Current concepts in the antimicrobial therapy of community-acquired pneumonia

The majority of community-acquired pneumonias (CAPs) are caused by typical bacterial pathogens, i.e., S. pneumoniae, H. influenzae or M. catarrhalis. Atypical pneumonias, i.e., legionnaires' disease, C. pneumoniae pneumonia and M. pneumoniae pneumonia are less common in frequency than typical bacterial pathogens, but are of considerable public health and therapeutic importance. The newest therapeutic considerations in CAP are related to monotherapy versus combination therapy, parenteral versus oral therapy, minimizing the emergence of penicillin-resistant pneumococci and an appreciation that comorbid factors in antibiotic selection are unimportant. Monotherapy using a respiratory quinolone or doxycycline covers both typical and atypical causes of CAPs and is equally efficacious and less expensive than double drug therapy. Except in patients unable to take oral medications/those in CCUs, patients with CAP may be started on i.v. antibiotic therapy, but should be switched to oral therapy after 48 hours/clinical defervescence. The combination of 2 days of i.v. therapy plus 12 days of oral therapy has been shown to be as effective as 14 days of i.v. therapy. The use of doxycycline or respiratory quinolones may forestall or eliminate the emergence of highly penicillin-resistant pneumococci, and, for this reason, these agents probably should be used preferentially over beta-lactam antibiotics to treat CAPs. The status of the host's immune system, particularly intact splenic function, and the underlying condition of the cardiorespiratory system are the critical factors in predicting mortality, morbidity, complications and hospital stay. However, antibiotic selection is not affected by comorbidities, and antibiotics should not be changed or added to the usual therapy of CAP because of comorbid factors. Multiple drug therapy does not improve the outcome, which is a function of underlying host factors.