Ureidopenicillins, aztreonam, and thienamycin: efficacy as single-drug therapy of severe infections and potential as components of combined therapy.

The ureidopenicillins (piperacillin, mezlocillin, and azlocillin), aztreonam, and thienamycin are new broad-spectrum beta-lactams with more potent antibacterial activity than the older cephalosporins and penicillins. However, therapy of severe infections with the ureidopenicillins alone is limited by the potential for emergence of resistant organisms, while monotherapy with aztreonam does not provide adequate coverage for Gram-positive aerobic organisms and anaerobes. In combination therapy with the aminoglycosides, the ureidopenicillins may be preferred to carbenicillin or ticarcillin in the treatment of Pseudomonas aeruginosa infections and in institutions with a high prevalence of carbenicillin or ticarcillin-resistant organisms. Double beta-lactam therapy with piperacillin plus either latamoxef (moxalactam) or ceftazidime may be advantageous in patients for whom aminoglycoside toxicity is a concern. Thienamycin is the most promising of the new beta-lactams for single-agent therapy of severe infections but may also be associated with the emergence of resistant P. aeruginosa during monotherapy. In febrile granulocytopenic patients or other severely ill patients at risk of severe P. aeruginosa infections, thienamycin or another antipseudomonal beta-lactam should be combined with an aminoglycoside.