Aztreonam treatment of gram-negative septicemia

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.

Updated evaluation of the activity of antibiotics in a burn centre

The results of microbiological tests performed in a burns unit between January 1989 and December 1990 have been analysed. Burn wound swabs and biopsies, blood cultures, central venous and urinary catheters, bronchial aspirates, pharyngeal swabs and faecal cultures for a total of 7950 examinations were considered. Staph. aureus was the most frequently isolated bacterium, followed by Staph. epidermidis, Pseud. aeruginosa and E. coli. The antibiograms have shown a low efficacy rate of cephalosporins, even of the latest generation, while with Gram-positive isolates the highest rates of activity were recorded by vancomycin and teicoplanin (100 per cent sensitivity). The situation seems better with Gram-negative organisms since they appear to be sensitive to a larger number of antimicrobial agents.

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.

Antimicrobial use in hospital-acquired infections

The appropriate use of antibiotics in nosocomial infections has been a goal of infectious disease practitioners and hospital epidemiologists since the emergence of resistant staphylococci more than 30 years ago. This challenge has assumed new proportions in the 1980s for many reasons. First, resistant gram-positive and gram-negative bacteria are increasingly common. Thus many traditional drugs or combinations of drugs lack efficacy. Second, there are so many new antibiotics available that it is difficult for any but the most knowledgeable to use each of them appropriately. Third, economic reality has forced hospitals and physicians to alter their activities and focus more on cost considerations than was ever necessary before. Last, infectious disease as a subspecialty in internal medicine is profoundly different in the 1980s; many infections must be controlled for life rather than cured because of underlying infection with human immunodeficiency virus, which suppresses immunity. The use of antibiotics is now rapidly changing and the state of the art in 1989 is likely to be outdated very soon as new pathogens emerge and new drugs are developed. The appropriate use of the quinolones is a great challenge that we now face. Can we preserve this valuable class of drugs, or will resistance develop quickly because of widespread, indiscriminate, and inappropriate use? To what extent can we phase out aminoglycoside use without compromising efficacy and without promoting the development of resistance? Do the monobactams have a real role to play in combination therapy? How should formularies approach the diverse cephalosporins that now inundate the market? These are only a few of the fundamental questions that must be addressed as this decade ends.