A single intramuscular dose of ceftriaxone changes nasopharyngeal bacterial flora in children with acute otitis media

The increasing prevalence of drug-resistant bacteria is attributed to the e xtensive use of antibiotics, which causes selective pressure on the nasopha ryngeal bacterial flora. Shortened courses of antibiotics have been propose d to decrease the development of resistant strains. We determined the effec t of a single intramuscular dose of ceftriaxone (50 mg/kg) on the nasophary ngeal bacterial flora in 167 children (median age 13 mo) with acute otitis media. Nasopharyngeal samples for bacterial culture were obtained before an d 5 d after treatment with ceftriaxone. Before treatment, Moraxella catarrh alis was isolated in 99 (59%) children, Streptococcus pneumoniae in 87 (52% ), and Haemophilus influenzae in 53 (32%). After treatment, M. catarrhalis was found in 62 (37%) children, which constitutes a 37% decrease in the col onization rate by this pathogen (p < 0.001). S. pneumoniae was isolated in 50 (30%; 43% decrease) and H. influenzae in 17 (10%; 68% decrease) children after treatment (p < 0.001 for both). Before treatment, 60% of pneumococca l isolates were sensitive to penicillin, 26% were of intermediate susceptib ility, and 14% were penicillin-resistant. Eradication of S. pneumoniae occu rred mainly in children with penicillin-sensitive isolates. As a consequenc e, only 24% of pneumococcal isolates that remained after treatment were sen sitive to penicillin, 59% were penicillin-intermediate, and 16% were penici llin-resistant. A single dose of ceftriaxone resulted in significant changes in the nasopha ryngeal bacterial flora, increasing the relative prevalence of pneumococcal strains with decreased susceptibility to penicillin.