Oritavancin microbiologic features and activity results from the surveillance program in the United States

Oritavancin is in the final stages of clinical development for treatment of acute bacterial skin and skin structure infections. This drug has demonstrated potent activity against staphylococci (minimum inhibitory concentration [MIC] for which 90% of isolates are inhibited [MIC(90)], 0.06 μg/mL), enterococci (MIC(90), ≤ 0.008 to 0.5 μg/mL), and streptococci (MIC(90), ≤ 0.008 to 0.12 μg/mL), including enhanced potency against vancomycin-resistant enterococci. During the clinical development of oritavancin, it was demonstrated that this molecule binds to plastic labware surfaces and that this feature was likely responsible for interlaboratory variability observed from in vitro investigations before 2006. Therefore, reference broth microdilution methods and MIC ranges for quality control strains were reestablished using media supplemented with a surfactant (polysorbate-80, 0.002%). These were followed by numerous experiments to reassess the in vitro characteristics of oritavancin; the results originating from those studies are summarized here. The oritavancin activity tested against a resistance surveillance collection of 12,367 Gram-positive clinical pathogens and resistant subsets from the United States (2008-2009) is also presented, with the highest MIC among staphylococci at only 0.25 μg/mL. In vitro results for oritavancin indicate wide potential use against Gram-positive pathogens.