Efficacy of telithromycin (HMR 3647) against enterococci in a mouse peritonitis model

We used a mouse peritonitis model to evaluate the in vivo efficacy of telit hromycin (HMR 3647) (TEL) and erythromycin (ERY) against four strains of En terococcus faecalis and three strains of Enterococcus faecium with differin g susceptibilities to TEL. TEL was highly active in vivo against fry-suscep tible (Ery(s)) and intermediate (Ery(i)) strains (MIC of TEL = 0.015 to 0.0 62 mug/ml) and showed less efficacy against fry-resistant (Ery(r)) isolates (MIC of TEL = 4 to 16 mug/ml), although this was overcome in part by a sec ond subcutaneous dose. Quinupristin-dalfopristin was also noted to have les s efficacy against Ery(r) versus Ery(s) or Ery(1) E. faecium strains, but t his difference was reduced by intravenous administration. In conclusion, TE L was more potent in vivo against enterococci than was ERY; its activity wa s lowered by the presence of erm(B)-mediated Ery(r).