General principles of antimicrobial therapy

The initial treatment of suspected life-threatening bacterial infection should be sufficiently broad to cover the likely causative agents. Definitive therapy depends on microbial isolation, identification, and, when indicated, in vitro susceptibility tests. Parenteral therapy should be used, at least initially, and optimal doses are necessary. The dose is particularly important when aminoglycosides are administered; a concern for potential side effects with use of these agents had engendered a tendency to administer inadequate doses. The problems leading to recurrence or persistence of fever during antimicrobial therapy include failure to diagnose and drain abscesses, superinfection, drug fever, and clinical or microbiologic errors. Combinations of antibiotics are indicated in severe infections due to Pseudomonas aeruginosa, enterococcal group D streptococci, and Cryptococcus neoformans. Laboratory assistance for the selection of antimicrobial therapy can be valuable but is not always necessary because certain microorganisms--for example, Streptococcus pneumoniae and S. pyogenes--have stable, predictable susceptibilities. Cautious conservatism is advocated with regard to the use of new antimicrobial agents.