In vitro evaluation of AZD2563, a new oxazolidinone, tested against unusual Gram-positive species

The recently introduced oxazolidinone, linezolid, has a spectrum and potency directed against Gram-positive organisms, including antimicrobial-resistant isolates. The newest agent in this class, AZD2563 was tested against uncommonly isolated Gram-positive species to establish the breadth of its spectrum. By reference broth microdilution methods, 120 strains were tested (48 Corynebacterium spp., 10 species 27 Listeria spp,, 2 species; 11 Micrococcus spp., 2 species; 23 Bacillus spp., 3 species, 6 Stomatococcus mucilaginosus and one strain each of 5 other species) against AZD2563 and compared to eight other agents. The AZD2563/linezolid MIC50 % inhibited at less than or equal to 4 mug/mL were: for corynebacteria (0.25/0.25 mug/mL 100/100%), Listeria spp. (2/2 mug/mL 100/100%), micrococcus spp. (1/1 mug/mL; 100/100%), Bacillus spp. (0.5/1 mug/mL; 100/100%), and S mucilaginosus (0.5/1 mug/mL; 100/100%). Using the MIC90 values, AZD2563 was slightly more potent than linezolid (two-fold). Only four genus- species groups had AZD2563 MICs of strains at 2 mug/mL (Aerococcus, Leaconostoe, Listeria, Rhodococcus), all other isolates were inhibited by less than or equal to 1 mug/mL. The AZD2563 potency and spectrum versus these rarer species was at least equal to linezolid, including some strains resistant to penicillins, macrolides-lincosamides, and fluoroquinolones. (C) 2002 Elsevier Science Inc. All rights reserved.