Activity of the ketolide telithromycin (HMR-3647) against erythromycin-susceptible and -resistant pneumococci isolated in the UK.

The novel ketolide telithromycin (formerly HMR-3647) was tested against a collection of pneumococci of varying sensitivity to erythromycin and clindamycin, isolated in geographically diverse UK hospitals. Telithromycin was highly active against erythromycin-susceptible pneumococci, the MIC(90) being 0.015 mg/l. Erythromycin-resistant pneumococci that contained the ermB gene, either alone or together with the mefE gene, were cross-resistant to other macrolides and to clindamycin, while erythromycin-resistant pneumococci that contained only the mefE gene were cross-resistant to azithromycin, clarithromycin and roxithromycin but remained susceptible to josamycin and clindamycin. Telithromycin was active against erythromycin-resistant pneumococci irrespective of their mechanism of macrolide resistance, although the MIC(90) (0.25 mg/l) was higher than that seen with erythromycin-sensitive isolates. Telithromycin thus appears to be a potentially useful drug in settings where pneumococcal resistance to macrolides is prevalent.