ABT-719 is a 2-pyridone antimicrobial with activity against enterococci, Escherichia coli, and Pseudomonas aeruginosa in experimental murine pyelonephritis. Therapeutic ED50s for ABT-719 against these infections were equal to or up to ten-fold lower than those for ciprofloxacin, used as a reference because of similarity in mode of action. Against E. faecalis, the therapeutic ED50s for ABT-719 were 4.5-13.6 mg/kg.day for sc administration and 6.8-8.9 mg/kg.day for oral administration. ABT-719 was more potent than ciprofloxacin and vancomycin against the E. faecalis strains, which showed ciprofloxacin and vancomycin resistance covering a range of MICs.