Norfloxacin, the first of a new class of fluoroquinolone antimicrobials, revisited.

Norfloxacin is the first in a series of new 4-quinolones that have been introduced into medical practice for the treatment of bacterial infections. This totally synthetic compound is a broad spectrum, bactericidal agent that is much more potent than the earlier analogs, i.e. nalixidic acid, pipemidic acid, cinoxacin, rosoxacin, and flumequine, is less likely to select for resistant mutants. While the compound has been used most widely in the treatment of urinary tract infections including pyelonephritis and prostatitis, utility has also been demonstrated in gastrointestinal and ophthalmological infections, gonorrhea, typhoid fever, the typhoid carrier state, as well as in the prophylaxis of traveler's diarrhea, biliary tract infections prior to surgery, and gram-negative bacillary infections in profoundly neutropenic patients.

L-658,310, a new injectable cephalosporin. I. In vitro antibacterial properties.

The in vitro antibacterial spectrum of L-658,310, a new semisynthetic cephalosporin, was compared with ceftazidime, aztreonam and piperacillin against a wide variety of randomly selected human clinical isolates. The compound was found to be a broad spectrum bactericidal agent that was more potent than any of the comparison drugs against glucose nonfermenting bacteria. It has especially potent activity against Pseudomonas aeruginosa including multiply-resistant strains. The superior activity of L-658,310 against this group of organisms is attributed to the presence of the dihydroxy substituents on the 2-methylisoindoline moiety of the compound. L-658,310 is not cross-resistant with either imipenem, ceftazidime or piperacillin (representatives of three different classes of beta-lactam compounds) against P. aeruginosa. The lack of cross-resistance with ceftazidime extends to other glucose nonfermenters and several strains of Enterobacteriaceae as well. The compound is active against bacteria known to possess either R-plasmid- or chromosomally-mediated beta-lactamases.

L-658,310, a new injectable cephalosporin. II. In vitro and in vivo interactions between L-658,310 and various aminoglycosides or ciprofloxacin versus clinical isolates of Pseudomonas aeruginosa.

Combinations of L-658,310 and an aminoglycoside or ciprofloxacin were tested against clinical isolates of Pseudomonas aeruginosa using a checkerboard broth dilution technique. Using the mean fractional bactericidal concentration of less than or equal to 0.5 as the criterion for synergy, the combinations L-658,310/tobramycin and L-658,310/ciprofloxacin against strains of P. aeruginosa resistant to the companion drug were synergistic. The data plotted as isobolograms showed synergy for all combinations tested. Synergy was clearly demonstrated in time-kill experiments. A greater than 3-log decrease in viable cell count for P. aeruginosa was seen after exposure for 24 hours to subinhibitory concentrations of the combined agents. In in vivo mouse models, the efficacy of L-658,310 against experimental P. aeruginosa bacteremias was enhanced by the addition of a low dose of an aminoglycoside to the treatment regimen, thus confirming the synergy demonstrated in time-kill experiments.

L-658,310, a new injectable cephalosporin. III. Experimental chemotherapeutics and pharmacokinetics in laboratory animals.

The therapeutic activity of L-658,310 was demonstrated in experimental bacteremias in normal, diabetic and neutropenic mice. Especially potent activity was shown against the usually difficult to control pathogens, Enterobacter cloacae and Pseudomonas aeruginosa, that were resistant to ceftazidime and/or gentamicin. Pharmacokinetic studies in mice showed a linear dose response in serum after the 20 and 50 mg/kg subcutaneous dose and urinary recoveries of administered dose of about 60% in 6 hours. Excretion was mainly by glomerular filtration. In a crossover design in rhesus monkeys, the pharmacokinetics of L-658,310 were similar to those of ceftazidime and suggest a moderately long half-life in serum of humans.

L-656,575 (OCP-9-176): a novel oxacephem. In vitro activity against aerobic and anaerobic clinical bacterial isolates.

L-656,575 (OCP-9-176) is a novel oxacephem superior to ceftazidime in in vitro activity against clinical isolates of Enterobacter species, methicillin-susceptible Staphylococcus aureus and Staphylococcus epidermidis, and multiply-resistant Pseudomonas aeruginosa. Our results suggest that L-656,575 has a high affinity for penicillin binding proteins of Pseudomonas and may bind preferentially to PBP-3 in this organism. L-656,575 is active against beta-lactamase derepressed Enterobacteriaceae and ceftazidime-resistant P. aeruginosa.

L-656,575 (OCP-9-176): a novel oxacephem. Pharmacokinetics and experimental chemotherapy.

L-656,575 is a new oxacephem that, based on studies in rhesus monkeys, is expected to have a moderately long half-life in humans. After administration of a 10-mg/kg dose by the intramuscular route to rhesus monkeys, peak serum concentrations of 32-54 micrograms/ml were seen at about 30 minutes, and the half-life was estimated to be 63 minutes. Urinary recovery of administered dose was greater than 94% in 6 hours. In mice given a 20-mg/kg dose by the subcutaneous route, a peak serum concentration of 22.9 microgram/ml was observed at 15 minutes after dosing, and the half-life in serum was about 18 minutes. Urinary recovery of the dose was 59% in 6 hours. In another study in mice, administration of probenecid did not extend the half-life of L-656,575, suggesting that the antibiotic is excreted primarily by glomerular filtration in this species. Binding to human plasma proteins was 30% at drug concentrations from 25-100 micrograms/ml. L-656,575 also was shown to be efficacious in experimental bacteremias due to Gram-positive and Gram-negative pathogens in mice, thus confirming the broad spectrum of activity demonstrated for L-656,575 in vitro.

Comparative susceptibilities of Campylobacter pylori to norfloxacin and other agents.

Twenty-one strains of Campylobacter pylori (Campylobacter pyloridis) were tested for susceptibility to norfloxacin and other agents by the serial agar dilution method. Ampicillin (MIC for 90% of isolates [MIC90], 0.016 micrograms/ml) and famotidine (MIC90, greater than 1,024 micrograms/ml) were, respectively, the most and the least active of the agents tested. Norfloxacin (MIC90, 1 microgram/ml) and imipenem (MIC90, 0.125 micrograms/ml) were substantially active against this organism.

Quaternary heterocyclylamino beta-lactams. VI. In vitro and in vivo antibacterial properties of L-642,946 and L-652,813, a long acting cephem.

Two newly described quaternary heterocyclylamino beta-lactams, L-642,946 and L-652,813, were shown to exhibit potent activity against a broad spectrum of aerobic and anaerobic bacteria in vitro. The activity of these agents in vitro translated well to chemotherapeutic activity in experimental bacteremias in mice. Substitution of the thiadiazine moiety of L-642,946 with a triazine moiety effected a marked change in the pharmacokinetics of the new derivative, L-652,813. In mice given a 20 mg/kg subcutaneous dose, the peak serum concentration and the half-life of L-652,813 were about three times greater than those of L-642,946 and the area under the serum concentration/time curve was increased by about 5-fold. The pharmacokinetics of L-652,813 in mice and in rhesus monkeys more closely resembled those of ceftriaxone which carries the same triazine moiety on the C-3 side chain.

Tentative interpretive criteria for in vitro antibacterial susceptibility testing with imipenem.

Imipenem is a member of a new class of highly potent beta-lactam antibiotics, carbapenems, with a very broad antibacterial spectrum. This study was undertaken to determine tentative interpretive criteria for in vitro susceptibility testing with 10-micrograms imipenem disks. A careful examination of the zone diameters and the corresponding MICs for 489 clinical isolates by regression-line analysis and the error rate-bounded classification scheme suggested the following guidelines: greater than or equal to 16 mm with an MIC correlate of less than or equal to 4 micrograms/ml for susceptible, 14 to 15 mm (8 micrograms/ml) for moderately susceptible, and less than or equal to 13 mm (greater than or equal to 16 micrograms/ml) for resistant. Lack of cross-resistance between imipenem and broad-spectrum cephalosporins such as cefotaxime and ceftazidime argues against their use as class disks to predict in vitro susceptibility of bacterial species to carbapenems.

Norfloxacin versus trimethoprim-sulphamethoxazole: efficacy in a model of ascending urinary tract infection in normal and streptozotocin-induced diabetic mice.

A model of ascending urinary tract infection due to an isolate of Escherichia coli was developed in normal and streptozotocin-induced mice to compare the efficacy of norfloxacin and trimethoprim-sulphamethoxazole. Norfloxacin and trimethoprim-sulphamethoxazole both were effective in reducing the number of colony forming units of E. coli from the kidneys of normal experimentally-infected mice, although norfloxacin yielded a greater quantitative reduction of colony forming units. Norfloxacin was substantially more effective than trimethoprim-sulphamethoxazole in reducing the number of colony forming units from kidney homogenates when the test animals were diabetic. This study supports the initiation of clinical trials to evaluate norfloxacin in diabetic patients.

In vitro antibacterial activity of norfloxacin and other agents against ocular pathogens.

302 clinical isolates representing 16 bacterial species most often implicated in ocular infections were tested in vitro against norfloxacin and a panel of antibacterial agents. On the basis of the 90% minimal inhibitory concentration (MIC90) data, norfloxacin was 4-32 times more active than the next best antimicrobial tested against Citrobacter freundii, Escherichia coli, Morganella morganii, Proteus mirabilis, Proteus vulgaris, Haemophilus influenzae, Neisseria gonorrhoeae and Staphylococcus epidermidis, with overall MIC90 less than or equal to 1 mg/l. Norfloxacin was equal in activity to polymyxin B against Klebsiella pneumoniae (MIC90 = 1 mg/l), and it ranked second to both polymyxin B against Pseudomonas aeruginosa and cotrimoxazole against Staphylococcus aureus, (MIC90 = 2 mg/l in each case). Along with neomycin and cotrimoxazole, norfloxacin (MIC90 = 1 mg/l) ranked second to gentamicin and tetracycline against Moraxella species. Compared to erythromycin (MIC90 less than or equal to 0.125 mg/l), norfloxacin (MIC90 less than or equal to 16 mg/l) was considerably less active against streptococci. Overall, norfloxacin was the most active agent in both potency and antibacterial spectrum against the test organisms. These results suggest the potential use of norfloxacin in the treatment of superficial bacterial infections of the eye.

Antibacterial efficacy of norfloxacin, trimethoprim-sulfamethoxazole, and gentamicin in experimentally-infected normal and streptozotocin-induced diabetic mice.

Systemic bacterial infections due to Escherichia coli MB 2884, Proteus mirabilis MB 3125 and Klebsiella pneumoniae MB 4005 were well controlled by treatment with norfloxacin both in normal and streptozotocin-induced diabetic mice. similar observations were made when trimethoprim-sulfamethoxazole was used against susceptible pathogens. Systemic infection due to Pseudomonas aeruginosa MB 4700 was well controlled by norfloxacin and gentamicin in normal mice; this infection was more refractory to treatment by both drugs in diabetic animals. These observations suggest that norfloxacin may be an effective drug in the treatment of bacterial infections which may occur under diabetic conditions, and further investigation is warranted.

In vitro effect of pH and glucose concentration on the antibacterial activity of norfloxacin in urine.

The in vitro effect of pH and glucose concentration on the antibacterial activity of norfloxacin in urine was studied. Norfloxacin effectively inhibited the growth of four gram-negative pathogens in urine in vitro at pH values of 6.0, 7.0, and 8.0. The antibacterial activity of norfloxacin in urine was reduced severalfold at pH 6, but minimum inhibitory concentrations (MICs) at this pH remained clinically significant. Glucose at concentrations of 200 mg/dl and 400 mg/dl (simulating glucosuria of diabetes) did not significantly affect the antibacterial activity of norfloxacin when tested against clinical isolates of Escherichia coli, Proteus mirabilis, Klebsiella pneumoniae, or Pseudomonas aeruginosa. Norfloxacin appears to be a highly effective antibiotic in vitro under conditions which simulate normal and diabetic states.

Effectiveness of the antimicrobial removal device, BACTEC 16B medium, and thiol broth in neutralizing antibacterial activities of imipenem, norfloxacin, and related agents.

The Antimicrobial Removal Device (ARD), BACTEC 16B medium, and Thiol broth were evaluated for their effectiveness in reducing the activity of imipenem (IPM), cefoxitin, moxalactam, and ceftazidime in blood samples. In addition, the capability of the ARD and Thiol broth to bind norfloxacin and the ARD to bind oxolinic and nalidixic acids in urine samples was investigated. At the highest concentrations of the drugs tested (32 micrograms/ml for the four beta-lactams and 256 micrograms/ml for the three quinolinecarboxylic acids), there was at least a 95% reduction in the in vitro activity of each of the antibacterial agents for treated versus untreated samples. Of the compounds tested in the ARD system, the organic acids were more completely removed than were the beta-lactams. The Thiol broth was more effective than the ARD and the BACTEC 16B medium in inactivating imipenem, but it had no effect on the antibacterial activity of norfloxacin.

Pharmacokinetic studies of norfloxacin in laboratory animals.

Pharmacokinetic studies were conducted with norfloxacin administered by the oral and subcutaneous routes to mice and rats, and by the oral route to rhesus monkeys. The compound was moderately well absorbed following oral dosing in these animal species. Serum levels in monkeys ranged from 1.0 to 2.35 micrograms/ml after an oral drug dose of 25 mg/kg of animal body weight and were similar to those in mice. Serum half-life of norfloxacin in rodents and monkeys was similar to that in humans. Concentrations of norfloxacin in tissues of mice, rats and monkeys were greater than those in serum suggesting a large volume of distribution for the drug.

Ethanol-cephalosporin antibiotic interactions: an animal model for the detection of disulfiram (Antabuse)-like effects.

Disulfiram (Antabuse)-like reactions occurring in patients undergoing antibacterial therapy with certain cephalosporin antibiotics, and after ingestion of ethanol, are well documented. A murine model is described which may prove useful in the detection of compounds likely to produce this effect. Eight cephem compounds (moxalactam, cefamandole, cefmetazole, cefonicid, cefmenoxime, cefoperazone, cefotiam, ceforanide) each carrying an N-methyltetrazolethiol substituent in the 3-position of the dihydrothiazine ring of the parent antibiotic were capable of inducing a disulfiram-like reaction in the test animals. Evidence is presented which strongly suggests a direct relationship between N-methyltetrazolethiol and related heterocyclic thiols and the ability to induce this reaction.

Multicenter evaluation of the proposed quality control limits and interpretive zone standards for in vitro susceptibility testing with norfloxacin.

A seven-center collaborative study was carried out to evaluate the in vitro performance of the 10 micrograms norfloxacin disks on the basis of previously proposed interpretive susceptibility zone standards and quality control parameters. Of 7,858 clinical isolates tested, 93.2, 4.9, and 1.9% fell into the susceptible, moderately susceptible, and resistant groups, respectively. The quality control data based on a total of 1,368 zone diameter measurements compared quite favorably with the proposed performance limits as follows: Escherichia coli ATCC 25922, 28 to 35 mm versus 28 to 36 mm; Staphylococcus aureus ATCC 25923, 21 to 29 mm versus 17 to 29 mm; and Pseudomonas aeruginosa ATCC 27853, 23 to 27 mm versus 22 to 29 mm.