- Background. One dose of intramuscular ceftriaxone has been recently licensed in the United States for the treatment of acute otitis media. However, data regarding the bacteriologic and clinical efficacy of this regimen in the treatment of nonresponsive acute otitis media are incomplete. Objectives. To determine the bacteriologic and clinical efficacy of a 1-day 50-mg/kg vs. a 3-day 50-mg/kg/day intramuscular ceftriaxone regimen in the treatment of nonresponsive acute otitis media in children. Patients and methods. In an open, prospective study 109 patients ages 3 to 36 months with culture-proved, nonresponsive acute otitis media were randomized to receive 1 (n = 49) or 3 (n = 60) 50-mg/kg/day intramuscular ceftriaxone doses, respectively. Middle ear fluid was aspirated for culture by tympanocentesis on the day of enrollment (Day 1); a second tympanocentesis with middle ear fluid culture was performed on Days 4 to 5. Additional middle ear fluid cultures were obtained if clinical relapse occurred after completion of therapy. Bacteriologic failure was defined by positive cultures on Days 4 to 5. Patients were followed until Day 28 after completion of therapy. Susceptibility of the middle ear pathogens was measured by E-test. Results. Organisms recovered (n = 133) were Streptococcus pneumoniae (30 and 35 isolates for the 1-day and 3-day treatment group, respectively), Haemophilus influenzae (26 and 38, respectively) and Moraxella catarrhalis (n = 4). Of the 30 S. pneumoniae isolated from the 1-day group, 27 (90%) and 6 (20%) were nonsusceptible to penicillin and ceftriaxone, respectively; 9 of 27 (33%) were fully resistant to penicillin. Thirty-four (97%) and 6 (17%) of the 35 S. pneumoniae isolated from the 3-day group were nonsusceptible to penicillin and ceftriaxone, respectively; 16 of 34 (47%) were fully resistant to penicillin. Bacterial eradication of all H. influenzae and penicillin-susceptible S. pneumoniae was achieved in both treatment groups. Bacterial eradication of 14 of 27 (52%) and 33 of 34 (97%) penicillin-nonsusceptible S. pneumoniae was achieved in the 1-day and 3-day group, respectively. Seven (50%) of the 14 patients from the 2 groups who did not achieve bacterial eradication did not improve clinically on Days 4 to 5 and required additional ceftriaxone treatment. Conclusion. The 3-day intramuscular ceftriaxone regimen was significantly superior to the 1-day intramuscular ceftriaxone regimen in the treatment of nonresponsive acute otitis media caused by penicillin-resistant S. pneumoniae.