In vitro activities of oxazolidinones U-100592 and U-100766 against penicillin-resistant and cephalosporin-resistant strains of Streptococcus pneumoniae.

Two oxazolidinones and ceftriaxone, imipenem, rifampin, and vancomycin were tested against 162 penicillin-intermediate and 68 penicillin-resistant strains of pneumococci. U-100592 is two- to fourfold more active than U-100766 against penicillin-resistant pneumococci. The MICs of U-100592 at which 90% of the isolates were inhibited were 0.25 and 0.5 microgram/ml for penicillin-intermediate and -resistant strains, respectively, and 0.5 microgram/ml for ceftriaxone-susceptible, -intermediate, and -resistant strains. U-100592 MICs for 7 of 230 strains (2 from blood, 3 from middle-ear fluid, and 2 from the upper respiratory tract) were 1 microgram/ml.