UTIs and two new antibiotics in the elderly

Of the new antimicrobials available for the treatment of urinary tract infections (UTIs), aztreonam and imipenem/cilastatin represent two structurally unique, but distinct, classes of beta-lactam antibiotics. Aztreonam has a directed spectrum of activity covering gram-negative bacilli usually associated with UTIs. In comparative clinical trials of patients with complicated UTIs, aztreonam is well-tolerated and is as effective as conventional control regimens, including aminoglycosides. On the other hand, the antimicrobial spectrum of imipenem/cilastatin includes not only gram-negative bacilli but also gram-positive cocci and anaerobes. As such, this broad-spectrum antibiotic should be reserved for the treatment of mixed infections.