Efficacy of clarithromycin treatment of acute otitis media caused by infection with penicillin-susceptible, -intermediate, and -resistant Streptococcus pneumoniae in the chinchilla.

Because of the increasing frequencies of recovery of penicillin-resistant Streptococcus pneumoniae from the middle ears of children with acute otitis media, non-beta-lactam antibiotics are being explored as treatment alternatives to amoxicillin. In this study, the efficacy of a 10-day course of clarithromycin was evaluated with chinchillas. After the pharmacokinetic profiles for clarithromycin were established, 180 animals were assigned to one of three susceptibility groups (n = 60/group; penicillin-susceptible, -intermediate, and -resistant S. pneumoniae), and the right middle ear was infected with the appropriate strain of S. pneumoniae. Equal numbers of animals in each group were treated orally beginning on day 2 with a 10-day course of clarithromycin (15 mg/kg of body weight; given twice a day) or amoxicillin as a control (20 mg/kg twice a day). On days 4, 9, and 13, otomicroscopy and tympanometry were performed, and on day 13, the middle ears were cultured for bacteria. The results showed 100% eradication of the challenge organism in both treatment groups for the susceptible strains of S. pneumoniae. Cultures were negative in 87 and 74% (P > 0.05) of the animals challenged with the intermediate resistant strains and in 100 and 56% (P < 0.05) of the animals challenged with the resistant strains and treated with clarithromycin and amoxicillin, respectively. There were no differences between treatments in the diagnosis of effusion for any group. These results support the use of the chinchilla to evaluate drug efficacy in the treatment of acute otitis media and show clarithromycin to be effective in sterilizing the middle ears of animals challenged with penicillin-susceptible, -intermediate, and -resistant strains of S. pneumoniae.