Multicenter in vitro comparative study of fluoroquinolones against 25,129 gram-positive and gram-negative clinical isolates.

In vitro activities of fleroxacin, ciprofloxacin, ofloxacin, and lomefloxacin were evaluated against 25,129 fresh bacterial isolates from 51 US hospital or medical center laboratories, beginning in October of 1990. Susceptibility rates were > or = 85% against most species of Gram-negative bacteria. Notable exceptions were Pseudomonas, Acinetobacter, Xanthomonas, and Providencia. The study drugs displayed similar activity against most Gram-negative species. At least 90% of oxacillin-susceptible staphylococci were susceptible but, of oxacillin-resistant strains, only approximately 60% of Staphylococcus epidermidis and 25% of Staphylococcus aureus were susceptible to the quinolones tested. Staphylococcus saprophyticus strains were less susceptible to fleroxacin (42%) than to the other compounds (79%-97%). Ofloxacin and ciprofloxacin were more active against streptococci, and none of the compounds demonstrated appreciable activity against enterococci. Thus, the spectra of activity of fluoroquinolones illustrate that they remain effective agents for the treatment of many types of infections caused by Gram-negative pathogens.

Dual-action cephalosporins incorporating a 3'-tertiary-amine-linked quinolone.

We have previously reported that linking quinolones to the cephalosporin 3'-position through an ester bond, a carbamate function, or a bond through a quaternary nitrogen produced cephalosporins with a dual mode of antibacterial action. We now describe a new class of dual-action cephalosporins, with greater chemical stability than those previously reported, in which the basic nitrogen of ciprofloxacin is bonded directly to the 3'-cephalosporin position, i.e., the two moieties are linked through a tertiary amine function. These compounds have demonstrated potent activity against a broad spectrum of Gram-positive and Gram-negative bacteria, including beta-lactam-resistant strains.

A multicenter study on the comparative in vitro activity of fleroxacin and three other quinolones: an interim report from 27 centers.

A multicenter study was designed to compare the in vitro activity of fleroxacin to that of three other oral quinolones (ciprofloxacin, ofloxacin, and lomefloxacin) against fresh clinical bacterial isolates in hospital or medical center laboratories throughout the United States. Each of the 50 centers was asked to test 500 gram-negative and gram-positive strains using the MicroScan (Baxter) microtiter system. This report includes the results of the study, begun in October 1990, on 12,013 isolates tested in 27 centers. Susceptibility was based on minimum inhibitory concentration (MIC) interpretive criteria from the National Committee for Clinical Laboratory Standards guidelines or published literature. Fleroxacin and the three other quinolones were all active against Enterobacteriaceae, with 95-97% of the strains susceptible. Against other aerobic gram-negative bacilli, 79-83% of the strains were susceptible to fleroxacin, ciprofloxacin, and ofloxacin, and 75% were susceptible to lomefloxacin. With regard to the gram-positive isolates, 79% were susceptible to ofloxacin, 74% to ciprofloxacin, and 52% to fleroxacin and lomefloxacin. The susceptibility data were further delineated for the various species in each of the three major bacterial groups. All four quinolones were highly active against Enterobacteriaceae and were moderate to excellent in activity against other aerobic gram-negative organisms. Activity against oxacillin-susceptible staphylococci was also excellent; however, all four agents were generally much less active against oxacillin-resistant strains. Ofloxacin and ciprofloxacin were clearly superior to fleroxacin and lomefloxacin against streptococci and enterococci.

Dual-action cephalosporins: cephalosporin 3'-quinolone carbamates.

A series of cephalosporins has been prepared in which the 3'-position was linked to the nitrogen of the antibacterial quinolone ciprofloxacin through a carbamate function. Like the ester-linked and quaternary-linked dual-action cephalosporins reported earlier, these carbamate-linked compounds exhibited a broad antibacterial spectrum derived from both cephalosporin-like and quinolone-like activities, suggesting a dual mode of action. Studies to elucidate details of the mechanism of action have been inconclusive. Ciprofloxacin liberated as a consequence of bacterial enzyme-mediated reactions may contribute to the second mode of action, although some evidence indicates that the intact carbamate-linked bifunctional molecules may possess intrinsically both beta-lactam and quinolone activities.

Dual-action cephalosporins: cephalosporin 3'-quaternary ammonium quinolones.

When cephalosporins exert their biological activity by reacting with bacterial enzymes, opening of the beta-lactam ring can lead to expulsion of the 3'-substituent. A series of cephalosporins was prepared in which antibacterial quinolones were linked to the 3'-position through a quaternary nitrogen. Like the 3'-ester-linked dual-action cephalosporins reported earlier, these compounds demonstrated a broad spectrum of antibacterial activity derived from cephalosporin-like and quinolone-like components, suggesting a dual mode of action.

In vitro and in vivo activity of carbamate-linked dual-action antibacterial Ro 24-4383.

Ro 24-4383 contains desacetylcefotaxime linked by a carbamate bond at the 3' position to ciprofloxacin. Ro 24-4383 was active against 99% of the 363 gram-positive and gram-negative aerobes tested in vitro, while the comparative agents cefotaxime and ciprofloxacin were active against 77 and 97%, respectively. The activities (ED50: mg/kg s.c.) of Ro 24-4383, cefotaxime and ciprofloxacin in systemic murine infections were: Escherichia coli 257, 1.4, less than 0.5, less than 0.2; Klebsiella pneumoniae A, 11, 30, 0.7; Enterobacter cloacae 5699, 3.2, 35, less than 0.2; Citrobacter freundii BS16, 3, 41, less than 0.5; Serratia marcescens SM, 35, greater than 100, 1.6; Pseudomonas aeruginosa 5712, 67, 100, 10; P. aeruginosa 8780, 33, 193, 3; Staphylococcus aureus Smith (oxacillin-susceptible), 12, 3.7, 1; S. aureus 753 (oxacillin-resistant), 28, greater than 100, 2; Streptococcus pneumoniae 6301, 10, 15, greater than 50, and S. pyogenes 4, 3.3, 1.6, 54. Ro 24-4383, although inactive against the S.-pneumoniae-induced pneumonia following one administration of the agent, was highly active (ED50 = 1.5) when three treatments were given following infection. Ro 24-4383 was active against the K.-pneumoniae-induced pneumonia (ED50 = 37), as well as the meningitis induced by S. pneumoniae (ED50 = 158) or K. pneumoniae (ED50 = 100). The protective effect of Ro 24-4383 was demonstrated when administered 8 h before infection with E. coli (ED50 = 37) and 4 h before infection with S. pyogenes (ED50 = 199).

Cephalosporin 3'-quinolone esters with a dual mode of action.

According to the generally accepted mechanism by which bacterial enzymes react with cephalosporins, opening of the beta-lactam ring can lead to the expulsion of a 3'-substituent. A series of dual-action cephalosporins was prepared in which antibacterial quinolones were linked to the cephalosporin 3'-position through an ester bond in the expectation that, in addition to exerting their own beta-lactam activity, these cephalosporins would act as prodrugs for the second antibacterial agent. Compared to parent cephalosporins in which the 3'-substituent was acetoxy, the bifunctional cephalosporins exhibited a broadened antibacterial spectrum, suggesting that a dual mode of action may indeed be operative.

In vivo evaluation of a dual-action antibacterial, Ro 23-9424, compared to cefotaxime and fleroxacin.

The dual-action antibacterial R 23-9424 (desacetylcefotaxime linked to the quinolone fleroxacin) is a new antibacterial agent with excellent in vitro activity. It was evaluated for in vivo efficacy in comparison with the cephalosporin cefotaxime and the quinolone component, fleroxacin. Ro 23-9424 demonstrated significant activity against all strains tested in systemic infections, including those strains resistant in vivo to cefotaxime (Staphylococcus aureus 753, Serratia marcescens SM and Pseudomonas aeruginosa 8780) and fleroxacin (Streptococcus pneumoniae 6301 and Streptococcus pyogenes. In prophylactic studies, Ro 23-9424 compared favorably with fleroxacin against Escherichia coli and with cefotaxime against S. pyogenes, but Ro 23-9424 was considerably more active than cefotaxime against E. coli and more active than fleroxacin against S. pyogenes. In a murine pneumonia model, Ro 23-9424 was equivalent in activity to cefotaxime against S. pneumoniae and more active than cefotaxime against Klebsiella pneumoniae. Fleroxacin was inactive against S. pneumoniae and about 20-fold more active than Ro 23-9424 against K. pneumoniae. In a murine meningitis infection caused by S. pneumoniae, Ro 23-9424 was 3 times as active as cefotaxime, while fleroxacin was inactive. When meningitis was induced by K. pneumoniae, Ro 23-9424 was as active as the quinolone, while cefotaxime was inactive. In a neutropenic (immunocompromised) model, Ro 23-9424 was more active than cefotaxime against P. aeruginosa and 5-fold less active than fleroxacin. In the control normal (immunocompetent) mouse infection, Ro 23-9424 was 3-fold more active than cefotaxime, but 10-fold less active than fleroxacin.

In vitro activities of a dual-action antibacterial agent, Ro 23-9424, and comparative agents.

The in vitro activity of the dual-action antibacterial agent Ro 23-9424 was compared with those of cefotaxime, ceftazidime, ciprofloxacin, fleroxacin, imipenem, and amikacin against 358 aerobes and anaerobes. The MIC ranges, MICs for 50 and 90% of the strains (MIC50s and MIC90s), and percentage of strains susceptible for each agent at the recommended susceptible MIC breakpoint were determined for each genus. The MIC90s (micrograms per milliliter) of the agents against members of the family Enterobacteriaceae were as follows: ciprofloxacin, 0.063; Ro 23-9424, fleroxacin, and imipenem, 0.5; ceftazidime, 2; amikacin, 4; and cefotaxime, 16. The MIC90s (micrograms per milliliter) against Pseudomonas and Acinetobacter spp. were as follows: ciprofloxacin, 2; ceftazidime and imipenem, 8; Ro 23-9424, 16; fleroxacin, 32; amikacin, 64; and cefotaxime, 128. Against gram-positive bacteria, excluding the enterococci, the MIC90s (micrograms per milliliter) were as follows: ciprofloxacin, 1; imipenem, 4; Ro 23-9424 and fleroxacin, 8; amikacin, 64; and ceftazidime and cefotaxime, greater than 128. Against gram-positive bacteria, including the enterococci, the MIC90s changed only for the following agents: Ro 23-9424, 16 micrograms/ml; and amikacin, 128 micrograms/ml. Strains of Branhamella catarrhalis, Haemophilus influenzae, and Neisseria gonorrhoeae were 100% susceptible to Ro 23-9424, cefotaxime, ciprofloxacin, and fleroxacin, while the other three agents showed somewhat less activity only against N. gonorrhoeae. Against anaerobes, imipenem was the most effective agent, while the activities of the other six agents were variable.

Effect of medium chain glycerides on enteral and rectal absorption of beta-lactam and aminoglycoside antibiotics.

The rat enteral and rabbit rectal models were utilized to study the effect of Capmul (medium chain glycerides) on the absorption of a selection of beta-lactam and aminoglycoside antibiotics. All tested non-orally available beta-lactam antibiotics (cefamandole, cefotaxime, moxalactam, cefoxitin, mezlocillin, carumonam, penicillin G and amdinocillin) showed increased absorption enterally in rats and rectally in rabbits when formulated with Capmul. The orally available beta-lactam antibiotics, cephalexin and cephradine, were not enhanced in their enteral or rectal absorption by Capmul in the two model systems. Ampicillin absorption was enhanced rectally and enterally by Capmul. Rectal absorption of the aminoglycoside antibiotics, tobramycin and gentamycin, was enhanced by Capmul while enteral absorption was not.

Enteral, oral, and rectal absorption of ceftriaxone using glyceride enhancers.

In vivo models in rodents and primates were used to investigate ways of overcoming the poor oral and rectal absorption of ceftriaxone. The sodium salt of ceftriaxone at 20 mg/kg was formulated in C8-C10 chain length, mono- and diglyceride extracts of coconut oil (Capmul) and administered intraduodenally to adult rats. Peak plasma levels of 17-52 micrograms/ml and bioavailability averaging 38% were attained. Significant plasma levels (42-45 micrograms/ml) were also demonstrated in squirrel monkeys with doses of 20 mg/kg ceftriaxone formulated in Capmul and given by the enteral route. Enteric-coated capsules containing this formulation were also orally administered to squirrel monkeys and gave high plasma levels (10-31 micrograms/ml) between 1 and 6 h following dosing. In rectal absorption studies, ceftriaxone formulated in Capmul as a suspension gave peak blood levels of 62-84 micrograms/ml (average bioavailability 42%) in the rabbit. In the baboon, rectal administration of ceftriaxone formulated with Capmul in a Witepsol H15 suppository gave Cmax levels ranging from 9 to 48 micrograms/ml, depending on the dose of the antibiotic and the drug/enhancer ratio.

Collaborative clinical laboratory study of a broth-disk test for determination of bacterial susceptibility to beta-lactams in combination with amdinocillin.

Methodology for the performance of synergistic antibiotic susceptibility studies has not been standardized. We addressed this problem collaboratively with combinations of amdinocillin and select other beta-lactam antibiotics by using a simple broth-disk test compared with a microdilution approach. Each method used the same drugs singly and in combination. The broth-disk test evaluated each agent and the combinations at concentrations that reflected the breakpoints for each drug; the same ratios of beta-lactam to amdinocillin were used in doubling dilutions with the microdilution method. Initially, each participant studied the same 50 members of the family Enterobacteriaceae; each bacterium was studied on three occasions. Thereafter, 500 representatives of Enterobacteriaceae isolated recently from clinical specimens were studied. Designated strains served as controls. Reproducibility between the two approaches studied in phase 1 of the investigation indicated good agreement between the methods, ranging from 87 to 100%. Agreement between the microdilution and broth-disk tests for the 2,551 clinical isolates ranged from 86 to 95%, with slightly better correlations between combination results than with the single agents. The findings indicate that antibiotic disks used routinely in the clinical laboratory can be used in a simple elution test to determine susceptibility of organisms to beta-lactam antibiotics alone and in combination with amdinocillin.

In vitro activity of Ro 19-5247 (T-2525) and interpretive criteria for disk diffusion susceptibility testing.

The activity of Ro 19-5247 (the active metabolite of the oral cephalosporin Ro 19-5248 [T-2588]) was compared with that of five orally active agents against a total of 331 bacterial strains. Ro 19-5247 was more active in vitro than amoxicillin, amoxicillin-clavulanate, cefaclor, cefuroxime, and cephalexin against members of the family Enterobacteriaceae. Amoxicillin-clavulanate and amoxicillin overall were more active than the other four agents against staphylococci. Ro 19-5247, amoxicillin-clavulanate, amoxicillin, and cefuroxime were equally active against nonenterococcal streptococci and more active than cefaclor and cephalexin. All six agents showed little or no activity against nonfermentative gram-negative bacteria. Against Streptococcus (Enterococcus) faecalis, only amoxicillin and amoxicillin-clavulanate were active. The interpretive criteria for in vitro susceptibility testing with 10- and 30-micrograms Ro 19-5247 disks were established by regression analysis to correlate the inhibitory zone sizes and MICs for the bacterial isolates. The suggested tentative zone size breakpoints for the 10-micrograms disk are as follows: susceptible, greater than or equal to 22 mm (MIC, less than or equal to 2 micrograms/ml); moderately susceptible, 20 to 21 mm (MIC, 4 micrograms/ml); and resistant, less than or equal to 19 mm (MIC, greater than or equal to 8 micrograms/ml).

Correlation of the results of antibiotic synergy and susceptibility testing in vitro with results in experimental mouse infections.

Recent clinical isolates (approximately 150 strains) of the family Enterobacteriaceae were examined by agar diffusion, microdilution, and the Autobac automated system for their responses to beta-lactam antibiotics singly and in combination with amdinocillin (formerly called mecillinam). The ratio of ampicillin, carbenicillin, and cephalothin to amdinocillin was maintained at a 10:1 ratio in most of the evaluations. The same isolates were studied in mice challenged with 100 to 1000 LD50s and treated with graded doses of the antibiotics singly and in combination. Efficacy in vivo was based on the concentration of antibiotic in milligrams per kilograms (mg/kg) required to protect 50% of the animals (PD50). After a single administration of the antibiotics, plasma levels were determined in the critical time period (30 min to 4 hr) during which the acute, overwhelming systemic infections could be controlled by appropriate therapy. Regression curves comparing in vivo and in vitro results were used to establish cut-off points for categorizing bacterial susceptibility in each of the laboratory tests for the single agents and combinations. A high degree of synergism between amdinocillin and the beta-lactam agents was demonstrated in animals (54 to 78% of the strains examined) and to a lesser extent by laboratory methodologies. There was an excellent correlation of in vivo and in vitro responses to ampicillin, carbenicillin, and cephalothin alone and in combination with amdinocillin for those species for which the single antibiotics are generally indicated. The correlations validated the chosen cut-off points. The correlation of in vivo and in vitro responses to the single or combined antibiotics was generally poorer for those species not usually responsive to the single antibiotics. The greatest difficulty in predicting proper in vivo responses, based on the results of in vitro tests, was observed with amdinocillin.

Mecillinam alone and in combination with ampicillin or moxalactam in experimental Escherichia coli meningitis.

The activity of mecillinam, ampicillin and moxalactam alone and in combination was determined in a lapin meningitis model and a mouse meningitis model against two Escherichia coli strains isolated from infants with meningitis. Both strains were highly susceptible in vitro to the antibiotics, and responded well in systemic mouse protection tests (PD50 less than 4 mg/kg). Continuous infusion of mecillinam in the lapin model over nine hours was effective in sterilizing the CSF of three of four animals infected with one strain. This prompt bacteriologic response to mecillinam alone precluded the possibility of constant infusion administration for synergy studies. Therefore, single dose administration was used to demonstrate the synergistic potential of mecillinam with ampicillin in the lapin meningitis model against the E. coli Kl # 2 strain. The combination of moxalactam and mecillinam was synergistic against the E. coli Kl # 2 strain in the mouse meningitis model. The synergistic potential of these combinations could not be reliably predicted by in vitro tests, time kill curves or systemic mouse protection tests.

In vivo activity of ceftriaxone (Ro 13-9904), a new broad-spectrum semisynthetic cephalosporin.

Ceftriaxone (Ro 13-9904) was compared with other newer beta-lactam antibiotics for activity in experimental infections of mice with Enterobacteriaceae, Haemophilus influenzae, Pseudomonas aeruginosa, and gram-positive bacteria. Overall, ceftriaxone was equal or superior to cefotaxime and cefoperazone against systemic infections. All three drugs were highly potent against most organisms but were considerably less active against P. aeruginosa. However, ceftriaxone tended to be more active than the other two agents against 8 of the 10 P. aeruginosa strains tested. Ceftriaxone, cefmenoxime (SCE 1365), and moxalactam were all highly active against systemic infections with 16 strains of Enterobacteriaceae, whereas ceftriaxone was more active against infections with two strains of streptococci. When the drugs were administered at various time intervals before infection, ceftriaxone was superior to cefotaxime, cefmenoxime, and moxalactam. This suggested that ceftriaxone might be eliminated from mice more slowly than the other drugs. In the case of cefotaxime, this was directly confirmed by microbiological assays of plasma samples. In a murine meningitis model induced by Klebsiella pneumoniae or Streptococcus pneumoniae, ceftriaxone was more active than ampicillin or cefotaxime. Ceftriaxone was more active than ampicillin, cefotaxime, piperacillin, cefamandole, or carbenicillin in a pneumococcal, pneumonia model in mice. These studies indicate that ceftriaxone is a potent, broad-spectrum cephalosporin with unusual pharmacokinetic properties.

Antibacterial activity of 2',3'-dideoxyadenosine in vivo and in vitro.

2',3'-Dideoxyadenosine (DDA) was shown not only to possess antibacterial activity in vitro against a variety of Enterobacteriaceae, but also to be effective in vivo, DDA was active in experimental mouse infections by the oral route against 5 Salmonella strains, 2 of 3 Arizona strains, 5 of 7 Citrobacter strains, 3 of 8 Klebsiella strains, 3 of 5 Escherichia strains, 1 of 3 Shigella strains, and 3 of 15 Serratia strains at concentrations generally well below the toxic level. Closely related compounds, with the exception of 2',3'-dideoxyinosine, were found to be inactive in vivo, indicating that a high degree of structural specificity was required for activity. The synthesis of deoxyribonucleic acid was inhibited by DDA in those strains susceptible in vitro to DDA, whereas ribonucleic acid and protein syntheses were not affected. The concentration of DDA which inhibited bacterial deoxyribonucleic acid synthesis by 50% was calculated based on the relative rates of deoxyribonucleic acid synthesis in ;the absence and in the presence of DDA. This value correlated well with the minimal inhibitory concentration determined by the in vitro broth dilution assay but not always with in vivo activity determined by the mouse protection test.

In vivo activity of amoxicillin and ampicillin against gram-positive bacteria: results of prophylactic studies.

In prophylactic treatment of intraperitoneal infections with Streptococcus pneumoniae (types 1 and 2) and Streptococcus pyogenes in mice, amoxicillin had a definite advantage over ampicillin in terms of protective effect. When the infecting agent was given to mice so as to produce an infection in the brain or lung (for example, S. pneumoniae given intracranially or intranasally), amoxicillin was also more effective prophylactically than ampicillin.

Studies on the in vitro development of drug resistance of Proteeae to sulfonamides, trimethoprim and combinations of a sulfonamide and trimethoprim.

A strain of Proteus mirabilis repeatedly subcultured in the presence of a combination of sulfisoxazole and 0.4 microgram/ml of trimethoprim and a strain of P. vulgaris subcultured in the presence of sulfamethoxazole and trimethoprim combined in a 5:1 ratio gradually developed resistance to the combinations. However, the level of resistance developed by the organisms exposed to the combination was always appreciably lower than the level of resistance developed by the same strains exposed to either the sulfonamide or trimethoprim alone.