Ciprofloxacin versus vancomycin in the therapy of experimental methicillin-resistant Staphylococcus aureus endocarditis

Ciprofloxacin in the Treatment of Gram-Positive Bacterial Peritonitis in Patients Undergoing CAPD

Fluoroquinolones may be a good alternative for the treatment of bacterial peritonitis in patients undergoing continuous ambulatory peritoneal dialysis (CAPD). To test their efficiency against Gram-positive bacteria, we treatedwith intraperitoneal (i.p.) ciprofloxac in 30 episodes of Gram-positive bacterial peritonitis without manifest tunnel infection of the peritoneal catheters. Treatment was sustained for 5 days, then orally for 10 further days. Clinical and bacteriological responses were satisfactory in 25 cases, but resolution of infection was slow in 5 cases of Staphylococcus aureus. The minimal inhibitory and bactericidal concentrations were 0.06250.50 and 0.125-1.0 μg/mL respectively, lower than the plasma and dialysate concentrations of the drug. Side effects were negligible. We conclude that ciprofloxacin provides a good therapeutic alternative to more widely used antibiotics for the empirical treatment of peritonitis in patients undergoing CAPD. However, combinations of antibiotics may be necessary, in Staphylococcus aureus peritonitis.

Comparative efficacies of human simulated exposures of telavancin and vancomycin against methicillin-resistant Staphylococcus aureus with a range of vancomycin MICs in a murine pneumonia model

Telavancin displays potent in vitro and in vivo activity against methicillin-resistant Staphylococcus aureus (MRSA), including strains with reduced susceptibility to vancomycin. We compared the efficacies of telavancin and vancomycin against MRSA strains with vancomycin MICs of ≥1 μg/ml in a neutropenic murine lung infection model. Thirteen clinical MRSA isolates (7 vancomycin-susceptible, 2 vancomycin-heteroresistant [hVISA], and 4 vancomycin-intermediate [VISA] isolates) were tested after 24 h, and 7 isolates (1 hVISA and 4 VISA isolates) were tested after 48 h of exposure. Mice were administered subcutaneous doses of telavancin at 40 mg/kg of body weight every 12 h (q12h) or of vancomycin at 110 mg/kg q12h; doses were designed to simulate the area under the concentration-time curve for the free, unbound fraction of drug (fAUC) observed for humans given telavancin at 10 mg/kg q24h or vancomycin at 1 g q12h. Efficacy was expressed as the 24- or 48-h change in lung bacterial density from pretreatment counts. At dose initiation, the mean bacterial load was 6.16 ± 0.26 log(10) CFU/ml, which increased by averages of 1.26 ± 0.55 and 1.74 ± 0.68 log in untreated mice after 24 and 48 h, respectively. At both time points, similar CFU reductions were noted for telavancin and vancomycin against MRSA, with vancomycin MICs of ≤2 μg/ml. Both drugs were similarly efficacious after 24 and 48 h of treatment against the hVISA strains tested. Against VISA isolates, telavancin reduced bacterial burdens significantly more than vancomycin for 1 of 4 isolates after 24 h and for 3 of 4 isolates after 48 h. These data support the potential utility of telavancin for the treatment of MRSA pneumonia caused by pathogens with reduced susceptibility to vancomycin.

Evaluation of daptomycin treatment of Staphylococcus aureus bacterial endocarditis: an in vitro and in vivo simulation using historical and current dosing strategies

OBJECTIVES

A failure to daptomycin therapy and subsequent emergence of a daptomycin non-susceptible isolate occurred during the 1990 clinical investigation of daptomycin for the treatment of Staphylococcus aureus bacteraemia and endocarditis. We attempted to determine if this occurrence was reproducible in vitro and if it could be prevented by various daptomycin dosing strategies.

METHODS

The daptomycin susceptible parent strain (SA-675) and the subsequent non-susceptible derivative (SA-684) were evaluated. In the rabbit endocarditis model, daptomycin 3 mg/kg every 8 h for 4 days was administered to simulate the study patient's pharmacokinetic exposure. Daptomycin doses of 1.5 and 3 mg/kg every 12 h and 6 and 10 mg/kg every 24 and 48 h were simulated in the in vitro model with simulated endocardial vegetations (SEVs).

RESULTS

Daptomycin significantly reduced bacterial counts of SA-675 in rabbits, but one in 10(5)-10(6) organisms from vegetations of one animal had an 8-fold increase in MIC. Daptomycin 1.5 mg/kg every 12 h in the in vitro model demonstrated no activity against either strain; reduced susceptibility emerged in SA-675 (4-fold increase in MIC). Bactericidal activity was noted with 6 and 10 mg/kg dosing against SA-675 with no resistance detected. The activity of the 6 mg/kg regimen was reduced against SA-684 but significantly improved activity was noted with 10 mg/kg daily.

CONCLUSIONS

The emergence of resistance was successfully recreated at suboptimal dosing regimens while the current recommended regimen of 6 mg/kg/day prevented the emergence of non-susceptible mutants. Daptomycin 10 mg/kg/day demonstrated even more enhanced killing. Further investigation with daptomycin 10 mg/kg is warranted.

In vitro and in vivo activities of a novel cephalosporin, BMS-247243, against methicillin-resistant and -susceptible staphylococci

The recent emergence of methicillin-resistant Staphylococcus aureus (MRSA) with decreased susceptibility to vancomycin has intensified the search for alternative therapies for the treatment of infections caused by this organism. One approach has been to identify a beta-lactam with improved affinity for PBP 2a, the target enzyme responsible for methicillin resistance in staphylococci. BMS-247243 is such a candidate, with MICs that inhibit 90% of isolates tested (MIC(90)s) of 4, 2, and 8 microg/ml for methicillin-resistant strains of S. aureus, S. epidermidis, and S. haemolyticus, respectively, as determined on plates with Mueller-Hinton agar and 2% NaCl. The BMS-247243 MICs for MRSA were minimally affected by the susceptibility testing conditions (inoculum size, prolonged incubation, addition of salt to the test medium) or by staphylococcal beta-lactamases. BMS-247243 MIC(90)s for methicillin-susceptible staphylococcal species ranged from < or = 0.25 to 1 microg/ml. The BMS-247243 MIC(90) for beta-lactamase-producing S. aureus strains was fourfold higher than that for beta-lactamase-nonproducing strains. BMS-247243 is hydrolyzed by staphylococcal beta-lactamases at 4.5 to 26.2% of the rates measured for cephaloridine. The affinity of BMS-247243 for PBP 2a was >100-fold better than that of methicillin or cefotaxime. BMS-247243 is bactericidal for MRSA, killing the bacteria twice as fast as vancomycin. These in vitro activities of BMS-247243 correlated with its in vivo efficacy against infections in animals, including the neutropenic murine thigh and rabbit endocarditis models involving MRSA strains. In conclusion, BMS-247243 has in vitro and in vivo activities against methicillin-resistant staphylococci and thus may prove to be useful in the treatment of infections caused by these multidrug-resistant organisms.

Comparison of a rabbit model of bacterial endocarditis and an in vitro infection model with simulated endocardial vegetations

Animal models are commonly used to determine the efficacy of various antimicrobial agents for treatment of bacterial endocarditis. Previously we have utilized an in vitro infection model, which incorporates simulated endocardial vegetations (SEVs) to evaluate the pharmacodynamics of various antibiotics. In the present study, we compared four experimental rabbit endocarditis protocols to an in vitro infection model in an effort to determine if these models are comparable. We have evaluated the activity of clinafloxacin, trovafloxacin, sparfloxacin, and ciprofloxacin in rabbit models against Staphylococcus aureus and Enterococcus spp. In vitro models were performed simulating the antibiotic pharmacokinetics obtained in the in vivo studies. Models were dosed the same as rabbit models, and SEVs were evaluated at the same time the rabbit vegetations were examined. Clinafloxacin and trovafloxacin were evaluated against methicillin-susceptible (MSSA1199) and -resistant (MRSA494) strains of S. aureus. Ciprofloxacin was studied against MSSA1199 and MSSA487. Sparfloxacin and clinafloxacin were evaluated against Enterococcus faecium SF2149 and Enterococcus faecalis WH245, respectively. We found that reductions in SEV bacterial density obtained in the in vitro model were similar to those obtained in rabbit vegetations, indicating that the SEV model may be a valuable tool for assessing antibiotic potential in the treatment of bacterial endocarditis.

Lysostaphin treatment of experimental methicillin-resistant Staphylococcus aureus aortic valve endocarditis

The emergence of clinical isolates of methicillin-resistant Staphylococcus aureus with reduced susceptibility to vancomycin has prompted a search for new and novel therapeutic agents active against S. aureus. Lysostaphin, a peptidase produced by Staphylococcus simulans, specifically cleaves the glycine-glycine bonds unique to the interpeptide cross-bridge of the S. aureus cell wall. The effectiveness of various regimens of dosing with intravenous lysostaphin was compared to that of vancomycin in the rabbit model of aortic valve endocarditis caused by a clinical methicillin-resistant S. aureus isolate. All animals were treated for a total of 3 days. The most active regimen, lysostaphin given three times daily, produced sterile vegetations in 10 of 11 treated rabbits, with a mean reduction in vegetation bacterial counts of 8.5 log10 CFU/g compared to the counts in the untreated controls. In contrast, vancomycin given twice daily sterilized no vegetations and reduced vegetation bacterial counts by only 4.8 log10 CFU/g. Lysostaphin given once daily was less effective, reducing mean vegetation bacterial counts by only 3.6 log10 CFU/g, but the combination of lysostaphin once daily and vancomycin twice daily reduced the mean vegetation bacterial density by 7.5 log10 CFU/g, a result that was significantly better than that for either regimen alone (P < 0.05). Lysostaphin was well tolerated by the rabbits, with no evidence of immunological reactions following up to 9 weeks of intravenous administration. We conclude that lysostaphin given alone or in combination with vancomycin is more effective in the treatment of experimental methicillin-resistant S. aureus aortic valve endocarditis than vancomycin alone.

Efficacy of LY333328 against experimental methicillin-resistant Staphylococcus aureus endocarditis

The in vivo efficacy of LY333328, a new glycopeptide antibiotic, was compared with that of vancomycin by using the rabbit model of left-sided methicillin-resistant Staphylococcus aureus endocarditis. Animals received LY333328 or vancomycin (25 mg/kg of body weight every 24 or 8 h, respectively) for 4 days. These drugs were equally effective in clearing bacteremia and in reducing bacterial counts in vegetations and tissues. We conclude that in this model, LY333328 was microbiologically effective and may be a therapeutic alternative to vancomycin.

Efficacy of trovafloxacin against experimental Staphylococcus aureus endocarditis

Trovafloxacin is a new fluoronaphthyridone chemically and functionally related to members of the fluoroquinolone class of antimicrobial agents. The in vivo efficacy of the drug was compared with that of vancomycin by using the rabbit model of left-sided endocarditis. Rabbits infected with either a nafcillin-susceptible or -resistant test strain were treated with trovafloxacin (13.3 mg/kg of body weight every 12 h) or vancomycin (25 mg/kg of body weight every 8 h) for 4 days. In comparison with untreated controls, both antimicrobial agents effectively cleared bacteremia and significantly reduced bacterial counts in vegetations and tissues of animals infected with either test strain. No resistance to trovafloxacin emerged in test strains during therapy. We conclude that in this model trovafloxacin is as efficacious as vancomycin is and may serve as a viable alternative to vancomycin for use in humans with similar infections.

Vancomycin or vancomycin plus netilmicin for methicillin- and gentamicin-resistant Staphylococcus aureus aortic valve experimental endocarditis

Using a rabbit model of aortic valve endocarditis, we studied the efficacy of vancomycin alone or in combination with netilmicin and/or rifampin against a methicillin- and gentamicin-resistant strain of Staphylococcus aureus (MGRSA). Antibiotics were given for 6 to 12 days, as follows: vancomycin (15 mg/kg of body weight every 12 h [BID] intravenously), vancomycin plus netilmicin (2.5 mg/kg BID intramuscularly), vancomycin plus rifampin (10 mg/kg BID intramuscularly), and vancomycin plus netilmicin plus rifampin at the same routes, dosages, and schedules mentioned above. Netilmicin was given to two additional groups at a higher dosage (6 mg/kg every 24 h intramuscularly) alone or in combination with vancomycin (15 mg/kg BID intravenously) for 12 days. All regimens resulted in undetectable bacterial counts in a significant proportion of vegetations (except netilmicin alone) or reduced the bacterial counts in the vegetations compared with the counts in the untreated controls (P<0.01 to P<0.001). No resistance to rifampin or netilmicin developed during therapy. It is concluded that in the treatment of experimental aortic valve endocarditis caused by MGRSA (i) vancomycin as monotherapy is as efficacious as the triple combination, (ii) the addition of netilmicin (once daily or BID) to vancomycin does not improve the efficacy of the latter antibiotic, even in the presence of rifampin, and (iii) a 12-day course in more effective than a 6-day one, but not at a statistically significant level.

Activity of quinolones against gram-positive cocci: clinical features

The potential role of the commercially available fluoroquinolones in the treatment of Gram-positive infections is discussed on the basis of data obtained from animal experiments and clinical trials. In respiratory tract infections, and particularly in community-acquired pneumonia, it is evident that the presently available quinolones cannot be prescribed empirically as first-line therapy because of their borderline activity against Streptococcus pneumoniae and anaerobes. Reports of pneumococcal seeding in other tissues during quinolone therapy render their administration a debatable issue. Experience in endocarditis is limited to the use of ciprofloxacin plus rifampicin in intravenous drug users with right-sided Staphylococcus aureus endocarditis. Patients with staphylococcal osteomyelitis are included among cases of other bone infections. In noncontrolled studies ciprofloxacin, ofloxacin and pefloxacin attained a staphylococcal eradication rate ranging from 70 to 100%, while the addition of rifampicin has been proven to reduce the emergence of resistant mutants during therapy. In soft tissue and skin structure infections that also involve Gram-negative bacteria, ciprofloxacin and ofloxacin eradicated 72.6 and 89% of staphylococci, respectively; however, the presence of diabetes or vascular disease compromised the success of treatment. In staphylococcal peritonitis complicating continuous ambulatory peritoneal dialysis, results with ciprofloxacin given intravenously or intraperitoneally were promising. In infections in neutropenic hosts, success of prophylaxis or therapy is still not clear, since colonisation and breakthrough bacteraemias with viridans streptococci and staphylococci have been reported. Furthermore, therapeutic results are compromised by the low response rate in Gram-positive infections. Despite the reported clinical efficacy of the newer fluoroquinolones, physicians should be alerted to the emergence of staphylococci resistant to fluoroquinolones, mainly methicillin-resistant variants.

Bactericidal activities of teicoplanin, vancomycin, and gentamicin alone and in combination against Staphylococcus aureus in an in vitro pharmacodynamic model of endocarditis

We adapted an in vitro pharmacodynamic model of infection to incorporate simulated endocardial vegetations. The bactericidal activities of teicoplanin, vancomycin, gentamicin, and various combinations of these drugs were studied against a strain of methicillin-susceptible Staphylococcus aureus obtained from a patient being treated for endocarditis at Detroit Receiving Hospital. Bacteria were grown overnight, concentrated, and added to a mixture of cryoprecipitate (80%) and thrombin (10%) to achieve approximately 5 x 10(9) CFU/g. Fibrin clots (8 to 10) were suspended into the model, removed at 24, 48, and 72 h in duplicate, weighed, and homogenized in 1.25% trypsin. Control experiments were conducted to characterize the growth kinetics. The following antibiotics were administered to simulate the pharmacokinetics of the drugs in humans: teicoplanin at 3 and 15 mg/kg of body weight, vancomycin at 15 mg/kg, and gentamicin at 1 mg/kg. Fibrin clot samples used to detect resistance were plated on antibiotic-containing tryptic soy agar plates. For the teicoplanin and vancomycin regimens, protein binding to cryoprecipitate, thrombin, and fibrin clot was determined to be 32, 43, and 50% and 26, 28, and 29%, respectively. In comparison with no treatment, vancomycin or teicoplanin at 15 mg/kg or either of these regimens combined with gentamicin significantly reduced bacterial counts (P < 0.0001). Monotherapy with teicoplanin at 3 mg/kg or gentamicin resulted in no killing activity. Combination treatment with teicoplanin at 3 mg/kg and gentamicin resulted in the killing of approximately 2 log10 CFU/g by 72 h and the development of resistance to gentamicin. The results obtained with the in vitro model of endocarditis are similar to the results reported by several investigators with the rabbit model of infective endocarditis. This unique infection model is useful for designing initial drug dosage regimens and may be predictive of drug efficacy against infective endocarditis.

Quinolone resistance in Pseudomonas aeruginosa and Staphylococcus aureus. Development during therapy and clinical significance

This review focuses on published information on the experimental as well as clinical data on the emergence of quinolone resistant isolates. In the course of clinical use of fluoroquinolones, only a sporadic emergence of quinolone resistance has been noted. The resistant organisms emerged particularly in certain clinical settings where large numbers of organisms frequently causing chronic infections are present and/or in loci where quinolone concentrations may not be optimal. In terms of occurrence in individuals, quinolone resistance has emerged most frequently in hospitalized and nursing-home patients with identifiable risk factors. Epidemiological studies revealed that in nearly all the cases studied one or one predominating quinolone resistant clone was selected that was horizontally transmitted. Thus, the emergence of quinolone resistance is not due to an independent selection of resistant strains in a number of patients, but to the clonal spread of one strain once it has acquired quinolone resistance. Therefore, the rate of quinolone resistance is very likely to be lower than reported.

CI-960, a new fluoroquinolone, for therapy of experimental ciprofloxacin-susceptible and -resistant Staphylococcus aureus endocarditis

CI-960 is a new fluoroquinolone with enhanced in vitro activity against gram-positive pathogens. The efficacy of the drug was compared with that of vancomycin by using the rabbit model of nafcillin- and ciprofloxacin-susceptible and -resistant Staphylococcus aureus endocarditis. Animals received intravenous therapy with CI-960, 20 mg/kg of body weight every 8 h, or vancomycin, 17.5 mg/kg every 6 h, for 4 days. In a comparison with the effects on untreated controls, both antimicrobial agents effectively cleared bacteremia and significantly reduced bacterial counts in vegetations and tissues of animals infected with any of the test strains. In some cases, the efficacy of CI-960 was superior to that of vancomycin. The therapeutic activity of CI-960 was reduced, but still very good, against ciprofloxacin-resistant strains. One rabbit infected with such a strain and treated with CI-960 was found to harbor a small number of vegetation-associated organisms resistant to the drug at fivefold its original MIC; this was associated with a microbiological, but not a clinical, failure of therapy. We conclude that CI-960 is as effective as vancomycin is in this model of a serious systemic S. aureus infection, including that caused by strains resistant to ciprofloxacin. Increases in CI-960 MICs may develop during therapy of infections caused by strains highly resistant to ciprofloxacin, but they appear unlikely to occur in ciprofloxacin-susceptible strains.

Long-term oral ciprofloxacin in the treatment of prosthetic valve endocarditis due to Pseudomonas aeruginosa

Prosthetic valve endocarditis caused by Pseudomonas aeruginosa is refractory to medical treatment alone and early valve replacement is necessary. We describe a 40-year-old patient in whom endocarditis developed in the early postoperative period, and reoperation was not considered feasible. Ciprofloxacin was administered orally in order to suppress bacteremia for 36 months. Long-term oral ciprofloxacin may provide an opportunity in the treatment of prosthetic valve endocarditis caused by Ps. aeruginosa in patients who are unfavorable candidates for reoperation.

Development of resistance to fleroxacin during therapy of experimental methicillin-susceptible Staphylococcus aureus endocarditis

The efficacy of fleroxacin was compared with that of vancomycin by using the rabbit model of methicillin-susceptible Staphylococcus aureus endocarditis. Animals received intravenous therapy with fleroxacin, 30 mg/kg every 8 h, or vancomycin, 17.5 mg/kg every 6 h, for 4 days. Both antimicrobial agents effectively cleared bacteremia and significantly reduced bacterial counts in vegetations and tissues compared with those in untreated controls. However, resistance to fleroxacin at 5- and 10-fold the MIC arose in the test strain of S. aureus in 73 and 27%, respectively, of animals that received the drug. Resistant isolates were found mainly in vegetations and were composed of up to 7% of the residual population recovered from that site. We conclude that fleroxacin is as effective as vancomycin in this model of a serious systemic S. aureus infection, but resistance to the drug may develop during therapy. If similar results are found with other strains of S. aureus during therapy with this or other fluoroquinolones, such data, when they are combined with the high incidence of fluoroquinolone resistance among S. aureus isolates being reported from selected institutions, would support the contention that these drugs should not be used as first-line therapeutic agents for S. aureus infections.

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.

Fluoroquinolones. New miracle drugs?

Fluoroquinolones are the newest antibiotics for treatment of some infections caused by highly resistant bacteria (eg, Pseudomonas aeruginosa). Clinically sound indications for these drugs include resistant infections of the urinary, intestinal, and respiratory tracts; otitis externa; osteomyelitis; foot infections in diabetic patients; and late infections complicating burns. Fluoroquinolone therapy is not indicated in children younger than 12 years old and patients with foreign bodies, abscesses, pelvic inflammatory disease, or infections requiring a prophylactic antibiotic. Drug interactions with antacids or theophylline may occur.

Ciprofloxacin-resistant methicillin-resistant Staphylococcus aureus in an acute-care hospital

Use of ciprofloxacin as an alternative to vancomycin for treatment of methicillin-resistant Staphylococcus aureus infection has been paralleled by the emergence of resistant strains. This phenomenon has also been noticed in our hospital. To confirm our observation, methicillin and ciprofloxacin susceptibilities were tested by disk diffusion and broth microdilution techniques. We studied 83 methicillin-resistant Staphylococcus aureus isolates obtained from various sources over a 4-month period. Ciprofloxacin resistance (MIC, greater than 2 micrograms/ml) was detected in 69 isolates (83%). Prior use of ciprofloxacin was reported for 24 of 69 patients with ciprofloxacin-resistant strains and 0 of 14 patients with ciprofloxacin-susceptible strains. The day of detection during the hospital stay and the location of the source patient were not significantly different between resistant and susceptible strains. Bacteriophage typing showed a higher occurrence of nontypeable strains among ciprofloxacin-resistant strains (54%). Review of our microbiology register showed a progressive increase in the rate of resistance to ciprofloxacin during the first year of use, with initial rates being about 10% and recent rates being higher than 80%. On the other hand, methicillin-susceptible S. aureus remained uniformly susceptible to ciprofloxacin (98.4%). We conclude that prior use of ciprofloxacin is an important factor for the selection of ciprofloxacin-resistant strains and that ciprofloxacin has limited usefulness against methicillin-resistant S. aureus.

Daptomycin compared with teicoplanin and vancomycin for therapy of experimental Staphylococcus aureus endocarditis

The efficacies of daptomycin, teicoplanin, and vancomycin were compared in the therapy of experimental Staphylococcus aureus endocarditis. Rabbits infected with either of two methicillin-susceptible strains (SA-12871 or its moderately teicoplanin-resistant derivative SA-12873) or a methicillin-resistant S. aureus strain (MRSA-494) were treated with daptomycin, 8 mg/kg of body weight, every 8 h; teicoplanin, 12.5 mg/kg (low-dose teicoplanin [teicoplanin-LD], excluding MRSA-494) or 40 mg/kg (high-dose teicoplanin [teicoplanin-HD]) every 12 h; or vancomycin, 17.5 mg/kg every 6 h, for 4 days. Compared with no treatment daptomycin, teicoplamin-HD, and vancomycin significantly reduced bacterial counts of all test strains in vegetations and renal and splenic tissues (P less than 0.001). Teicoplanin-LD was equally effective against SA-12871 but failed against SA-12873, with three of six animals still being bacteremic at the end of therapy. For SA-12871, daptomycin was as effective as teicoplanin-HD and was superior to teicoplanin-LD and vancomycin (P = 0.02) in lowering vegetation bacterial counts. There were no differences between daptomycin, teicoplanin-HD, or vancomycin in the reduction of bacterial counts in tissues for any of the test strains. In rabbits infected with SA-12871, vegetations from 33% of teicoplanin-LD-treated, 6% of teicoplanin-HD-treated, and 13% of daptomycin-treated animals yielded organisms for which there were up to eightfold increases in the MICs. Resistance may have contributed to early death in one daptomycin-treated animal. No increases in the MICs for the test strain were detected in animals infected with SA-12873 or MRSA-494. We conclude that in this model and against these strains of S. aureus, daptomycin and teicoplanin-HD are as efficacious as vancomycin, but diminished susceptibility to both can develop during therapy.

Ciprofloxacin therapy of experimental endocarditis caused by methicillin-resistant Staphylococcus epidermidis

Ciprofloxacin or rifampin was significantly (P less than 0.05) more effective than vancomycin or the combination of vancomycin plus gentamicin for the treatment of Staphylococcus epidermidis experimental endocarditis. There were no significant differences in efficacy among any of the combinations of antimicrobial agents that included ciprofloxacin or rifampin. One animal treated with rifampin alone and one treated with the combination of vancomycin, rifampin, and gentamicin were found to be infected with rifampin-resistant strains of S. epidermidis during therapy. Resistant subpopulations of S. epidermidis were not detected during therapy with any other antimicrobial agent used alone or in combination. Ciprofloxacin alone or in combination with rifampin was effective therapy against S. epidermidis experimental endocarditis.

An update on the efficacy of ciprofloxacin in animal models of infection

Although animal models of infection are associated with certain limitations in interpretation, properly performed studies provide important information for evaluating the efficacy of new antimicrobial agents in the treatment of human disease. The antibacterial efficacy of the newer quinolones, particularly ciprofloxacin, has undergone extensive evaluation in several animal models. Efficacy has been demonstrated in animal models of pneumonia, endocarditis, meningitis, skin and soft-tissue infections, septic arthritis, burn wound sepsis, empyema, intra-abdominal abscess, osteomyelitis, prostatitis, sinusitis, urinary tract infection, chronic gastroenteritis, granuloma pouch infection, and Pseudomonas septicemia. More recent studies have evaluated the efficacy of ciprofloxacin in animal models of tuberculosis and syphilis, as well as in infections caused by the intracellular pathogens Salmonella typhimurium, Legionella pneumophila, and Listeria monocytogenes.

Ciprofloxacin in patients with bacteremic infections. The Spanish Group for the Study of Ciprofloxacin

The efficacy and safety of ciprofloxacin in the treatment of 68 episodes of bacteremia were studied. Patients were treated intravenously (30 cases), orally (13 cases), or with sequential intravenous/oral therapy (25 cases). Intravenous doses ranged from 200 to 400 mg per day and oral doses ranged from 1,000 to 1,500 mg per day. According to the criteria of McCabe and Jackson, 39 cases had nonfatal and 29 had ultimately fatal underlying diseases. The clinical condition of patients at the start of therapy was critical or poor in 40 cases and fair or good in 28. Sixty-four of the 68 episodes of bacteremia were monomicrobial and the remaining four were polymicrobial. The causative micro-organisms were: Escherichia coli (18 episodes), Pseudomonas aeruginosa (13 episodes), Acinetobacter sp. (10 episodes), Salmonella sp. (seven episodes), Enterobacter sp. (six episodes), Proteus sp. (four episodes), Serratia sp. (four episodes), Haemophilus influenzae (three episodes), Klebsiella sp. (three episodes), Staphylococcus aureus (2 episodes), and Morganella morganii (two episodes). Overall clinical efficacy of ciprofloxacin was 94 percent (64 of 68 patients). Bacteremia persisted in four patients (failure rate of 6 percent). Five organisms persisted: Acinetobacter sp. (two patients), P. aeruginosa (one patient), Enterobacter sp. (one patient), and Serratia sp. (one patient). Side effects were phlebitis associated with intravenous administration (four cases), dizziness (four cases), and superinfection (six cases). Superinfecting organisms and sites were as follows: Enterococcus faecalis, wound (2 cases); Candida sp., urinary tract infection (one case); Acinetobacter anitratus (ciprofloxacin resistant), urinary tract infection (one case); Staphylococcus epidermidis, blood (one case); and Clostridium perfringens, blood (one case). Ciprofloxacin administered either intravenously, orally, or intravenously followed by the oral route is effective therapy in the treatment of severe bacteremic infections.

Fluoroquinolone antimicrobial agents

The fluoroquinolones, a new class of potent orally absorbed antimicrobial agents, are reviewed, considering structure, mechanisms of action and resistance, spectrum, variables affecting activity in vitro, pharmacokinetic properties, clinical efficacy, emergence of resistance, and tolerability. The primary bacterial target is the enzyme deoxyribonucleic acid gyrase. Bacterial resistance occurs by chromosomal mutations altering deoxyribonucleic acid gyrase and decreasing drug permeation. The drugs are bactericidal and potent in vitro against members of the family Enterobacteriaceae, Haemophilus spp., and Neisseria spp., have good activity against Pseudomonas aeruginosa and staphylococci, and (with several exceptions) are less potent against streptococci and have fair to poor activity against anaerobic species. Potency in vitro decreases in the presence of low pH, magnesium ions, or urine but is little affected by different media, increased inoculum, or serum. The effects of the drugs in combination with a beta-lactam or aminoglycoside are often additive, occasionally synergistic, and rarely antagonistic. The agents are orally absorbed, require at most twice-daily dosing, and achieve high concentrations in urine, feces, and kidney and good concentrations in lung, bone, prostate, and other tissues. The drugs are efficacious in treatment of a variety of bacterial infections, including uncomplicated and complicated urinary tract infections, bacterial gastroenteritis, and gonorrhea, and show promise for therapy of prostatitis, respiratory tract infections, osteomyelitis, and cutaneous infections, particularly when caused by aerobic gram-negative bacilli. Fluoroquinolones have also proved to be efficacious for prophylaxis against travelers' diarrhea and infection with gram-negative bacilli in neutropenic patients. The drugs are effective in eliminating carriage of Neisseria meningitidis. Patient tolerability appears acceptable, with gastrointestinal or central nervous system toxicities occurring most commonly, but only rarely necessitating discontinuance of therapy. In 17 of 18 prospective, randomized, double-blind comparisons with another agent or placebo, fluoroquinolones were tolerated as well as or better than the comparison regimen. Bacterial resistance has been uncommonly documented but occurs, most notably with P. aeruginosa and Staphylococcus aureus and occasionally other species for which the therapeutic ratio is less favorable. Fluoroquinolones offer an efficacious, well-tolerated, and cost-effective alternative to parenteral therapies of selected infections.

Ciprofloxacin and rifampin, alone and in combination, for therapy of experimental Staphylococcus aureus endocarditis

The therapeutic activities of ciprofloxacin (25 mg/kg every 8 h), rifampin (10 mg/kg every 24 h), ciprofloxacin plus rifampin, and vancomycin (17.5 mg/kg every 6 h) were compared by using the rabbit model of Staphylococcus aureus endocarditis. Animals infected with one of two test strains (SA1199 or SA487) were randomized into treatment groups and received 6 days of therapy. For SA1199, ciprofloxacin plus rifampin was most effective at reducing vegetation bacterial counts. For SA487, ciprofloxacin plus rifampin was as effective as vancomycin but less effective than ciprofloxacin alone. Resistance to ciprofloxacin at 5- and 10-fold the MIC emerged in the test strain in 82 and 55%, respectively, of rabbits infected with SA1199 and receiving ciprofloxacin monotherapy. The combination of ciprofloxacin and rifampin decreased these frequencies to 60% (P = 0.27) and 10% (P = 0.04). No resistance to ciprofloxacin was found in rabbits infected with SA487. We conclude that ciprofloxacin and ciprofloxacin plus rifampin are as efficacious as vancomycin in this model and that combining rifampin with ciprofloxacin may decrease the frequency at which high-level resistance to ciprofloxacin emerges. However, with respect to improved efficacy, the combination of ciprofloxacin and rifampin is unpredictable and may be detrimental.

Efficacy of fleroxacin in experimental methicillin-resistant Staphylococcus aureus endocarditis

The efficacy of fleroxacin versus that of vancomycin was assessed by using the rabbit model of methicillin-resistant Staphylococcus aureus endocarditis. Animals were treated with fleroxacin (30 mg/kg of body weight every 8 h) or vancomycin (17.5 mg/kg every 6 h) for 4 days. These antimicrobial agents were equally effective in clearing bacteremia, reducing bacterial counts in vegetations and tissues, and curing endocarditis. However, resistance to fleroxacin at fivefold the MIC arose in the test strain of S. aureus in 8% of animals that received the drug. We conclude that fleroxacin is as efficacious as vancomycin in this model of a serious systemic S. aureus infection, but modest resistance to fleroxacin may develop during therapy.

Efficacy of pefloxacin-fosfomycin in experimental endocarditis caused by methicillin-resistant Staphylococcus aureus

The efficacies of pefloxacin, fosfomycin, and both of these agents in combination against methicillin-resistant Staphylococcus aureus were assessed in a rat endocarditis model. The combination prevented emergence of the fosfomycin and pefloxacin resistance seen in 36 and 4%, respectively, of animals receiving either agent alone and was more effective than either agent in sterilizing cardiac vegetations.

Ciprofloxacin therapy of experimental endocarditis caused by methicillin-susceptible or methicillin-resistant Staphylococcus aureus

Ciprofloxacin was more effective (P less than 0.01) than either imipenem or nafcillin therapy of experimental methicillin-susceptible Staphylococcus aureus endocarditis in rabbits after 2 or 3 days of treatment. There was no significant difference between results of treatment of methicillin-susceptible S. aureus experimental endocarditis with ciprofloxacin and results with the combination of nafcillin and gentamicin. Ciprofloxacin was more effective (P less than 0.01) than vancomycin therapy of experimental methicillin-resistant S. aureus endocarditis after 3 days of treatment. After 5 days of treatment, there was no significant difference between the results of treatment of experimental methicillin-resistant S. aureus endocarditis with ciprofloxacin and results with vancomycin.

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.