In vitro activity of azthreonam, a monobactam antibiotic

Inoculum effect of β-lactam antibiotics

The phenomenon of attenuated antibacterial activity at inocula above those utilized for susceptibility testing is referred to as the inoculum effect. Although the inoculum effect has been reported for several decades, it is currently debatable whether the inoculum effect is clinically significant. The aim of the present review was to consolidate currently available evidence to summarize which β-lactam drug classes demonstrate an inoculum effect against specific bacterial pathogens. Review of the literature showed that the majority of studies that evaluated the inoculum effect of β-lactams were in vitro investigations of Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumoniae, Haemophilus influenzae and Staphylococcus aureus. Across all five pathogens, cephalosporins consistently displayed observable inoculum effects in vitro, whereas carbapenems were less susceptible to an inoculum effect. A handful of animal studies were available that validated that the in vitro inoculum effect translates into attenuated pharmacodynamics of β-lactams in vivo. Only a few clinical investigations were available and suggested that an in vitro inoculum effect of cefazolin against MSSA may correspond to an increased likeliness of adverse clinical outcomes in patients receiving cefazolin for bacteraemia. The presence of β-lactamase enzymes was the primary mechanism responsible for an inoculum effect, but the observation of an inoculum effect in multiple pathogens lacking β-lactamase enzymes indicates that there are likely multiple mechanisms that may result in an inoculum effect. Further clinical studies are needed to better define whether interventions made in the clinic in response to organisms displaying an in vitro inoculum effect will optimize clinical outcomes.

Comparative antimicrobial efficacy of selected root canal irrigants on commonly isolated microorganisms in endodontic infection

Objective:

This study aims to evaluate and compare the antimicrobial efficacy of three selected root canal irrigants (BioPure MTAD, metronidazole, aztreonam) against microbes commonly isolated from polymicrobial microbiota of root canal infection.

Materials and Methods:

This study was designed with four experimental groups (Group I – Bacteroides fragilis, Group II – Propionibacterium acnes, Group III – Enterococcus faecalis, Group IV – Candida albicans) based on the microbes selected for the study. Group I and Group II bacteria were used to compare and evaluate antimicrobial effect of BioPure MTAD, metronidazole, aztreonam, and normal saline. Group III and Group IV bacteria were used to compare and evaluate antimicrobial efficacy of BioPure MTAD, aztreonam, and normal saline. Normal saline was used as a control irrigant in this study. Agar disc diffusion method was applied to assess and compare the antimicrobial action of selected irrigants.

Results:

Metronidazole was found to be the most effective root canal irrigant against B. fragilis and P. acnes among the tested irrigants. Mean zone of inhibition against E. faecalis has been shown to be maximum by BioPure MTAD, followed by aztreonam. Antifungal effect against C. albicans was only shown by BioPure MTAD.

Conclusions:

Overall, BioPure MTAD is the most effective root canal irrigant as it has shown an antibacterial effect against all the tested microorganisms. However, metronidazole showed maximum antibacterial effect against obligate anaerobes. Aztreonam also showed an antibacterial effect in the present study, raising its possibility to be used as a root canal irrigant in the future.

Aztreonam—An Overview

Aztreonam is the first synthetic monobactam to undergo clinical studies in the U.S. Aztreonam has excellent activity against P. aeruginosa and Enterobacteriaceae, but poor activity against anaerobic and gram-positive organisms. Aztreonam has poor oral bioavailability, but can be given intramuscularly or intravenously in doses of 1–2 g q6–12h. Clinical trials of aztreonam have shown it to be effective in infections of urine, lung, skin, blood, bones and joints, and abdomen with an adverse reaction profile similar to β-lactams. Aztreonam may be an alternate to aminoglycoside therapy, with the advantage of not being nephrotoxic.

Topics in Clinical Microbiology: Pseudomonas cepacia

Pseudomonas cepacia was first reported in the literature by Burkholder as a phytopathogen responsible for sour skin, a disease of onion bulbs. Similar bacteria were isolated from other sources and given various names including Pseudomonas multivorans, Pseudomonas kingii, and EO-1. The synonymy of these organisms with P. cepacia was eventually established. The first descriptions of human disease due to Pseudomonas cepacia were two reports of infective endocarditis. Subsequently, a series of postoperative urinary tract infections secondary to contaminated disinfectant solution were reported and P. cepacia became identified as a cause of nosocomial infection. P. cepacia has demonstrated a low level of virulence and invasiveness in the general population, but it has been shown to cause severe infection in patients with underlying diseases. Moreover, its nutritional versatility and ability to survive in antiseptic solutions make it a superb agent for causing hospital-acquired infection.

Recovery method development of sodium chloride-susceptible methicillin-resistant Staphylococcus aureus isolates from ground pork samples

The growth of certain methicillin-resistant Staphylococcus aureus (MRSA) isolates could be inhibited by NaCl higher than 2.5%. The objective of this study was to develop an enrichment method to recover NaCl-susceptible MRSA isolates from meat samples. The growth of 12 MRSA and 10 non-MRSA strains was measured in Mueller-Hinton (MH) broth supplemented with 2.5%, 4%, 6.5%, and 7.5% NaCl. Selective agents, including aztreonam, polymyxin B, NaCl, nalidixic acid, and NaN3, were determined for their inhibitory effect to MRSA and non-MRSA strains in MH broth. Based on these data, a two-step enrichment method was developed to recover both NaCl-susceptible and -resistant MRSA isolates in meat products. Comparing to the enrichment method that only used MH broth supplemented with 6.5% NaCl, five additional NaCl-susceptible MRSA isolates were recovered from 92 retail ground pork samples by this newly developed two-step enrichment method. To the best of our knowledge, this is the first study that considers NaCl-susceptible MRSA recovery from ground pork samples. The application of this new enrichment method might expand the diversity of MRSA isolates recovered from various samples.

Comparative antimicrobial efficacy of Metapex, Metronidazole, BioPure MTAD, Aztreonam on Bacteroides fragilis and Propionibacterium acne

Aim:

The purpose of this study was to evaluate the comparative antibacterial efficacy of Biopure MTAD, Metapex, Metronidazole, and Aztreonam against two obligate anerobic bacteria.

Materials and Methods:

Antimicrobial efficacy of selected medicaments against two obligate anaerobic bacteria Bacteroides fragilis and Propionibacterium acnes was done by Agar disc-diffusion method. Pre-sterilized Whatman paper discs, 6 mm in diameter and soaked with the test solution, were prepared and placed onto the previously seeded agar Petri plates. Each plate was incubated in anaerobic jar for anerobic environment at 37°C for 48 hours. A zone of inhibition was recorded for each plate and the results were analysed statistically. Saline and ethanol used as control group in this study.

Results:

Biopure MTAD, Metapex and Metronidazole were effective against all the selected microorganisms. Aztreonam was effective against Bacteroides fragilis. Saline and ethanol used as control were ineffective.

Conclusions:

Metronidazole showed the superior antibacterial property amongst the tested medicaments.

In vitro and in vivo properties of BAL30376, a β-lactam and dual beta-lactamase inhibitor combination with enhanced activity against Gram-negative Bacilli that express multiple β-lactamases

BAL30376 is a triple combination comprising a siderophore monobactam, BAL19764; a novel bridged monobactam, BAL29880, which specifically inhibits class C β-lactamases; and clavulanic acid, which inhibits many class A and some class D β-lactamases. The MIC(90) was ≤ 4 μg/ml (expressed as the concentration of BAL19764) for most species of the Enterobacteriaceae family, including strains that produced metallo-β-lactamases and were resistant to all of the other β-lactams tested. The MIC(90) for Stenotrophomonas maltophilia was 2 μg/ml, for multidrug-resistant (MDR) Pseudomonas aeruginosa it was 8 μg/ml, and for MDR Acinetobacter and Burkholderia spp. it was 16 μg/ml. The presence of the class C β-lactamase inhibitor BAL29880 contributed significantly to the activity of BAL30376 against strains of Citrobacter freundii, Enterobacter species, Serratia marcescens, and P. aeruginosa. The presence of clavulanic acid contributed significantly to the activity against many strains of Escherichia coli and Klebsiella pneumoniae that produced class A extended-spectrum β-lactamases. The activity of BAL30376 against strains with metallo-β-lactamases was largely attributable to the intrinsic stability of the monobactam BAL19764 toward these enzymes. Considering its three components, BAL30376 was unexpectedly refractory toward the development of stable resistance.

In vitro properties of BAL30072, a novel siderophore sulfactam with activity against multiresistant gram-negative bacilli

BAL30072 is a new monocyclic beta-lactam antibiotic belonging to the sulfactams. Its spectrum of activity against significant Gram-negative pathogens with beta-lactam-resistant phenotypes was evaluated and was compared with the activities of reference drugs, including aztreonam, ceftazidime, cefepime, meropenem, imipenem, and piperacillin-tazobactam. BAL30072 showed potent activity against multidrug-resistant (MDR) Pseudomonas aeruginosa and Acinetobacter sp. isolates, including many carbapenem-resistant strains. The MIC(90)s were 4 microg/ml for MDR Acinetobacter spp. and 8 microg/ml for MDR P. aeruginosa, whereas the MIC(90) of meropenem for the same sets of isolates was >32 microg/ml. BAL30072 was bactericidal against both Acinetobacter spp. and P. aeruginosa, even against strains that produced metallo-beta-lactamases that conferred resistance to all other beta-lactams tested, including aztreonam. It was also active against many species of MDR isolates of the Enterobacteriaceae family, including isolates that had a class A carbapenemase or a metallo-beta-lactamase. Unlike other monocyclic beta-lactams, BAL30072 was found to trigger the spheroplasting and lysis of Escherichia coli rather than the formation of extensive filaments. The basis for this unusual property is its inhibition of the bifunctional penicillin-binding proteins PBP 1a and PBP 1b, in addition to its high affinity for PBP 3, which is the target of monobactams, such as aztreonam.

Understanding the longevity of the beta-lactam antibiotics and of antibiotic/beta-lactamase inhibitor combinations

Microbial resistance necessitates the search for new targets and new antibiotics. However, it is likely that resistance problems will eventually threaten these new products and it may, therefore, be instructive to review the successful employment of beta-lactam antibiotic/beta-lactamase inhibitor combinations to combat penicillin resistance. These combination drugs have proven successful for more than two decades, with inhibitor resistance still being relatively rare. The beta-lactamase inhibitors are mechanism-based irreversible inactivators. The ability of the inhibitors to avoid resistance may be due to the structural similarities between the substrate and inhibitor.

Aztreonam

Aztreonam is the first monobactam and is unique among beta-lactam antibiotics for its spectrum of activity that is exclusively active against gram-negative aerobic bacteria. Broad clinical experience with this agent supports its use in the treatment of adults with severe or complicated urologic infections. Aztreonam may be safely used in patients with penicillin allergy. With a spectrum of activity that is comparable to the aminoglycosides but without the potential for ototoxicity or nephrotoxicity, aztreonam represents a rational choice of therapy for treatment of systemic urinary tract infections due to susceptible organisms.

Aztreonam: a review of the first monobactam

Aztreonam represents the first synthetic monobactam marketed in the United States and is being viewed as a nontoxic alternative to the aminoglycosides. Advantages of aztreonam over the aminoglycosides include lack of ototoxicity and nephrotoxicity and better penetration into the CSF. Additional advantages include its use in penicillin and cephalosporin allergic patients. Disadvantages of aztreonam compared to the aminoglycosides include the cost of the drug (50 times more expensive than gentamicin), the lack of post antibiotic effect, resistance to P. aeruginosa, and lack of significant activity against Enterobacter cloacae and E. aerogenes. There are insufficient clinical trials to document the superiority of aztreonam over the "gold standard" therapy for gram-negative infections--the aminoglycosides. The restricted anti-microbial spectrum of aztreonam has been proposed as an advantage. Theoretically, this would permit targeting of a gram-negative pathogen with minimal disruption of the (largely anaerobic) intestinal flora. In fact, use of this drug has been associated with colonization of gram-positive organism, especially enterococci. Although aztreonam appears to be an excellent antibiotic, its use has been limited by its relatively high cost, narrow spectrum of activity, and the availability of numerous alternative agents.

Aztreonam pharmacokinetics in burn patients

The pharmacokinetics of aztreonam in eight adult patients with severe burn injuries (total body surface area burn, 49% +/- 21% [mean +/- standard deviation]) were studied. The time of initiation of study following burn injury was 7.0 +/- 1.4 days. Four patients at first dose and at steady state were studied. Aztreonam concentrations were measured by high-performance liquid chromatography, and a two-compartment model was used to fit the data. No significant differences in any pharmacokinetic parameters between first dose and steady state were observed. Volume of distribution of the central compartment after first dose (0.14 liters/kg) and volume of distribution at steady state (0.31 liters/kg) were approximately 30% higher than those reported for other patient populations. Total drug clearance and renal drug clearance when normalized to creatinine clearance (CLCR) were similar to those previously reported for other critically ill patients. CLCR was strongly correlated with renal drug clearance (r = 0.94) and total drug clearance (r = 0.95). The extent and degree of burn (percent second or third degree burn) were poorly correlated with all pharmacokinetic parameters with the exception of the volume of distribution at steady state, which was correlated with both total body surface area burn (r = 0.95) and percent second degree burn (r = 0.83). Aztreonam pharmacokinetics are altered as a result of thermal injury; however, CLCR can be used to assess the clearance of aztreonam in burn patients.

Effects of aztreonam on fecal flora and on vitamin K metabolism

The effects of aztreonam on fecal flora and on descarboxy prothrombin (PIVKA-II) in plasma and gamma-carboxyglutamic acid (Gla) in urine as an index of vitamin K metabolism were studied in seven children (age range, 2 months to 2 years) with urinary tract infections. Daily doses of aztreonam were 60 to 80 mg/kg. Stool specimens were obtained before the treatment, on days 3 to 5 of aztreonam use, and from 3 to 5 days after the cessation of treatment. The counts of enterobacteria decreased (P less than 0.01) and those of streptococci increased (P less than 0.05) during aztreonam treatment. The anaerobic organisms, especially bifidobacteria and bacteroides, showed no marked change. PIVKA-II and Gla were investigated before and during the treatment with aztreonam. PIVKA-II was not detected in seven patients before or during aztreonam use. There were no significant differences in the levels of Gla in urine before or during the treatment.

Aztreonam susceptibility testing. A retrospective analysis

Aztreonam is a structurally and immunologically unique beta-lactam antibiotic with activity exclusively against aerobic gram-negative micro-organisms. Between 1983 and 1988, its antimicrobial spectrum was evaluated against more than 5,800 fresh clinical isolates at a 300-bed community teaching hospital. Only 1.1 percent of Enterobacteriaceae isolates were resistant to aztreonam over the five-year study period, an incidence similar to that observed with aminoglycoside antibiotics. Aztreonam was found to be more active than third-generation cephalosporins and comparable with mezlocillin against Enterobacter spp., Morganella, and Citrobacter freundii. Although aztreonam was somewhat less active against nonfermenting gram-negative bacilli, such as Pseudomonas and Acinetobacter, overall more than 90 percent of Pseudomonas aeruginosa isolates were susceptible. Ceftazidime was the most active beta-lactam tested against nonfermenters. Against aerobic gram-positive cocci, aztreonam possessed no clinically useful activity. No significant change in susceptibility to aztreonam was observed over the five-year study period for Enterobacteriaceae. For third-generation cephalosporins, however, a trend toward increased resistance was noted, particularly for Enterobacter spp. and C. freundii. A 50 percent increase in resistance to aztreonam was observed over the five-year study period for nonfermenters, particularly P. aeruginosa and Acinetobacter anitratus. Similar increases in resistance were seen with other beta-lactams and gentamicin. Based on its potent in vitro activity, aztreonam appears to be a useful agent and a desirable alternative to aminoglycoside antibiotics for the treatment of pure aerobic gram-negative bacillary infections, or as a component in combination therapy against mixed infections.

Antipseudomonal therapy in cystic fibrosis: aztreonam and amikacin versus ceftazidime and amikacin administered intravenously followed by oral ciprofloxacin

In order to determine the optimal antipseudomonal therapy in patients with cystic fibrosis aztreonam plus amikacin was compared to ceftazidime plus amikacin, and these two-week hospital regimens were followed by oral ciprofloxacin given for four weeks. Fifty-six cases of acute pulmonary exacerbation of the disease in 42 patients associated with isolation of Pseudomonas aeruginosa from the sputum were randomly treated with either aztreonam or ceftazidime (300mg/kg/day i.v.; maximum daily dose 12g) in combination with amikacin (36mg/kg/day i.v.; maximum daily dose 1,500mg). Other aspects of the two-week treatment were constant. The two therapy groups were comparable in all respects. Both regimens were well tolerated and resulted in similar improvements in clinical, bacteriologic, radiologic and laboratory findings, and pulmonary function. Fifty patients could be reevaluated after subsequent outpatient therapy consisting of oral ciprofloxacin (30mg/kg/day; maximum daily dose 1,500mg) given for four weeks. During this period, the clinical and laboratory improvements persisted, and the rate of eradication of Pseudomonas aeruginosa from sputum decreased from 62% to 34%. Ciprofloxacin was well tolerated and there was no drug toxicity or serious adverse effect. In the 25 prepubertal patients there was neither subjective nor objective evidence of skeletal drug toxicity. In patients with cystic fibrosis, aztreonam or ceftazidime in combination with amikacin represents an effective and safe systemic anti-pseudomonal therapy. Subsequent oral ciprofloxacin therapy for four weeks prolongs the beneficial effects and is well tolerated.

A comparison of monobactam antibiotics in surgical infections

The introduction of gentamicin almost 20 years ago provided an effective option for the treatment of gram-negative bacillary infections. During the past few years, the availability of aztreonam (a monobactam), imipenem (a carbapenem), and newer cephalosporins within vitro activities comparable with aminoglycosides against many gram-negative bacilli, has stimulated a reassessment of the role of aminoglycosides in treating these infections. When determining the role of new antimicrobials as potential replacements for more established agents, the clinical focus should be on three factors: comparative efficacy, safety, and cost. Consideration of cost is relevant only when efficacy and safety are equivalent. Other factors, such as comparative in vitro antimicrobial activity, pharmacokinetics, and effect on normal flora can also influence the selection of an antimicrobial regimen. A new class of antimicrobials, the monobactams, is the focus of this review. The only member of this class currently in clinical use is aztreonam. A comparison with aminoglycosides is particularly relevant because aztreonam is active against aerobic gram-negative bacilli. This review will discuss the acknowledged concerns with aminoglycoside use and compare the characteristics of aztreonam and currently marketed aminoglycosides.

In vitro antimicrobial activity of tigemonam, a new orally administered monobactam

At five geographically separate medical centers, over 6,000 clinical bacterial isolates were tested for their susceptibility to tigemonam by the broth microdilution method. The antimicrobial spectrum of tigemonam was similar to that of aztreonam, but with two differences. Aztreonam was more active against Pseudomonas spp., and tigemonam was more active against some streptococci. Tigemonam was highly resistant to hydrolysis by the eight beta-lactamase enzymes tested. A significant (greater than a fourfold increase in the MICs of tigemonam) inoculum effect occurred when 3 of 13 isolates were tested with inocula of 5 X 10(5) and 1 X 10(7) CFU/ml. Tigemonam was bactericidal for all but 1 of the 13 isolates. Of the four quality-control strains recommended by the National Committee for Clinical Laboratory Standards, only Escherichia coli ATCC 25922 provided on-scale results. The proposed MIC quality-control range of tigemonam for E. coli ATCC 25922 is 0.13 to 0.5 micrograms/ml.

National Committee for Clinical Laboratory Standards agar dilution susceptibility testing of anaerobic gram-negative bacteria

One hundred nine recent clinical isolates of anaerobic gram-negative bacteria were tested in triplicate by the National Committee for Clinical Laboratory Standards agar dilution procedure for their susceptibility to 32 antimicrobial agents. All isolates were inhibited by imipenem, but there were significant numbers of strains resistant to other beta-lactam drugs, and therefore the in vitro response to these antimicrobial agents cannot be predicted. This was particularly true for the bile-resistant or Bacteroides fragilis group. beta-Lactamase production was detected in 82% of the bacteroides with the nitrocefin test. Clavulanic acid combined with amoxicillin and ticarcillin and sulbactam combined with ampicillin resulted in synergistic activity against all beta-lactamase-positive organisms. Ceftizoxime was the most active of the cephalosporins. Two percent of the isolates were resistant to chloramphenicol and metronidazole. Clindamycin resistance was detected in 38% of the B. fragilis group, which is a marked increase from the 4% detected 10 years ago at this institution.

Compatibility of clindamycin phosphate with aztreonam in polypropylene syringes and with cefoperazone sodium, cefonicid sodium, and cefuroxime sodium in partial-fill glass bottles

The stability and compatibility of clindamycin phosphate admixed with four beta-lactams, an experimental monobactam (aztreonam), and three cephalosporins (cefoperazone sodium, cefonicid sodium, and cefuroxime sodium), were studied. Aztreonam alone and the combination of clindamycin phosphate-aztreonam were prepared in duplicate polypropylene syringes. Each cephalosporin antibiotic as well as the three clindamycin phosphate-cephalosporin combinations were admixed in duplicate 100 ml partial-fill glass bottles containing either dextrose 5% in water or NaCl 0.9%. All solutions were examined, antibiotic concentrations were determined, and pH was measured at the time of admixture and 1, 4, 8, 12, 24, and 48 hours later. The solutions were maintained at room temperature under fluorescent lighting for the length of the study. Antibiotic concentrations were determined by drug-specific high performance liquid chromatographic assays. Significant instability or incompatibility was defined as a decrease in concentration of greater than ten percent relative to the initial concentration measured at the time of admixture. All antibiotics were stable for 48 hours. In the combination studies, clindamycin was stable for 48 hours, both in partial-fill glass bottles and syringes. Aztreonam, cefoperazone, cefonicid, and cefuroxime were also stable for 48 hours.

The epidemiology of Pseudomonas cepacia in patients with cystic fibrosis

Pseudomonas cepacia has emerged as an important nosocomial pathogen colonizing and infecting the respiratory tract of patients with cystic fibrosis (CF). Although assessment of outcomes associated with P. cepacia colonization has been difficult, controlled studies have shown that colonized patients experience more adverse outcomes compared with those not colonized. In the United States, an increasing trend in national incidence and prevalence of P. cepacia colonization has been shown, but cases have been unevenly distributed in a few centers. These estimates, however, may be biased by intercenter differences in laboratory methods for detecting P. cepacia in patient sputum. The source and mode of transmission of P. cepacia have not been adequately demonstrated, and may vary from center to center. Until further studies elucidate the epidemiology of P. cepacia in patients with CF, it may be prudent for CF centers to consider the use of selective media to isolate P. cepacia from sputa of patients with CF, to conduct investigations of clusters of P. cepacia-colonized patients, and to consider adopting infection control precautions recommended for control of multiply resistant gram negative organisms.

Activity of cefmetazole against anaerobic bacteria

The in vitro activity of cefmetazole versus that of other antimicrobial drugs was assessed against 374 clinical isolates of Bacteroides spp., Clostridium spp., and anaerobic gram-positive cocci. Compared with cefoxitin, cefmetazole showed good activity against Bacteroides fragilis, other Bacteroides species, and anaerobic cocci. It was somewhat less active than cefoxitin against Bacteroides thetaiotaomicron, B. ovatus, B. distasonis, and B. vulgatus and somewhat more active against Clostridium spp.

Cephalosporin, carbapenem, and monobactam antibiotics

Cephalosporin and related antibiotics are highly effective bactericidal agents of relatively low toxicity. The spectrum of activity varies with the drug but is usually broad. The first-generation cephalosporins, and especially cefazolin, are most active against sensitive staphylococci and streptococci. Most second-generation (except cefoxitin) and third-generation cephalosporins show substantial activity against Haemophilus influenzae. All cephalosporins (except cefsulodin) are active against Klebsiella, Escherichia coli, and Proteus mirabilis, whereas only the third-generation agents have pronounced activity against the other Enterobacteriaceae. Imipenem (a carbapenem) is active against essentially all pathogenic organisms, but aztreonam (a monobactam) is active against only aerobic gram-negative bacilli. Advantages associated with some of the new cephalosporins are once-daily administration and high cerebrospinal fluid levels. With the development of new cephalosporins, however, new toxicities have become apparent, and superinfections and induction of resistance have become greater problems. The cephalosporins are among the most expensive antibiotics in use today; thus, use of these expensive agents must be justified by lower toxicity, greater efficacy, or both in comparison with drugs of more reasonable cost.

Absence of rapidly developing resistance during treatment of cystic fibrosis patients with aztreonam

The in vitro activity of aztreonam and 10 other antibiotics was determined for clinical isolates of Pseudomonas aeruginosa from 18 cystic fibrosis patients obtained before, at the end of, and 7-14 days after the completion of therapy with aztreonam. The percent of isolates susceptible to aztreonam at each sampling period were 79%, 78%, and 81% respectively.

In vitro activity of aztreonam combined with tobramycin and gentamicin against clinical isolates of Pseudomonas aeruginosa and Pseudomonas cepacia from patients with cystic fibrosis

The in vitro activity of aztreonam combined with tobramycin and with gentamicin was assessed in 78 clinical isolates of Pseudomonas aeruginosa and 11 clinical isolates of Pseudomonas cepacia from patients with cystic fibrosis. Synergy was detected in 56.4% of P. aeruginosa isolates and 60% of P. cepacia isolates with the aztreonam-tobramycin combination and in 49.3% of P. aeruginosa isolates and 81.8% of P. cepacia isolates with the aztreonam-gentamicin combination. No antagonism was observed. These combinations merit clinical evaluation in the treatment of patients with cystic fibrosis.

Effect of broad-spectrum parenteral antibiotics on composition of intestinal microflora of humans

We compared the effects of four beta-lactam drugs with widely differing antibacterial and pharmacological properties on the composition of the intestinal flora. Cefoxitin, piperacillin, cefoperazone, and aztreonam were given intravenously for 9 days to healthy volunteers. Cefoperazone reduced the numbers of aerobic and anaerobic bacteria to undetectable levels. At the other extreme, cefoxitin had little effect on the normal flora. Aztreonam markedly reduced the numbers of aerobes, whereas piperacillin had a variable effect on both aerobic and anaerobic bacteria. There was extensive overgrowth of enterococci in subjects given cefoxitin or aztreonam, which have little activity against this species, and of yeasts in subjects given cefoperazone or piperacillin. Cefoperazone reached concentrations of 2,727 to 8,840 micrograms/g in the feces, whereas the other agents were generally undetectable. These results show that the new beta-lactam antibiotics produce widely varying effects on the fecal microflora after parenteral administration and that these effects are consistent with the antibacterial and pharmacological properties of the drugs.

Surgically treated gangrenous or perforated appendicitis. A comparison of aztreonam and clindamycin versus gentamicin and clindamycin

A randomized, double-blinded, controlled clinical study of 84 patients with surgically treated gangrenous or perforated appendicitis was done to compare the efficacy of the combination of aztreonam, the first monobactam antibiotic, with gentamicin when either was combined with clindamycin. Fifty-six patients who were treated with aztreonam and clindamycin (A/C) and 28 patients who were treated with gentamicin and clindamycin (G/C) fulfilled criteria for evaluation. A matched historic control group of 56 G/C patients was also included for comparison. All measures of outcome, including days of fever, hospitalization, antibiotic therapy, and the incidence of antibiotic failures, were similar. It was concluded that aztreonam was as effective as gentamicin in this study and may offer some advantages with regard to toxicity and serum drug level monitoring.

Single-dose pharmacokinetics of aztreonam in children with cystic fibrosis

The single-dose pharmacokinetics of aztreonam was evaluated in 10 clinically stable subjects with cystic fibrosis. Each child received 30 mg aztreonam/kg intravenously over 2 to 3 minutes. Multiple timed blood samples were obtained over 8 hours for determination of aztreonam elimination kinetics; all urine excreted for 24 hours was collected in timed aliquots for the determination of aztreonam and its microbiologically inactive metabolite, SQ 26,992. Aztreonam pharmacokinetic parameters were determined by model-independent methods. Mean t1/2, steady-state volume distribution, and body clearance were 1.3 hr, 0.25 L/kg, and 127.2 ml/min/1.73m2, respectively. In 9 of the 10 subjects, two-compartment pharmacokinetic analysis was possible and compared favorably with model-independent parameter estimates. Twenty-four-hour urinary recovery of aztreonam was 76.3% of the administered dose; 2.6% was recovered as the metabolite SQ 26,992. The renal clearance of aztreonam averaged 92.5 ml/min/1.73m2. When these data are combined with in vitro susceptibility data for aztreonam against Pseudomonas aeruginosa isolated from the sputum of patients with cystic fibrosis, a dose of 200 mg aztreonam/kg/day divided six hourly would be predicted to maintain serum concentrations above the minimum inhibitory concentration (MIC) for these organisms for the majority of the dosing interval.

Aztreonam in the treatment of severe urinary tract infections in pediatric patients

Aztreonam was administered to 30 patients, ages 0.03 to 15.4 years, with severe and in 21 cases complicated urinary tract infections caused by members of the family Enterobacteriaceae and Pseudomonas aeruginosa which were resistant to ampicillin and susceptible to the study drug in vitro. A mean dose of 47.7 mg/kg was given intramuscularly every 12 h to 26 patients. In four patients with renal insufficiency, the dose was reduced according to pharmacokinetic data. Permanent urine sterilization and clinical cure were achieved in 22 patients, 13 of whom had urological malformations. In two patients with P. aeruginosa and Proteus mirabilis infections, the treatment failed. Another patient had an Escherichia coli reinfection 21 days after the end of therapy. Four patients with various urological abnormalities had gram-positive superinfections, and two patients had gram-negative superinfections during and at the end of therapy: all six had indwelling ureteric splints or pyelostomy as predisposing conditions. No adverse clinical effects were observed. Some transient and slight or moderate alterations were observed at the end of treatment: eosinophilia (nine cases), elevation of hepatic enzymes (eight cases), prolongation of prothrombin time (three cases), and neutropenia (one case). A pharmacokinetic study was performed in six patients with normal renal function and in seven patients with various degrees of renal insufficiency. The elimination half-life of the drug was inversely correlated with the glomerular filtration rate. At the dosage used, aztreonam proved effective for severe urinary tract infections caused by members of the family Enterobacteriaceae in pediatric patients.

Associated mortality and clinical characteristics of nosocomial Pseudomonas maltophilia in a university hospital

We studied the spectrum of clinical disease in 99 patients with nosocomial Pseudomonas maltophilia isolates at the University of Virginia Hospital from 1981 through 1984. The annual rate of isolation increased from 7.1 to 14.1 per 10,000 patient discharges. A crude mortality rate of 43% was documented in all patients from whom the organism was cultured, and the data include 12 patients with nosocomial bacteremia (four deaths). Risk factors associated with death for patients having a P. maltophilia isolate included the following: requirement for care in any intensive care unit during hospitalization (P = 0.0001), patient age over 40 years (P = 0.002), and a pulmonary source for the P. maltophilia isolate (P = 0.003). All P. maltophilia isolates were susceptible to trimethoprim-sulfamethoxazole, 60% of the isolates were resistant to all aminoglycosides (amikacin, tobramycin, and gentamicin), and more than 75% of the isolates were resistant to all beta-lactam antibiotics. The antibiotic susceptibility pattern allows for a niche exploitable in the hospital microbial environment by an organism with a marked associated mortality.

Aztreonam

Aztreonam is a new, totally synthetic beta-lactamase agent--the first monobactam. It is highly resistant to hydrolytic inactivation caused by plasmid-mediated (except PSE-2 enzyme found in some Pseudomonas species) or chromosomally mediated beta-lactamases (except for K1 produced by rare strains of Klebsiella oxytoca). Accordingly, aztreonam remains active against many pathogens that are resistant to other beta-lactam antibiotics. The drug exhibits directed antibacterial activity against gram-negative organisms and is effective as monotherapy against most Enterobacteriaceae and Hemophilus and Neisseria species, including beta-lactamase-producing strains; it is not active against anaerobes or gram-positive organisms. Before culture results are known, it may be necessary to administer the agent empirically in combination with other antibiotics. Aztreonam is rapidly distributed to most body tissues and fluids when administered parenterally. Its serum half-life is 1.7 hours, suggesting a dosing interval of 6-8 hours for severe or life-threatening infections and 8-12 hours for moderately severe infections and urinary tract infections. It is primarily eliminated unchanged in the urine and in much lesser amounts as a microbiologically inactive metabolite; slight biliary excretion may occur. Aztreonam is well-tolerated, lacking any serious adverse hematologic, otic, or renal system effects. Its lack of effect on anaerobes helps to maintain resistance against colonization. Particularly in light of its safety and unique properties, aztreonam promises to be a useful alternative to aminoglycoside therapy.

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

Aztreonam (azthreonam; SQ 26,776) is the first member of a new class of beta-lactam antibiotics, the monobactams. Aztreonam is selectively active against Gram-negative aerobic bacteria and inactive against Gram-positive bacteria. Thus, in vitro, aztreonam is inhibitory at low concentrations (MIC90 less than or equal to 1.6 mg/L) against Enterobacteriaceae except Enterobacter species, and is active against Pseudomonas aeruginosa, 90% of pseudomonads being inhibited by 12 to 32 mg/L. Aztreonam is inactive against Gram-positive aerobic bacteria and anaerobes, including Bacteroides fragilis. Therefore, when administered alone, aztreonam has minimal effect on indigenous faecal anaerobes. Aztreonam must be administered intravenously or intramuscularly when used to treat systemic infections, since absolute bioavailability is very low (about 1%) after oral administration. Since elimination half-life is less than 2 hours, 6- or 8-hourly administration is used in the treatment of moderately severe or severe infections, although 12-hourly injection is adequate in less severe systemic and some urinary tract infections. Therapeutic trials have shown aztreonam to be effective in Gram-negative infections including complicated infections of the urinary tract, in lower respiratory tract infections and in gynaecological and obstetric, intra-abdominal, joint and bone, skin and soft tissue infections, uncomplicated gonorrhoea and septicaemia. In comparisons with other antibiotics, aztreonam has been at least as effective or more effective than cefamandole in urinary tract infections and similar in efficacy to tobramycin or gentamicin. Where necessary, aztreonam and the standard drug have both been combined with another antibiotic active against Gram-positive and/or anaerobic bacteria. Aztreonam has been effective in eradicating pseudomonal infections in most patients (except in patients with cystic fibrosis), but the inevitably limited number of pseudomonal infections available for study prevents any conclusions as to the relative efficacy of aztreonam compared with other appropriate regimens against these infections. Thus, with an antibacterial spectrum which differs from that of other antibiotics, aztreonam should be a useful alternative to aminoglycosides or 'third generation' cephalosporins in patients with proven or suspected serious Gram-negative infections.

Intraphagocytic bactericidal activity of ofloxacin compared with that of aztreonam and ceftriaxone against Serratia marcescens

Addition of phenylbutazone (2 mg/ml) to 55 vol % of fresh defibrinated human blood permitted leukocytic ingestion of serum-resistant Serratia marcescens bacteria, but blocked phagocytic killing activity. The group A (phage tail) bacteriocin bA+ 16 served to kill extraphagocytic test bacteria. At greater than or equal to 2 X MBC, the DNA gyrase inhibitor ofloxacin revealed potent intraphagocytic bactericidal activity against S. marcescens test bacteria (99% kill; 3 h observation period) which corresponded to that of the control drug rifampin (97% kill). The monobactam aztreonam (11% kill) and the third generation cephalosporin ceftriaxone (14% kill) corresponded to cefotaxime (26% kill) in terms of suboptimal intraphagocytic activity. Ofloxacin and aztreonam yielded additive effects following combination of supra-(2 X MIC) and inhibitory (MIC), but not sub-inhibitory (0.5 X MIC) concentrations with 55 vol % of defibrinated human blood against S. marcescens and Escherichia coli control strain ATCC 25922; sub- and inhibitory concentrations of ceftriaxone yielded indifferent effects.

Penetration of aztreonam into cerebrospinal fluid of patients with and without inflamed meninges

Aztreonam was administered as a single, 2-g intravenous dose to 25 patients with noninflamed meninges and to 9 patients with inflamed meninges. It was well tolerated and was detected in the cerebrospinal fluid at the initial sampling period at 1 h after the end of infusion. Aztreonam levels in the cerebrospinal fluid of patients with inflamed meninges were four times higher than those recorded for the same time period in patients with noninflamed meninges. Aztreonam concentrations in cerebrospinal fluid in the presence of normal and inflamed meninges exceeded the inhibitory and bactericidal concentrations for most gram-negative bacteria. Thus, a multiple-dose treatment regimen with 2-g intravenous doses every 6 h appears to be appropriate for clinical trials of aztreonam for the treatment of gram-negative bacillary meningitis which is caused by susceptible organisms.

Treatment of gram-negative infections with aztreonam

Twenty-one patients with serious gram-negative infections were treated with aztreonam. Twenty of these were clinical and microbiologic cures; there was one clinical improvement with microbiologic persistence. No bacteria became resistant. Cure rates were: bone and joint (11 of 11); skin and soft tissue (six of six); pneumonia (two of two); perinephric abscess (one of one); and intra-abdominal abscess (zero of one). The bacteria responsible for these infections included Pseudomonas aeruginosa (12), Serratia marcescens (two), Enterobacter gergoviae (three), Enterobacter aerogenes (two), Escherichia coli (one), Citrobacter diversus (one), and Hemophilus influenzae (one). Aztreonam was well tolerated. Significant serum glutamic-oxaloacetic transaminase/serum glutamic-pyruvic transaminase elevations developed in three patients, but none was symptomatic and all resolved after therapy was stopped. Two patients in whom a rash developed were receiving other antibiotics (vancomycin and metronidazole), making the cause of the rash unclear. Diarrhea developed in a single patient with Pseudomonas osteomyelitis, who also was receiving cefazolin for Staphylococcus aureus superinfection of his decubitus ulcer. Aztreonam was highly effective against gram-negative bacilli, including P. aeruginosa. The only clear-cut side effect was an asymptomatic rise in serum glutamic-oxaloacetic transaminase/serum glutamic-pyruvic transaminase levels in three patients.

Aztreonam plus clindamycin as therapy for pelvic infections in women

Aztreonam, a new monobactam antibiotic with specific gram-negative aerobic activity, was used in combination with clindamycin in the treatment of 40 women with pelvic infection, including post-partum endometritis, pelvic inflammatory disease, and post-hysterectomy pelvic cellulitis. Clinical cure was achieved in 87 percent of patients. Failure was related to the limited gram-positive aerobic spectrum of clindamycin. All aerobic gram-negative enteric organisms were sensitive in vitro to less than 0.125 microgram/ml of aztreonam.

Effectiveness of aztreonam for the treatment of gonorrhea

Aztreonam, 1 g intramuscularly, was compared with spectinomycin, 2 g intramuscularly, for uncomplicated gonorrhea. There were no failures with either drug. For aztreonam, there were 26 urethral, 3 rectal, and 3 endocervical sites that were infected. Aztreonam in a single dose of 1 g intramuscularly is satisfactory therapy for uncomplicated urethral gonorrhea in men and may be effective for rectal and endocervical infection as well.

In vitro studies of investigational beta-lactams as possible therapy for Pseudomonas aeruginosa endocarditis

The inadequacy of the present medical therapy of Pseudomonas aeruginosa endocarditis prompted an investigation of the in vitro activities of aztreonam, cefsulodin, and imipenem compared with that of ticarcillin against 37 strains of P. aeruginosa isolated from patients with endocarditis. Inhibitory and bactericidal activities were studied for each beta-lactam alone and in combination with tobramycin. All agents showed excellent inhibitory activity. Imipenem was the most inhibitory beta-lactam yet lacked inhibitory synergy against 95% of the strains and bactericidal synergy against 62%. Tolerance to imipenem was seen in six strains. Aztreonam alone was bactericidal against 46% of the strains (at 16 micrograms/ml) and showed bactericidal synergy in 70%. Cefsulodin alone was even less active but similar to aztreonam synergistically. Ticarcillin and tobramycin inhibited all strains as single agents and showed universal bactericidal synergy in combination. None of the new beta-lactams showed consistent superiority to the presently used agent, ticarcillin.

Susceptibilities of 45 clinical isolates of Proteus penneri

Patterns of susceptibility of 45 Proteus penneri clinical isolates to 14 antimicrobial agents were evaluated by a macrobroth dilution method. All strains were highly susceptible to ceftizoxime, ceftazidime, moxalactam, cefoxitin, gentamicin, tobramycin, netilmicin, and, with few exceptions, to amikacin, piperacillin, and cefoperazone. Most strains were susceptible to cefotaxime and ceftriaxone. All strains were resistant to cefazolin and cefsulodin.

Comparative activities of aztreonam and cefotaxime against Escherichia coli and Bacteroides spp. in pure and mixed cultures

The activities of aztreonam and cefotaxime against one Escherichia coli strain and three Bacteroides strains have been studied by using pure and mixed cultures of aerobic and anaerobic bacteria. A fixed concentration (8 micrograms/ml) of cefotaxime or aztreonam killed E. coli that was exposed in pure culture, but the pressure of Bacteroides spp. in the same system deteriorated cefotaxime, allowing the full growth of E. coli after 24 h. On the other hand, the presence of Bacteroides spp. produced less deterioration of aztreonam, which reduced the initial E. coli inoculum. This observation could be useful in clinical practice when treating mixed aerobic and anaerobic infections.

Antimicrobial spectrum of Win 49375

Win 49375 had excellent activity against members of the family Enterobacteriaceae and staphylococcal species. Its activity against Pseudomonas aeruginosa was equal to that of gentamicin. Win 49375 had moderate activity against clostridia but little against Bacteroides fragilis. The drug showed a marked inoculum effect at 10(8) CFU/ml and a slight decrease in potency at pH 5.

Aztreonam compared with gentamicin for treatment of serious urinary tract infections

52 patients with serious urinary tract infections were randomised to receive either aztreonam (35) or gentamicin (17). In the aztreonam group 23 patients had unqualified cures, 6 cures with relapse, and 6 cures with reinfection; the comparable numbers in the gentamicin group were 9, 1, and 4. There were no failures with aztreonam and 3 with gentamicin. The most important determinant of outcome was the presence or absence of urological abnormalities. 11 further patients, with renal failure or gentamicin-resistant isolates, treated with aztreonam were all cured. Toxic effects were limited to symptomless liver-function-test abnormalities with aztreonam , whereas deterioration in renal function occurred in 4 gentamicin-treated subjects. Urinary colonisation with group D streptococci occurred in 14 of 46 aztreonam -treated patients (1 required treatment) compared with only 1 of 17 gentamicin-treated patients. 97% of 309 consecutive gram-negative urinary isolates tested, including 50 Pseudomonas aeruginosa, were susceptible in vitro to aztreonam and 91% to gentamicin. Aztreonam may prove an effective and safe alternative to the aminoglycosides.

Purification and properties of an inducible cephalosporinase from Pseudomonas maltophilia GN12873

An inducible cephalosporinase was purified from Pseudomonas maltophilia GN12873. The pI was 8.4, and the molecular weight was ca. 56,000 by gel filtration or 27,000 by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, suggesting that this enzyme had two subunits. The optimal pH and optimal temperature were 7.5 and 45 degrees C, respectively. Enzyme activity was inhibited by clavulanic acid, sulbactam, cephamycin derivatives, carbapenem antibiotics, iodine, HgCl2, and p-chloromercuribenzoate. The enzyme showed a broad substrate profile, hydrolyzing cephaloridine, cefazolin, cefsulodin, penicillin G, ceftizoxime, and ampicillin at a high rate.

In vitro antimicrobial activity of aztreonam alone and in combination against bacterial isolates from pediatric patients

We examined 134 pediatric clinical isolates of Enterobacteriaceae, Pseudomonas aeruginosa, and gram-positive cocci for susceptibility to aztreonam alone and in combination with seven other antibiotics. All 98 gram-negative isolates were susceptible to aztreonam with similar inhibitory and bactericidal activity. Combinations of aztreonam with cefoxitin, ampicillin, or clindamycin were generally indifferent or additive. Synergism was occasionally seen against enteric organisms with aztreonam plus cefoxitin or clindamycin. Combinations of tobramycin and aztreonam were synergistic (62%) against P. aeruginosa; aztreonam plus piperacillin or ticarcillin was additive. Aztreonam did not affect the activity of nafcillin against Staphylococcus aureus, or of ampicillin against species of Streptococcus group B or D. Antagonism was seen only with aztreonam plus cefoxitin against Enterobacter species, but not at clinically significant concentrations. Several combinations of antibiotics with aztreonam should be appropriate for initial therapy of infections in children without major risks of antibacterial antagonism.

Cefoxitin inactivation by Bacteroides fragilis

We have surveyed the susceptibility of 1,575 clinical isolates of the Bacteroides fragilis group of organisms to cefoxitin and eight other antimicrobial agents. Eleven isolates, 0.7% of the total, were highly cefoxitin resistant and had minimum inhibitory concentrations of greater than or equal to 64 micrograms/ml. These isolates were also resistant to other beta-lactam antibiotics. Of 11 isolates, 4 were able to inactivate cefoxitin in broth cultures, as measured by microbiological and high-pressure liquid chromatography assays. Two distinct patterns of cefoxitin breakdown products were detected by high-pressure liquid chromatography analysis. The beta-lactamase inhibitors clavulanic acid and sulbactam failed to show synergism with cefoxitin. These data demonstrate that members of the B. fragilis group have acquired a novel resistance mechanism enabling them to inactivate cefoxitin.