Issues In Antimicrobial Treatment

1. Bactericidal vs bacteriostatic antibiotics: Based on whether they kill or inhibit growth, antimicrobial agents are traditionally classified as bactericidal or bacteriostatic, respectively. This classification is an oversimplification, as an antimicrobial agent may be partially bactericidal or bacteriostatic for one species of bacteria and fully bactericidal for another. General dogma is that pneumonia should be treated only with bactericidal drugs. The rationale given to support this is that colonies of bacteria within the consolidated area are protected from host defenses, especially neutrophils. In other body sites these neutrophils would usually eliminate organisms inhibited by bacteriostatic antibiotics.

2. Single vs multiple antimicrobial therapy: Pneumonia is generally regarded as being easy to treat. Therefore, in most cases acceptable cure rates can be obtained using a single antibiotic. However, nosocomial pneumonia, especially in critically ill patients, usually requires combination antibiotic therapy. The rationale for this is that antibiotics that act by different mechanisms could serve to expand antibiotic coverage, reduce toxicity from lower individual doses of the drug, or act synergisti-cally and potentially lower the development of antibiotic resistance. The most work in this area has examined only immunocompromized hosts, and it may not be appropriate to extrapolate that evidence to other settings. Among the different agents, aminoglycosides have been shown to be particularly effective in empirically treating severe nosocomial pneumonias and in treating pneumonia due to Pseudomonas aeruginosa, Acinetobacter sp., and ^-lactamase producing Gram-negative organisms.

3. Optimal duration of treatment of antibiotics: Early experience established that pneumonia could not be cured by short courses that may have been appropriate to cure other infections such as urinary tract infections. Trials of longer duration were more successful, eventually leading to the widely followed practice of treating pneumonia for 2 wk, although there is no evidence to support this. The Pneumonia Patient Outcomes Research Study showed that it remains common practice today despite the fact that more than half of all cases could be reliably cured by a shorter duration of treatment. It has been felt, however, that Chlamydia pneumonia should be treated for 3 wk and Mycoplasma infections for 2 wk with either doxycycline or erythromycin. However, the newer macrolides can be given for shorter periods, 5 d for azithromycin and 10 d for clarithromycin (25).

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