Aztreonam, a new monobactam antimicrobial

The chemistry, in vitro activity, pharmacokinetics, adverse reactions, and clinical use of the monobactam antimicrobial aztreonam are reviewed. Aztreonam, an investigational agent nearing approval in the United States and Canada, is the first in a class of monobactam antimicrobials to be evaluated extensively in vitro and in vivo. It has a narrow spectrum of activity, encompassing only aerobic gram-negative Microorganisms including Pseudomonas aeruginosa and most multiply resistant Enterobacteriaceae. Aztreonam has no useful activity against gram-positive or anaerobic Microorganisms. In preliminary studies, aztreonam achieved high tissue concentrations and was usually well tolerated. Approximately 65-75% of an administered dose is excreted unchanged into the urine, and the elimination half-life is 1.6-2.2 hours in subjects with normal renal function. Dosage should be adjusted in patients with renal impairment. Aztreonam was shown equivalent to gentamicin and cefamandole for treating serious urinary-tract infections and produced cure rates greater than 85% in gonococcal, lower respiratory tract, orthopedic, serious urinary tract, acute uncomplicated lower urinary-tract, gynecologic, and intraabdominal infections. Development of resistance during therapy may be less likely with aztreonam than with other new cephalosporins. Aztreonam will probably have an important role in antimicrobial therapy, but much further study is necessary to assess clinical efficacy and toxicity. The clinical importance of aztreonam's superior activity under anaerobic conditions compared with aminoglycosides and the theoretical reduced alteration in GI colonization resistance must be assessed in controlled trials. Evaluation of aztreonam versus ceftazidime, the carbapenems, and the carboxyquinolones is needed, and the likelihood of gram-positive superinfection, especially with enterococci, must be further assessed.