General principles of antimicrobial therapy.

In the initial therapy of life-threatening infections in which a bacterial cause is suspected, the emphasis should be on broad antibiotic coverage in contrast to definitive therapy, which is dependent on microbial isolation and, when indicated, in vitro susceptibility tests. In severe infections, antimicrobial agents should be given parenterally, at least initially. The need for optimal dosage is emphasized. This is particularly important when aminoglycosides are administered, for there is a tendency to use inadequate dosage because of concern for potential side effects with these agents. The problems leading to recurrence and 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 in severe infections due to Pseudomonas aeruginosa, enterococcal group D streptococci, Klebsiella pneumoniae, and Cryptococcus neoformans. Laboratory aid for the selection of antimicrobial therapy can be of great value but need not always be done, because certain microorganisms have stable, predictable susceptibilities, for example, Streptococcus pneumoniae and Streptococcus pyogenes. Cautious conservatism is advocated with regard to the use of new antimicrobial agents.