In vitro activity of RP 59500 (quinupristin dalfopristin) and ramoplanin against vancomycin-resistant Enterococcus faecium

Vancomycin-resistant Enterococcus faecium (VREF) collected between July 1991 and February 1994 were tested in vitro against RP 59500 and ramoplanin using agar dilution and standard macro broth dilution procedures. Colony counts were determined at 0, 4, and 24 h. RP 59500 had an MIC range of less than or equal to 0.5-8 mu g/ml with an MIC(90) of 2 mu g/ml and a MBC range of less than or equal to 0.5-16 mu g/ml with an MBC(90) of 16 mu g/ml. Ramoplanin had an MIC range of less than or equal to 0.125-1 mu g/ml with an MBC range of less than or equal to 0.125-1 mu g/ml. The MIC(90) for ramoplanin was 1 mu g/ml and the MBC(90) was 4 mu g/ml for the tested isolates, Against these isolates of E. faecium, RP 59500 was bactericidal at 8X MIC, a potentially achievable level using a high drug dosage.(10) Ramoplanin was bactericidal at 2X MIC.