Aztreonam: the first monobactam.

A novel screening procedure led to isolation of the structurally unique, bacterially produced, monocyclic beta-lactam antibiotics early in 1979. These naturally occurring "monobactams" were not clinically useful as antibiotics because of their poor antibacterial properties. They were, however, found to interact with certain penicillin-binding proteins of bacteria and thus to interfere with the biosynthesis of bacterial cell walls. The focus of monobactam development then turned toward increasing the binding activity of the beta-lactam ring of the molecule. Aztreonam was the first compound to emerge that fulfilled the objectives of the program. It is relatively inactive against gram-positive and anaerobic bacteria but is extremely effective against aerobic gram-negative bacteria, even in low concentrations. In addition, it is highly resistant to enzymatic hydrolysis by beta-lactamases and demonstrates a high degree of stability against plasmid-mediated gram-negative lactamases. With the chromosomally mediated beta-lactamases, on the other hand, aztreonam can act either as an inhibitor or as a poor substrate. It is unique in that it does not induce production of chromosomally mediated enzymes. Interference with normal gut flora by the use of broad-spectrum antibiotics can result in decreased defense capacity and can lead to intestinal colonization by resistant pathogenic organisms. Therapy directed specifically against the invading pathogen is thus preferred. Such directed therapy is provided by aztreonam. Its narrow spectrum can, if necessary, be broadened by combining it with other antibiotics while continuing to maintain an alternative to the more generalized "shotgun" therapy with its attendant side effects such as disturbances of the natural gut flora, diarrhea, and the emergence of resistant bacteria.