The fluoroquinolones: pharmacology, clinical uses, and toxicities in humans

Comparative study with enoxacin and netilmicin in a pharmacodynamic model to determine importance of ratio of antibiotic peak concentration to MIC for bactericidal activity and emergence of resistance

An in vitro pharmacokinetic model was used to study the comparative antibacterial activities of multiple-dose regimens of enoxacin and netilmicin. Strains of Pseudomonas aeruginosa, Klebsiella pneumoniae, Escherichia coli, and Staphylococcus aureus were exposed to changing drug concentrations, mimicking human two-compartment pharmacokinetics. Oral administration was simulated for the quinolone, and intravenous administration was simulated for the aminoglycoside. Similar ratios of peak concentration to MIC resulted in similar changes in bacterial concentrations over time with both compounds. Following the initial dose, a rapid bactericidal effect occurred, with a greater than 99% reduction of the bacterial counts within 4 h at peak concentrations more than three times the MIC. However, bacterial regrowth occurred within 24 h unless the peak concentration/MIC ratio exceeded 8:1 (P less than 0.01). For the regrowing bacteria, MICs were four- to eightfold higher, and little or no bactericidal effect occurred following the second and subsequent doses. These data demonstrate the equally potent bactericidal activity of orally administered enoxacin and intravenously administered netilmicin. Selection of resistant subpopulations was similar with each drug. The peak concentration/MIC ratio may be an important parameter in the clinical use of quinolone and aminoglycoside antibiotics.

Effect of inoculum size on in vitro activity of norfloxacin against fecal anaerobic bacteria. Rationale for selective decontamination of the digestive tract

Previous studies have shown that anaerobic bacteria are susceptible to norfloxacin at the levels attained in the feces. Conversely, studies in laboratory animals and neutropenic humans using norfloxacin for selective decontamination of the digestive tract have shown that norfloxacin markedly reduces the aerobic enteric flora without reducing fecal anaerobic flora. In an effort to resolve this paradox, the effect of a 10(9) colony-forming units (cfu)/ml inoculum, which is more reflective of actual fecal counts than the standard 10(5) cfu/ml inoculum, on the activity of norfloxacin against two fecal Escherichia coli isolates and 16 fecal anaerobic isolates was studied. The results showed a marked inoculum effect at 10(9) cfu/ml for most anaerobic isolates but not for the E. coli strains tested. At 256 micrograms/ml, all E. coli were killed while the anaerobic bacteria maintained colony counts greater than or equal to 10(9) cfu/ml. Hence, the lack of anaerobic activity (minimal inhibitory concentration greater than or equal to 512 micrograms/ml) at higher fecal inocula might explain the utility of norfloxacin in selective decontamination of the bowel.

RO23-6240, a new orally absorbed quinolone: in vitro comparison with other broad-spectrum oral antimicrobial agents and imipenem

A total of 626 clinical isolates were tested for their susceptibility to RO23-6240 and other broad-spectrum antimicrobial agents. RO23-6240 showed good activity against strains of Enterobacteriaceae, Acinetobacter, and P. aeruginosa. RO23-6240 MIC90s ranged from 0.032 to 4 micrograms/ml for these strains. RO23-6240 also showed good activity against staphylococci, both methicillin-susceptible and -resistant strains. The activity in vitro of RO23-6240 was comparable with that of norfloxacin and ofloxacin, and more active than imipenem, trimethoprim-sulfamethoxazole, cefaclor, and amoxycillin/clavulanate potassium. As with the other quinolones tested, increases in inoculum size produced moderate increases in the MICs and MBCs of RO23-6240.

Penetration of enoxacin into bronchial secretions

Enoxacin is a potent quinolone derivative with marked activity against gram-negative bacteria and staphylococci. The oral preparation has a potential role in treatment of gram-negative-bacterial lower respiratory infections if found to give adequate bronchial (sputum) concentrations. A study was done to determine the concomitant serum and bronchial concentrations of oral enoxacin after dosing with 600 mg, single dose; 400 mg, single dose; and 400 mg every 12 h, four doses. Blood and bronchial secretions were collected from 20 patients predose and 2, 5, and 9 h postdose. Bronchial secretions were obtained from tracheostomies, endotracheal tubes, or bronchoscopy. Levels of enoxacin in serum and sputum were measured by high-pressure liquid chromatography. Mean peak bronchial secretion levels were similar for the 400-mg dose schedules (2.2 and 2.4 micrograms/ml) but were significantly higher with the 600-mg dose (4.0 micrograms/ml) (P less than 0.05). Significant concentrations in bronchial secretions were still achievable at 9 h postdose (1.3 to 2.3 micrograms of enoxacin per ml). The mean ratios of enoxacin concentrations in sputum to those in serum at various time intervals for all groups were as follows: at 2 h, 0.55 +/- 0.34; at 5 h, 1.04 +/- 0.72; at 9 h, 0.97 +/- 0.62. Considering that most gram-negative bacteria are inhibited by 1.0 microgram of enoxacin per ml in vitro, this study shows that oral enoxacin in practical doses achieves a concentration in bronchial secretions that is adequate to treat most gram-negative-bacterial lower respiratory infections.

In vitro activity of ciprofloxacin and ofloxacin against the Mycobacterium avium-intracellulare complex

The in vitro activity of ciprofloxacin and ofloxacin against strains of Mycobacterium avium-intracellulare complex were studied by the standard 1% proportion method. Thirty-eight of 100 strains (30%) were inhibited by ciprofloxacin at 2 micrograms/ml and 11 of 30 strains (37%) were inhibited by ofloxacin at 8 microm/ml. Patients having these more susceptible isolates may potentially benefit from therapy with these agents [corrected].

Nalidixic acid in children: retrospective matched controlled study for cartilage toxicity

The new fluoroquinolones allow effective oral therapy of infections due to Pseudomonas aeruginosa. Studies on efficacy and safety of these promising agents are not recommended in childhood because of cartilage toxicity which has been observed in growing animals. However, the first quinolone antimicrobial, nalidixic acid, showed identical arthropathic effects in young animals and is licensed for paediatric use. A review of the hospital charts revealed 11 patients who had received nalidixic acid over nine to 600 days and were available for control examination three to 12 years later. For each nalidixic acid case a carefully selected matched pair, who had never received nalidixic acid, was identically analyzed. Three patients from the nalidixic acid and three from the control group reported arthralgia, which was judged to have no relation to drug therapy. Growth curve and both functional and radiological joint findings were completely normal in all cases. These results suggest that quinolone-associated arthropathy does not occur in children, even after long-term therapy.

Comparative in vitro activities of pefloxacin, ofloxacin, enoxacin and ciprofloxacin against 256 clinical isolates

The antibacterial activity of four new fluoroquinolone carboxylic acids, pefloxacin, ofloxacin, enoxacin and ciprofloxacin, against 256 clinical isolates was investigated by means of an agar dilution method. Generally, all quinolones tested had a high activity against Gram-negative bacteria. More than 90% of Enterobacteriaceae strains were inhibited by a quinolone concentration of 0.4 microgram/ml. Also strains usually resistant to conventional beta-lactam antibiotics, and sometimes to third-generation cephalosporins, like Enterobacter spp., Serratia spp, and Yersinia spp. were susceptible to the tested quinolones. Ciprofloxacin was 5 to 25-fold more potent on a weight basis against Enterobacteriaceae than the other quinolones. Neisseria meningitidis, Neisseria gonorrhoeae, and Haemophilus influenzae were extremely susceptible to the new quinolones. Ciprofloxacin was about 10 times more potent against Pseudomonas aeruginosa than the other quinolones, and was the only quinolone that was sufficiently active against all tested P. aeruginosa strains (MIC less than or equal to 0.4 microgram/ml). The activity against Gram-positive bacteria was considerably lower. All the quinolones investigated had an acceptable activity against many of the methicillin-sensitive and methicillin-resistant Staphylococcus aureus and coagulase-negative staphylococci. The majority of the Streptococcus spp. tested was quinolone-resistant, and was Listeria monocytogenes. Generally, it was evident that ciprofloxacin was more potent on a weight basis than the other quinolones, but this difference was counterbalanced by a higher achievable serum concentration for ofloxacin. Some of the investigated fluoroquinolones might constitute valid therapeutical alternatives to beta-lactam antibodies and aminoglycosides in the treatment of serious bacterial infections.

Ofloxacin. A review of its antibacterial activity, pharmacokinetic properties and therapeutic use

Ofloxacin is one of a new generation of fluorinated quinolones structurally related to nalidixic acid. It is an orally administered broad spectrum antibacterial drug active against most Gram-negative bacteria, many Gram-positive bacteria and some anaerobes. Ciprofloxacin is the only other quinolone with superior in vitro antibacterial activity. However, the pharmacokinetic profile of ofloxacin is superior to that of ciprofloxacin, with more rapid absorption and a peak serum concentration several times higher. Moreover, ofloxacin achieves high concentrations in most tissues and body fluids. The results of clinical trials with ofloxacin have confirmed the potential for use in a wide range of infections, which was indicated by its in vitro antibacterial and pharmacokinetic profiles. It has proven effective against a high percentage of infections caused by Gram-negative organisms, slightly less effective against Gram-positive infections, and effective against some anaerobic infections. Clinical efficacy has also been confirmed in a variety of systemic infections as well as in acute and chronic urinary tract infections, and ofloxacin has generally appeared to be at least as effective as alternative orally administered antibacterial drugs. Ofloxacin is well tolerated and, although experience with the drug in clinical practice to date is limited, bacterial resistance does not appear to develop readily. Thus, ofloxacin is an orally active drug which offers a valuable alternative to other broad spectrum antibacterial drugs.

In vitro activity of RO 23-6240 (AM-833): a new fluoroquinolone

The in vitro activities of RO 23-6240 (AM-833) and four comparative fluoroquinolones were studied. Minimal inhibitory concentrations (MICs) of RO 23-6240, which inhibited at least 90% of strains, were less than or equal to 0.03-1 microgram/ml for Staphylococcus aureus, Staphylococcus epidermidis, Enterobacteriaceae, Acinetobacter anitratus Aeromonas hydrophila, Branhamella catarrhalis, and Haemophilus influenzae, 2-8 micrograms/ml for Staphylococcus saprophyticus, streptococci, diphtheroids, and Pseudomonas spp., and 1-32 micrograms/ml for anaerobic species. MICs of ofloxacin, pefloxacin, norfloxacin, and ciprofloxacin paralleled those of RO 23-6240. With all five drugs, MICs were minimally affected by inoculum size and minimal bacterial concentrations (MBCs) were always within two dilution steps (log2) of MICs.

Ofloxacin pharmacokinetics in renal failure

The pharmacokinetics of ofloxacin were investigated in 12 normal subjects and 21 uremic patients after the administration of a single oral 200-mg dose. An open three-compartment body model was used to calculate ofloxacin pharmacokinetic parameters. In healthy subjects, the peak plasma level averaged 2.24 +/- 0.90 micrograms/ml and was obtained at 0.83 +/- 0.31 h. The absorption rate constant was 4.22 +/- 1.64 h-1. The terminal half-life was 7.86 +/- 1.81 h. The apparent volume of distribution was 2.53 +/- 0.78 liters/kg. Total body and renal clearances were 241.4 +/- 53.8 and 196.5 +/- 42.9 ml/min per 1.73 m2, respectively. A total of 68.4 +/- 11.9% of the dose was recovered unchanged in 24-h urine. In uremic patients, the terminal half-life increased in relation to the degree of renal failure: from 8 h in normal subjects to 37 h in severely uremic patients. Renal insufficiency did not significantly modify the peak plasma level, the apparent volume of distribution, the fractional clearance, or the nonrenal clearance of ofloxacin. However, the time to peak level was delayed in patients with creatinine clearance of less than 30 ml/min. Linear relationships were found between ofloxacin pharmacokinetic parameters and glomerular filtration rate data. Ofloxacin is only very slightly removed by hemodialysis. Dosage adjustments of ofloxacin in uremic patients are proposed.

Concentration of norfloxacin in human gallbladder tissue and bile after single-dose oral administration

Concomitant concentrations of norfloxacin in serum and in gallbladder tissue and bile were determined in 10 patients after a single oral dose of 400 mg given before cholecystectomy. Concentrations in gallbladder bile ranged from 0.6 to 15.6 micrograms/ml, with a mean bile/serum ratio of 7.0. The mean concentration in gallbladder tissue was 1.8 +/- 0.8 (standard error) micrograms/g.

Treatment of bone, joint, and soft-tissue infections with oral ciprofloxacin

We treated 52 patients with orally administered ciprofloxacin. In this study of 34 men and 18 women who completed therapy and who could be evaluated, there were 29 patients with nonhematogenous osteomyelitis, 20 patients with skin or soft-tissue infections, and 3 patients with joint infections. During the study, 92 isolates of pathogenic facultative aerobic bacteria, including 37 members of the family Enterobacteriaceae, 30 Staphylococcus aureus isolates, and 21 Pseudomonas aeruginosa isolates, were recovered, and 88 (96%) of the isolates were found to be susceptible to ciprofloxacin. Of the 29 patients with osteomyelitis, 14 have not experienced relapse after a follow-up of at least 1 year. Overall, 61% of infections were resolved, as judged by both clinical and microbiological criteria, during therapy. One patient developed Streptococcus salivarius sepsis during ciprofloxacin therapy, and one patient developed a rash which required discontinuation of ciprofloxacin. Otherwise, there were no serious reactions or complications.

Efficacy and safety of oral ciprofloxacin for treatment of serious urinary tract infections

Eighty-three patients with serious urinary tract infections were treated with oral ciprofloxacin. Of these patients, 79 were hospitalized, and 41 had known structural or neurologic abnormalities of the urinary tract. The most common pathogens were members of the family Enterobacteriaceae (MICs, less than or equal to 0.06 microgram/ml), Pseudomonas aeruginosa (MICs, 0.13 to 2 micrograms/ml), and Enterococcus faecalis (MICs, 0.5 to 2 micrograms/ml). Sixty-eight patients were able to be evaluated for determining efficacy; all responded symptomatically, and all urinary pathogens were eradicated on days 3 to 5 of treatment. Five patients, who were treated for a relatively short duration (2 to 10 days), relapsed 5 to 9 days posttreatment. Six patients became colonized with yeasts during treatment, and seven patients developed bacterial reinfections 5 to 9 days posttreatment. All patients whose infections relapsed or who developed infections with new organisms had neurogenic bladders, structural abnormalities of the genitourinary tract, or urinary catheters. There was no instance of bacteria developing resistance during treatment. Ciprofloxacin probably caused nausea with or without vomiting in 7 of the 83 patients, headache in 3 patients, and mild elevation of hepatic enzymes in 2 patients; other adverse reactions were observed but were probably not drug related. Oral ciprofloxacin was effective and safe for the treatment of serious urinary tract infections caused by a variety of bacterial pathogens.

In vitro activity of amifloxacin (WIN 49,375) compared with those of ciprofloxacin and ofloxacin

The in vitro activity of the novel fluoroquinolone derivative, amifloxacin (WIN 49,375), was compared with the activities of ciprofloxacin and ofloxacin. A total of 500 clinical isolates of Gram-negative and Gram-positive bacteria were included, and the minimal inhibitory concentration (MIC) was determined by an agar dilution method. All drugs were highly active against Enterobacteriaceae, but ciprofloxacin showed the highest activity on a weight-for-weight basis (MIC 90% less than or equal to 0.03 mg/l). Ciprofloxacin was the most active agent against Pseudomonas isolates; all isolates being inhibited by 0.25 mg/l or less. The staphylococcal isolates were inhibited by ciprofloxacin and ofloxacin at relatively low concentrations (MIC 100% = 1 mg/l), whereas amifloxacin showed moderate activity against the majority of these isolates. Ciprofloxacin was highly active against enterococci, ofloxacin was moderately active, and amifloxacin was inactive. All Neisseria gonorrhoeae isolates were susceptible to the lowest concentrations of the agents that were employed in the study (0.03 mg/l).

Effect of oral ofloxacin on fecal bacteria in human volunteers

Intestinal members of the family Enterobacteriaceae were eliminated in five human volunteers treated with oral ofloxacin for 5 days. No emergence of resistant Enterobacteriaceae was observed. Counts of group D streptococci were significantly reduced. Colonization by Candida sp. was observed in all five volunteers during ofloxacin treatment. The anaerobic flora was fairly stable from one sample to another before treatment and was not substantially modified by ofloxacin.

Bactericidal activities of ten different fluoroquinolones against selected Enterobacteriaceae

Ten fluoroquinolone compounds and two other 4-quinolones were tested in a microdilution system. Minimal inhibitory concentrations and minimal bactericidal concentrations were determined with 1 X 10(7) and 5 X 10(5) colony forming units per milliliter. All 12 compounds were bactericidal. Continued inhibition by drug carried over in the subcultured samples was documented and that represents a potential source of technical error that needs to be controlled when determining minimal bactericidal concentrations for these extremely potent drugs.

Comparison of in vitro activity of quinolone antibiotics and vancomycin against gentamicin- and methicillin-resistant Staphylococcus aureus by time-kill kinetic studies

Quinolone antibiotics have been proposed as possible alternatives to vancomycin for methicillin-resistant Staphylococcus aureus infections. We investigated the activities of amifloxacin, ciprofloxacin, norfloxacin, and vancomycin by time-kill kinetic studies. Antibiotic concentrations of 0, 1.0, and 4.0 times the MIC were used against four strains of gentamicin- and methicillin-resistant S. aureus. Staphylococci were plated onto ciprofloxacin-containing agar at all time points, in repeat time-kill kinetic studies. Macrobroth dilution MICs and MBCs were determined. Ciprofloxacin levels were measured by bioassay. Replica plating was performed from the original susceptible inoculum (MIC, 0.125 micrograms/ml) onto ciprofloxacin-supplemented agar. At 4.0 times the MIC, only with ciprofloxacin was there regrowth at 24 and 48 h. All four strains of staphylococci grew on agar supplemented with 1 microgram of ciprofloxacin per ml; three of four grew on agar supplemented with 2 micrograms of ciprofloxacin per ml. MICs and MBCs for these resistant clones ranged from 8 to 32 micrograms/ml. No degradation in activity or amount of ciprofloxacin could be detected in the bioassay. Replica-plated staphylococci grew on agar containing 1 microgram/ml but not higher concentrations of ciprofloxacin at 48 h. Amifloxacin and norfloxacin sustained bactericidal activity comparable to that of vancomycin. We conclude that heteroresistant subpopulations of gentamicin- and methicillin-resistant S. aureus can emerge under antibiotic selection pressure. Such resistant clones may then mutate in the presence of subinhibitory concentrations of antibiotic to higher levels of ciprofloxacin resistance.

The comparative activity of pefloxacin, enoxacin, ciprofloxacin and 13 other antimicrobial agents against enteropathogenic microorganisms

In this study, we compared the activity of pefloxacin, enoxacin and ciprofloxacin against 269 enteropathogenic strains (Campylobacter jejuni, enteropathogenic Escherichia coli, Salmonella typhi, Shigella spp., Vibrio cholerae and Yersinia enterocolitica) with that of rosoxacin, flumequin, nifuroxazide, erythromycin, chloramphenicol, ampicillin, cefotaxime, tetracycline, amikacin, netilmicin, sulfamethoxazole, trimethoprim and co-trimoxazole. Pefloxacin, enoxacin and ciprofloxacin were always among the most active compounds. Furthermore, resistant strains or strains with elevated MIC values were not found. The MIC90 value for these three compounds was less than or equal to 0.25 mg/l, except for C. jejuni where it was 0.3 mg/l and 1.4 mg/l for pefloxacin and enoxacin, respectively.

Failure of norfloxacin to eradicate Chlamydia trachomatis in nongonococcal urethritis

Norfloxacin has some activity in vitro against Chlamydia trachomatis and Ureaplasma urealyticum, although not at levels attainable in serum. In this study, norfloxacin was administered (400 mg orally twice daily for 10 days) to men with acute nongonococcal urethritis. Of 25 men from whom C. trachomatis was initially isolated, 21 had the organism reisolated at the first follow-up visit posttreatment, and there were minimal changes in the number of inclusion-forming units in culture. Ultimately, all but 1 of the 22 men from whom C. trachomatis was initially isolated and who were monitored became clinical failures within 42 +/- 7 days posttreatment. The clinical outcome was significantly better for men from whom U. urealyticum was initially isolated but from whom C. trachomatis was not isolated. Of 27 men, 17 became and stayed culture negative for U. urealyticum at follow-ups, and clinically, 15 no longer had nongonococcal urethritis. Of these 15, all 12 monitored until at least 42 +/- 7 days posttreatment remained improved. Of 26 men from whom neither C. trachomatis nor U. urealyticum was initially isolated, 18 improved and all 15 who were monitored until at least 42 +/- 7 days posttreatment remained improved. Thus, although norfloxacin attains high levels in urine and has good tissue penetration, it had essentially no activity against chlamydial urethritis in men. It had better, but incomplete, activity against U. urealyticum. For quinolones to show promise in vivo against C. trachomatis, either the MICs will need to be much lower or the levels attained in serum will have to be much higher.

Influence of oral intake of seven different antibiotics on faecal short-chain fatty acid excretion in healthy subjects

Faecal excretion of short-chain fatty acids (SCFAs) has been measured by gas chromatography in groups of six or seven healthy subjects before, during, and after they received the antibiotics bacitracin, co-trimoxazol, doxycycline, erythromycin, nalidixic acid, ofloxazin, or vancomycin orally for 6 days. Intake of bacitracin and vancomycin had pronounced effects on faecal SCFAs excretion and reduced median total concentration of SCFAs from 105.4 mmol/kg to 21.8 mmol/kg and from 69.3 mmol/kg to 19.4 mmol/kg, respectively (p less than 0.05). Erythromycin had moderate effects on the faecal SCFAs excretion, whereas small or no changes were seen during intake of co-trimoxazol, doxycycline, nalidixic acid, and ofloxacin. 2-Methylbutyric acid, a SCFA not previously seen in human faeces, was found in the faeces of all subjects (median concentration before intake of antibiotic, 1.3 mmol/kg). Bacitracin, erythromycin, nalidixic acid, and vancomycin were detected in high concentrations in faeces during therapy, whereas trimethoprim, doxycycline, and ofloxacin were found in relatively low concentrations. In conclusion, some, but not all, peroral antimicrobials induce changes in faecal SCFAs, most likely reflecting changes in the colonic ecosystem.

Norfloxacin in the therapy of uncomplicated gonorrhea

In an open study, 70 patients with uncomplicated anogenital Neisseria gonorrhoeae infection were evaluated to determine the efficacy and safety of a single oral dose of norfloxacin (800 mg). Norfloxacin cured all 31 male urethral and 25 endocervical infections. All 63 isolates of N. gonorrhoeae tested were inhibited by 0.05 microgram of norfloxacin per ml.

Determination of norfloxacin and ciprofloxacin concentrations in serum and urine by high-pressure liquid chromatography

A high-pressure liquid chromatographic method for the determination of norfloxacin or ciprofloxacin concentrations in body fluids was developed and compared with a standard bioassay. The high-pressure liquid chromatographic assay utilizes a reverse-phase C18 column, an internal standard, and fluorescence detection, with reproducibility studies yielding coefficients of variation ranging from 0.6 to 3.7% and 0.9 to 2.7% for norfloxacin and ciprofloxacin, respectively. Correlation coefficients with the bioassay were 0.966 for norfloxacin and 0.952 for ciprofloxacin.

Cross-resistance of nalidixic acid resistant Enterobacteriaceae to new quinolones and other antimicrobials

One hundred urine isolates Enterobacteriaceae screened for resistance to 30 micrograms nalidixic acid by disc diffusion test were examined by MIC determination for in vitro susceptibility to nalidixic acid, ciprofloxacin, enoxacin, gentamicin, nitrofurantoin, trimethoprim, cephalexin and ceftazidime. Those resistant to nalidixic acid and also gentamicin or a cephalosporin were further examined to determine the mechanism of resistance. Compared to the total urine isolates of Enterobacteriaceae from the same time period, this population as a whole was less susceptible to all antimicrobials tested except gentamicin. Strains that exhibited multiple resistance had the conventional mechanisms of resistance to those antimicrobials. No multiply resistant strains had a permeability barrier due to outer membrane protein alterations causing cross-resistance to chemically unrelated classes of antimicrobials.

Susceptibility of Eikenella corrodens to newer and older quinolones

The susceptibilities of 44 clinical strains and a reference strain (ATCC 23834) of Eikenella corrodens were determined by agar dilution. All isolates were very susceptible (MICs, less than 2 micrograms/ml) to amifloxacin, ciprofloxacin, difloxacin, enoxacin, norfloxacin, ofloxacin, and Win 35439.

Diffusion of ofloxacin into the cerebrospinal fluid in patients with bacterial meningitis

Ofloxacin diffusion into cerebrospinal fluid (CSF) was evaluated in nine patients with bacterial meningitis. Patients were under treatment with i.v. amoxicillin (100 mg/kg/day), and during the first five days they were also given oral ofloxacin, 200 mg b.i.d. On days 2 and 5, blood and CSF samples were collected for assays by both HPLC and microbiological techniques. Samples were obtained 2 h (n = 2), 4 h (n = 1), 6 h (n = 2), 8 h (n = 2) and 12 h (n = 2) after the ofloxacin dose respectively. Concentration in CSF was 50 to 60% of that in serum and there was no significant difference between results with the two assay techniques.

Antibiotics in the second half of the 1980s. Areas of future development and the effect of new agents on aminoglycoside use

Articles in this supplement have examined in detail the role of aminoglycosides in the therapy of infections, addressing problems of resistance, toxicity, and efficacy. This article discusses other agents and their potential utility and effect on aminoglycosides. Penem antibiotics, which have activity against only aerobic gram-negative bacteria, have recently been synthesized. These agents have proved effective in animal experiments; to date, however, results of human clinical trials are not available. Carboxypenicillins and ureidopenicillins will still have to be administered with aminoglycosides in patients with serious life-threatening infections or in those institutions in which organisms such as Klebsiella, Enterobacter, and Pseudomonas exhibit high levels of resistance. What will be the role of aminothiazolyl cephalosporins? In some institutions, these agents might be used as sole therapy, particularly if they become less costly as a result of competition. In other settings, concern over the resistance of organisms, such as Enterobacter cloacae, Citrobacter freundii, Serratia marcescens, and Pseudomonas aeruginosa, will result in the use of aminoglycosides with these relatively beta-lactamase-stable cephalosporins. It will be necessary to monitor the development of resistance to the new antibiotics and to determine whether the use of aminoglycosides plus third-generation cephalosporin combinations results in decreased resistance. Other agents to be considered include the directed therapy monobactams aztreonam and carumonam, the broad-spectrum carbapenem imipenem, and the penems under development. It is unclear whether these compounds might be used with aminoglycosides in critically ill, infected patients. It is also unclear what role oral beta-lactamase-stable cephalosporins will have in the therapy of nosocomial infections, since they probably will not be effective against many of the urinary or cutaneous infections that are treated with aminoglycosides. Quinolone agents can be used successfully against many infections. However, the likelihood of bacterial resistance developing and their potential for toxicity are still unknown. Thus, despite the emergence of many new agents, it appears that the time-tested aminoglycosides will continue to play an important role in antimicrobial therapy for some time to come.

In vitro activity of CI-934, a new quinolone, compared with that of other quinolones and other antimicrobial agents

The in vitro activity of CI-934, a new 4-quinolone, was determined against gram-positive and gram-negative bacteria. The MICs for 90% of the isolates tested were 0.25 microgram/ml for Streptococcus pneumoniae, 0.5 microgram/ml for Streptococcus faecalis, 0.25 microgram/ml for staphylococci, including methicillin-resistant strains, and less than or equal to 1.0 microgram/ml for Escherichia coli, Salmonella and Shigella spp., Klebsiella spp., Proteus spp., and Citrobacter spp. CI-934 had activity superior to that of other quinolones against streptococci by four- to eightfold. Against members of the family Enterobacteriaceae, ciprofloxacin was 2- to 18-fold more active; ofloxacin and norfloxacin were twofold more active or similar to CI-934. CI-934 inhibited ampicillin-cephalothin-resistant urinary isolates of E. coli, Klebsiella pneumoniae, and Proteus mirabilis and cefoxatime-resistant Acinetobacter spp., Citrobacter freundii, Enterobacter cloacae, Proteus vulgaris, and Morganella morganii. The medium, inoculum size, and oxygen concentration, as well as the addition of serum, had not major effect on the activity of CI-934. Magnesium at a concentration of 9 mM increased MICs and MBCs four- to eightfold, and testing at pH 6 increased MICs as much as 32- to 64-fold for some organisms in comparison with MICs at pH 7. The frequency of spontaneous mutation to resistance was comparable to that for other new quinolones, but resistant isolates could be selected by repeated subculture.

New 4-quinolones in the treatment of urinary tract infections

The new fluorinated quinolones norfloxacin, ciprofloxacin and pefloxacin were evaluated in urinary infections. Bacteriological cure rates in both uncomplicated and complicated urinary tract infections ranged from 85% to 99%. Clinical cure rates were often lower due to the underlying conditions in the urinary tract. Patients with neurological bladder disease were cured in a relatively high percentage of their Pseudomonas infection after three months treatment with norfloxacin. Pharmacokinetics of ciprofloxacin in prostatic tissue and fluid will probably offer an advance in the treatment of chronic urinary infections due to an infectious prostatic focus. Definitely drug related side effects (of gastro-intestinal, neurological or allergic nature) were mild in most cases. The new 4-quinolones should be followed with interest concerning their activity in urological infections in general as well as specifically. The minor influence on the natural human flora and the possibility to decrease plasmid-mediated resistance are of major importance.