A drug combination of the streptogramins, quinupristin and dalfopristin was approved for IV use in the
treatment of infections caused by vancomycin-resistant Enterococcus faeci um bacteremia as well as
skin/skin structure infections caused by MRSA and methicillin-sensitive Streptococcus pyogenes. Certain
strains of E. faecium are resistant to essentially all
other antibiotics, including vancomycin. The streptogramin type A compound dalfopristin binds to the 50S
ribosomal subparticle, resulting in a conformational change in the substrate. It appears that dalfopristin
binding creates a high-affinity binding site for quinupristin, accounting for the synergy.
