Comparative efficacy of ciprofloxacin, azlocillin, and tobramycin alone and in combination in experimental Pseudomonas sepsis

Alteration in the pharmacokinetic disposition of ciprofloxacin by simultaneous administration of azlocillin

Healthy subjects were given single intravenous doses of ciprofloxacin, azlocillin, and the two drugs simultaneously on separate occasions. High-pressure liquid chromatographic analysis was used to assay the concentrations of both drugs in serum and urine. Pharmacokinetic parameters were calculated by noncompartmental methods. The total body (CL), renal (CLR), and nonrenal (CLNR) clearances; steady-state volume of distribution (Vss); and fractional urinary excretion of ciprofloxacin were all markedly decreased with the simultaneous administration of azlocillin. The disposition of azlocillin was unchanged when it was given with ciprofloxacin compared to when it was given alone. The pharmacokinetic parameters (mean +/- standard deviation) of ciprofloxacin given alone versus in combination with azlocillin were as follows: CL, 52.2 +/- 9.2 versus 33.9 +/- 6.0 liters/h (P less than 0.0005); CLR, 26.5 +/- 4.8 versus 16.2 +/- 4.2 liters/h (P less than 0.0005); CLNR, 25.8 +/- 5.5 versus 17.7 +/- 4.0 liters/h (P less than 0.03); Vss, 224 +/- 30 versus 166 +/- 41 liters (P less than 0.01); fractional urinary excretion, 0.56 +/- 0.06 versus 0.43 +/- 0.04 (P less than 0.002), respectively. This interaction resulted in significantly higher and more prolonged concentrations of ciprofloxacin in serum, which may be beneficial in the treatment of serious gram-negative bacterial infections, but it could also produce greater toxicity or result in more pronounced effects on oxidative drug metabolism of other medications.

Serum bactericidal activity from intravenous ciprofloxacin and azlocillin given alone and in combination to healthy subjects

Ciprofloxacin plus azlocillin have been shown to exhibit in vitro synergy versus a variety of organisms, including Pseudomonas aeruginosa. This study examined this interaction in vivo, testing serum bactericidal activity (SBA) in six healthy male subjects after intravenous administration of ciprofloxacin 4 mg/kg (C), azlocillin 60 mg/kg (A), and the two simultaneously (C/A). Eight different organisms were tested: four isolates of P. aeruginosa with varying susceptibilities to C and A, and one isolate each of Escherichia coli (EC), Staphylococcus aureus (SA) Serratia marcescens (SM), and Klebsiella pneumoniae (KP), all of which were susceptible to both drugs. Blood samples were collected at the end of 30-min infusions and at 4 and 8 hr. Reciprocal titers were plotted versus time and area under the bactericidal titer curve (AUBC) calculated to assess antibacterial interactions. Results indicated that P. aeruginosa-1 (PA-1), EC, and KP were synergistically killed by C/A. AUBC for PA-1 were C = 36, A = 11, C/A = 144, p less than 0.05. AUBC for EC were C = 1059, A = 180, C/A = 1504, p = 0.05. AUBC for KP were C = 327, A = 97, C/A = 584, p = 005. Additive effects were demonstrated versus all of the other organisms except Serratia marcescens, where an indifferent effect was observed. Ciprofloxacin plus azlocillin may be a useful combination of the treatment of selected Gram-negative bacillary infections.

Comparative efficacy of ciprofloxacin, azlocillin, imipenem/cilastatin and tobramycin in a model of experimental septicemia due to Pseudomonas aeruginosa in neutropenic mice

The in vivo activity of ciprofloxacin against Pseudomonas aeruginosa was studied in a septicemia model in neutropenic mice and compared to that of other antibiotics with established activity against P. aeruginosa. When given as a single agent, ciprofloxacin proved to be as effective as imipenem/cilastatin, whereas azlocillin and tobramycin were rather ineffective. After infection with higher challenge inocula, combinations of two (synergistic) antibiotics were more effective than single agent therapy in most instances. The combination of ciprofloxacin with azlocillin was at least as effective as that of imipenem/cilastatin with tobramycin. Selection of mutants with decreased sensitivity to ciprofloxacin occurred during therapy, however, post-therapy MICs of ciprofloxacin did not exceed a level of 1 mg/l and rises of MICs did not detrimentally influence treatment outcome. Taken together with the results of earlier studies, our data encourage the use of ciprofloxacin in gram-negative septicemia in neutropenic patients.

Cross-resistance of Pseudomonas aeruginosa to ciprofloxacin, extended-spectrum beta-lactams, and aminoglycosides and susceptibility to antibiotic combinations

The susceptibilities of 270 clinical isolates of Pseudomonas aeruginosa from diverse sources (82 burn patients, 76 cystic fibrosis [CF] patients, and 112 other sources) to ciprofloxacin and three other quinolones, nine extended-spectrum beta-lactams, and three aminoglycosides were determined by an agar dilution method in cation-supplemented Mueller-Hinton medium. Ciprofloxacin, ceftazidime, imipenem, and aztreonam were the most active. MICs for burn isolates were consistently higher than those for other isolates for most antibiotics, whereas those for CF strains were consistently lower. Multidrug resistance to aminoglycosides and beta-lactams occurred in 21% of the burn isolates, 2.6% of the CF isolates, and 8.9% of the other isolates. Ninety percent of these strains remained susceptible to ciprofloxacin. Seven percent of the isolates were resistant to ciprofloxacin (MIC, greater than or equal to 2 micrograms/ml). Concurrent resistance to ciprofloxacin and beta-lactams or aminoglycosides was rare (1.8 to 4%). Analysis by Spearman rank correlation revealed a high degree of correlation of MICs among antibiotics within the same class, except for imipenem. An inoculum effect was observed for all antibiotics between 10(6) and 10(4) CFU (P less than 0.05), with those for piperacillin and cefoperazone being the most pronounced (16-fold and 8-fold differences, respectively), and was least apparent for the quinolones, aminoglycosides, imipenem, and aztreonam (twofold differences). Selected strains for which there were high MICs of ciprofloxacin (greater than or equal to 1 micrograms/ml) were tested against ciprofloxacin in combination with other agents in a checkerboard agar dilution assay. Synergistic (summated fractional inhibitory concentration, </=0.5) interactions at clinically achievable concentrations were most frequent with mezlocillin (33%), piperacillin (21%), and (7.6%), aztreonam (3.7%), and the aminoglycosides (3.7%). Antagonism (summated fractional inhibitory concentration, >/= 4) was observed in only one instance (with gentamicin).

Efficacy of ciprofloxacin alone and in combination with azlocillin in experimental endocarditis due to Pseudomonas aeruginosa

The efficacy of ciprofloxacin alone and in combination with azlocillin was compared with that of azlocillin plus tobramycin in a rat model of aortic valve endocarditis due to Pseudomonas aeruginosa. MICs against the infecting strain of ciprofloxacin, azlocillin and tobramycin were 0.125, 8, and 0.5 mg/l, respectively. Antimicrobials were administered 24 h after bacterial challenge and for six days. Mean peak/trough serum levels for ciprofloxacin (50 mg/kg i.v. q 12 h), azlocillin (500 mg/kg i.v. q 12 h) and tobramycin (6.5 mg/kg i.v. q 12 h) were: 10.5/0.2, 386/less than 16, and 6.2/less than 0.6 mg/l, respectively. Ciprofloxacin alone was more effective than the combination azlocillin-tobramycin in increasing survival (p less than 0.05), sterilizing blood (p less than 0.05) and valves (p less than 0.001), and in reducing bacterial titers in vegetations (p less than 0.001). Ciprofloxacin-azlocillin combination was not more effective than ciprofloxacin alone. Drug resistance was not encountered in post-treatment isolates with any therapy regimen.

Inhibition of Pseudomonas aeruginosa exoenzyme expression by subinhibitory antibiotic concentrations

We examined the effects of subinhibitory concentrations of ciprofloxacin, tobramycin, and ceftazidime on Pseudomonas aeruginosa exoenzyme expression in vitro and in vivo. Exotoxin A, exoenzyme S, phospholipase C, elastase, and total protease activities were suppressed by antibiotics at concentrations as low as 1/20 of the MIC over a 24-h period in broth. Continuous 10-day exposure of P. aeruginosa DG1 broth cultures to antibiotic levels equal to 1/10 of the MIC reduced exoenzyme S activity in all treatment groups. Elastase activity was reduced only by ciprofloxacin and tobramycin treatment. This suppressive effect of the antibiotics persisted throughout the 10 days and was not influenced by the increase in MIC of ciprofloxacin detected during the course of the experiment. Rats chronically infected with P. aeruginosa were treated with subinhibitory doses of antibiotics and compared with untreated controls. Bacterial numbers in lung homogenates from each of the four study groups were identical. However, the lungs from antibiotic-treated rats had significantly less histological damage than those from control rats (P less than 0.001). The protective effect was greatest for ciprofloxacin and tobramycin. Further, P. aeruginosa isolates from ciprofloxacin- and tobramycin-treated rats demonstrated significantly less exoenzyme S and elastase activity than isolates from untreated rats (P less than 0.001). Isolates from ceftazidime-treated lungs expressed less exoenzyme S activity (P less than 0.001) but an equivalent amount of elastase activity as isolates from controls. The suppression of P. aeruginosa exoenzymes may arrest progressive lung injury during chronic P. aeruginosa lung infections.

Bactericidal activity of ciprofloxacin compared with that of cefotaxime in normal volunteers

We compared ciprofloxacin (200 mg) with cefotaxime (2 g) when each was administered intravenously over a 30-min period to six volunteers in a crossover manner 1 week apart. To integrate the pharmacologic and microbiologic activity, inhibitory and bactericidal activities in serum were obtained for both antibiotics 1 and 6 h after administration against 10 strains of Escherichia coli, 10 strains of Klebsiella pneumoniae, 15 strains of Pseudomonas aeruginosa, and 10 strains each of methicillin-susceptible and -resistant Staphylococcus aureus. Geometric mean bactericidal titers for E. coli 1 h after the infusion were 1:60 for ciprofloxacin and 1:252 for cefotaxime, and for K. pneumoniae they were 1:20 and 1:256, respectively. However, geometric mean titers were poor for both antibiotics against methicillin-susceptible S. aureus (less than 1:2 for ciprofloxacin versus 1:5 for cefotaxime) and methicillin-resistant S. aureus (less than 1:2 for both antibiotics), as well as against P. aeruginosa (1:3 for ciprofloxacin versus 1:2 for cefotaxime). These data suggest that ciprofloxacin may be useful for the treatment of serious infections caused by E. coli and K. pneumoniae. However, caution is suggested when this dose of ciprofloxacin is used in situations in which septicemia is caused by P. aeruginosa or S. aureus and originates outside the urinary tract.