenic Vibrio species to norfloxacin and six other antimicrobial agents. Antimicrob Agents Chemother 1985; 28: 442- 445.

Reinhardt JF, George WL: Comparative in vitro activities of selected antimicrobial agents against Aeromonas species and Plesimonas shigelloides. Antimicrob Agents Chemother 1985; 27: 643-645.

Shungu DL, Weinberg E, Gadebusch HH: In vitro antibacterial activity of norfloxacin (MK-0366, AM-715) and other agents against gastrointestinal tract pathogens. Antimicrob Agents Chemother 1983; 23: 86-90.

Crumplin GC, Kenworth M, Hirst T: Investigations into the mechanism of action of the antibacterial agent norfloxacin. J An- timicrob Chemother 1984; 13 (suppl B): 9-23.

Kayser FH: The quinolones: mode of action and mechanism of resistance. Res Clin Forum 1985; 7: 17-27.

Zweerink MM, Edison A: Inhibition of Micrococcus luteus DNA- gyrase by norfloxacin and ten other quinolone carboxylic acids. Antimicrob Agents Chemother 1986; 29: 598-601.

Ito A, Hirai K, lnoue M, et al: In vitro activity of AM 715, a new nalidixic acid analog. Antimicrob Agents Chemother 1980; 17: 103-108.

Lesher GY, Froelich EJ, Gruett MD, et al: 1,8-Naphthyridine derivatives. A new class of chemo-therapeutic agents. J Med Pharmacol 1962; 5: 1063-1066.

Turner FJ, Ringel SM, Martin JF, et al: Oxolinic acid, a new synthetic antimicrobial agent. Antimicrob Agents Chemother 1967; 475-479.

Wick WE, Preston DA, White WA, Gordee RS: Compound 64716, a new synthetic antibacterial agent. Antimicrob Agents Chemother 1973; 4: 415-420.

Albrecht R: Development of antibacterial agents of the nalidixic acid type. Prog Drug Res 1977; 21: 9-l 04.

Schentag JJ, Domagala JM: Structure-activity relationships with the quinolone antibiotics. Res Clin Forum 1985; 7: 9-13.

Wright HT, Nurse KC, Goldstein DJ: Yeast glycl- and leucyl- transfer RNA synthetases. Science 1981; 213: 455-456.

Cozzarelli NR: DNA gyrase and the supercoiling of DNA. Sci- ence 1980; 207: 953-960.

Gellerl ZM: DNA topoisomerases. Annu Rev Biochem 1981; 50: 879-910.

Watson JD: Molecular biology of the gene, 2nd ed. New York: W.A. Benjamin, Inc., 1970; 66-85, 255-276.

Felsenfeld G: DNA. Sci Am 1985; 253: 58-67. Wolfson JS, Hooper DC: The fluoroquinolones: structures,

mechanisms of action and resistance, and spectra of activity in vitro. Antimicrob Agents Chemother 1985; 28: 581- 586.

Newsom SWB: The antimicrobial spectrum of norfloxacin. J An- timicrob Chemother 1984; 13 (suppl B): 25-31.

Shungu DL, Tutlane V, Gadebusch HH: Multicenter evaluation of the proposed quality control limits and interpretive zone

47.

48.

49.

50. 51.

52.

53.

54.

55.

56.

57.

58.

59. 60.

61.

62.

63.

64.

65.

66.

standards for in vitro susceptibility testing with norfloxacin. J Clin Microbial 1983; 18: 988-991.

Gay JD, DeYoung DR, Roberts GD: In vitro activities of norfloxa- tin and ciprofloxacin against Mycobacterium tuberculosis, M. avium complex, M. chelonei, M. fortuitum, and M. kansasii. Antimicrob Agents Chemother 1984; 26: 94-96.

Simon C, Lindner U: In vitro activity of norfloxacin against Myco- plasma hominis and Ureaplasma urealyticum. Eur J Clin Mi- crobiol 1983; 2: 479-480.

Meier-Ewert H, Weil G, Millott G: In vitro activity of norfloxacin against Chlamydia trachomatis. Eur J Clin Microbial 1983; 2: 271-272.

Corrado ML: Personal communication. Shungu DL, Weinberg E, Gadebusch HH: Tentative interpretive

standards for disk diffusion susceptibility testing with norfloxa- tin (MK-0366, AM-715). Antimicrob Agents Chemother 1983; 23: 256-260.

Neu HC, Labthavikul P: In vitro activity of norfloxacin, a quinolone carboxylic acid, compared with that of p-lactams, aminoglycosides, and trimethoprim. Antimicrob Agents Chemother 1982; 22: 23-27.

Shah PM, Chard M, Stille W: In vitro activity of norfloxacin in urine compared to that of cinoxacin, nalidixic acid and pipemidic acid. Eur J Clin Microbial 1982; 2: 272-274.

Greenwood D, Osman M, Goodwin J, et al: Norfloxacin: activity against urinary tract pathogens and factors influencing the emergence of resistance. J Antimicrob Chemother 1984; 13: 315-323.

Lacey RW, Lord VL, Howson GL: Bactericidal effects of norfloxacin towards bacteria in urine. J Antimicrob Chemother 1984; 13 (suppl B): 49-54.

Goldstein JC, Citron DM, Corrado ML: Effect of inoculum size on in vitro activity of norfloxacin against fecal anaerobic bacteria. Am J Med 1987; 82 (suppl 6B): 84-87.

Crumplin GC, Smith JT: Nalidixic acid: an antibacterial paradox. Antimicrob Agents Chemother 1975; 8: 251-261.

Stamey TA, Brangonje J: Resistance to nalidixic acid. JAMA 1976; 236: 1857-l 860.

Fromtling RA, Abruzzo GK: Unpublished data. Neu HC: The effects of cations upon the activity of quinolone

agents. Quinolones Bulletin, April 1985. Duckworth GJ, Williams JD: Frequency of appearance of resis-

tant variants to norfloxacin and nalidixic acid. J Antimicrob Chemother 1984; 13 (suppl B): 33-38.

Tenney JH, Maack RW, Chippendale GR: Rapid selection of organisms with increasing resistance on subinhibitory concentrations of norfloxacin in agar. Antimicrob Agents Chemo- ther 1983; 23: 188-189.

Sanders CC, Sanders WE, Goering RV, Werner V: Selection of multiple antibiotic resistance by quinolones, p-lactams, and aminoglycosides with special reference to cross resistance between unrelated drug classes. Antimicrob Agents Chemo- ther 1984; 26: 797-801.

Barry AL, Jones RN: Cross-resistance among cinoxacin, ciprofloxacin, DJ-6783, enoxacin, nalidixic acid, norfloxacin and oxolinic acid after in vitro selection of resistant populations. Antimicrob Agents Chemother 1984; 25: 775-777.

Dougherty TJ, Saukkonen JJ: Membrane permeability changes associated with DNA gyrase inhibitors in Escherichia coli. Antimicrob Agents Chemother 1985; 28: 200-206.

Piddock WV, Wise R: The effect of altered porin expression in Escherichia coli upon susceptibility to 4-quinolones. J An- timicrob Chemother 1986; 18: 547-549.

June 26, 1967 The American Journal ol Medlclne Volume 62 (suppl 66) 17

norfloxacin, a fluoroquinolone antibacterial agent

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