Comparative activities of ciprofloxacin, ticarcillin, and tobramycin against experimental Pseudomonas aeruginosa pneumonia

Animal models in the pharmacokinetic/pharmacodynamic evaluation of antimicrobial agents

Animal infection models in the pharmacokinetic/pharmacodynamic (PK/PD) evaluation of antimicrobial therapy serve an important role in preclinical assessments of new antibiotics, dosing optimization for those that are clinically approved, and setting or confirming susceptibility breakpoints. The goal of animal model studies is to mimic the infectious diseases seen in humans to allow for robust PK/PD studies to find the optimal drug exposures that lead to therapeutic success. The PK/PD index and target drug exposures obtained in validated animal infection models are critical components in optimizing dosing regimen design in order to maximize efficacy while minimize the cost and duration of clinical trials. This review outlines the key components in animal infection models which have been used extensively in antibiotic discovery and development including PK/PD analyses.

Antibiotics improve survival and alter the inflammatory profile in a murine model of sepsis from Pseudomonas aeruginosa pneumonia

Differing antibiotic regimens can influence both survival and the inflammatory state in sepsis. We investigated whether the addition and/or type of antimicrobial agent could effect mortality in a murine model of Pseudomonas aeruginosa pneumonia-induced sepsis and if antibiotics altered systemic levels of cytokines. FVB/N mice were subjected to intratracheal injection of pathogenic bacteria and were given gentamicin, imipenem, or 0.9% NaCl 2 h after surgery, which continued every 12 h for a total of six doses. Survival at 7 days (n = 24 in each group) was 100% for mice given gentamicin, 88% for mice given imipenem, and 8% for sham mice treated with 0.9% NaCl (P < 0.0001). Systemic interleukin (IL) 6 levels were assayed 6 h postoperatively on all mice to see if they were predictive of outcome. Plasma IL-6 levels above 3,600 pg/mL were associated with a 100% mortality, levels under 1,200 pg/mL were associated with a 100% survival, and levels between 1,200 and 3,600 pg/mL had no utility in predicting mortality. In a separate experiment, mice were sacrificed at 3, 6, 12 or 24 h after instillation of P. aeruginosa and were assayed for levels of TNF-alpha, IL-6, IL-10, and IL-12. Significant alterations in the proinflammatory cytokines TNF-alpha and IL-6 were present at all time points except 3 h between mice treated with antibiotics and sham controls. In contrast, statistically significant differences in the anti-inflammatory cytokine IL-10 were present between the groups only at 6 h, and levels of IL-12 were similar at all time points. These results indicate that both gentamicin and imipenem increase survival at least 10-fold in a model of pneumonia-induced monomicrobial sepsis, and this is predominantly associated with a down-regulation of proinflammatory cytokines.

Should Pseudomonas aeruginosa isolates resistant to one of the fluorinated quinolones be tested for the others? Studies with an experimental model of pneumonia

A clinical isolate of Pseudomonas aeruginosa resistant to pefloxacin (Pef) but susceptible to ciprofloxacin (Cip) was studied to compare the in vitro and in vivo activities of Pef, ofloxacin (Ofl), and Cip. The time-kill curve method showed no bactericidal activity for Pef and Ofl, but a reduction of 4 log10 CFU/ml was achieved with Cip at 1 h. A model of experimental P. aeruginosa pneumonia was used to evaluate in vivo the relevance of the difference in susceptibility observed in vitro. At 36 h, a 100% cumulative survival rate was observed in Cip-treated rats, which was far higher than the survival rate obtained with Pef (53%) or Ofl (46%) (P < 0.001). At 4 h, no bacteremia was observed in Cip-treated rats, whereas 93% of the Pef-treated rats and 80% of the Ofl-treated rats were bacteremic (P < 0.001). The best pulmonary bacterial clearance was observed with Cip. Interestingly, Pef and Ofl, to which the strain was resistant in vitro, showed a fairly good in vivo activity despite sub-MIC concentrations. Cip was more effective than Pef and Ofl in terms of pulmonary and systemic bactericidal activity and provided the best survival rate in animals. We conclude that differences between the different quinolones in terms of the organism's sensitivity assessed in vitro may be relevant and that it might be useful to reconsider the use of a quinolone to which P. aeruginosa shows resistance if the organism shows sensitivity to no other agent.

Effects of the combination of lipopolysaccharide-specific monoclonal antibodies and sparfloxacin against Pseudomonas aeruginosa pneumonia in neutropenic mice

The effects of the combination of a murine monoclonal antibody (MAb) specific for the O side chain of Pseudomonas aeruginosa Fisher immunotype 1 lipopolysaccharide and sparfloxacin in a neutropenic mouse model of P. aeruginosa pneumonia were examined. Under the condition that neither MAb at a dose of 500 micrograms per mouse administered intravenously nor a suboptimal dose of oral sparfloxacin (5 mg/kg of body weight) protected mice from challenge with a fatal dose, the combination therapy with MAb and sparfloxacin caused a significant increase in the survival rate (P less than 0.001 compared with either treatment alone). The effect of the combination was closely correlated to bacterial killing in plasma and lung tissue of infected mice. In vitro, a significant MAb-dependent, complement-mediated killing of P. aeruginosa was documented in the presence of sparfloxacin at one-half the MIC, while the killing was not observed in the absence of sparfloxacin. These in vivo and in vitro data suggest the usefulness of combination therapy with a lipopolysaccharide-reactive immunoglobulin G MAb and sparfloxacin in neutropenic patients with P. aeruginosa pneumonia.

Teicoplanin plus ciprofloxacin versus gentamicin plus piperacillin in the treatment of febrile neutropenic patients

Teicoplanin plus ciprofloxacin was compared with gentamicin plus piperacillin for the empirical treatment of fever in 80 neutropenic patients. A favourable response was seen in 78% of patients receiving teicoplanin plus ciprofloxacin and in 49% receiving gentamicin plus piperacillin (p less than 0.05). When microbiologically documented episodes were analysed separately, the response to teicoplanin plus ciprofloxacin was favourable in 81% of patients whereas only 35% responded favourably to gentamicin plus piperacillin (p = 0.034). Gram-positive organisms accounted for 76% of bacterial isolates, Staphylococcus epidermidis being the most common pathogen. Ten of 12 (83%) Staphylococcus epidermidis infections resolved when treated with teicoplanin plus ciprofloxacin as compared with 2 of 8 (25%) treated with gentamicin plus piperacillin. Teicoplanin is at least as effective as gentamicin plus piperacillin in the empirical treatment of febrile neutropenic patients and may be more effective in situations where gram-positive organisms are prevalent. The high incidence of gram-positive infections in our unit justifies the use of an agent with specific activity against gram-positive organisms in the first-line antibiotic regimen.

Comparative efficacies of ciprofloxacin, amoxicillin, amoxicillin-clavulanic acid, and cefaclor against experimental Streptococcus pneumoniae respiratory infections in mice

Experimental respiratory infections were established in mice by intranasal inoculation of Streptococcus pneumoniae. Inoculation of 10(7) CFU of either S. pneumoniae 1629 or S. pneumoniae 7 produced a fatal pneumonia in nontreated mice 2 to 3 days after infection. Oral therapy was commenced 1 h after infection and was continued three times a day for 2 days. The doses used in mice produced peak concentrations in serum and lung tissue similar to those measured in humans. Ciprofloxacin failed to eliminate either strain of pneumococcus from mouse lungs at any of the doses tested (40, 80, or 160 mg/kg of body weight) by the end of therapy (33 h). Mice that received ciprofloxacin at 160 mg/kg were clear of S. pneumoniae 7 5 days later, whereas persistence and regrowth of S. pneumoniae 1629 resulted in the death of 20% of animals treated with ciprofloxacin. Therapy with cefaclor (20 mg/kg) produced an effect similar to that of ciprofloxacin. In contrast, amoxicillin (10 and 20 mg/kg) and amoxicillin-clavulanic acid (10/5 and 20/10 mg/kg) were significantly (P less than 0.05) more effective in eliminating both strains of S. pneumoniae from the lungs by the end of therapy and, by 168 h, had prevented mortality in 80 to 100% of treated animals. The efficacy of ciprofloxacin against these experimental pneumococcal respiratory infections was poor, despite good penetration into lung tissue, and is a reflection of the low in vitro activity of the quinolone against S. pneumoniae, one of the most common pathogens in community-acquired pneumonia.

Evaluation of quinolones in experimental animal models of infections

Many discriminative experimental animal models of infection have been utilized in the evaluation of newer fluoroquinolones. In vivo efficacy of many of the newer agents has been shown in experimental models of meningitis, endocarditis, pneumonia, urinary tract infections, pyelonephritis, osteomyelitis, abscesses of various types, septic arthritis, gastroenteritis, salmonellosis, listeriosis, tuberculosis, syphilis, sinusitis, prostatitis and burn wound sepsis, among others. This review focuses on recent developments in a few selected areas. Although the limitations of animal model studies are well described, these results provide a rationale for the appropriate clinical usage of the newer fluoroquinolones in humans.

A randomized study of teicoplanin plus ciprofloxacin versus gentamicin plus piperacillin for the empirical treatment of fever in neutropenic patients

We compared the combination of teicoplanin plus ciprofloxacin with gentamicin plus piperacillin for the empirical treatment of fever in 80 neutropenic patients. A favourable clinical response rate was achieved in 28/38 (74%) patients receiving teicoplanin plus ciprofloxacin and in 17/35 (49%) of those receiving gentamicin plus piperacillin (P = 0.05). Microbiologically documented infections accounted for 55% of febrile events. When these episodes were analysed separately, response to teicoplanin plus ciprofloxacin remained unchanged at 74% whereas only 35% patients responded to gentamicin and pieracilin (P = 0.034). Gram-positive organisms accounted for 78% bacterial isolates with Staphylococcus epidermidis the most common pathogen. Ten out of 12 (83%) Staph. epidermidis infections resolved when treated with teicoplanin and ciprofloxacin as compared with a response rate of only two out of eight (25%) with gentamicin and piperacillin (P = 0.032). The combination of teicoplanin and ciprofloxacin was associated with no severe drug-related adverse events; by contrast, two patients receiving gentamicin plus piperacilin were withdrawn owing to adverse drug reactions, one with acute renal failure and one following a severe allergic reaction to piperacillin. We conclude that teicoplanin with ciprofloxacin is more effective than gentamicin plus piperacillin for the empirical treatment of febrile neutropenic patients. The high incidence of Gram-positive infection in our unit probably justifies the use of a specific anti-Gram-positive agent in the first-line antibiotic regimen.

Oral ciprofloxacin treatment of Pseudomonas aeruginosa osteomyelitis

Twenty-two adult patients with osteomyelitis due to Pseudomonas aeruginosa were enrolled in an open, prospective cooperative study to determine the efficacy of oral ciprofloxacin therapy in a dosage of 750 mg twice a day. Twenty patients received a complete course of treatment and could be assessed for efficacy. There were 12 men and 8 women, with a mean age of 55 years. Six patients had undergone previous, unsuccessful attempts at therapy. Eight patients had clinically important underlying conditions. The most common sites of infection were the sternum (six patients), hip (four patients), vertebrae (four patients), and tibia (two patients). Initial surgical debridement was performed in 18 of the 20 assessable patients. The mean duration of treatment was 2.85 months (range, 1 to 4 months), and that of the follow-up was 27 months (range, 6 to 52 months). Cure was achieved in 19 of the 20 (95%) patients. The only significant adverse effect (which prompted discontinuation of therapy) was severe nausea in one case. Oral ciprofloxacin coupled with adequate debridement is an effective, convenient, and safe therapy in patients with acute and subacute P. aeruginosa osteomyelitis.

Ibuprofen attenuates the inflammatory response to Pseudomonas aeruginosa in a rat model of chronic pulmonary infection. Implications for antiinflammatory therapy in cystic fibrosis

Chronic pulmonary infection in cystic fibrosis (CF) results in an inflammatory response with persistent neutrophil influx, which contributes to lung damage. Attenuating the response with antiinflammatory agents might delay progression of lung disease. We investigated the effects of the nonsteroidal antiinflammatory agent, ibuprofen, in a rat model of chronic Pseudomonas endobronchial infection and inflammation. The areal percentage of lung inflammation 14 days after animal inoculation with Pseudomonas-containing agarose beads was significantly less in animals treated with ibuprofen (35 mg/kg orally twice daily) (39 +/- 26% SD) compared to animals given placebo (55 +/- 25% SD) (p less than 0.05). Ibuprofen did not increase the pulmonary burden of Pseudomonas, and the ibuprofen-treated infected animals gained weight better than placebo-treated controls. The administered dose of ibuprofen provides plasma concentrations sufficient to inhibit the release of leukotriene B4 (LTB4) from rat neutrophils in vitro. Since LTB4 is a potent pro-inflammatory product that promotes neutrophil adherence, aggregation, migration, degranulation, and superoxide release, inhibition of its production by ibuprofen could inhibit inflammatory damage to the lung in this model. These data in an animal model, taken together with the success of a preliminary trial of alternate-day steroid therapy in mildly affected patients with CF, suggest that antiinflammatory therapy with ibuprofen should be considered for a new therapeutic strategy in CF.

Clinical utility of new quinolones in treatment of osteomyelitis and lower respiratory tract infections

In the eight major clinical studies published on use of oral quinolones in therapy of contiguous osteomyelitis, clinical and microbiologic cure/improvement rates were 75% and 73%, respectively, when drug therapy was combined with appropriate surgical debridement. This included many cases of polymicrobial osteomyelitis, as well as infection caused by recalcitrant pathogens such as Pseudomonas aeruginosa. In contrast, the response of staphylococcal osteomyelitis to oral quinolones, especially in cases caused by methicillin-resistant strains, appeared suboptimal. Quinolones appear to have a limited role in the treatment of community-acquired pneumonia, since other established antibiotic regimens have been proven effective in such situations. Quinolones may play an important role in the treatment of nosocomially acquired aerobic gram-negative bacillary pneumonia, either as primary parenteral therapy or as transitional oral therapy when affected patients become outpatients. In cystic fibrosis-associated acute exacerbations of chronic pseudomonal pneumonitis, the outcome of oral ciprofloxacin therapy was very satisfactory in the six major studies reported (approximately 85% improvement rates). In three comparative studies oral quinolone treatment of such pulmonary exacerbations resulted in clinical response rates equivalent to those for aminoglycoside plus beta-lactam therapy given intravenously. Quinolone-resistant Pseudomonas aeruginosa strains were commonly isolated from sputum during treatment; however, such patients continued to respond clinically to quinolone treatment, and sputum became rapidly repopulated with quinolone-susceptible Pseudomonas aeruginosa strains after discontinuation of therapy.

Intravenous ciprofloxacin as empirical treatment of febrile neutropenic patients

A randomized study of treatment with ciprofloxacin combined with benzylpenicillin (CB) versus a standard regimen of netilmicin combined with piperacillin (NP) as first-line empiric therapy was conducted in febrile neutropenic patients. Ninety-six patients were evaluable for determination of efficacy: 50 patients received CB and 46 patients received NP. There was no significant difference between the two groups in terms of age or primary diagnosis. Overall clinical response rate at the end of therapy was 66 percent for CB and 65 percent for NP. Microbiologic assessment revealed more pathogens eradicated by CB (64 percent) and fewer persisting (4 percent) than in the NP group (52 percent eradicated, 13 percent persisting). Only 10 percent of patients in the CB group had treatment-related adverse reactions as opposed to 28 percent of the NP-treated patients; these were predominantly renal impairment and were likely to have been due to the aminoglycoside. Staphylococcus epidermidis was the most commonly isolated pathogen, accounting for 38 percent of all isolates and 30 percent of all patients in whom treatment failed. Although streptococci accounted for 18 percent of the isolated pathogens, no treatment failures or superinfections were due to these organisms. This indicates an advantage of combining ciprofloxacin with benzylpenicillin. We conclude that the CB regimen is as effective as the NP treatment and is associated with fewer side effects.

Necrotizing external otitis treated with ciprofloxacin. A case report

Necrotizing (malignant) external otitis is a severe infection caused by Pseudomonas aeruginosa which occurs mainly in elderly diabetics or in immuno-depressed patients (Chandler, 1968). The management of this condition requires the association between an aminoglycoside antibiotic and an antipseudomonal beta-lactamic, given parenterally during a 4 to 6 week period. Sometimes it is necessary to continue the therapy for months until there is no evidence of residual disease (Strauss et al., 1982). Ciprofloxacin is a quinolone with antipseudomonal activity which can be taken orally, and it is a useful alternative to the current treatment. The authors report a case of necrotizing external otitis which was successfully treated with ciprofloxacin.

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

Ciprofloxacin is one of a new generation of fluorinated quinolones structurally related to nalidixic acid. The primary mechanism of action of ciprofloxacin is inhibition of bacterial DNA gyrase. It is a broad spectrum antibacterial drug to which most Gram-negative bacteria are highly susceptible in vitro and many Gram-positive bacteria are susceptible or moderately susceptible. Unlike most broad spectrum antibacterial drugs, ciprofloxacin is effective after oral or intravenous administration. Ciprofloxacin has been most extensively studied following oral administration. It attains concentrations in most tissues and body fluids which are at least equivalent to the minimum inhibitory concentration designated as the breakpoint for bacterial susceptibility in vitro. The results of clinical trials with orally and intravenously administered ciprofloxacin have confirmed the potential for its use in a wide range of infections, which was suggested by its in vitro antibacterial and pharmacokinetic profiles. It has proven an effective treatment for many types of systemic infections as well as for both acute and chronic infections of the urinary tract. Ciprofloxacin generally appeared to be at least as effective as alternative orally administered antibacterial drugs in the indications in which they were compared, and in some indications, to parenterally administered antibacterial therapy. However, further studies are needed to fully clarify the comparative efficacy of ciprofloxacin and standard antibacterial therapies. Bacterial resistance to ciprofloxacin develops infrequently, both in vitro and clinically, except in the setting of pseudomonal respiratory tract infections in cystic fibrosis patients. The drug is also well tolerated. Thus, as an orally active, broad spectrum and potent antibacterial drug, ciprofloxacin offers a valuable alternative to broad spectrum parenterally administered antibacterial drugs for use in a wide range of clinical infections, including difficult infections due to multiresistant pathogens.

Oral ciprofloxacin treatment for Salmonella typhimurium infection of normal and immunocompromised mice

Oral treatment of Salmonella typhimurium infection with ciprofloxacin was compared with conventional chemotherapy with ampicillin or chloramphenicol in normal (CFW1) and immunocompromised (C57BL/6) mice. Administration of the antibiotics for 12 days reduced the number of bacteria in livers and the mortality of C57BL/6 mice significantly. Ciprofloxacin was considerably more effective than ampicillin in prolongation of the mean survival time of these mice. Similar to conventional chemotherapeutic agents, ciprofloxacin did not prevent fatal disease in most C57BL/6 mice when the treatment lasted 12 days only. On the other hand, ciprofloxacin cured lethal S. typhimurium illness in immunocompromised mice after long-term oral chemotherapy for 26 days at a dosage of 100 mg/kg twice a day. This was not achieved by either ampicillin or chloramphenicol. In normal mice, 12 days of therapy with ciprofloxacin was sufficient for a significant decrease in both the number of viable bacteria in livers and the mortality of lethally infected mice. The results provide a basis for an alternative antibiotic treatment by the oral route in immunocompromised hosts with systemic infections.

Comparative activities of ciprofloxacin and ceftazidime against Klebsiella pneumoniae in vitro and in experimental pneumonia in leukopenic rats

The antibacterial activities of ciprofloxacin and ceftazidime against Klebsiella pneumoniae in vitro and in vivo were compared. Although there was only a minor difference between the MBCs of both drugs, the bacterial killing rate of ciprofloxacin in vitro was very fast in comparison with that of ceftazidime. Similarly, the intravenous administration of ciprofloxacin at 1 h after bacterial inoculation resulted in effective bacterial killing in the lungs of leukopenic rats. This killing was dose dependent, in contrast to the dose-independent bactericidal effect of ceftazidime. The high antibacterial activity of ciprofloxacin in the lungs as compared with that of ceftazidime was also reflected in its therapeutic efficacy in K. pneumoniae pneumonia and septicemia in leukopenic rats when these infections were treated at 6-h intervals over 4 days, starting at 5 h after bacterial inoculation. Concentrations of ciprofloxacin and ceftazidime in lung tissue were not significantly different. Regarding the antibacterial activity of both drugs against K. pneumoniae in relation to the bacterial growth rate in vitro and in the lungs of leukopenic rats, ciprofloxacin killed K. pneumoniae organisms that were not actively growing, whereas ceftazidime did not. In addition, it was demonstrated that when the intravenous administration of antibiotic was delayed from 1 h up to 24 h after bacterial inoculation, ceftazidime lost its antibacterial activity in the lungs and blood of leukopenic rats, whereas ciprofloxacin was still very effective. These data suggest that the capacity of an antibiotic to kill bacteria at a slow growth rate may be relevant for its therapeutic effect in established infections, in which slowly growing bacteria form a substantial part of the total bacterial population.

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.

Bactericidal activity of ciprofloxacin against amikacin- and cefotaxime-resistant gram-negative bacilli and methicillin-resistant staphylococci

The MICs and MBCs of ciprofloxacin were determined for clinical isolates of antibiotic-resistant aerobic bacteria. Decreased susceptibility to ciprofloxacin of cefotaxime- and amikacin-resistant Serratia marcescens and amikacin-resistant Pseudomonas aeruginosa strains were noted. The data suggest that ciprofloxacin susceptibility should be carefully monitored in treating patients with hospital-acquired bacterial infections.

Use of ciprofloxacin in the treatment of Pseudomonas aeruginosa infections

The therapeutic efficacy and safety of ciprofloxacin was studied in 30 patients with Pseudomonas aeruginosa infections. In 20 patients ciprofloxacin was given alone and in 10 patients (including 8 compromised hosts) in combination with an aminoglycoside (9) or azlocillin (1). Ciprofloxacin was given in doses of 500 mg orally or 200-300 mg i.v. every 12 h. In patients receiving only ciprofloxacin clinical cure with eradication of bacteria was obtained in 15 patients (75%) with infections of bone and joint (6), skin and soft tissue (4), lung (2), middle ear (2) and CSF (1). Two patients with lymphoma and Pseudomonas aeruginosa pneumonia died. In patients receiving combination therapy a definite therapeutic success was achieved in four (40%). Three patients with Pseudomonas aeruginosa septicemia died. In seven patients nine bacterial strains with decreasing susceptibility of ciprofloxacin (increase in MIC from less than or equal to 0.5 micrograms/ml to 2-16 micrograms/ml) were selected (6 Pseudomonas aeruginosa, 1 Enterobacter cloacae, 1 Serratia marcescens, 1 Staphylococcus aureus). Ciprofloxacin was well tolerated. This new quinolone seems to be suitable for single drug treatment of Pseudomonas aeruginosa infections in patients with normal host defense mechanisms, while its therapeutic potential in compromised hosts requires further evaluation.

Comparative evaluation of ciprofloxacin, enoxacin, and ofloxacin in experimental Pseudomonas aeruginosa pneumonia

The therapeutic activity of ciprofloxacin, enoxacin, and ofloxacin was evaluated in guinea pigs with acute and chronic experimental Pseudomonas aeruginosa pneumonia. Intratracheal instillations of P. aeruginosa resulted in fatal pneumonia in all untreated animals within 36 h. Among treatment groups (80 mg/kg [body weight] per day), cumulative survival rates were: 47%, ciprofloxacin; 55%, enoxacin; and 42%, ofloxacin. These rates were not significantly different. Intrapulmonary killing of P. aeruginosa was equivalent 3 h after a single dose of ciprofloxacin or ofloxacin (20 mg/kg) or enoxacin (40 mg/kg). The combination of ciprofloxacin with azlocillin, ceftazidime, or tobramycin did not increase the efficacy of intrapulmonary killing of P. aeruginosa over that of ciprofloxacin alone. A chronic, nonfatal bronchopneumonia was induced in guinea pigs by intratracheal instillation of microscopic agar beads impregnated with a mucoid strain of P. aeruginosa. Compared with no treatment, ciprofloxacin and enoxacin produced greater than or equal to 99.9% intrapulmonary killing, and ofloxacin sterilized the lungs completely, after 4 days of treatment. In no quinolone-treated animal did resistant strains of P. aeruginosa emerge during 4-day treatment periods. In further studies with the chronic model, oral and parenteral ciprofloxacin treatment were found to be equivalent in efficacy. We conclude that several quinolone derivatives may be effective for the treatment of P. aeruginosa pneumonia and that combinations of quinolones with beta-lactams or aminoglycosides may not increase efficacy against P. aeruginosa pneumonia.

Synergy of ciprofloxacin and azlocillin in vitro and in a neutropenic mouse model of infection

Combinations of ciprofloxacin with azlocillin, piperacillin and ticarcillin were tested in vitro against clinical isolates. Azlocillin plus ciprofloxacin showed synergy against 30% of Pseudomonas aeruginosa isolates; it was either synergistic or additive against 78% of all isolates tested even those resistant to the beta-lactam. Synergism was rarely noted for Klebsiella pneumoniae, Escherichia coli, Enterobacter spp. or Branhamella spp. isolates. Minimum inhibitory concentrations of ciprofloxacin plus azlocillin, plus piperacillin and plus ticarcillin against Pseudomonas spp. were reduced 4 or 2 fold, respectively. However, the combination azlocillin plus ciprofloxacin showed primarily indifference against gram-positive strains. Neutropenic mice infected with a lethal challenge of Pseudomonas spp. were protected by a combination of azlocillin and ciprofloxacin. Its additive and/or synergistic effects and expanded spectrum of activity against streptococci, methicillin-resistant staphylococci and JK corynebacteria may provide an alternative to traditional therapy.

Activities of pefloxacin and ciprofloxacin in experimentally induced Pseudomonas pneumonia in neutropenic guinea pigs

Pefloxacin and ciprofloxacin are two new quinoline carboxylic acid derivatives that have activity in vitro against a wide range of gram-negative bacteria, including Pseudomonas aeruginosa. Using a well-standardized model of Pseudomonas pneumonia in neutropenic guinea pigs, we tested the efficacy in vivo of these new agents. Both were highly effective in increasing survival and decreasing bacterial counts in the lungs of surviving animals. Pefloxacin and ciprofloxacin were significantly better (P less than 0.05) than aminoglycosides or beta-lactams tested in prior studies with this model, and they were as effective as combination therapy with aminoglycosides and beta-lactams. Resistance to either ciprofloxacin or pefloxacin did not emerge during the study period. Further studies with these drugs in the therapy of Pseudomonas sp. infections are warranted.