In Vivo Efficacy of the Ketolide ABT-773 (Cethromycin) against Enterococci in a Mouse Peritonitis Model

Abstract

Using six Enterococcus faecalis and five Enterococcus faecium strains, the ketolide ABT-773 (ABT), now known as cethromycin, was found to have in vivo efficacy against both erythromycin (ERY)-susceptible (Ery ^s ) and -intermediate (Ery ⁱ ) enterococci (ABT 50% protective doses [PD ₅₀ s], 0.5 to 4.1 and 10.3 to 16.2 mg/kg of body weight, respectively). Against four highly Ery-resistant (Ery ^r ) strains for which ABT MICs were low, ABT showed much greater activity (PD ₅₀ , 6.3 to 32.5 mg/kg) than ERY (PD ₅₀ , >200 mg/kg) but was not protective for strains for which ABT MICs were high. In conclusion, ABT-773 showed in vivo efficacy and considerably greater activity than ERY in a mouse peritonitis model.