In vitro activity of antibiotics commonly used in the treatment of otitis media against Streptococcus pneumoniae isolates with different susceptibilities to penicillin.

Susceptibilities of 82 clinical isolates of Streptococcus pneumoniae, including 25 from the middle-ear fluid, were evaluated against antibiotics commonly used in the treatment of acute otitis media. Potentially significant resistance occurred in 6% of the isolates to erythromycin and an erythromycin-sulfisoxazole combination. The combination of trimethoprim and sulfamethoxazole was synergistic for 95% of the isolates. Only 2.5% of all of the isolates were resistant to both erythromycin-sulfisoxazole and trimethoprim-sulfamethoxazole. The presently used drug regimens should be effective against the majority of S. pneumoniae isolates in otitis media.