Trimethoprim-sulfamethoxazole (TMP-SMX) is often used as first- or second-line therapy for acute otitis media. Studies have demonstrated clinical efficacy for this treatment, but little information on its bacteriologic efficacy is available. Recent pneumococcal surveillance studies have found frequent resistance to TMP-SMX, often in association with resistance to other antibiotics, especially penicillin. Leiberman and associates investigated the bacteriologic and clinical efficacy of a 10-day regimen of TMP-SMX (4 to 20 mg per kg twice daily) in children with acute otitis media.

Children three to 36 months of age with acute otitis media and a positive initial middle ear fluid culture by tympanocentesis were enrolled in the study. A second tympanocentesis was performed three to four days after TMP-SMX therapy was initiated. Children with a positive culture on treatment day 4 or 5 were considered to have bacteriologic failure. Additional cultures of middle ear fluid were obtained if clinical relapse occurred. Children were determined to have clinical failure if no change in pretreatment signs and symptoms occurred, if those signs and symptoms worsened or if additional antibiotic therapy was required. If children had bacteriologic failure but showed clinical improvement, they continued to receive TMP-SMX until the end of the treatment course.

Most of the 54 study subjects were younger than one year. Haemophilus influenzae alone was the most common pathogen cultured from the middle ear (50 percent of children), followed by combined infection with Streptococcus pneumoniae and H. influenzae (24 percent), and S. pneumoniae alone (20 percent). Of the 40 H. influenzae isolates, 70 percent were susceptible to TMP-SMX, and 30 percent were highly resistant to the drug combination. Bacteriologic failure occurred in 21 patients (39 percent) on day 4 or 5. Of the eight patients with clinical failure (15 percent), seven also had bacteriologic failure. Ten patients relapsed after the completion of treatment.

Although TMP-SMX has been reported to have satisfactory clinical efficacy in children, the authors noted that increasing resistance to penicillin, TMP-SMX, oral cephalosporins and macrolide antibiotics has been reported. In their study, clinical treatment failure was usually associated with bacteriologic failure. The high bacteriologic failure rate when infants and young children with acute otitis media are treated with TMP-SMX implies that this drug combination may no longer be an appropriate empiric therapy in children with acute otitis media.