In vitro and in vivo studies of three antibiotic combinations against gram-negative bacteria and Staphylococcus aureus

Modified tetra-oxygenated xanthones analogues as anti-MRSA and P. aeruginosa agent and their synergism with vancomycin

Five isolated xanthones from the C. cochinchinense and G. mangostana were evaluated and tested for antibacterial activities. Isolated 4 and 5 exhibited potent anti-MRSA and P. aeruginosa activity, but showed poor pharmacokinetic properties via ADMET prediction. It led us to improve pharmacokinetic properties of 4 and 5 by partially modifying them in acidic condition yielding fourteen analogues. It was found that analogues 4b, 4d and 5b possessed proper pharmacokinetic properties, while only 4b exhibited the best anti-MRSA and P. aeruginosa activity. The SEM results indicated that 4b may interact with or damage the cell wall of MRSA and P. aeruginosa. Moreover, a combination of 4b and vancomycin exhibits synergistic effect against both MRSA and P. aeruginosa at MIC value of 4.98 (MIC = 18.75 μg/mL for 4b) and 9.52 μg/mL (MIC = 75 μg/mL for 4b), respectively.

Dual beta-lactam therapy for serious Gram-negative infections: is it time to revisit?

We are rapidly approaching a crisis in antibiotic resistance, particularly among Gram-negative pathogens. This, coupled with the slow development of novel antimicrobial agents, underscores the exigency of redeploying existing antimicrobial agents in innovative ways. One therapeutic approach that was heavily studied in the 1980s but abandoned over time is dual beta-lactam therapy. This article reviews the evidence for combination beta-lactam therapy. Overall, in vitro, animal and clinical data are positive and suggest that beta-lactam combinations produce a synergistic effect against Gram-negative pathogens that rivals that of beta-lactam-aminoglycoside or beta-lactam-fluoroquinolone combination therapy. Although the precise mechanism of improved activity is not completely understood, it is likely attributable to an enhanced affinity to the diverse penicillin-binding proteins found among Gram negatives. The collective data indicate that dual beta-lactam therapy should be revisited for serious Gram-negative infections, especially in light of the near availability of potent beta-lactamase inhibitors, which neutralize the effect of problematic beta-lactamases.

Sensitivity of 523 Blood Culture Isolates to 33 Antibiotics

523 blood culture isolates collected during 18 months (July 1980-December 1981) were analysed by the agar dilution method for sensitivity to 33 antibiotics. Breakpoints corresponding to the SIR system were used but for N-formimidoyl-thienamycin (N-f-thienamycin), azthreonam and fosfomycin serial dilutions were made. Aminoglycosides (netilmicin, gentamicin, amikacin and tobramycin) inhibited from 90 to 86% of the strains. This was comparable to the percentage inhibited by some cephalosporins (cefotaxime, cefoperazone, ceftazidime, ceftriaxone, cefuroxime, cephamandole and moxalactam) ranging from 95 to 89%. A very high number of strains (99%) were inhibited by N-f-thienamycin. By combination of certain antibiotics more than 99% of the strains could be inhibited.

Overview of synergy with reference to double beta-lactam combinations

Combination antimicrobial therapy is used to expand the bacterial coverage over a single agent, to prevent the emergence of resistant organisms, to decrease toxicity by allowing lower doses of both agents, or for synergy. Synergy is one of the most common of these reasons, especially in serious infections. The introduction of new broad-spectrum beta-lactam antimicrobials has led to their combination in the treatment of seriously ill patients. Whereas a combination of an aminoglycoside and a beta-lactam antimicrobial is frequently synergistic, much less is known about synergy between combinations of beta-lactams. In vitro testing shows most combinations of two beta-lactams to be indifferent or additive in their effects; rarely does synergy occur. Antagonism can sometimes be seen, particularly with combinations involving cefoxitin or imipenem, especially if the treated organism is Enterobacter or Pseudomonas. Results of clinical trials comparing double beta-lactam (DBL) therapy with aminoglycoside/beta-lactam combinations show no difference in clinical response rates. Highly active DBL combinations may substitute for standard aminoglycoside-containing regimens in certain situations, even though they are not reliably synergistic. However, in the treatment of seriously ill patients such combinations may be less desirable.

Activity of cefotiam in combination with beta-lactam antibiotics on enterobacterial hospital strains

By using checkerboard titrations the effect of cefotiam combined with different beta-lactam antibiotics on fifty strains of Enterobacteriaceae moderately susceptible (minimal inhibiting concentration greater than or equal to 8 mg/l) or resistant (minimal inhibiting concentration greater than or equal to 64 mg/l) to cefotiam was evaluated. The following compounds were tested: cefamandole, cefazolin, cefmenoxime, cefotaxime, cefotiam, ceftazidime, cefuroxime, mecillinam and piperacillin. The synergistic effect varied markedly. The combination cefotiam-mecillinam showed the highest rate of synergistic activity. Antagonism was found in 1% of the combinations.

Empiric antimicrobial therapy for febrile granulocytopenic cancer patients. Lessons from four EORTC trials

The experience from four EORTC trials on antimicrobial therapy for febrile granulocytopenic cancer patients (GCP) is reviewed. A general conclusion from these trials is that studies of the management of infection in GCP should include sufficient numbers of eligible patients to allow for evaluation of bacteremic patients at highest risk of death. The need for large collaborative studies stems directly from these considerations.

Use of cephalosporins in the immunologically compromised patient

Infection is a major threat to patients with neutropenia, particularly those with haematological malignancies who are undergoing chemotherapy. Early use of an empirical antibiotic regimen with the broadest possible spectrum of activity is recommended until culture data can guide the choice. A standard combination in many centres is an amino-glycoside and a semisynthetic penicillin with antipseudomonal activity or a cephalosporin. However, no regimen can adequately cover all potential pathogens and in these patients, who are exposed to many toxic insults, the choice of antibiotics may significantly increase the incidence of side effects, particularly nephrotoxicity. There has, therefore, been considerable interest in simpler, less toxic (and less expensive) regimens and the concept of monotherapy has been explored. Although recent studies using ceftazidime alone have supported this as an effective approach, there remain several issues to resolve; and on a more cautionary note preliminary results from the latest EORTC study, which recruited more than 1200 patients, suggest that in Gram-negative bacteraemia, conventional combination therapy remains the treatment of choice in neutropenia. While monotherapy is attractive in an environment of low drug resistance when exposure to third generation cephalosporins is infrequent, this is rarely the case. In addition, the widespread use of tunnelled catheters for venous access had led to an increase in Gram-positive infections, and the more intensive immunosuppression to the emergence of fungal infections. Although these tend not to be rapidly fatal, their presence must be considered in designing treatment strategies. The influence of the host and treatment on the type of infection and the relative merits of the differing concepts in therapy are explored in detail in this article.

Aminoglycosides plus beta-lactams against gram-negative organisms. Evaluation of in vitro synergy and chemical interactions

Combination antibiotic therapy has been used mainly to broaden the antibacterial spectrum and prevent the development of resistance. Antibiotic combinations proven to be synergistic in vitro are associated with a significantly better in vivo response, particularly in the compromised host in whom traditional treatment combines an antipseudomonal penicillin plus an aminoglycoside. Several investigators have examined combining new agents, such as the third-generation cephalosporins (cefotaxime, ceftriaxone, ceftizoxime, ceftazidime, cefoperazone, and moxalactam), aztreonam, or the ureidopenicillins, with amikacin. When compared with combinations of an older cephalosporin, carbenicillin or ticarcillin, plus gentamicin or tobramycin, these newer combinations produce higher rates of clinically meaningful synergy and rapid enhancement of in vitro bactericidal activity against the difficult-to-treat Enterobacteriaceae (i.e., Serratia, Citrobacter, Enterobacter, Providencia, and indole-positive Proteus species). This effect, without any evidence of antagonism, has been reported even for strains moderately or completely resistant to the former antibiotics. Unsatisfactory and unpredictable synergistic interactions against both resistant and susceptible strains of Pseudomonas aeruginosa--the most difficult nosocomial pathogen to treat--have been noted with combinations of tobramycin or gentamicin plus cefotaxime, moxalactam, or cefoperazone. Conversely, the use of amikacin plus various beta-lactams against multi-resistant strains is more frequently synergistic. Agents have been observed to exhibit such synergy in the following order of activity, from most to least synergistic: ceftazidime, ceftriaxone, moxalactam, aztreonam, cefotaxime, azlocillin, cefoperazone, cefsulodin, and carbenicillin. The combination of amikacin plus imipenem or ciprofloxacin against strains of P. aeruginosa resistant to the former and moderately resistant to the latter was recently reported to have a low probability of synergy; the combination of two of the newer beta-lactams had mostly an unpredictable or even antagonistic result. In vitro studies have also demonstrated that high concentrations of the antipseudomonal penicillins can inactivate the aminoglycosides. Among the latter compounds, the inactivation order, from most to least inactivated, was as follows: tobramycin, gentamicin, netilmicin, and amikacin. To date, the reports of aminoglycoside inactivation by the newer cephalosporins have been rather contradictory; only moxalactam has been shown produce a significant decrease in activity.

Combination therapy and monotherapy in the treatment of severe infection in the immunocompromised host

Profoundly granulocytopenic patients in whom fever develops are likely to have gram-negative septicemia, which may rapidly be fatal. These patients require early empiric therapy with a synergistic bactericidal combination of antibiotics that should be chosen on the basis of in vitro studies, animal models, and results of volunteer and clinical trials. From in vitro studies, it is apparent that the degree of synergy between an aminoglycoside and a beta-lactam is determined mainly by the aminoglycoside. Amikacin is the most synergistic of the aminoglycosides. A combination of an aminoglycoside such as amikacin plus a beta-lactam active against Pseudomonas is probably still the best empiric therapy available. The newer compounds and beta-lactam combinations still have to be proven effective in the clinical setting of the persistently and profoundly granulocytopenic patient with fever and bacteremia.

Comparison of the serum bactericidal activity of ceftriaxone/piperacillin and ceftriaxone/netilmicin

The serum bactericidal activities of ceftriaxone, netilmicin, piperacillin and the combinations of ceftriaxone with each of the two other antibiotics were compared 1, 4 and 24 h after i.v. infusion in six volunteers. One hundred and one clinical isolates were used, including Staphylococcus aureus, Pseudomonas aeruginosa and various Enterobacteriaceae. The highest bactericidal titers were found against the Enterobacteriaceae, geometric means of 1:741 and 1:851 being obtained for ceftriaxone/netilmicin and ceftriaxone/piperacillin respectively. Against Staphylococcus aureus the geometric mean bactericidal titers of ceftriaxone/piperacillin (1:105) were markedly higher than ceftriaxone/netilmicin (1:35). Low bactericidal activity was exhibited by all drugs and combinations tested against Pseudomonas aeruginosa; a geometric mean bactericidal titer of 1:4.6 was achieved. The serum bactericidal activity of the double beta-lactam combinations was found to be at least equal to that of the combination containing a cephalosporin and an aminoglycoside.

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.

Cefotaxime plus amikacin as empiric therapy in the treatment of febrile episodes in neutropenic patients with hematologic malignancies

Between October 1980 and October 1981, cefotaxime plus amikacin were used in the treatment of 131 febrile episodes that occurred in 108 neutropenic patients with hematologic malignancies. The overall clinical response was 86.2%. Fevers of unknown origin and clinically or microbiologically documented infections responded in 88.8 and 84.4% of the cases, respectively. Renal toxicity occurred in 3.8% of the cases. In vitro studies showed that cefotaxime and amikacin were active against 78.7 and 94.7% of the pathogens, respectively, despite the high frequency (31%) of multiply resistant strains of Pseudomonas aeruginosa (defined as in vitro simultaneously resistant to carbenicillin, gentamicin, tobramycin and sisomicin) isolated from blood and infected sites. Synergy studies performed against 35 gram-negative bacilli isolated from blood revealed the presence of synergism between cefotaxime and amikacin in 54% of the cases. The peak levels of bactericidal activity in the serum of patients receiving cefotaxime plus amikacin showed median values of 1:128 and 1:8 against Escherichia coli and P. aeruginosa septicemias, respectively.

Comparative study of the serum bactericidal activity of cefoperazone alone and in combination with amikacin or mezlocillin against gram-negative bacilli and Staphylococcus aureus

Serum bactericidal activity (SBA) was studied in vitro after intravenous administration of cefoperazone alone or in combination with mezlocillin or amikacin to human volunteers. One hour after the infusion, cefoperazone (2 g), cefoperazone + mezlocillin (5 g) and cefoperazone + amikacin (500 mg) achieved comparable activity against Escherichia coli and Klebsiella pneumoniae (100% of the strains being killed by a 1:8 or greater dilution). The activity of the three regimens was also similar against Pseudomonas aeruginosa (87-96% of the sera had an SBA greater than or equal to 1:8) and somewhat less for Staphylococcus aureus (52-60% with SBA greater than or equal to 1:8). Six and ten hours after administration, the SBAs were much lower for all regimens; a small advantage for cefoperazone + mezlocillin against K. pneumoniae could be shown in comparison to the other regimens.

Susceptibility and tolerance of beta-lactamase-producing, methicillin-sensitive strains of Staphylococcus aureus towards seven broad-spectrum penicillins

The activity of penicillin G, ampicillin, carbenicillin, ticarcillin, azlocillin, mezlocillin and piperacillin against 102 beta-lactamase-producing, methicillin-sensitive strains of Staphylococcus aureus was determined by agar dilution (method A) and broth microdilution (method B) techniques. By NCCLS breakpoint criteria, 4% of the strains were "sensitive" to penicillin and ampicillin, and almost 100% were "sensitive" to the other drugs when method A was used. Results with method B were only significantly lower as far as the cumulative percentage of strains "sensitive" to azlocillin, mezlocillin and piperacillin was concerned (63-71%). Bactericidal effects at "sensitive" levels were observed in 0-2% (penicillin, ampicillin), 31-35% (carbenicillin, ticarcillin) and 10-14% (azlocillin, mezlocillin, piperacillin). While differences in MIC and MBC levels ranged from 0 to 8 dilution steps, tolerance (a greater than 32-fold difference) was seen in at least 9-22% of all strains (depending on the drug tested); experimental limitations, however, excluded a determination of tolerance in all our strains. In a semi-quantitative nitrocefin assay, "strong" beta-lactamase production was correlated to high MIC and/or MBC levels.

Cefotaxime. A review of its antibacterial activity, pharmacological properties and therapeutic use

SYNOPSIS

Cefotaxime is a new 'third generation' semisynthetic cephalosporin administered intravenously or intramuscularly. It has a broad spectrum of activity against Gram-positive and Gram-negative aerobic and anaerobic bacteria, and is generally more active against Gram-negative bacteria than the 'first' and 'second generation' cephalosporins. Although cefotaxime has some activity against Pseudomonas aeruginosa, on the basis of present evidence it cannot be recommended as sole antibiotic therapy for pseudomonal infections. However, cefotaxime has been effective in treating infections due to other 'difficult' organisms, such as multidrug-resistant Enterobacteriaceae. Like other cephalosporins, cefotaxime is effective in treating patients with complicated urinary tract and lower respiratory tract infections, particularly pneumonia caused by Gram-negative bacilli. High response rates have also been achieved in patients with Gram-negative bacteraemia. Although favourable clinical results have been obtained in patients with infections caused by mixed aerobic/anaerobic organisms (such as peritonitis or soft tissue infections), the relatively low in vitro activity of cefotaxime against Bacteroides fragilis may restrict its usage in situations where this organism is the suspected or proven pathogen. In preliminary studies, males and females treated with a single intramuscular dose of cefotaxime for uncomplicated gonorrhoea caused by penicillinase-producing strains of Neisseria gonorrhoeae responded very favourably. Encouraging results have also been reported in open studies in children including neonates, treated with cefotaxime for meningitis and various other serious infections. In some situations, cefotaxime has been given in combination with another antibiotic such as an aminoglycoside, but the merits of such a combination have not been clearly established. Whether cefotaxime alone is appropriate therapy for conditions previously treated with aminoglycosides (other than pseudomonal infections) also needs additional clarification, but if established as equally effective in such conditions cefotaxime offers potentially important clinical and practical advantages in its apparent lack of serious adverse effects and freedom from the need to undertake drug plasma concentration monitoring.

Therapy with antibiotics in leukemic patients

The recovery of an adequate granulocyte count after chemotherapy is the most important prognostic factor in neutropenic patients. In granulocytopenic patients, the risk of infection is very high and its course usually severe. Empiric antibiotic treatment must be started as soon as fever rises and blood cultures have been taken. The combination of an anti-pseudomonas penicillin with an aminoglycoside is presently the standard empiric therapy for febrile granulocytopenic patients. If the clinical response is inadequate, antimicrobial therapy should be adjusted to a bactericidal activity of greater than 1:16 in the serum. If antibiotic therapy fails, a fungal infection should be considered and amphotericin B added empirically. Patients must be closely supervised for superinfections. Therapeutic transfusions of granulocytes have proven useful in severe granulocytopenia and when antibiotic therapy has failed.