In-vitro activity of dirithromycin against Chlamydia pneumoniae.

The in-vitro susceptibilities of 12 strains of Chlamydia pneumoniae were determined for dirithromycin, a new macrolide antibiotic, erythromycyclamine, its active metabolite, and erythromycin. Both dirithromycin and erythromycyclamine had an MIC90 of 2 mg/L, as compared with 0.062 mg/L for erythromycin. The combination of dirithromycin and erythromycyclamine appeared to be additive. Determination of the role of dirithromycin for the treatment of C. pneumoniae infection will depend on the results of prospective, controlled studies utilizing culture.