Importance of dose and duration of beta-lactam therapy in nasopharyngeal colonization with resistant pneumococci.

Antibiotic use greatly influences the nasopharyngeal carriage of drug-resistant Streptococcus pneumoniae and is considered to be one of the most important risk factors for carriage of such organisms. Several studies have shown a reduction in the prevalence of resistant strains following reduced antibiotic consumption. This indicates that it may be possible to reduce resistance rates by changing prescribing patterns. Studies suggest that antibiotics present at low levels tend to select strains with low-level penicillin resistance, that intermediate antibiotic levels may pose the danger of selection of pneumococci with high-level penicillin resistance and that attainment of high levels of antibiotics may reduce the selective pressure for penicillin resistance. High-dose beta-lactam (amoxicillin) therapy has been shown to reduce the selection of resistant pneumococci in the nasopharynx. Likewise, short-course antibiotic therapy has reduced colonization by resistant strains. Finally, the effect of the antibiotic appears to differ according to the beta-lactam prescribed. Studies suggest that selection by cephalosporins occurs at higher frequencies than that by amoxicillin; this may be explained by the reduced activity of cephalosporins against penicillin-resistant S. pneumoniae.