Efficacy and safety of aztreonam-clindamycin versus tobramycin-clindamycin in the treatment of lower respiratory tract infections caused by aerobic gram-negative bacilli

Plazomicin is effective in a non-human primate pneumonic plague model

The efficacy of plazomicin for pneumonic plague was evaluated in a non-human primate model. African Green monkeys challenged with a lethal aerosol of Yersinia pestis [median (range) of 98 (15-331) LD_50s] received placebo (n=12) or 'humanized' dose regimens (6.25, 12.5 or 25mg/kg every 24h) of plazomicin (n=52) after the onset of fever for a duration of 5 or 10days. All animals treated with placebo died, while 36 plazomicin-treated animals survived through study end. The majority (33/36) were either in the 10-day (high-/mid-/low-dose) or 5-day high-dose groups. The findings suggest an exposure range of plazomicin for treatment of pneumonic/bacteremic Y. pestis infection in humans.

Efficacy and safety of aminoglycoside monotherapy: systematic review and meta-analysis of randomized controlled trials

OBJECTIVES

This study sought to compare the efficacy and adverse effects of any aminoglycoside as a single antibiotic with other antibiotics for the treatment of patients with infection.

METHODS

Systematic review of the literature and meta-analysis. We searched for randomized controlled trials comparing the efficacy of single aminoglycoside antibiotic treatment with one or more non-aminoglycoside antibiotic for patients with infection in the Cochrane Library, MEDLINE, EMBASE, LILACS, databases of ongoing trials and conference proceedings. Two reviewers assessed trial eligibility, quality and extracted data. Pooled relative risks (RR) with 95% confidence intervals (CI) were calculated for dichotomous data.

RESULTS

The search yielded 37 trials of which 26 included patients with urinary tract infection. Aminoglycosides were equally effective as comparators in the analysis of the primary outcomes, all-cause mortality (RR 1.11, 95% CI 0.68, 1.81, 9 trials, 503 patients) and treatment failure (RR 1.10, 95% CI 0.96, 1.27, 32 trials, 1890 patients). Aminoglycosides were associated with a significantly higher rate of bacteriological failure at end of therapy (RR 1.44, 95% CI 1.21, 1.72, 27 trials, 1668 patients). Subgroup analyses according to quality of trial, type of antibiotics, source of infection and rate of clinical sepsis did not alter the outcomes. Less adverse effects in total but more nephrotoxic effects were observed in patients treated with aminoglycosides.

CONCLUSIONS

The present data support the use of aminoglycosides for urinary tract infections. The paucity of trials including patients with sepsis or reporting on mortality precludes firm recommendations for patients with infections other than of the urinary tract.

Treatment of nosocomial postoperative pneumonia in cancer patients: a prospective randomized study

BACKGROUND

Nosocomial pneumonia continues to be associated with high morbidity and mortality in cancer patients.

METHODS

In an attempt to find an optimal treatment for this infection, nonneutropenic cancer patients with postoperative nosocomial pneumonia were randomized to receive either piperacillin/tazobactam (P/T) 4.5 g i.v. every 6 hours (30 patients) or clindamycin (Cl) 900 mg plus aztreonam (Az) 2 g i.v. every 8 hours (22 patients). Amikacin 500 mg i.v. every 12 hours was given to all patients for the first 48 hours.

RESULTS

The two groups were comparable for the characteristics of pneumonia that included gram-negative etiology and duration of intubation. Response rates were 83% for patients who received P/T and 86% for those who received Cl/Az (P > .99). There were no serious adverse events; however, at our center the cost of the P/T regimen was $73.86 compared with $99.15 for the Cl/Az regimen.

CONCLUSIONS

The two regimens had comparable high efficacy, and P/T had a slight cost advantage. Either of these antibiotic regimens combined with an aminoglycoside could lead to favorable outcome in cancer patients at high risk for nosocomial pneumonia.

Carbapenems and monobactams: imipenem, meropenem, and aztreonam

Imipenem and meropenem, members of the carbapenem class of beta-lactam antibiotics, are among the most broadly active antibiotics available for systemic use in humans. They are active against streptococci, methicillin-sensitive staphylococci, Neisseria, Haemophilus, anaerobes, and the common aerobic gram-negative nosocomial pathogens including Pseudomonas. Resistance to imipenem and meropenem may emerge during treatment of P. aeruginosa infections, as has occurred with other beta-lactam agents; Stenotrophomonas maltophilia is typically resistant to both imipenem and meropenem. Like the penicillins, the carbapenems have inhibitory activity against enterococci. In general, the in vitro activity of imipenem against aerobic gram-positive cocci is somewhat greater than that of meropenem, whereas the in vitro activity of meropenem against aerobic gram-negative bacilli is somewhat greater than that of imipenem. Daily dosages may range from 0.5 to 1 g every 6 to 8 hours in patients with normal renal function; the daily dose of meropenem, however, can be safely increased to 6 g. Infusion-related nausea and vomiting, as well as seizures, which have been the main toxic effects of imipenem, occur no more frequently during treatment with meropenem than during treatment with other beta-lactam antibiotics. The carbapenems should be considered for treatment of mixed bacterial infections and aerobic gram-negative bacteria that are not susceptible to other beta-lactam agents. Indiscriminate use of these drugs will promote resistance to them. Aztreonam, the first marketed monobactam, has activity against most aerobic gram-negative bacilli including P. aeruginosa. The drug is not nephrotoxic, is weakly immunogenic, and has not been associated with disorders of coagulation. Aztreonam may be administered intramuscularly or intravenously; the primary route of elimination is urinary excretion. In patients with normal renal function, the recommended dosing interval is every 8 hours. Patients with renal impairment require dosage adjustment. Aztreonam is used primarily as an alternative to aminoglycosides and for the treatment of aerobic gram-negative infections. It is often used in combination therapy for mixed aerobic and anaerobic infections. Approved indications for its use include infections of the urinary tract or lower respiratory tract, intra-abdominal and gynecologic infections, septicemia, and cutaneous infections caused by susceptible organisms. Concurrent initial therapy with other antimicrobial agents is recommended before the causative organism has been determined in patients who are seriously ill or at risk for gram-positive or anaerobic infection.

The monobactams

The monobactam antibiotics are synthetic compounds, although monocyclic beta-lactam compounds have been found in nature in various soil bacteria. Although additional orally and parenterally administered monobactams are under investigation, the first marketed monobactam was aztreonam. This agent has an antimicrobial spectrum similar to that of gentamicin and tobramycin, aminoglycoside antibiotics. Aztreonam, however, is not nephrotoxic, is weakly immunogenic, and has not been associated with disorders of coagulation. Aztreonam may be administered intramuscularly or intravenously; absorption after oral administration is poor. The primary route of elimination is the urine. The serum half-life of the drug in patients with normal renal function is 1.5 to 2.1 hours; the recommended dosing interval in patients with normal renal function is every 8 hours. Dosage adjustment is necessary in patients with renal impairment. The strictly gram-negative aerobic spectrum of aztreonam limits its use as a single empiric agent. Approved indications for its use include infections of the urinary tract or lower respiratory tract, intra-abdominal and gynecologic infections, septicemia, and cutaneous infections caused by susceptible organisms. Concurrent initial therapy with other antimicrobial agents is recommended before the causative organism (or organisms) has been determined in patients who are seriously ill and at risk for gram-positive or anaerobic infections.

Gram-negative bacillary pneumonia in the nosocomial setting. Role of aztreonam therapy

Gram-negative bacterial pneumonia is the leading cause of fatal nosocomial infection in this country. Predisposing factors include altered upper respiratory tract flora and altered barriers that normally protect the sterile lower respiratory tract from invasion by pharyngeal bacteria. Aztreonam, which is highly active against most gram-negative pathogens and which does not cause nephrotoxicity, has been evaluated in the treatment of nosocomial pneumonia. In vitro and pharmacokinetic data on aztreonam indicate that this agent provides an alternative agent for use when resistance to cephalosporin and aminoglycoside antibiotics has developed. Data further suggest that aztreonam may interact synergistically with aminoglycosides against gram-negative pathogens. Clinical study supports the usefulness of aztreonam against gram-negative nosocomial pneumonia. Since aztreonam is inactive against gram-positive and anaerobic bacteria, it must be used in combination with other antibiotics when these pathogens are suspected.

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.

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.

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.

Efficacy and safety of aztreonam versus tobramycin for aerobic gram-negative bacilli lower respiratory tract infections

Aztreonam therapy was evaluated for the management of 80 patients with gram-negative bacilli lower respiratory tract infections. Study results confirmed its efficacy and safety for this indication.